CN118868680A

CN118868680A - Electric tool, brushless motor control method thereof, control module thereof and storage medium

Info

Publication number: CN118868680A
Application number: CN202410334742.1A
Authority: CN
Inventors: 湛康; 龚燕
Original assignee: Positec Power Tools Suzhou Co Ltd
Current assignee: Positec Power Tools Suzhou Co Ltd
Priority date: 2023-04-27
Filing date: 2024-03-22
Publication date: 2024-10-29

Abstract

The present invention relates to an electric tool comprising: a control unit for selectively adjusting a control signal of the driving circuit to maintain the target rotation speed of the brushless motor when the actual rotation speed of the brushless motor deviates from the target rotation speed; the control module adjusts the control phase of the control signal and comprises a non-overlapping control phase and an overlapping control phase, wherein the non-overlapping control phase adjusts the duty ratio of the control signal, the overlapping control phase adjusts the overlapping angle of the control signal, and the control module is also used for adjusting the lead angle of the switching element; in a non-overlapping control stage, the control component detects phase current of the electric tool and adjusts a lead angle according to the phase current, wherein the phase current and the lead angle are in a first relation; in the overlapping control stage, the control component corrects the first relation to enable the phase current and the lead angle to be in a second relation; the change rate of the lead angle along with the phase current in the second relation is smaller than that of the lead angle along with the phase current in the first relation, so that the phase change accuracy of the speed stabilization stage of the overlapped angle is improved, and the efficiency of the brushless motor is improved.

Description

Electric tool, brushless motor control method thereof, control module thereof and storage medium

Technical Field

The present invention relates to an electric tool, and more particularly, to an electric tool, a brushless motor control method, a control module, and a storage medium.

Background

The electric tool is widely applied to the working environments such as families, gardens and the like, and brings great convenience to the life and the operation of people. The electric tool can be powered by a battery pack, and after a switch of the electric tool is powered on, the motor rotates and drives the transmission mechanism to realize various power operations.

In order to achieve a desired rotation speed, the existing power tool is generally adjusted by adjusting a PWM (Pu l se width modu l at ion ) duty ratio of a switching element. When a larger rotational speed is desired, this can be achieved by increasing the conduction angle of the switching elements, i.e. by applying an overlap angle to the switching elements for control. Meanwhile, in order to improve the output efficiency of the motor, it is also necessary to control the lead angle of the switching element. However, the inventor found that when the same lead angle control manner is adopted in the phase of adjusting the PWM duty ratio and in the phase of adjusting the overlap angle, the motor output efficiency is low and even the normal operation of the motor is affected due to inaccurate commutation in the phase of adjusting the overlap angle.

Disclosure of Invention

The invention provides an electric tool, which can improve the output efficiency of a brushless motor, prolong the endurance time of the electric tool and does not need to increase the hardware cost.

A power tool, comprising: a battery pack; a brushless motor including a stator assembly and a rotor rotating around the stator assembly, the stator assembly for receiving the power of the battery pack and driving the rotor to rotate; a driving circuit including a plurality of switching elements for controlling supply of electric power from the battery pack to the brushless motor; the control assembly comprises a position detection module, a control module and a control module, wherein the position detection module is used for detecting the position of the rotor and generating a position signal, and the control assembly is used for calculating the actual rotating speed of the brushless motor according to the position signal and adjusting a control signal of the switching element when the actual rotating speed deviates from a target rotating speed so as to enable the brushless motor to reach the target rotating speed; the control module adjusts the control phase of the control signal including a non-overlapping control phase in which the control module adjusts the duty cycle of the control signal and an overlapping control phase in which the control module adjusts at least the overlapping angle of the control signal; the control assembly is also used for adjusting the lead angle of the control signal to control the driving output of the electric tool; in the non-overlapping control stage, the control component detects phase current of the electric tool and adjusts the lead angle according to a preset first relation according to the phase current; during the overlap control phase, the control component corrects the first relationship and adjusts the lead angle according to the corrected second relationship; the rate of change of the lead angle with the phase current in the second relationship is smaller than the rate of change of the lead angle with the phase current in the first relationship.

In one embodiment, during the overlap control phase, the control component controls the lead angle to decrease in response to the overlap angle increasing at the same phase current.

In one embodiment, the control component controls the advance angle to continuously vary in response to a continuous variation of the overlap angle at the same phase current.

In one embodiment, in the overlap control phase, in the second relationship, in response to an increase in the overlap angle, the control component controls the advance angle change so that a rate of change of the advance angle with the phase current change decreases.

In one embodiment, during the non-overlapping control phase, the first relationship comprises:

Wherein AA is the advance angle, I is the phase current, a is a constant, a is positively correlated with the phase difference angle between the position detection module and the counter potential, k is a constant, k is positively correlated with the armature reaction strength of the brushless motor, n is the index of the phase current, and n is more than or equal to 1 and less than or equal to 3.

In one embodiment, during the overlap control phase, the second relationship comprises:

wherein AA is the advance angle, I is the phase current, CB is the overlap angle, a is a constant, a is positively correlated with the phase difference angle between the position detection module and the counter potential, k is a constant, k is positively correlated with the armature reaction strength of the brushless motor, n is the index of the phase current, n is not less than 1 and not more than 3, m is the index of the overlap angle coefficient (CB/60), and m is not less than 1 and not more than 3.

In one embodiment, during the overlap control phase, the magnitude of the overlap angle is related to a rotational speed difference between the target rotational speed and an actual rotational speed, and the control component controls the overlap angle to increase in response to an increase in the rotational speed difference.

In one embodiment, the adjustment of the overlapping angle includes: and in each commutation period, the control component adjusts the overlapping angle according to preset increment, wherein the value range of the preset increment is any value in the range of 0.01-0.5 degrees.

In one embodiment, the control component prioritizes the duty cycle when the actual rotational speed is less than the target rotational speed; the control component preferentially adjusts the overlap angle when the actual rotational speed is greater than the target rotational speed.

In one embodiment, the brushless motor comprises a three-phase brushless inductive motor; the position detection module of the brushless motor includes three position detection units.

A power tool, comprising: a battery pack; a brushless motor including a stator assembly and a rotor rotating around the stator assembly, the stator assembly for receiving the power of the battery pack and driving the rotor to rotate; a driving circuit including a plurality of switching elements for controlling supply of electric power from the battery pack to the brushless motor; the control assembly comprises a position detection module, a control module and a control module, wherein the position detection module is used for detecting the position of the rotor and generating a position signal, and the control assembly is used for calculating the actual rotating speed of the brushless motor according to the position signal and adjusting a control signal of the switching element when the actual rotating speed deviates from a target rotating speed so as to enable the brushless motor to reach the target rotating speed; the control module adjusts the control phase of the control signal including a non-overlapping control phase in which the control module adjusts the duty cycle of the control signal and an overlapping control phase in which the control module adjusts at least the overlapping angle of the control signal; the control assembly is also used for adjusting the lead angle of the control signal to control the driving output of the electric tool; in the overlap control phase, the control module adjusts the lead angle according to a phase current of the brushless motor, wherein in response to the overlap angle increasing, the control module controls the lead angle so that a rate of change of the lead angle with a change of the phase current decreases.

In one embodiment, during the non-overlapping control phase, the control component adjusts the lead angle according to a preset first relationship; in the overlapping control stage, the control component adjusts the lead angle according to a preset second relation; the rate of change of the lead angle with the phase current is smaller in at least part of the phases in the second relationship than in the first relationship.

A control method of a brushless motor of an electric tool, wherein the brushless motor includes a stator assembly and a rotor rotating around the stator assembly; the electric tool includes: a position detection module for detecting a position of the rotor and generating a position signal; a driving circuit including a plurality of switching elements for controlling supply of electric power from the battery pack to the brushless motor;

The control method of the brushless motor comprises the following steps: receiving the position signal and calculating the actual rotating speed of the brushless motor according to the position signal; judging whether the actual rotating speed reaches the target rotating speed or not; adjusting a control signal of the switching element when the actual rotational speed deviates from the target rotational speed so that the actual rotational speed reaches the target rotational speed, a control phase of the control signal including a non-overlapping control phase in which a duty ratio of the control signal is adjusted, and an overlapping control phase in which at least an overlapping angle of the control signal is adjusted; in the non-overlapping control stage, receiving phase current and adjusting the lead angle of a control signal according to a preset first relation according to the phase current so as to control the driving output of the electric tool; and in the overlapping control stage, receiving phase current and adjusting the lead angle of the control signal according to the phase current according to a preset second relation so as to control the driving output of the electric tool, wherein the change rate of the lead angle along with the phase current is smaller than that of the lead angle along with the phase current in the first relation.

In one embodiment, the method further comprises: in the overlap control phase, the advance angle is controlled to decrease in response to the increase in the overlap angle at the same phase current.

In one embodiment, the method further comprises: in the overlap control phase, the advance angle is adjusted so that the smaller the rate of change of the advance angle with the phase current is in response to the overlap angle increasing.

A control module for a brushless motor of a power tool, wherein the brushless motor comprises: a stator assembly and a rotor rotating around the stator assembly; the electric tool includes: a position detection module for detecting a position of the rotor and generating a position signal; a driving circuit including a plurality of switching elements for controlling supply of electric power from the battery pack to the brushless motor;

The control module is connected with the brushless motor and used for controlling the brushless motor to operate according to a target rotating speed, and the control module comprises: the receiving unit is used for receiving the position signal sent by the position detection module; a calculation unit for calculating an actual rotation speed of the brushless motor based on the position signal; a judging unit configured to judge whether the actual rotation speed reaches the target rotation speed; a control unit configured to adjust a control signal of the switching element when the actual rotation speed deviates from the target rotation speed so that the actual rotation speed reaches the target rotation speed, the control unit adjusting a control phase of the control signal including a non-overlapping control phase in which the control unit adjusts a duty ratio of the control signal and an overlapping control phase in which the control unit adjusts at least an overlapping angle of the control signal; in a non-overlapping control stage, the control unit is further used for receiving phase currents and adjusting the lead angle according to the phase currents according to a preset first relation; in the overlapping control stage, the control unit is further configured to receive a phase current and adjust the lead angle according to the phase current according to a preset second relationship, where a rate of change of the lead angle with the phase current is smaller than a rate of change of the lead angle with the phase current in the first relationship.

A computer-readable storage medium having stored therein a computer program loaded and executed by a processor to implement the method of controlling a brushless motor of the aforementioned power tool.

A power tool, the power tool comprising: a battery pack; the brushless motor comprises a stator assembly and a rotor rotating around the stator assembly, and the stator assembly is connected with the battery pack; an inverter circuit including a plurality of switching elements for controlling supply of electric power from the battery pack to the brushless motor; a control assembly including a position detection module for detecting a position signal of the brushless motor, the control assembly for calculating an actual rotational speed of the brushless motor based on the position signal, and for maintaining the target rotational speed of the brushless motor by selectively adjusting a duty ratio and/or an overlap angle of the switching element when the actual rotational speed deviates from the target rotational speed; the control component is also used for detecting the phase current of the electric tool and adjusting the lead angle of the switching element according to the phase current so as to control the driving output of the electric tool; the rate of change of the lead angle with the phase current is smaller in the phase where the control module adjusts the overlap angle of the switching element than in the phase where the control module adjusts the duty cycle of the switching element.

In one embodiment, the rate of change of the lead angle with the phase current is related to the overlap angle in the phase of adjusting the overlap angle of the switching element.

In one embodiment, the greater the overlap angle, the smaller the rate of change of the lead angle with the phase current.

In one embodiment, the lead angle is continuously varied with the overlap angle during the phase of the control assembly adjusting the overlap angle of the switching elements.

In one embodiment, the second relationship is:

AA＝(a+k*I)*(1-CB/60)

wherein AA is the lead angle, I is the phase current, CB is the overlap angle, a is a constant, a is positively correlated with the phase difference angle between the position detection module and the counter potential, and k is correlated with the parameter of the brushless motor.

In one embodiment, the brushless motor comprises a three-phase brushless inductive motor; the brushless motor position detection module comprises three position detection units.

Drawings

FIG. 1 is a schematic diagram of a power tool according to an embodiment of the present application;

FIG. 2 is a schematic diagram of a motor control circuit in a power tool according to an embodiment of the present application;

FIG. 3 is a schematic diagram of a driving circuit according to an embodiment of the present application;

FIG. 4is a schematic diagram of a driving circuit for controlling a driving circuit when no overlap angle is applied according to an embodiment of the present application;

FIG. 5 is a schematic diagram of a control timing diagram of a driving circuit for applying an overlap angle according to an embodiment of the present application;

FIG. 6 is a graph showing the variation of the lead angle with current according to an embodiment of the present application;

FIG. 7 is a graph comparing motor efficiency with torque for controlling motor control mode with and without lead angle at the constant speed stage of overlap angle according to one embodiment of the present application;

Fig. 8 is a flowchart of a control method of a brushless motor according to an embodiment of the present application;

fig. 9 is a schematic diagram of a control module of a brushless motor according to an embodiment of the application.

Detailed Description

In order to solve the above-mentioned problems, embodiments of the present invention provide an electric power tool and a control method thereof. Embodiments of the present invention are described in detail below with reference to the accompanying drawings.

The technical solutions in the embodiments of the present invention are clearly and completely described, and it is obvious that the described embodiments are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

It will be understood that when an element is referred to as being "disposed on" another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present. The terms "vertical," "horizontal," "left," "right," and the like are used herein for illustrative purposes only and are not meant to be the only embodiment.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

Fig. 1 is a schematic diagram of an electric tool according to the present application. The power tools include garden tools such as mower 101, pruner 102, mower 103, blower 104, etc., it should be understood that the illustrated tool types are not limiting to the power tools of the present application, and the power tools include impact tools such as screwdrivers, etc., and polishing tools such as angle grinders, etc.

As shown in fig. 2, the above-mentioned electric tools each include a battery pack 110, a brushless motor 120, a driving circuit 130, and a control unit 140.

Wherein, the battery pack 110 is detachably mounted on the electric tool for providing electric power to the electric tool.

Brushless motor 120 includes a stator winding and a rotor, the stator winding including three-phase windings, each phase winding being connected to battery pack 110 through drive circuit 130.

The driving circuit 130 is configured to convert the dc power output from the battery pack 110 into ac power, and supply the brushless motor 120 with power. The driving circuit 130 includes a plurality of switching elements connected between the battery pack 110 and the brushless motor 120, and the plurality of switching elements are controlled by the control unit 140 to perform switching operation, thereby transferring the electric power of the battery pack 110 to the brushless motor 120.

Fig. 3 is a schematic diagram of the driving circuit 130 according to the present embodiment. The driving circuit 130 is a three-phase bridge driving circuit, which includes six switching elements, and is divided into an upper arm and a lower arm. The six switching elements include three upper switching elements Q1, Q3, Q5 and three lower switching elements Q2, Q4, Q6, the three upper switching elements Q1, Q3, Q5 constituting an upper arm, and the three lower switching elements Q2, Q4, Q6 constituting a lower arm. The switching element may be a field-effect transistor (MOSFET) or a triode. Each pair of upper and lower switching elements is connected in series, for example a MOSFET, i.e. the source of the upper switching element is connected to the drain of the lower switching element. And the connection point of the source electrode of each pair of upper side switching elements and the drain electrode of the lower side switching element is respectively connected with each phase winding (U phase, V phase and W phase) in the three-phase windings in a one-to-one correspondence manner. The drain electrode of each upper side switching element is connected to the positive electrode output end of the battery pack, and the source electrode of each lower side switching element is connected to the negative electrode output end of the battery pack. The gates of the switching elements are connected to the control component 140, and are controlled by control signals output by the control component 140. The three upper switches Q1, Q3, Q5 are driven by high control signals UH, VH, and WH, respectively, output by the control component 140, and the three lower switches Q2, Q4, Q6 are driven by low control signals UL, VL, and WL, respectively, output by the control component 140. The control unit 140 determines the switching frequency of the switching element in the driving circuit 130 according to the signal feedback of the brushless motor to control the rotation speed of the brushless motor 120. That is, the control assembly 140 may adjust the rotational speed of the brushless motor 120 by adjusting the duty cycle of the control signal.

The control assembly 140 includes a position detection module 141, the position detection module 141 being positioned adjacent the rotor and being operable to detect the rotor position and generate a position signal. The control assembly 140 receives the position signal and calculates the actual rotational speed of the brushless motor 120 based on the position signal. As one example, the position detection module 141 may be a hall sensor. When the electric tool is in the steady-speed operation mode, the control component 140 may determine whether the actual rotation speed deviates from the target rotation speed according to the actual rotation speed calculated by the position signal and the target rotation speed corresponding to the steady-speed mode. If the actual rotation speed deviates from the target rotation speed, the control unit 140 adjusts the control signal of the switching element to adjust the actual rotation speed of the brushless motor 120 so that the actual rotation speed of the brushless motor 120 is maintained at the target rotation speed.

The control phase in which the control component 140 adjusts the control signal includes at least a non-overlapping control phase in which the control component 140 adjusts the duty cycle of the switching element to adjust the rotational speed of the brushless motor 120. The duty cycle in each phase on-time determines the duration of the voltage supplied to the motor, and in general the greater the duty cycle, the longer the duration of the voltage supplied to the motor in the on-time, and the greater the rotational speed of the motor. If the actual speed of the motor is lower than the target speed, the motor speed may be increased by increasing the duty cycle of each phase control signal, and if the actual speed of the motor is higher than the target speed, the motor speed may be decreased by decreasing the duty cycle of each phase control signal. The duty cycle is adjusted from an initial value of the duty cycle to 100%, wherein the initial value of the duty cycle is a duty cycle value corresponding to the idle rotation speed when the electric tool is started, and the duty cycle is adjusted from 50% to 100% assuming that the initial value of the duty cycle is 50%.

In one embodiment, the speed is adjusted by adjusting the duty cycle in a closed loop control manner. Specifically, the control component 140 adjusts the duty cycle in small steps each time, detects the actual rotational speed once every time the duty cycle is adjusted, and adjusts the duty cycle again in small steps according to the difference between the detected actual rotational speed and the target rotational speed. That is, the control component 140 will adjust the amplitude of the next duty cycle based on the actual rotational speed of the last duty cycle output. For example, the control component 140 may adjust the duty cycle according to a preset duty cycle adjustment amplitude, and determine whether the actual rotational speed reaches the target rotational speed after each adjustment, and stop the adjustment when the actual rotational speed reaches the target rotational speed. For example, the preset duty cycle may be adjusted by 1% each time the control assembly 140 adjusts the duty cycle until the detected actual rotational speed reaches the target rotational speed.

Fig. 4 shows a driving sequence diagram of the driving circuit 130 when the duty ratio of the control signal of the three-phase brushless motor is 100%, that is, the conduction angle of each phase reaches 120 °. As can be seen from fig. 4, when the PWM duty cycle increases to 100% of its maximum value that can be adjusted, the duty cycle cannot be adjusted any more. At this time, if the actual rotation speed of the motor still does not reach the target rotation speed, the rotation speed of the motor cannot be continuously increased by increasing the duty ratio, so that the electric tool cannot reach the desired output.

In order to further increase the rotational speed of the power tool to achieve the target rotational speed, the control stage in which the control assembly 140 adjusts the control signal may further include an overlap control stage in which the control assembly 140 further adjusts the overlap angle of the switching elements to adjust the rotational speed of the brushless motor 120. The motor speed is increased by adjusting the overlap angle of the switching elements, i.e. by increasing the on-time per phase. Because the conduction time of each phase is increased, the conduction angles of the two adjacent phases are partially overlapped during phase change, as shown in fig. 5, and the dotted line part is the electrical angle, i.e. the overlapping angle, of the control signals of the two adjacent phases. By increasing the overlap angle, the conduction angle of each phase can be further improved to be larger than 120 degrees. For example, when the overlap angle is 5 °, the conduction angle per phase is 125 °, and when the overlap angle is 10 °, the conduction angle per phase is 130 °. It will be appreciated that the overlap angle can be adjusted in the range of 0 deg. to 60 deg., i.e. the conduction angle per phase is not more than 180 deg. at maximum.

In one example, the amount of adjustment of the overlap angle is related to the difference between the actual rotational speed and the target rotational speed. When the overlap angle adjustment stage is started, the actual rotation speed is the rotation speed of the motor corresponding to the condition that the duty ratio is 100 percent and the overlap angle is 0 degree, namely when the overlap angle adjustment is started, the size of the overlap angle is related to the rotation speed difference value between the rotation speed of the motor corresponding to the condition that the duty ratio is 100 percent and the overlap angle is 0 degree and the target rotation speed. And in the overlap angle adjustment period, if the actual rotating speed deviates from the target rotating speed again, determining the size of the overlap angle according to the rotating speed difference between the current actual rotating speed and the target rotating speed. Wherein, the larger the rotational speed difference value is, the larger the overlap angle is. When the adjustment of the overlap angle is performed, the adjustment may be performed in a closed loop manner, that is, the control module 140 adjusts the overlap angle with a small angle according to the difference between the actual rotation speed and the target rotation speed, detects the difference between the current actual rotation speed and the target rotation speed after the adjustment, determines the influence of the overlap angle on the rotation speed, and then adjusts the overlap angle again according to the current actual rotation speed and the target rotation speed until the rotation speed reaches the target rotation speed.

In one embodiment, the adjustment of the overlap angle includes: and adjusting the overlapping angle according to a preset increment in each commutation period, wherein the value range of the preset increment is any value in the range of 0.01-0.5 degrees. That is, the overlap angle needs to be adjusted every time the phase is changed, and the adjustment amount of the overlap angle is a preset increment, wherein the increment refers to an amount by which the overlap angle is increased or decreased every time. The preset increment may be 0.01 °, 0.03 °, 0.05 °, 0.07 °, 0.1 °, 0.2 °, 0.3 °, 0.4 °,0.5 °, or the like. The incremental angle of each adjustment may be the same or different. Through adopting the preset increment of little angle to adjust, can avoid the overcurrent protection that causes because motor phase current is too big after single regulation, ensure that the motor can stable operation.

In another example, the overlapping control phase may be entered when the duty cycle does not reach 100%, for example, when the duty cycle is 70%, the adjacent two phases are controlled to overlap at the time of phase change, and the duty cycle of the control signal of the overlapping portion is also 70%. That is, during the overlap control phase, the control component 140 can adjust not only the magnitude of the overlap angle of the control signal, but also the duty cycle of the control signal.

In summary, during operation of the electrical tool, the actual rotational speed of the motor may be adjusted by adjusting the duty cycle and/or the overlap angle of the control signal.

Further, in the working process of the brushless motor, not only the duty ratio and/or the overlap angle of the control signal are/is required to be adjusted to realize the stable speed of the electric tool, but also the accurate phase change of the brushless motor is required to be controlled in the stable speed process so as to improve the working efficiency of the brushless motor. Because the motor coil is an inductive load, relative to the loading voltage on the coil, the phase current generated on the coil has certain time delay, so that the phase current phase on the coil is delayed behind the phase voltage, the output torque of the motor cannot reach the expected torque, the efficiency of the motor is affected, and noise is generated. To improve such a problem and to improve the efficiency, some correction methods may be adopted, such as advancing the phase of the phase current by advancing the phase of the phase applied voltage, and improving the motor efficiency by matching the phase of the phase induced voltage with the phase of the phase current to achieve maximum torque. The phase lead angle of such a phase voltage is referred to as "lead angle". Based on this, the control component 140 is further configured to adjust the lead angle of the control signal during the speed regulation process, so as to control the electric tool to perform phase inversion at a suitable time, thereby improving the output efficiency of the brushless motor 120.

In this embodiment, the control module 140 detects a parameter related to the load of the power tool and adjusts the lead angle according to the parameter. The parameters related to the load may be a phase current, a phase voltage, a rotation speed, etc. of the electric tool, and in this embodiment, the phase current of the electric tool is collected, and the lead angle is adjusted according to the phase current. The phase current refers to the magnitude of the current flowing through the winding in the brushless motor.

In the non-overlapping control stage, the control component adjusts the lead angle according to a preset first relation, wherein the first relation is a positive correlation relation between the lead angle and the phase current. When the duty ratio of the control signal is larger, the energizing time of the stator winding is longer, and the phase current generated on the winding is larger, so that the lead angle is larger. In this example, the first relationship between the phase current and the lead angle is stored in the memory of the control unit 140 in advance, so that the control unit 140 can obtain the lead angle according to the first relationship stored in advance and the phase current of the brushless motor in the non-overlapping control stage, and perform the commutation control according to the lead angle.

In the overlap control stage, the inventor finds through experiments that if the lead angle is adjusted according to the phase current by continuing to adopt the first relation, after the lead angle is inserted, the phase current is too large, so that the temperature of the brushless motor is too high, overheat protection is generated, or short-circuit protection is directly caused due to the too large phase current, and the motor is stopped due to protection when the motor just enters the overlap control stage. If the lead angle of the phase voltage is not adjusted, the phase is directly changed according to the Hall signal output by the position detection module, namely, the phase is changed when the Hall signal is detected, the motor is not stopped, but the brushless motor can not reach the maximum torque when in operation due to inaccurate phase change, the output efficiency of the motor is low, and further, the battery pack endurance time of the electric tool is short, so that the use experience of a user is influenced.

In this way, in the overlap control stage, in order to accurately commutate the brushless motor and improve the output efficiency of the brushless motor, it is necessary to correct the first relationship between the phase current and the lead angle and adjust the lead angle in accordance with the corrected second relationship. Compared with the first relation, the change rate of the lead angle with the phase current in the second relation is smaller than that of the lead angle with the phase current in the first relation. Wherein, the change rate of the lead angle with the phase current refers to the ratio between the change amount of the lead angle and the change amount of the phase current. That is, the same phase current variation amount corresponds to a different amount of change in the advance angle in the non-overlap control phase and the overlap control phase, and the amount of change in the advance angle in the overlap control phase is smaller, for example, in the non-overlap control phase, the phase current is increased by 5A, the advance angle is increased by 5 °, and in the overlap control phase, the phase current is increased by 5A, the advance angle is increased by only 3 °.

Specifically, the lead angle is positively correlated with the load size, and in the non-overlapping control phase, the phase current is positively correlated with the load, that is, the size of the phase current can represent the load size, so that in the non-overlapping control phase, the lead angle can be adjusted according to the phase current according to the positive correlation of the lead angle and the phase current. In the overlapping control stage, the phase of the control signal is advanced due to the introduction of the overlapping angle, so that weak magnetic current is generated, that is, the phase current contains a weak magnetic current component, and the weak magnetic current reflects the condition that the load is not present, so that the detected phase current cannot accurately represent the load. If the lead angle is still adjusted according to the relation of the non-overlapping control phases according to the actually acquired phase currents, the lead angle is excessively large. According to the embodiment, the first relation is corrected in the overlapping control stage, the lead angle is adjusted according to the corrected second relation according to the phase current, compared with the non-overlapping control stage, the change rate of the lead angle along with the phase current is reduced, the influence of the weak magnetic current is counteracted, the phase change is more accurate, the output efficiency of the brushless motor is improved, and the endurance time of the electric tool can be further improved.

When the rate of change of the lead angle along with the phase current in the non-overlapping control phase and the overlapping control phase needs to be detected, the control component 110 can directly collect the phase voltage and the phase current of the three-phase brushless motor, and meanwhile, the control component 110 is also connected to a position detection module, so that the Hall signal generated by the position detection module is structured, and the phase voltage waveform, the phase current waveform and the Hall signal are displayed in real time through an external oscilloscope. The current steady-speed stage can be judged to be a non-overlapping control stage or an overlapping control stage according to the phase voltage. When the conduction angle of the phase voltage is less than or equal to 120 degrees, the phase voltage is currently in a non-overlapping control stage, and when the conduction angle of the phase voltage is greater than 120 degrees, the phase voltage is currently in an overlapping control stage. Whether the lead angle control exists or not and the size of the lead angle can be detected by combining the phase voltage with the Hall signal. If the phase change point of the phase voltage is overlapped with the Hall signal, the lead angle control does not exist in the speed stabilizing control stage, otherwise, the lead angle control exists, and further, the size of the lead angle can be obtained according to the time difference between the phase change point of the phase voltage and the Hall signal. According to the values of the plurality of lead angles and the corresponding phase current acquired by the non-overlapping control stage and the overlapping control stage at each detection point, the change rate of the lead angles of the non-overlapping control stage and the overlapping control stage along with the phase current can be acquired.

In one embodiment, during the overlap control phase, the lead angle is related to both the phase current and the overlap angle. Wherein, in response to the overlap angle increasing, the control component 140 adjusts the lead angle such that the rate of change of the lead angle with phase current decreases. I.e. the larger the overlap angle, the smaller the rate of change of the lead angle with the phase current. Specifically, the larger the overlap angle is, the larger the weak magnetic current component in the phase current is, and the smaller the change rate of the lead angle with the phase current is, the influence of the weak magnetic current component can be counteracted.

When the relation between the change rate of the lead angle with the phase current and the overlap angle needs to be detected, the magnitude of the overlap angle of each commutation period can be detected according to the method of the foregoing embodiment, the magnitude of the phase current and the magnitude of the lead angle in the commutation period with the same magnitude of the overlap angle are collected, for example, the magnitude of the phase current and the magnitude of the lead angle in each commutation period under the commutation period with the overlap angle of 10 ° are collected, the change rate of the lead angle with the phase current in the case with the overlap angle of 10 ° is calculated according to the magnitude of the phase current and the magnitude of the lead angle in the commutation period, and the magnitude of the phase current and the magnitude of the lead angle in each commutation period under the commutation period of 10.5 ° are collected, and the change rate of the lead angle with the phase current in the case with the overlap angle of 10.5 ° is calculated according to the magnitude of the phase current and the magnitude of the lead angle in each commutation period, so on, and the relation between the change rate of the lead angle with the phase current and the overlap angle can be detected.

Further, during the overlap control phase, the control component 140 controls the lead angle to decrease in response to an increase in the overlap angle at the same phase current, i.e., the lead angle varies inversely with the overlap angle at the same phase current.

When the change rule between the advance angle and the overlap angle needs to be detected, the change rule can be obtained by measuring an electric tool with partial working condition change. As shown in fig. 1, the electric tool may be a tool whose working conditions are often changed when the mower 101, the pruner 102, the mower 103, etc. are working, and when the tool is working, the load of the electric tool is changed due to different degrees of density of grass and branches. By detecting the phase voltage and the hall signal of the electric tool in the foregoing manner, it is judged whether the electric tool reaches the overlap angle control stage. When the electric tool reaches the overlapping angle control stage, phase current, phase voltage and Hall signals of a brushless motor are obtained in real time when the electric tool runs under different loads, corresponding graphs of the phase voltage, the phase current and the Hall signals are generated, the time of the same phase current under each working condition is found, the phase voltage and the Hall signals corresponding to the same phase current are respectively obtained, the size of an overlapping angle is calculated according to the phase voltage, and an advance angle is calculated according to the time difference between a phase change point of the phase voltage and the Hall signals, so that the advance angle corresponding to each overlapping angle under the same phase current can be obtained, and the change rule of the advance angle along with the overlapping angle is judged.

Of course, as shown in fig. 1, for a part of electric tools with constant loads, for example, the blower 104 may also change the rotation speed of the electric tool by manually pulling the trigger of the blower several times, so as to change the phase current of the brushless motor, find the time of the same phase current under different working conditions, respectively obtain the phase voltage and the hall signal corresponding to the same phase current, calculate the size of the overlap angle according to the phase voltage, calculate the advance angle according to the time difference between the phase change point of the phase voltage and the hall signal, and determine the change rule of the advance angle along with the overlap angle.

As a specific example, the control module 140 obtains the lead angle according to the phase current and performs the phase change according to the obtained lead angle in the non-overlapping control phase when the power tool is operated. The first relation is a positive correlation relation that the lead angle changes along with the phase current, and the first relation is that:

Wherein AA is the lead angle, I is the phase current of the brushless motor, a is a constant, and k is the current coefficient. The constant a is related to the difference between the hall signal and the back emf, a being negative when the hall signal leads the back emf and positive when the hall signal lags the back emf. In a three-phase brushless motor, the hall signal typically lags behind the back emf, i.e., a is a positive value. The value of a is related to the angle of the hysteresis back electromotive force of the Hall signal, and the larger the angle of the hysteresis back electromotive force of the Hall signal is, the larger the value of a is. In general, the constant a has a value in the range of 0 ° or more and 60 ° or less. When the wiring form of the motor (triangle connection or Y connection) and the position of the Hall sensor are determined, the angle of the Hall signal lagging back to the back electromotive force is also determined, and the constant a is determined accordingly. The current coefficient k is related to the intensity of armature reaction of the brushless motor, and the higher the armature reaction is, the higher the k value is. n is an index of phase current, n is more than or equal to 1 and less than or equal to 3, n is larger, the number of terms of the polynomial is more, the exponent power of the phase current is higher, and the precision of the lead angle obtained according to phase current adjustment is also higher. But the greater n, the greater the computational effort required by the control assembly 140 and, correspondingly, the higher the processor accuracy requirements and the higher the cost in the control assembly 140.

Illustratively, when n=1, the first relationship is:

AA＝a+k1*I

In this embodiment, since the advance angle AA is in the range of 0 ° to 60 °, the value of (k 1×i) is in the ranges of (0-a) to (60-a), and when a is 0, the value of (k 1×i) is in the range of 0 to 60. Further, in this embodiment, the k1 value corresponding to the optimal efficiency point of the different motors may be obtained in advance through a calibration manner based on the value range of (k 1×i). For example, the value of the constant a can be obtained after the brushless motor is determined. And operating the brushless motor in a non-overlapping control stage, acquiring a phase current I corresponding to a certain target speed, calculating a value range of k1 based on the value ranges of I and k1, sequentially taking a plurality of values from small to large or from large to small of k1, respectively calculating a plurality of lead angles according to the plurality of k1 values, carrying out phase inversion according to the plurality of lead angles, and acquiring the output efficiency of the motor under the plurality of lead angles, wherein the k1 value corresponding to the lead angle with the maximum output efficiency is the optimal value. After k1 is obtained, the values of k1 and a are stored in the memory of the control module 140, so that during the process of controlling the electric tool, the control module 140 obtains the corresponding advance angle AA according to the collected phase current I and the pre-stored first relation.

When AA and I are linear, the control assembly 140 requires low computational effort to calibrate k1, and the control assembly 140 is low cost.

Of course, n may be 2 or 3, and when n=2, the first relationship is:

AA＝a+k1*I+k2*I*I

Wherein the value range of (k1+k2+II) is (0-a) to (60-a);

When n=3, the first relationship is:

AA＝a+k1*I+k2*I*I+k3*I*I*I，

wherein the value range of (k1+k2+k3+k1 is (0-a) to (60-a).

In the above formula, the physical meaning and the value range of a are the same as those of a in the linear relation, and k1, k2 and k3 depend on the parameters of the motor. Similarly, k1, k2 can also find the optimal value through the calibration method described above, and this embodiment will not be described herein. The greater n, the more complex the manner in which k1, k2, or k3 is obtained by calibration, the higher the computational effort and accuracy required by the control assembly 140 and, correspondingly, the higher the cost.

It should be noted that, in the non-overlapping control stage, the control component 140 may acquire the lead angle according to a linear primary first relationship or a nonlinear high-order first relationship in the whole process of the duty cycle steady speed, or may acquire the lead angle according to a linear primary first relationship in part of the stages, and acquire the lead angle according to a nonlinear high-order first relationship in part of the stages.

In the overlap control phase, the control module 140 acquires the lead angle according to the phase current and the overlap angle according to the second relationship, and performs commutation according to the acquired lead angle. Wherein the second relationship is:

Wherein AA is the lead angle, I is the phase current, CB is the overlap angle, a is a constant, and k is the current coefficient. The constant a is related to the difference between the hall signal and the back emf, preferably the constant a is equal to the difference between the hall signal and the back emf. A is negative when the hall signal leads the back emf and positive when the hall signal lags the back emf. In a three-phase brushless motor, the hall signal typically lags behind the back emf, i.e., a is a positive value. The value of a is related to the angle of the hysteresis back electromotive force of the Hall signal, and the larger the angle of the hysteresis back electromotive force of the Hall signal is, the larger the value of a is. In general, the constant a has a value in the range of 0 ° or more and 60 ° or less. When the wiring form of the motor (triangle connection or Y connection) and the position of the Hall sensor are determined, the angle of the Hall signal lagging back to the back electromotive force is also determined, and the constant a is determined accordingly. The current coefficient k is related to the intensity of armature reaction of the brushless motor, and the higher the armature reaction is, the higher the k value is. kn is the same as kn in the first relationship, and when the first relationship is determined, kn in the second relationship is also determined. For example, when the first relationship is aa=a+k1×i, the second relationship after the first relationship is corrected may be:

AA＝(a+k1*I)*(1-(CB/60)^m)

wherein the value range of m is more than or equal to 1 and less than or equal to 3, and the larger m is, the higher the corresponding advance angle precision is. In the second relationship, the values of m and n may be the same or different.

Illustratively, the second relationship may be:

Aa= (a+k1×i) ×1-CB/60)

Aa= (a+k1) I+k2I 1- (CB/60) ²) or

2X I i. 2I +k3. I) (1- (CB/60) ³) or

Aa= (a+k1×i+k2×i) ×1- (CB/60) ³) and the like

As can be seen from the above formula, the first relationship and the second relationship are both continuous, that is, in the non-overlapping control stage, each duty cycle corresponds to a phase current value, each phase current value corresponds to a lead angle, and in the overlapping control stage, each overlapping angle corresponds to a phase current value, and each phase current value corresponds to a lead angle. That is, the variation relationship of the lead angle with the duty ratio and the overlap angle is a continuously varying relationship, thereby facilitating precise adjustment of the lead angle, and by improving the adjustment accuracy, the output efficiency of the brushless motor can be improved.

As a specific example, the first relationship is: aa=a+k I, the second relationship is: aa= (a+k×i) ×1-CB/60. The first relation is adopted to obtain the advance angle in the whole phase of regulating the duty ratio speed stabilization, and the second relation is adopted to obtain the advance angle in the whole phase of regulating the overlap angle speed stabilization. Fig. 6 is a graph showing a change in the lead angle with the phase current in a two-dimensional plane having the phase current as the X axis and the lead angle as the Y axis when the first relationship and the second relationship are adopted. In fig. 6, a curve S1 is a curve of a first relationship, that is, a curve of a change of the lead angle with the phase current when the duty ratio is 100% or less, and curves S2, S3 and S4 are curves of a relationship of the lead angle with the phase current when the duty ratio is 100% or less. The curve S2 is a curve of the relationship between the corresponding lead angle and the phase current when the lead angle is CB1, the curve S3 is a curve of the relationship between the corresponding lead angle and the phase current when the lead angle is CB2, and the curve S4 is a curve of the relationship between the corresponding lead angle and the phase current when the lead angle is CB3, CB1 < CB2 < CB3. In the figure, I1 is a phase current corresponding to a duty cycle of 100%. And when the phase current is 0-I1, the duty ratio speed stabilizing control is adopted, and when the phase current exceeds I1, the overlap angle speed stabilizing control is adopted. As can be seen from fig. 6, the curves S2, S3 and S4 are located below the extension line of the curve S1 (the broken line portion of the curve S1), i.e., the slopes of the curves S2, S3 and S4 are smaller than the slope of the curve S1, regardless of the change in the overlap angle. That is, the rate of change of the lead angle with the phase current is smaller in the overlap control phase than in the non-overlap control phase. In the overlap control stage, the slopes of the curve S2, the curve S3 and the curve S4 decrease in sequence as the overlap angle increases, that is, the rate of change of the lead angle with the phase current decreases. When the overlap angle is 55 ° or more and less than 60 °, the variation amplitude of the lead angle with the current is less than 0.1 °, that is, the lead angle is hardly changed with the increase of the phase current.

The application can reduce the influence of weak magnetic current in the stable speed stage of the overlap angle by reducing the change rate of the advance angle along with the phase current in the overlap control stage, improves the commutation accuracy and improves the output efficiency of the motor.

As described above, if the first relation is not corrected in the overlap control stage, the advance angle is still adjusted according to the first relation, which may cause the phase current to be higher due to the generation of the weak current, and further cause the temperature rise of the brushless motor to be too high, the electric tool immediately performs high temperature protection after entering the overlap control stage, and the motor is stopped and cannot work. If the advance angle is not regulated in the overlapping control stage, the phase change is carried out only according to the Hall signal, so that the phase change is inaccurate, and the output efficiency of the motor is low. Fig. 7 is a graph showing the change of the motor efficiency with torque when the motor is operated with or without the lead angle control calculated in the overlap control stage according to the second relation. The motor efficiency is calculated by the ratio of the output power of the motor to the output power of the battery pack (i.e., the input power of the motor). In the figure, the horizontal axis represents the torque of the motor, the vertical axis represents the efficiency of the motor, the curve L1 represents the motor efficiency with the lead angle control versus torque, and the curve L2 represents the motor efficiency without the lead angle control versus torque. As can be seen from the figure, the motor output efficiency is higher than that without the lead angle control in the control scheme with the lead angle control under the same torque. In this embodiment, only the output efficiency of the motor with the motor torque at 0-0.3 n×m is tested, and the efficiency of the motor with the motor torque exceeding 0.3n×m is not tested, because when the torque exceeds 0.3n×m, the motor phase current without the lead angle control is too large, the temperature of the battery pack is also increased along with the motor phase current, and the motor is easily burned up after the torque is increased continuously, so that potential safety hazards exist.

According to the application, the phase change is carried out by adopting the lead angle in the overlapping control stage, and the relation between the lead angle and the phase current is regulated, so that the change rate of the lead angle along with the phase current in the overlapping control stage is smaller than that of the lead angle along with the phase current in the non-overlapping control stage, the phase change accuracy in the overlapping control stage is improved, the output torque of the brushless motor is improved, and the output efficiency of the brushless motor is improved. Because of the improvement of the output efficiency of the brushless motor, the power supply endurance time of the battery pack for the electric tool is also prolonged. In the working process of the electric tool, the load of the motor can influence the rotating speed, and the electric quantity of the battery pack can be gradually reduced along with the use of the tool, so that the rotating speed of the motor can be reduced. In order to maintain the motor speed at the target speed, when the battery pack capacity is reduced, the duty ratio and/or the overlap angle of the driving circuit are/is adjusted to perform speed stabilization. For a battery pack with rated voltage of 60V, when a brushless motor with rated power of about 2000W is supplied, the overlap angle steady speed is started when the electric quantity of the battery pack is reduced to about 50% of full electric quantity. Therefore, if the commutation of the overlapping control stage is inaccurate, the battery pack capacity can be quickly reduced to a protection value, and the use experience of a user is affected. By adopting the relation to adjust the lead angle, the endurance time of the battery pack can be prolonged. And moreover, due to the improvement of the output efficiency of the motor, the switching loss of a switching element in a driving circuit on a motor control board is reduced, so that the heating value of the control board is reduced, and the overheat protection caused by overhigh temperature of the control board due to inaccurate phase change can be avoided.

In one embodiment, the brushless motor comprises a three-phase brushless sensored motor, the position detection module of the three-phase brushless sensored motor comprises three position detection units, i.e. the three-phase brushless sensored motor comprises three hall sensors, and the electrical angles installed between the three hall sensors differ by 120 °. The lead angle control method provided by the embodiment can be applied to a three-phase brushless inductive motor.

When the actual rotating speed of the motor is smaller than the target rotating speed in the working process of the electric tool, the adjusting priority of the duty ratio of the driving signal is higher than the priority of the overlapping angle; when the actual rotation speed is greater than the target rotation speed, the adjustment priority of the overlap angle of the drive signals is higher than the priority of the duty ratio. That is, when the speed is required to be increased, the duty ratio is preferentially adjusted, and after the duty ratio reaches 100%, if the target rotation speed is not reached yet, the overlap angle is adjusted; and when the speed is reduced, the overlapping angle is preferentially reduced, and when the overlapping angle reaches 0 DEG, if the target rotating speed is not reached yet, the duty ratio is adjusted.

In one embodiment, the steady speed mode of the power tool may be switched automatically or manually by the user. When the automatic switching is performed, the electric tool is powered on and then enters an idle mode. In the idle mode, the control assembly 140 detects a parameter of the power tool in real time and immediately switches to the load mode when the parameter of the power tool indicates that the power tool is experiencing a load. Wherein, in the no-load mode, the motor of the electric tool keeps working at a first rotation speed; in the load mode, the motor of the power tool is operated at a second rotational speed, the first rotational speed being less than the second rotational speed. In this embodiment, the parameter of the electric tool may be the motor phase current or the motor rotational speed. After the electric tool is switched from the no-load mode to the load mode, the load mode can be kept to work all the time until the power is off, so that the rotating speed is prevented from being switched back and forth in the working process, and the working efficiency of the electric tool can be improved. Of course, after the electric tool is switched to the load mode, the current load can be detected in real time, and when the current load becomes smaller, the electric tool is switched to the idle mode (namely, the second rotating speed is switched to the first rotating speed), so that the electric energy consumption of the electric tool can be reduced, and the endurance time of the electric tool can be prolonged.

As yet another example, the steady-speed mode of operation of the power tool may also be triggered by a user. When triggered by a user, the electric tool is provided with a trigger module, receives a control instruction sent by the user, and sends the control instruction to the control component 140, so that the control component 140 controls the tool to work at a steady speed according to the user instruction. For example, a gear adjustment module may be provided on the power tool, the gear adjustment module having a plurality of gears, each gear corresponding to a target speed. The gear adjusting module comprises a man-machine operation interface and is used for being adjusted by a user. The control component 140 receives the gear control signal sent by the gear adjusting module, obtains a target speed corresponding to the gear according to the gear control signal, and performs speed up control or speed down control according to the difference between the current speed and the target speed.

In the embodiment, the electric tool can respectively work at different rotation speeds during idle load and heavy load, on one hand, the work efficiency of the electric tool can be improved through the stable speed work, so that the output power of the electric tool cannot be changed due to factors such as reduction of the battery pack electric quantity, and the like, and the high-efficiency work can be ensured when the battery pack is low in electric quantity; on the other hand, the low-rotation-speed working is adopted in light load, and the rotation speed is increased in heavy load, so that the energy of the battery pack can be saved.

Yet another embodiment of the present application provides a power tool, as shown in fig. 2, each of which includes a battery pack 110, a brushless motor 120, a driving circuit 130, and a control assembly 140.

The control assembly 140 includes a position detection module 141, the position detection module 141 being positioned adjacent the rotor and being operable to detect the rotor position and generate a position signal. The control module 140 receives the position signal, calculates the actual rotational speed of the brushless motor 120 based on the position signal, and adjusts the signal of the control strand of the switching element to maintain the target rotational speed of the brushless motor when the actual rotational speed deviates from the target rotational speed of the power tool.

The control phase in which the control component 140 adjusts the control signal includes a non-overlapping control phase in which the control component 140 adjusts the duty cycle of the control signal and an overlapping control phase in which the control component 140 adjusts at least the overlapping angle of the control signal. That is, during the overlap control phase, the duty cycle of the control signal may be 100%, where the control component 140 adjusts only the overlap angle of the control signal; of course, the duty cycle of the control signal may be less than 100%, and the control module 140 may adjust the duty cycle of the control signal and the overlap angle of the control signal.

The control assembly 140 is also used to adjust the lead angle of the control signal to control the drive output of the power tool.

When the control module 140 adjusts the control signal of the switching element, the control module 140 adjusts the lead angle according to the phase current of the electric tool, wherein the larger the overlap angle is, the smaller the change rate of the lead angle with the change of the phase current is.

Further, in the present embodiment, the advance angle control is also performed in the non-overlapping control stage of the electric power tool. Specifically, during the non-overlap control phase, the control component 140 adjusts the lead angle according to a preset first relationship, and during the overlap control phase, the control component adjusts the lead angle according to a preset second relationship. In the second relation, the change rate of the lead angle with the phase current is smaller than that of the lead angle with the phase current in the first relation at least in part of the phases. That is, in the overlap control phase, there is at least a part of the period in which the rate of change of the lead angle with the phase current is smaller than that in the non-overlap control phase. Preferably, the rate of change of the lead angle with the phase current is smaller throughout the overlap control phase than the rate of change of the lead angle with the phase current in the non-overlap control phase.

Further, at the same phase current, the control component 140 controls the lead angle to decrease in response to the overlap angle increasing.

Further, the first relationship is:

wherein AA is a lead angle, I is a phase current, a is a constant, a is positively correlated with the phase difference angle between the position detection module and the counter potential, k is a constant, k is positively correlated with the armature reaction strength of the brushless motor, n is an index of the phase current, and n is more than or equal to 1 and less than or equal to 3.

The second relationship is:

wherein AA is a lead angle, I is a phase current, CB is an overlap angle, a is a constant, a is positively correlated with the phase difference angle between the position detection module and the counter potential, k is a constant, k is positively correlated with the armature reaction strength of the brushless motor, n is an index, n is not less than 1 and not more than 3, m is an index of an overlap angle coefficient (CB/60), and m is not less than 1 and not more than 3.

Regarding the specific limitation of the electric tool, reference may be made to the previous embodiment, and this embodiment is not repeated here. According to the embodiment, the lead angle is adjusted according to the phase current in the overlapping control stage, the phase is converted by the lead angle, and the change rate of the lead angle along with the phase current is smaller along with the increase of the overlapping angle, namely the lead angle depends on the two factors of the overlapping angle and the phase current, so that the adjustment of the lead angle in the overlapping control stage is more accurate, the output efficiency of the brushless motor is improved, and the duration of a battery pack is further improved.

A further embodiment of the present application provides a control method of a brushless motor, wherein the brushless motor is the brushless motor described in the foregoing embodiment, the control method being performed by a control unit of an electric tool, as shown in fig. 8, the control method comprising:

Step S10: receiving a position signal sent by a position detection module, and calculating the actual rotating speed of the brushless motor according to the position signal;

Step S20: judging whether the actual rotating speed reaches the target rotating speed or not;

Step S30: when the actual rotating speed deviates from the target rotating speed, adjusting the control signal so that the actual rotating speed reaches the target rotating speed, wherein a control stage of the control signal comprises a non-overlapping control stage and an overlapping control stage, the duty ratio of the control signal is adjusted in the non-overlapping control stage, and at least the overlapping angle of the control signal is adjusted in the overlapping control stage; receiving phase currents and adjusting the lead angle of a control signal according to the phase currents according to a preset first relation in a non-overlapping control stage; and in the overlapping control stage, receiving the phase current and adjusting the lead angle of the control signal according to a preset second relation, wherein the change rate of the lead angle along with the phase current in the second relation is smaller than that of the lead angle along with the phase current in the first relation.

In one embodiment, the control method further includes: in the overlap control phase, the control lead angle is reduced in response to the increase in the overlap angle being large at the same phase current.

In one embodiment, the control method further includes: in the overlap control phase, in response to an increase in the overlap angle, the lead angle is adjusted so that the lead angle decreases with the rate of change of the phase current.

For the specific embodiment of the control method for adjusting the lead angle of the brushless motor, refer to the foregoing specific embodiment of the electric tool, and will not be described herein.

According to the control method, the speed stabilization can be performed by adjusting the duty ratio and/or the overlapping angle of the driving signals of the switching element, and the advance angle of the driving signals is also controlled when the duty ratio and/or the overlapping angle are adjusted, the advance angle is obtained according to the first relation between the phase current and the advance angle to perform phase change control in a non-overlapping control stage, and the advance angle is obtained according to the second relation between the phase current and the advance angle by correcting the first relation in the overlapping control stage, so that accurate phase change can be realized in different speed stabilization stages, and the efficiency of the motor is improved while the speed stabilization operation of the motor is maintained.

An embodiment of the present application also provides a computer-readable storage medium in which a computer program is stored, the computer program being loaded by a processor and executing the control method of the aforementioned power tool.

As shown in fig. 9, a further embodiment of the present application provides a control module for controlling the aforementioned motor, the control module comprising:

The receiving unit is used for receiving the position signal sent by the position detection module;

A calculation unit for calculating an actual rotation speed of the brushless motor based on the position signal;

a judging unit for judging whether the actual rotation speed reaches the target rotation speed;

The control unit is used for adjusting the control signal when the actual rotating speed deviates from the target rotating speed so as to enable the actual rotating speed to reach the target rotating speed, the control signal is used for controlling the on and off of a switching element in the driving circuit, the control stage of the control signal comprises a non-overlapping control stage and an overlapping control stage, the control unit adjusts the duty ratio of the control signal in the non-overlapping control stage, and the control unit at least adjusts the overlapping angle of the control signal in the overlapping control stage.

In the non-overlapping control stage, the receiving unit is also used for receiving phase current, and the control unit is used for adjusting the lead angle according to the phase current according to a preset first relation;

In the overlapping control stage, the receiving unit is further used for receiving phase currents, and the control unit is used for adjusting the lead angle according to the phase currents according to a preset second relation, wherein the change rate of the lead angle along with the phase currents in the second relation is smaller than that of the lead angle along with the phase currents in the first relation.

In one embodiment, the control unit controls the advance angle to decrease in response to an increase in the overlap angle at the same phase current in the overlap control phase.

In one embodiment, the control unit controls the advance angle to continuously vary in response to a continuous variation of the overlap angle at the same phase current.

In one embodiment, the control unit controls the change of the lead angle such that the rate of change of the lead angle with the phase current decreases in response to an increase in the overlap angle.

In the overlap control phase, the second relationship includes:

Wherein AA is a lead angle, I is a phase current, CB is an overlap angle, a is a constant, a is positively correlated with the phase difference angle between the position detection module and the counter potential, k is a constant, k is positively correlated with the armature reaction strength of the brushless motor, n is an index of the phase current, n is not less than 1 and not more than 3, m is an index of an overlap angle coefficient (CB/60), and m is not less than 1 and not more than 3.

The control module can perform speed stabilization by adjusting the duty ratio and/or the overlapping angle of the driving signals of the switching element when the electric tool is in speed stabilization, and also control the lead angle of the driving signals when the duty ratio and/or the overlapping angle are adjusted, acquire the lead angle according to the first relation between the phase current and the lead angle to perform phase change control in a non-overlapping control stage, acquire the lead angle according to the second relation between the phase current and the lead angle in an overlapping control stage by correcting the first relation, so that accurate phase change can be realized in different speed stabilization stages, the efficiency of the motor is improved while the stable operation of the motor is maintained, and the duration of a battery pack is prolonged.

Claims

1. An electric power tool, characterized in that the electric power tool comprises:

A battery pack;

a brushless motor including a stator assembly and a rotor rotating around the stator assembly, the stator assembly for receiving the power of the battery pack and driving the rotor to rotate;

A driving circuit including a plurality of switching elements for controlling supply of electric power from the battery pack to the brushless motor;

The control assembly comprises a position detection module, a control module and a control module, wherein the position detection module is used for detecting the position of the rotor and generating a position signal, and the control assembly is used for calculating the actual rotating speed of the brushless motor according to the position signal and adjusting a control signal of the switching element when the actual rotating speed deviates from a target rotating speed so as to enable the brushless motor to reach the target rotating speed;

The control module adjusts the control phase of the control signal including a non-overlapping control phase in which the control module adjusts the duty cycle of the control signal and an overlapping control phase in which the control module adjusts at least the overlapping angle of the control signal;

the control assembly is also used for adjusting the lead angle of the control signal to control the driving output of the electric tool;

in the non-overlapping control stage, the control component detects phase current of the electric tool and adjusts the lead angle according to a preset first relation according to the phase current;

during the overlap control phase, the control component corrects the first relationship and adjusts the lead angle according to the corrected second relationship;

The rate of change of the lead angle with the phase current in the second relationship is smaller than the rate of change of the lead angle with the phase current in the first relationship.

2. The power tool of claim 1, wherein the control assembly controls the lead angle to decrease in response to the overlap angle increasing at the same phase current during the overlap control phase.

3. The power tool of claim 2, wherein the control assembly controls the advance angle to continuously vary in response to a continuous variation of the overlap angle at the same phase current.

4. The power tool according to claim 1, wherein in the overlap control phase, in the second relation, in response to an increase in the overlap angle, the control component controls the advance angle change so that a rate of change of the advance angle with the phase current change decreases.

5. The power tool of claim 1, wherein during the non-overlapping control phase, the first relationship comprises:

6. The power tool of claim 1, wherein during the overlap control phase, the second relationship comprises:

7. The power tool according to claim 1, wherein in the overlap control phase, a magnitude of the overlap angle is correlated with a rotational speed difference between the target rotational speed and an actual rotational speed, and the control component controls the overlap angle to increase in response to an increase in the rotational speed difference.

8. The power tool of claim 7, wherein the manner of adjusting the overlap angle comprises: and in each commutation period, the control component adjusts the overlapping angle according to preset increment, wherein the value range of the preset increment is any value in the range of 0.01-0.5 degrees.

9. The power tool of claim 1, wherein the control assembly preferentially adjusts the duty cycle when the actual rotational speed is less than the target rotational speed;

The control component preferentially adjusts the overlap angle when the actual rotational speed is greater than the target rotational speed.

10. The power tool of claim 1, wherein the brushless motor comprises a three-phase brushless inductive motor;

the position detection module of the brushless motor includes three position detection units.

11. An electric power tool, characterized in that the electric power tool comprises:

A battery pack;

In the overlap control phase, the control module adjusts the lead angle according to a phase current of the brushless motor, wherein in response to the overlap angle increasing, the control module controls the lead angle so that a rate of change of the lead angle with a change of the phase current decreases.

12. The power tool of claim 11, wherein during the non-overlapping control phase, the control assembly adjusts the lead angle according to a preset first relationship;

In the overlapping control stage, the control component adjusts the lead angle according to a preset second relation;

The rate of change of the lead angle with the phase current is smaller in at least part of the phases in the second relationship than in the first relationship.

13. The power tool of claim 11, wherein the control assembly controls the lead angle to decrease in response to the overlap angle increasing at the same phase current during the overlap control phase.

14. The power tool of claim 11, wherein during the non-overlapping control phase, the first relationship comprises:

15. The power tool of claim 14, wherein during the overlap control phase, the second relationship comprises:

16. A control method of a brushless motor of an electric tool, wherein the brushless motor includes a stator assembly and a rotor rotating around the stator assembly;

The electric tool includes:

A position detection module for detecting a position of the rotor and generating a position signal;

The control method of the brushless motor is characterized by comprising the following steps:

receiving the position signal and calculating the actual rotating speed of the brushless motor according to the position signal;

judging whether the actual rotating speed reaches the target rotating speed or not;

Adjusting a control signal of the switching element when the actual rotational speed deviates from the target rotational speed so that the actual rotational speed reaches the target rotational speed, a control phase of the control signal including a non-overlapping control phase in which a duty ratio of the control signal is adjusted, and an overlapping control phase in which at least an overlapping angle of the control signal is adjusted;

In the non-overlapping control stage, receiving phase current and adjusting the lead angle of a control signal according to a preset first relation according to the phase current so as to control the driving output of the electric tool;

And in the overlapping control stage, receiving phase current and adjusting the lead angle of the control signal according to the phase current according to a preset second relation so as to control the driving output of the electric tool, wherein the change rate of the lead angle along with the phase current is smaller than that of the lead angle along with the phase current in the first relation.

17. The method of controlling a brushless motor of a power tool according to claim 16, characterized in that the method further comprises:

in the overlap control phase, the advance angle is controlled to decrease in response to the increase in the overlap angle at the same phase current.

18. The method of controlling a brushless motor according to claim 16, characterized in that the method further comprises:

in the overlap control phase, the advance angle is adjusted so that the smaller the rate of change of the advance angle with the phase current is in response to the overlap angle increasing.

19. A control module for a brushless motor of a power tool, wherein the brushless motor comprises:

a stator assembly and a rotor rotating around the stator assembly;

The electric tool includes:

the brushless motor control device is characterized in that the control module is connected with the brushless motor and used for controlling the brushless motor to operate according to a target rotating speed, and the control module comprises:

a judging unit configured to judge whether the actual rotation speed reaches the target rotation speed;

A control unit configured to adjust a control signal of the switching element when the actual rotation speed deviates from the target rotation speed so that the actual rotation speed reaches the target rotation speed, the control unit adjusting a control phase of the control signal including a non-overlapping control phase in which the control unit adjusts a duty ratio of the control signal and an overlapping control phase in which the control unit adjusts at least an overlapping angle of the control signal;

In a non-overlapping control stage, the control unit is further used for receiving phase currents and adjusting the lead angle according to the phase currents according to a preset first relation;

In the overlapping control stage, the control unit is further configured to receive a phase current and adjust the lead angle according to the phase current according to a preset second relationship, where a rate of change of the lead angle with the phase current is smaller than a rate of change of the lead angle with the phase current in the first relationship.

20. A computer-readable storage medium, in which a computer program is stored, the computer program being loaded and executed by a processor to implement a method of controlling a brushless motor of a power tool according to any one of claims 16 to 18.