JP2007274764A - Apparatus and method for controlling three-phase brushless dc motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a controller for three-phase brushless DC motors wherein, even when a switching element in an inverter circuit is overloaded, the load on the switching element can be reduced without reducing a motor current. <P>SOLUTION: The controller 30 is configured to vary a duty ratio indicating a ratio of time for which upper-arm switching elements are on and lower-arm switching elements are off, and thereby PWM-control a three-phase inverter circuit. The controller includes means 44, 46, 36 for, when it is determined that the switching elements are in overload state in which an overloaded switching element is present only in either the upper-arm switching elements or the lower-arm switching elements, adjusting the PWM duty ratio of each phase determined based on a voltage command value of each phase toward such a direction that the current passed through the arm on the overloading side is reduced. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a control device and a control method for a three-phase brushless DC motor that PWM-controls a three-phase inverter circuit that supplies power to the three-phase brushless DC motor.

  For example, a three-phase brushless DC motor is widely used as a motor for an electric power steering (EPS) of an automobile. In the control of such a three-phase brushless DC motor, in order to protect the switching element in the three-phase voltage source inverter circuit as a power conversion circuit from damage, a measure for limiting the armature current at the time of overload is performed.

  Specifically, as shown in FIG. 1, a current limit map that determines the maximum armature current according to the element temperature as a load of the switching element is provided, and the current is applied to the switching element at the time of overload. The load is reduced. According to the map of FIG. 1, when the element temperature exceeds the threshold value Tjth, the value of the maximum armature current is gradually decreased from Imax. Tjmax indicates the maximum element temperature.

  However, according to the above-described control, since the motor current is reduced as the overload process, the output torque of the motor is reduced, and as a result, the necessary assist by the motor cannot be obtained. Also, in the case of operating conditions with a temporary motor lock state, or when the heat dissipation structure is biased, load concentration on some switching elements occurs, and overload processing is likely to occur. In these cases as well, sufficient assistance from the motor cannot be obtained.

  As a prior art document related to the present invention, Patent Document 1 below discloses a method for controlling a three-phase brushless DC motor by a load. Patent Document 2 below discloses a drive circuit for a brushless DC motor having a PWM circuit for controlling the rotational speed. Further, Patent Documents 3 and 4 below disclose a method for driving a three-phase brushless DC motor.

JP 2003-324986 A Japanese Patent No. 3131157 JP 2004-328912 A JP 2003-289687 A

  The present invention has been made in view of the above-described problems, and an object thereof is to reduce the load of the switching element without reducing the motor current even when the switching element in the inverter circuit is overloaded. It is an object of the present invention to provide a control device and a control method for a three-phase brushless DC motor that can reduce the noise.

  In order to achieve the above object, according to the present invention, in each phase of a three-phase inverter circuit that supplies power to a three-phase brushless DC motor, the upper arm switching element is on and the lower arm switching element is off. A control device for a three-phase brushless DC motor that PWM-controls a three-phase inverter circuit by changing a duty ratio indicating a time ratio, wherein the load detection unit detects a load of each switching element, and the load detection unit Overload determination means for determining whether or not an overload switching element exists only in one of the upper arm switching element and the lower arm switching element, based on the output of PWM of each phase determined based on the voltage command value of each phase when determined to be in the overload state by the means The Yuti ratio control apparatus for a three-phase brushless DC motor the current flowing through the overload side arm is anda PWM duty ratio adjusting means for adjusting the direction to decrease is provided.

  According to the present invention, in each phase of the inverter circuit that supplies power to the motor, the inverter circuit is PWM-controlled by changing the duty ratio that indicates the time ratio of the ON state and the OFF state of each switching element. A control device for the motor, the load detection means for detecting the load of each switching element, and whether or not the overload switching element is present is determined based on the output of the load detection means Overload determination means, and when the overload determination means determines that the overload state is present, the PWM duty ratio of each phase determined based on the voltage command value of each phase is set to the arm on the overload side. There is provided a motor control device comprising PWM duty ratio adjusting means for adjusting the flowing current in a decreasing direction.

  According to the present invention, in each phase of the inverter circuit that supplies power to the motor, the inverter circuit is PWM-controlled by changing the duty ratio that indicates the time ratio of the ON state and the OFF state of each switching element. A control method for a motor, wherein a load detection step for detecting a load of each switching element and whether or not an overload switching element exists is determined based on an output of the load detection step Overload determination step, and when the overload determination step determines that the overload state exists, the PWM duty ratio of each phase determined based on the voltage command value of each phase is set to the arm on the overload side. There is provided a method for controlling a motor comprising a PWM duty ratio adjusting step for adjusting a flowing current in a decreasing direction.

  In the control device and the control method of the three-phase brushless DC motor according to the present invention, if there is an overload state in the upper arm switching element of the three-phase inverter circuit, the PWM duty ratio is reduced in each phase, As a result of a decrease in the time during which current flows through the upper arm and an increase in the time during which current flows through the lower arm, the overload state of the upper arm switching element is eliminated. At that time, each phase voltage is lowered, but the interphase voltage, that is, the voltage between the motor terminals is kept constant, so that the motor current does not decrease.

  Similarly, if any of the lower arm switching elements of the three-phase inverter circuit is in an overload state, the PWM duty ratio is increased in each phase, so that the time during which current flows to the upper arm increases and the lower arm As a result of the decrease in the time during which the current flows, the overload state of the lower arm switching element is eliminated. At that time, each phase voltage rises, but the interphase voltage, that is, the voltage between the motor terminals is kept constant, so that the motor current remains constant.

  Therefore, according to the present invention, the load on the switching element in an overload state can be reduced by distributing the load to the upper arm switching element and the lower arm switching element without reducing the output torque of the motor.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 2 is a diagram showing a configuration of a three-phase brushless DC motor system to which an embodiment of the control device according to the present invention is applied. In the figure, reference numeral 10 denotes a permanent magnet synchronous motor, reference numeral 12 denotes a machine such as an electric power steering for an automobile assisted by the motor, reference numeral 14 denotes a DC power source such as a battery, reference numeral 20 denotes a three-phase voltage source inverter circuit, reference numeral Reference numeral 30 denotes a control device.

  In the three-phase voltage source inverter circuit 20, a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) having a low driving power, a high switching speed, and a long allowable short-circuit time is used as a switching element. Conventionally, in order to protect the switching element from damage, a measure for limiting the armature current at the time of overload has been implemented.

  The control device 30 includes a current command value calculation unit 32, a voltage command value calculation unit 34, a PWM command value calculation unit 36, a MOSFET drive circuit 38, a rotation angle sensor (resolver) 40, a current sensor 42, a temperature sensor 44, an overload process. Part 46 and the like. Here, the current command value calculation unit 32 receives the command torque and calculates each phase current command value, but also performs a current reduction process during an overload. The voltage command value calculation unit 34 receives each phase current command value from the current command value calculation unit 32 and calculates a corresponding phase voltage command value (three-phase sine wave voltage command value).

  The PWM command value calculation unit 36 receives each phase voltage command value from the voltage command value calculation unit 34 and calculates each phase PWM command value, that is, each phase duty ratio, and performs PWM reduction processing described later. For each of the U-phase, V-phase, and W-phase, the MOSFET drive circuit 38 turns on the upper arm MOSFET while the duty ratio signal is active, while turning the lower arm MOSFET when the duty ratio signal is inactive. Each gate signal to be turned on is output.

  The rotation angle sensor (resolver) 40 detects the angle (electrical angle) of the rotor of the motor 10. The current sensor 42 detects the actual current value of each phase. The temperature sensor 44 is installed in the vicinity of each MOSFET and detects the temperature of each MOSFET. The overload processing unit 46 determines and processes the load state of each MOSFET based on the temperature of each MOSFET.

  FIG. 3 is a flowchart showing a processing procedure of the overload processing unit 46. This process is executed at a predetermined time period. 4A and 4B are diagrams showing maps in which the upper limit value and the lower limit value of the PWM duty ratio are determined according to the switching element temperature. First, in step 102, it is determined whether there is a switching element in an overload state based on the temperature detected by the temperature sensor 44. If there is no overload element, this routine ends.

  If it is determined in step 102 that there is an overloaded switching element, the process proceeds to step 104. In step 104, the location of the switching element in an overload state, that is, which side (U phase, V phase, or W phase) of the element (upper arm or lower arm) is stored.

  Next, at step 106, it is determined whether or not an overload switching element exists only in one of the upper arm switching element and the lower arm switching element. If there is an overload switching element in both the upper arm switching element and the lower arm switching element, the process proceeds to step 108. In step 108, since load reduction treatment by PWM control cannot be performed, it is determined to limit the current value as usual, and the maximum current value is calculated based on the map of FIG. Separately, the current command value calculation unit 32 performs a current reduction process.

  On the other hand, if it is determined in step 106 that an overloaded switching element exists only in one of the upper arm switching element and the lower arm switching element, the process proceeds to step 110. In step 110, it is determined whether the overloaded switching element is an upper arm element or a lower arm element.

  If it is determined in step 110 that the overloaded switching element is an upper arm element, the process proceeds to step 112, and a PWM command value (in accordance with the switching element temperature) (see FIG. 4A) is referred to. (Duty ratio) upper limit value LIMAXPWM is determined, and this routine ends. According to the map of FIG. 4A, when the element temperature exceeds the threshold value Tjth, the value of the PWM command upper limit value LIMAXPWM is gradually decreased from 100. Tjmax indicates the maximum element temperature.

  On the other hand, if it is determined in step 110 that the overloaded switching element is a lower arm element, the process proceeds to step 114, and the PWM command corresponding to the switching element temperature is referred to with reference to the map of FIG. The lower limit value LIMINPWM of the value (duty ratio) is determined, and this routine ends. According to the map of FIG. 4B, when the element temperature exceeds the threshold value Tjth, the value of the PWM command lower limit value LIMINPWM is gradually increased. Tjmax indicates the maximum element temperature. After execution of step 108, 112 or 114, the routine ends.

  FIG. 5 is a flowchart showing a processing procedure of the PWM command value calculation unit 36. This process is executed at a predetermined time period. First, in step 202, the U-phase voltage command value VU, the V-phase voltage command value VV, and the W-phase voltage command value VW are received from the voltage command value calculation unit 34, and the U-phase PWM command value PWMU, A V-phase PWM command value PWMV and a W-phase PWM command value PWMW are calculated.

PWMU = VU * PWMK / VB + PWMC + LIOFF
PWMV = VV * PWMK / VB + PWMC + LIOFF
PWMW = 3 * (PWMC + LIOFF) −PWMU−PWMV

  In the above formula, PWMC is a PWM command value equivalent to 50%. PWMK is a conversion coefficient from the voltage command value to the PWM command value. VB is a drive voltage monitor value. Furthermore, LIOFF is a reduced offset value (initial value is 0) calculated by the steps described later.

Next, in step 204, it is determined whether or not the calculated phase PWM command values PWMU, PWMV, and PWMW satisfy the hardware limitation, that is, whether they are within the following ranges. Note that MINDUTY and MAXDUTY are an upper limit value and a lower limit value, respectively, due to hardware limitations.
MINDUTY <PWMU <MAXDUTY,
MINDUTY <PWMV <MAXDUTY, and MINDUTY <PWMW <MAXDUTY

  If it is determined in step 204 that there is a PWM command value that does not satisfy the hardware restrictions, the process proceeds to step 206. In step 206, it is determined to limit the current value, and this routine ends. Separately, the current command value calculation unit 32 performs a current reduction process.

  On the other hand, if it is determined in step 204 that all PWM command values satisfy the hardware limitation, the process proceeds to step 208. In step 208, the overload processing unit 46 calculates the PWM # using the PWM command values PWMU, PWMV, and PWMW with the command value of the phase in which the overload element exists as PWM # (# is U, V, or W). It is determined whether or not the PWM command upper limit value LIMAXPWM is exceeded.

If it is determined in step 208 that PWM #> LIMAXPWM, the process proceeds to step 210. In step 210, a reduced offset value LIOFF is calculated by the following arithmetic expression. Note that the calculated LIOFF has a negative value.
LIOFF = LIMAXPWM-PWM #

  On the other hand, if it is determined in step 208 that PWM # ≦ LIMAXPWM, the process proceeds to step 212. In step 212, it is determined whether or not the command value PWM # (# is U, V or W) of the phase in which the overload element exists is less than the PWM command lower limit value LIMINPWM calculated by the overload processing unit 46. If it is determined that PWM # ≧ LIMINPWM, this routine ends.

On the other hand, if it is determined that PWM # <LIMINPWM, the process proceeds to step 214. In step 214, a reduced offset value LIOFF is calculated by the following arithmetic expression. Note that the calculated LIOFF has a positive value.
LIOFF = LIMINPWM-PWM #

  Since LIOFF is updated after execution of step 210 or 214, the process proceeds to step 216, and the PWM command value is recalculated. The calculation contents are the same as those in step 202. After execution of step 216, the routine ends.

  In the above embodiment, if there is an overload in the upper arm MOSFET of the three-phase voltage source inverter circuit 20, the PWM duty ratio is lowered in each phase, so that the time during which current flows in the upper arm is reduced. As a result of the decrease and the time during which current flows to the lower arm, the overload state of the upper arm MOSFET is eliminated. At that time, each phase voltage is lowered, but the interphase voltage, that is, the voltage between the motor terminals is kept constant, so that the motor current does not decrease.

  Similarly, if the lower arm MOSFET of the three-phase voltage source inverter circuit 20 is in an overload state, the PWM duty ratio is increased in each phase, so that the time during which current flows through the upper arm increases. As a result of a decrease in the time during which current flows through the arm, the overload state of the lower arm MOSFET is eliminated. At that time, each phase voltage rises, but the interphase voltage, that is, the voltage between the motor terminals is kept constant, so that the motor current remains constant.

It is a figure which shows the current limiting map which defined the maximum armature current according to switching element temperature. It is a figure which shows the structure of the three-phase brushless DC motor system to which one Embodiment of the control apparatus by this invention is applied. It is a flowchart which shows the process sequence of an overload process part. (A) And (B) is a figure which shows the map which defined the upper limit and lower limit of PWM duty ratio according to switching element temperature, respectively. It is a flowchart which shows the process sequence of a PWM command value calculating part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Permanent magnet synchronous motor 12 Machines, such as an electric power steering for motor vehicles 14 DC power supply 20 Three-phase voltage type inverter circuit 30 Control apparatus 32 Current command value calculating part 34 Voltage command value calculating part 36 PWM command value calculating part 38 MOSFET drive circuit 40 Rotation angle sensor (resolver)
42 Current sensor 44 Temperature sensor 46 Overload processing section

Claims (5)

In each phase of the three-phase inverter circuit that supplies power to the three-phase brushless DC motor, the duty ratio indicating the time ratio that the upper arm switching element is on and the lower arm switching element is off is changed to A control device for a three-phase brushless DC motor that PWM-controls an inverter circuit,
Load detection means for detecting the load of each switching element;
Overload determination means for determining whether or not an overload switching element exists in only one of the upper arm switching element and the lower arm switching element based on the output of the load detection means;
When the overload determination means determines that the overload state exists, the PWM duty ratio of each phase determined based on the voltage command value of each phase is set so that the current flowing through the arm on the overload side decreases. PWM duty ratio adjusting means for adjusting;
A control device for a three-phase brushless DC motor.   The control device for a three-phase brushless DC motor according to claim 1, wherein the load detecting means is a temperature detecting element installed in the vicinity of each switching element.   The PWM duty ratio adjusting means decreases the upper limit value of the duty ratio when the temperature of the upper arm switching element exceeds the threshold value, and increases the lower limit value of the duty ratio when the temperature of the lower arm switching element exceeds the threshold value. The control device for a three-phase brushless DC motor according to claim 2. A motor control device that performs PWM control of an inverter circuit by changing a duty ratio indicating a time ratio of an ON state and an OFF state of each switching element in each phase of the inverter circuit that supplies electric power to the motor. ,
Load detection means for detecting the load of each switching element;
Overload determination means for determining whether or not an overload switching element exists based on an output of the load detection means;
When the overload determination means determines that the overload state exists, the PWM duty ratio of each phase determined based on the voltage command value of each phase is set so that the current flowing through the arm on the overload side decreases. PWM duty ratio adjusting means for adjusting;
A motor control apparatus comprising: A motor control method for PWM controlling an inverter circuit by changing a duty ratio indicating a time ratio of an ON state and an OFF state of each switching element in each phase of an inverter circuit that supplies electric power to the motor. ,
A load detection step for detecting a load of each switching element;
Based on the output of the load detection step, an overload determination step for determining whether or not an overload switching element exists is in an overload state;
When it is determined in the overload determination step that the overload state is present, the PWM duty ratio of each phase determined based on the voltage command value of each phase is set so that the current flowing through the arm on the overload side decreases. PWM duty ratio adjustment step to adjust;
A motor control method comprising:

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