JP2005253268A - Inverter control device, control program and control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inverter control device which enables an optimum dead time compensation corresponding to the supply current to a motor, while simplifying the constitution of a motor control system. <P>SOLUTION: A dead time compensation circuit 30 is constituted of a high level counter 32, a multiplexer 34 and a ROM 36. The high level counter 32 takes in a current command value and the magnitude comparison results of carrier signals from a comparator 28, and counts them to obtain the duty ratio of a PWM signal. The multiplexer 34 and the ROM 36 read a dead time compensation value Kd corresponding to the duty ratio to add the value to a dead time set value Td. The result is subtracted from a current command value I by a subtractor 26 to set a dead time without employing a current detector, resulting in simplifying the constitution of a motor control system. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an inverter control technique for controlling on / off of a plurality of switching elements constituting an inverter, and more particularly to an inverter control technique for setting a dead time for preventing a short circuit when two switching elements connected in series are turned on / off.

  In a DC brushless motor, an AC synchronous motor, and the like, a magnetic field is generated by energizing a coil wound around a stator, and the rotor is driven and controlled. The energization control of the coil is performed by giving an on / off signal for PWM control by an inverter control device to a plurality of switching elements constituting the inverter.

  When switching on and off a switching element, if an on signal is simultaneously applied to two switching elements connected in series and energized, the high voltage side and the low voltage side of the power supply are short-circuited, preventing this. Therefore, it is common to set a dead time for the on / off signal to the two switching elements.

  Japanese Patent Application Laid-Open No. 2002-272182 describes an example of a dead time setting method according to the prior art. This conventional technology compensates for the dead time according to the polarity of the current supplied from the inverter to the motor in order to reduce the current distortion and torque ripple caused by the dead time during low speed operation and low load operation. Is going.

JP 2002-272182 A Japanese Patent No. 3062900

  However, in the dead time compensation of the above document, a current detector is provided to determine the polarity of the supply current. According to this configuration, a complicated circuit such as a current detector and a filter for removing the output noise of the current detector is required, and the configuration of the motor control system is complicated and the manufacturing cost increases. .

  The present invention has been made in view of the above-described circumstances, and provides an inverter control device that enables optimal dead time compensation in accordance with the supply current to the motor while simplifying the configuration of the motor control system. With the goal.

  In order to achieve the above-described object, the present invention is an inverter control device that provides an on / off signal corresponding to a command value to a plurality of switching elements constituting an inverter, and is provided to two switching elements connected in series. A dead time setting means for setting a dead time for preventing a short circuit in the on / off signal is provided, and the dead time setting means has a dead time compensation means for adjusting the dead time based on the command value. .

  Further, it is preferable that the dead time compensation means obtains a duty ratio of the on / off signal based on the command value and adjusts the dead time according to the duty ratio.

  Further, it is preferable that the dead time compensating means obtains a duty ratio by counting a result of comparing the command value with a carrier signal.

  The dead time compensation means preferably counts the result of comparing the command value with the carrier signal in the clock cycle when the clock cycle for generating the carrier signal is changed.

  In order to achieve the above-described object, the present invention obtains a command value for generating an on / off signal to each switching element in a control device that controls an inverter composed of a plurality of switching elements. And a step of setting the dead time adjusted according to the command value to an on / off signal to be applied to two switching elements connected in series.

  In order to achieve the above object, the present invention provides a control method for controlling an inverter composed of a plurality of switching elements, and obtains a command value for generating an on / off signal to each of the switching elements. And a step of setting a dead time adjusted according to the command value to an on / off signal to be given to two switching elements connected in series.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a configuration diagram showing an outline of the motor control system according to the first embodiment. This motor control system is mounted on an electric vehicle or a hybrid vehicle and used as a drive source for the vehicle. The motor control system includes a DC power source 10, an inverter 12, a synchronous motor 14, and an inverter control device 20. The inverter control device 20 controls the inverter 12 to generate a three-phase AC current, and the synchronous motor 14 is rotationally controlled.

  Between the high potential and low potential of the DC power supply 10, two switching elements (transistors) UP and UN, VP and VN, WP and WN are connected in series for each phase (U phase, V phase, W phase), Furthermore, the inverter 12 is configured by connecting a conductive line leading to each phase coil between these two switching elements. Hereinafter, of the two switching elements connected in series, the high-potential side switching elements UP, VP, and WP are referred to as upper elements, and the low-potential side switching elements UN, VN, and WN are referred to as lower elements.

  The inverter control device 20 includes three current control units provided for each phase, and inputs a current command value for generating a three-phase AC current to each of the current control units, and switches each of the switching elements UP, UN, VP. , VN, WP, WN are controlled by PWM (Pulse Width Modulation). As a result, a desired three-phase alternating current is generated from the direct current power source, and the output torque value, rotation speed, and the like of the synchronous motor 14 are controlled. The synchronous motor 14 includes a rotor and a stator therein, and the rotor is rotationally driven by supplying a three-phase alternating current from the inverter 12 to each phase coil wound around the stator. This driving force is transmitted to the wheels to drive the vehicle.

  Next, the operation of the current control unit of the inverter control device 20 will be described in more detail. FIG. 2 is a block diagram showing a configuration of the U-phase control unit, and FIG. 3 is a timing chart showing a change with time of an internal signal of the U-phase control unit. Although the U phase control unit will be described as an example, the configuration and operation of the V phase control unit and the W phase control unit are the same.

  The up / down counter 24 repeatedly increases and decreases the count value to generate a triangular wave that is a carrier signal. In other words, the count value is incremented (+1) every time a pulse signal having a fixed period is input from the clock generation unit 22, and when the count value reaches the upper limit value (127 in this embodiment), the count value is decremented (−1). ). Thereafter, every time a pulse signal is input, the count value is decremented (−1), and when the count value reaches the lower limit value (0 in this embodiment), incrementing of the count value (+1) is started again. The up / down counter 24 generates a triangular wave by repeating the above processing, and outputs it.

  A current command value I calculated to control the synchronous motor 14 to a desired output torque value, rotation speed, etc. is input to the U-phase control unit. The current command value is a value indicating an alternating current corresponding to the rotation of the synchronous motor 14, and changes in a sine wave shape with the passage of time. The current command value input to the U-phase control unit branches in the U-phase control unit and is transmitted as two signals Ip and In. One of the two current command values is an upper element control signal Ip, and the other is a lower element control signal In. In the present embodiment, a current command value is input to each current control unit, but a voltage command value may be input.

  The current command value Ip for controlling the upper element is input to the subtractor 26, where the dead time set value Td 'is subtracted. As a result, the upper element control current command value Ip ′ (broken line) is slightly smaller than the original current command value I (solid line). Thereafter, the current command value Ip ′ output from the subtractor 26 is taken into the comparator 28 for controlling the upper element, and the triangular wave generated by the up / down counter 24 is compared with the magnitude. Here, when the current command value Ip ′ is larger than the triangular wave, an ON signal is output from the comparator 28 to the upper element UP, and the upper element UP is controlled to be in a conductive state. Further, when the current command value Ip ′ is smaller than the triangular wave, an off signal is output, and the upper element UP is controlled to be in a cut-off state.

  On the other hand, the current command value In for controlling the lower element is directly taken into the lower element control comparator 29 (without subtracting the dead time set value Td ′) and generated by the up / down counter 24. The triangle wave and the magnitude are compared. Here, when the current command value In is smaller than the triangular wave, an ON signal is output from the comparator 29 to the lower element UN, and the lower element UN is controlled to be conductive. When the current command value In is larger than the triangular wave, an off signal is output, and the lower element UN is controlled to be in a cut-off state.

  By the above-described generation process of the on / off signal, an off signal is output to the lower element UN during a period when the on signal is output to the upper element UP, and a lower element UN is output during a period when the off signal is output to the upper element UP. A turn-on signal is output. However, a period in which an ON signal is output to the upper element UP and a period in which an ON signal is output to the lower element UN are obtained by subtracting the dead time set value Td ′ from the current command value Ip for upper element control. In between, a dead time is set in which both elements are in a cut-off state.

  Due to this dead time, the simultaneous conduction state of the switching elements UP and UN of each phase connected in series is avoided, and a short circuit between the high potential and the low potential is prevented. The specific value of the dead time required to reliably avoid simultaneous conduction differs depending on factors such as the type of switching element and the delay variation of the gate drive circuit, but in the photocoupler method, it is about 2 μs to 5 μs. In the withstand voltage IC method, it is about 500 ns to 700 ns.

  In the U-phase control unit having the above-described configuration, a tail current flows through the switching elements UP and UN immediately after switching the switching elements UP and UN from the conductive state to the cutoff state. Although the time during which the tail current flows varies depending on the amount of current flowing through the U-phase coil, a dead time compensation circuit 30 is provided to optimize the dead time according to the amount of current. The dead time compensation circuit 30 includes a high level counter 32, a multiplexer (MPX) 34, and a ROM 36 in which a dead time compensation value table is stored.

  The high level counter 32 takes in the output signal from the comparator 28 to the upper element UP, and obtains the duty ratio of PWM control based on this. That is, when one cycle of the carrier signal starts and ends, it is determined at every predetermined time whether the output signal of the comparator 28 is an on signal or an off signal, and is an on signal. Only the count value is incremented (+1). Thereby, the time ratio (duty ratio) at which the ON signal is output in one cycle of the carrier signal is obtained.

  The start and end of one cycle of the carrier signal may be recognized when the carrier signal output from the up / down counter 24 is taken in and the value becomes a predetermined value (for example, “0”). In order to simplify the processing, it is preferable to reduce the number of bits of the counter. In this embodiment, an 8-bit counter is used.

  The multiplexer 34 is an 8-bit decoder configured as a logic circuit. When the count value is taken from the high level counter 32, the value range to which the count value belongs is determined. That is, the range of the count value is divided into five value ranges of “0 to 94”, “95 to 123”, “124 to 131”, “132 to 160”, and “161 to 255”. Any one value range to which the count value belongs is determined from the inside, and the determination result is output to the ROM 36.

  The ROM 36 stores a table in which each time range is associated with a dead time compensation value. A table of dead time compensation values is shown in FIG. In this table, when the counter value is “124 to 131”, the current command value I is near zero, and the current value flowing through the coil is almost the same as the current command value I. The dead time is not adjusted as a value corresponding to 0.0 μsec ”. On the other hand, when the counter value exceeds “160” or falls below “95”, the current command value is a large value and the current flowing through the coil is also large, so that the current flows through the switching element at the time of turn-off. Since the time of the tail current becomes long, the dead time is extended by setting the dead time compensation value to a value corresponding to, for example, “1.0 μsec”.

  When the ROM 36 fetches the determination result of the multiplexer 34, the ROM 36 reads out the dead time compensation value Kd corresponding to the range of the determination result from the table and outputs it to the adder 42. In the adder 42, the dead time compensation value Kd is added to the dead time set value Td. Thereby, the dead time set value Td is adjusted according to the current command value, and the adjusted dead time set value Td 'is generated. This dead time setting value Td 'is subtracted from the upper element control current command value Ip, so that the dead time is set in the on / off signal. In this way, the dead time is adjusted according to the amount of current applied to each phase coil, and motor control is optimized.

  In the present embodiment, the dead time compensation circuit 30 includes the 8-bit counter 32, the 8-bit decoder 34, and the ROM 36. However, the present invention is not limited to this as long as the above processing is performed. For example, the high level counter 32 and the multiplexer 34 can be configured as an arithmetic processing unit (CPU), and a program can be executed to perform processing equivalent to the above. Further, a register may be used instead of the ROM 36.

  In the present embodiment, the dead time compensation circuit 30 selects the dead time set value Kd after comparing the current command value and the carrier signal to obtain the duty ratio, but in other embodiments, the dead time set value Kd is selected. The time compensation circuit 30 may be configured to select the dead time setting value Kd corresponding to the magnitude of the current command value without performing the magnitude comparison between the current command value and the carrier signal.

  What is characteristic in the above-described embodiment is that the dead time compensation value Kd corresponding to the magnitude of the current command value is obtained and the dead time is adjusted based on this. By adopting such a configuration, it is not necessary to provide a current detector and detect an actual current value (actual current value), so that the configuration of the motor control system can be simplified. Therefore, manufacture of a vehicle becomes easy and cost can be suppressed low. In addition, when the actual current value is detected by the current detector and the dead time is corrected, the correction processing throughput increases, but if the dead time is corrected by the current command value, the throughput decreases, and the motor control system The responsiveness of can be made high.

  In the present embodiment, when the dead time compensation value Kd is obtained, the duty ratio of PWM control is obtained. Since the duty ratio represents a time ratio during which the switching element is energized, it is a numerical value that most directly reflects the current flowing through the switching element when switching from the energized state to the cutoff state. Therefore, it is particularly preferable for optimizing the dead time to obtain the duty ratio of the PWM control and determine the dead time compensation value Kd according to the duty ratio.

  In the present embodiment, since the dead time compensation value Kd is obtained according to the current command value, the capacity of the ROM 36 can be kept small. In other words, when the actual current value is detected using a current detector as in the prior art, a large number of dead times depend on the amplitude of the current command value, the frequency of the current command value, and other factors related to dead time compensation. In contrast to this, a compensation value table is required. On the other hand, when the dead time compensation value Kd is obtained according to the current command value as in the present embodiment, the same table can be used regardless of the above factors. The capacity of the ROM 36 can be small.

  Next, a motor control system according to the second embodiment will be described. The configuration of the motor control system according to the second embodiment is substantially the same as that of the first embodiment, and only a part of the internal configuration of each phase control unit is different from that of the first embodiment. FIG. 5 is a block diagram showing the configuration of the U-phase control unit according to the second embodiment.

  In the second embodiment, the carrier cycle is changed in order to perform optimal motor control. In other words, each phase control unit is provided with a frequency dividing circuit 44 that changes the clock cycle, and the clock generation unit 22 outputs a carrier cycle switching signal that designates the optimum carrier cycle for this. The clock is changed to a clock having a cycle corresponding to the carrier cycle switching signal and then input to the up / down counter 24. As a result, the carrier period generated by the up / down counter 24 is switched to one of a plurality of different periods (in this embodiment, 0.5 kHz, 1.0 kHz, 1.5 kHz).

  However, when the carrier cycle change control is performed as described above, if the high level counter 32 determines and counts the output signal of the comparator 28 at regular time intervals, there is the following problem. That is, as can be understood by comparing the case where the carrier period shown in FIG. 6A is small and the case where the carrier period shown in FIG. 6B is large, when the carrier period changes, the time width of the ON signal changes, Even when the duty ratio is the same, the numbers counted are different from each other. As a result, as shown in FIGS. 7A to 7C, a plurality of dead time compensation value tables stored in the ROM 36 are required according to each carrier period. Along with this, processing for selecting a table corresponding to the carrier cycle from a plurality of tables is also required.

  In order to avoid such a situation that the processing of each phase control unit becomes complicated in this way, in the second embodiment, the high-level counter 32 takes in the clock output from the frequency dividing circuit 44 and the clock timing. Every time, the output signal of the comparator 28 is judged and counted. According to this configuration, even when the carrier period is changed, the range of the count value of the high level counter does not change, so the processing of the dead time compensation circuit is not complicated. Further, only one dead time compensation value table (for example, only FIG. 7C) can be used, and the capacity of the ROM 36 can be kept small.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments, and various modifications can be made within an equivalent range.

  For example, in the above embodiment, the case where the motor control system is mounted on the vehicle has been described. However, the motor control system may be used for other purposes. Further, the control target of the motor control system is not limited to the synchronous motor, but may be other types of motors such as a DC brushless motor.

It is a block diagram of the motor control system which concerns on embodiment. It is a block diagram of the U-phase control part of the inverter control apparatus which concerns on embodiment. It is a timing chart which shows a time-dependent change of each signal in a U phase control part. It is explanatory drawing which shows a dead time compensation table. It is a block diagram of the U-phase control part of the inverter control apparatus which concerns on 2nd embodiment. It is a timing chart which shows an on-off signal when a carrier cycle is changed. It is explanatory drawing which shows a dead time compensation table.

Explanation of symbols

  10 DC power supply, 12 inverter, 14 synchronous motor, 20 inverter control device, 22 clock generator, 24 up / down counter, 26 subtractor, 28, 29 comparator, 30 dead time compensation circuit, 32 high level counter, 34 multiplexer, 36 ROM, 42 adder, 44 frequency divider, Td, Td ′ dead time set value, UP, UN, VP, VN, WP, WN switching elements.

Claims (6)

An inverter control device that gives an on / off signal corresponding to a command value to a plurality of switching elements constituting the inverter,
A dead time setting means for setting a dead time for preventing a short circuit in an on / off signal given to two switching elements connected in series;
The dead time setting means includes a dead time compensation means for adjusting the dead time based on the command value. The inverter control device according to claim 1,
The dead time compensation means obtains a duty ratio of an on / off signal based on the command value, and adjusts the dead time according to the duty ratio. The inverter control device according to claim 2,
The dead time compensation means obtains a duty ratio by counting the result of comparing the command value with the carrier signal, and an inverter control device. The inverter control device according to claim 3,
The dead time compensating means counts the result of comparing the command value with the carrier signal in the clock cycle when the clock cycle for generating the carrier signal is changed. In a control device that controls an inverter composed of a plurality of switching elements,
Obtaining a command value for generating an on / off signal to each of the switching elements;
Setting a dead time adjusted according to the command value to an on / off signal to be given to two switching elements connected in series;
Inverter control program to execute A control method for controlling an inverter composed of a plurality of switching elements,
Obtaining a command value for generating an on / off signal to each of the switching elements;
Setting a dead time adjusted according to the command value to an on / off signal to be given to two switching elements connected in series;
An inverter control method comprising:

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