Motor control device

Abstract

The one aspect of the motor control device according to the present invention controls a n-phase motor (where n is an integer greater than or equal to 3) and comprises: a power conversion circuit which is connected to the n-phase motor and which performs mutual conversion between DC power and n-phase AC power; and a control unit which controls the power conversion circuit on the basis of an n-phase duty-cycle command value updated at a predetermined update cycle. When the control unit predicts, on the basis of the n-phase duty-cycle command value, that voltage fluctuations of connection terminals in at least two phases of connection terminals in n phases connected to the n-phase motor occur in the same direction at the same timing, the control unit delays the occurrence timing of the voltage fluctuation of one connection terminal of the connection terminals in the two phases by a first time and advances the occurrence timing of the voltage fluctuation of the other connection terminal by a second time. The total value of the first time and the second time is such a predetermined time period that overlap does not occur to timings of the voltage fluctuations of predetermined connection terminals in two phases.

Description

[Technical Field]

[0001] This invention relates to a motor control device. This application claims priority based on Japanese Patent Application No. 2021-162377, filed in Japan on September 30, 2021, the contents of which are incorporated herein by reference. [Background technology]

[0002] Patent Document 1 discloses a technique for an inverter device that supplies a three-phase AC voltage to a three-phase motor, in which a three-phase PWM (Pulse Width Modulation) signal is generated using three types of basic voltage vectors, and a switching signal is generated to each of the at least six switching elements included in the inverter device based on the three-phase PWM signal. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Patent No. 3447366 [Overview of the project] [Problems that the invention aims to solve]

[0004] For example, at the moment when the switching timings of two phases of a three-phase PWM signal coincide, the potential difference (shaft voltage) between the motor's output shaft and the motor case can fluctuate significantly. This can potentially cause noise. Separately, galvanic corrosion can occur in the motor's rotor bearings due to the shaft voltage. Research by the inventors of this invention has revealed that this noise, in particular, may contribute to the occurrence of galvanic corrosion. [Means for solving the problem]

[0005] One aspect of the motor control device of the present invention is a motor control device for controlling an n-phase motor (where n is an integer of 3 or more), comprising: a power conversion circuit connected to the n-phase motor and performing mutual conversion between DC power and n-phase AC power; and a control unit that controls the power conversion circuit based on an n-phase duty cycle command value that is updated at a predetermined update cycle, wherein, based on the n-phase duty cycle command value, the control unit predicts that voltage fluctuations at at least two of the n-phase connection terminals connected to the n-phase motor will occur in the same direction and at the same timing, delays the timing of the voltage fluctuation at one of the two connection terminals by a first hour, and advances the timing of the voltage fluctuation at the other connection terminal by a second hour, the sum of the first hour and the second hour being a predetermined time during which the timings of the voltage fluctuations at the two connection terminals do not overlap. [Effects of the Invention]

[0006] According to the above aspect of the present invention, a motor control device capable of reducing noise is provided. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is a schematic circuit block diagram showing the configuration of a motor control device in one embodiment of the present invention. [Figure 2] Figure 2 schematically illustrates the principle by which a three-phase PWM signal is generated based on a three-phase duty cycle command value. [Figure 3] Figure 3 is a timing chart showing an example where the rising edge timing of the V-phase PWM signal and the rising edge timing of the W-phase PWM signal coincide. [Figure 4] Figure 4 is a timing chart showing an example of a three-phase PWM signal generated by the comparison technique when the rising edge timing of the V-phase PWM signal and the rising edge timing of the W-phase PWM signal match. [Figure 5]FIG. 5 is a timing chart showing an example of a three-phase PWM signal generated according to the present embodiment when the rising edge timing of the V-phase PWM signal matches the rising edge timing of the W-phase PWM signal. [Figure 6] FIG. 6 is a timing chart showing an example in which the rising edge timing of the V-phase PWM signal matches the rising edge timing of the W-phase PWM signal in a state where the duty ratios of the V-phase PWM signal and the W-phase PWM signal are close to 100%. [Figure 7] FIG. 7 is a timing chart showing an example of a three-phase PWM signal generated by a comparative technique when the rising edge timing of the V-phase PWM signal matches the rising edge timing of the W-phase PWM signal in a state where the duty ratios of the V-phase PWM signal and the W-phase PWM signal are close to 100%. [Figure 8] FIG. 8 is a timing chart showing an example of a three-phase PWM signal generated by a comparative technique when the rising edge timing of the V-phase PWM signal matches the rising edge timing of the W-phase PWM signal in a state where the duty ratios of the V-phase PWM signal and the W-phase PWM signal are close to 100%. [Figure 9] FIG. 9 is a timing chart showing an example of a three-phase PWM signal generated according to the present embodiment when the rising edge timing of the V-phase PWM signal matches the rising edge timing of the W-phase PWM signal in a state where the duty ratios of the V-phase PWM signal and the W-phase PWM signal are close to 100%. [Figure 10] FIG. 10 is a timing chart showing an example in which the rising edge timing of the U-phase PWM signal matches the rising edge timing of the V-phase PWM signal in a state where the duty ratios of the U-phase PWM signal and the V-phase PWM signal are close to 0%. [Figure 11] FIG. 11 is a timing chart showing an example of a three-phase PWM signal generated by a comparative technique when the rising edge timing of the U-phase PWM signal matches the rising edge timing of the V-phase PWM signal in a state where the duty ratios of the U-phase PWM signal and the V-phase PWM signal are close to 0%. [Figure 12] FIG. 12 is a timing chart showing an example of a three-phase PWM signal generated according to the present embodiment when the rising edge timing of the U-phase PWM signal coincides with the rising edge timing of the V-phase PWM signal in a state where the duty ratios of the U-phase PWM signal and the V-phase PWM signal are close to 0%. [Figure 13] FIG. 13 is a timing chart showing an example of a three-phase PWM signal generated according to the present embodiment when the rising edge timing of the V-phase PWM signal coincides with the rising edge timing of the W-phase PWM signal in a state where the duty ratio of the V-phase PWM signal is increasing and the duty ratio of the W-phase PWM signal is decreasing. [Figure 14] FIG. 14 is a timing chart showing an example of a three-phase PWM signal generated according to the present embodiment when the falling edge timing of the V-phase PWM signal coincides with the falling edge timing of the W-phase PWM signal in a state where the duty ratio of the V-phase PWM signal is increasing and the duty ratio of the W-phase PWM signal is decreasing. [Figure 15] FIG. 15 is a timing chart showing an example of each waveform of the upper gate control signal G1 of the U-phase, the lower gate control signal G2 of the U-phase, the terminal voltage Vu of the U-phase, the upper gate control signal G3 of the V-phase, the lower gate control signal G4 of the V-phase, and the terminal voltage Vv of the V-phase when the directions of the currents in the U-phase and the V-phase are both in the direction from the power conversion circuit to the three-phase motor. [Figure 16] FIG. 16 is a timing chart showing an example of each waveform of the upper gate control signal G1 of the U-phase, the lower gate control signal G2 of the U-phase, the terminal voltage Vu of the U-phase, the upper gate control signal G3 of the V-phase, the lower gate control signal G4 of the V-phase, and the terminal voltage Vv of the V-phase when the directions of the currents in the U-phase and the V-phase are both in the direction from the three-phase motor to the power conversion circuit.

Embodiments for Carrying Out the Invention

[0008] Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings. Figure 1 is a schematic circuit block diagram showing the configuration of the motor control device 10 in this embodiment. As shown in Figure 1, the motor control device 10 controls a three-phase motor 20. As an example, the three-phase motor 20 is an inner rotor type three-phase brushless DC motor. The three-phase motor 20 is also, for example, a drive motor (traction motor) mounted on an electric vehicle.

[0009] The three-phase motor 20 has a U-phase terminal 21u, a V-phase terminal 21v, a W-phase terminal 21w, a U-phase coil 22u, a V-phase coil 22v, and a W-phase coil 22w. Although not shown in Figure 1, the three-phase motor 20 has a motor case and a rotor and stator housed in the motor case. The rotor is a rotating body that is rotatably supported inside the motor case by bearing components such as rotor bearings. The rotor has an output shaft that is coaxially connected to the rotor and penetrates the radially inner side of the rotor in the axial direction. The stator is fixed inside the motor case, surrounding the outer surface of the rotor, and generates the electromagnetic force necessary to rotate the rotor.

[0010] The U-phase terminal 21u, V-phase terminal 21v, and W-phase terminal 21w are metal terminals exposed from the surface of the motor case. The U-phase terminal 21u is connected to the U-phase connection terminal 13u of the motor control device 10. The V-phase terminal 21v is connected to the V-phase connection terminal 13v of the motor control device 10. The W-phase terminal 21w is connected to the W-phase connection terminal 13w of the motor control device 10. The U-phase coil 22u, V-phase coil 22v, and W-phase coil 22w are excitation coils provided on the stator. As an example, the U-phase coil 22u, V-phase coil 22v, and W-phase coil 22w are star-connected inside the three-phase motor 20.

[0011] The U-phase coil 22u is connected between the U-phase terminal 21u and the neutral point N. The V-phase coil 22v is connected between the V-phase terminal 21v and the neutral point N. The W-phase coil 22w is connected between the W-phase terminal 21w and the neutral point N. By controlling the energization states of the U-phase coil 22u, the V-phase coil 22v, and the W-phase coil 22w by the motor control device 10, an electromagnetic force necessary to rotate the rotor is generated. When the rotor rotates, the output shaft also rotates in synchronization with the rotor.

[0012] The motor control device 10 includes a power conversion circuit 11 and an MCU (Microcontroller Unit) 12. The power conversion circuit 11 is connected to the three-phase motor 20 and performs mutual conversion between DC power and three-phase AC power. When the power conversion circuit 11 functions as an inverter, the power conversion circuit 11 converts the DC power supplied from the DC power source 30 into three-phase AC power and outputs it to the three-phase motor 20. As an example, the DC power source 30 is one of a plurality of batteries mounted on an electric vehicle.

[0013] The power conversion circuit 11 includes an upper-arm switch Q for the U-phase UH and an upper-arm switch Q for the V-phase VH and an upper-arm switch Q for the W-phase WH and a lower-arm switch Q for the U-phase UL and a lower-arm switch Q for the V-phase VL and a lower-arm switch Q for the W-phase WL . In this embodiment, each arm switch is, for example, an IGBT (Insulated Gate Bipolar Transistor).

[0014] The collector terminal of the upper-arm switch Q for the U-phase UH the collector terminal of the upper-arm switch Q for the V-phase VH and the collector terminal of the upper-arm switch Q for the W-phase WH are each connected to the positive terminal of the DC power source 30. The emitter terminal of the lower-arm switch Q for the U-phase UL the emitter terminal of the lower-arm switch Q for the V-phase VL and the emitter terminal of the lower-arm switch Q for the W-phase WLThe emitter terminals are connected to the negative terminals of the DC power supply 30.

[0015] U-phase upper arm switch Q UH The emitter terminals are U-phase connection terminal 13u and U-phase lower arm switch Q. UL It is connected to the collector terminals of each of them. In other words, the U-phase upper arm switch Q UH The emitter terminal is connected to the U-phase terminal 21u of the three-phase motor 20 via the U-phase connection terminal 13u. V-phase upper arm switch Q VH The emitter terminal has a V-phase connection terminal 13V and a V-phase lower arm switch Q. VL It is connected to the collector terminals of each of them. In other words, the V-phase upper arm switch Q VH The emitter terminal is connected to the V-phase terminal 21V of the three-phase motor 20 via the V-phase connection terminal 13V. W-phase upper arm switch Q WH The emitter terminals are W-phase connection terminal 13w and W-phase lower arm switch Q. WL It is connected to the collector terminals of each of them. In other words, the W-phase upper arm switch Q WH The emitter terminal is connected to the W-phase terminal 21w of the three-phase motor 20 via the W-phase connection terminal 13w.

[0016] U-phase upper arm switch Q UH The gate terminal, V-phase upper arm switch Q VH The gate terminal and the W-phase upper arm switch Q WH The gate terminals are, It is connected to the output terminal of MCU12. Also, the U-phase lower arm switch Q UL The gate terminal, V-phase lower arm switch Q VL The gate terminal and the W-phase lower arm switch Q WL The gate terminals are also connected to the output terminals of the MCU12.

[0017] As described above, the power conversion circuit 11 is composed of a three-phase full-bridge circuit having three upper arm switches and three lower arm switches. The power conversion circuit 11, configured in this way, performs mutual conversion between DC power and three-phase AC power by controlling the switching of each arm switch by the MCU 12.

[0018] The MCU 12 is a control unit that controls the power conversion circuit 11 based on three-phase duty cycle command values ​​that are updated at a predetermined update cycle. The three-phase duty cycle command values ​​include the U-phase duty cycle command value DU, the V-phase duty cycle command value DV, and the W-phase duty cycle command value DW. The MCU 12 has an MCU core 12a and a PWM module 12b.

[0019] The MCU core 12a performs a command value calculation process to calculate at least three-phase duty cycle command values ​​according to a program pre-stored in memory (not shown). Although not shown in Figure 1, the MCU 12 receives torque command values ​​output from a higher-level control device. For example, the higher-level control device is an ECU (Electronic Control Unit) mounted on an electric vehicle. For example, the MCU core 12a calculates q-axis current command values ​​and d-axis current command values ​​based on the torque command values, and calculates three-phase duty cycle command values ​​as three-phase voltage command values ​​based on these current command values. Since torque control of the three-phase motor 20 is a known technique, a detailed explanation is omitted in this specification.

[0020] The MCU core 12a outputs the calculated three-phase duty cycle command values, namely the U-phase duty cycle command value DU, the V-phase duty cycle command value DV, and the W-phase duty cycle command value DW, to the PWM module 12b. Based on the U-phase duty cycle command value DU, the V-phase duty cycle command value DV, and the W-phase duty cycle command value DW, the PWM module 12b generates gate control signals that are supplied to the gate terminals of each arm switch included in the power conversion circuit 11.

[0021] The gate control signal is controlled by the U-phase upper arm switch Q. UHThe U-phase upper gate control signal G1 supplied to the gate terminal and the U-phase lower arm switch Q UL This includes the U-phase lower gate control signal G2 supplied to the gate terminal. The gate control signal also includes the V-phase upper arm switch Q VH The V-phase upper gate control signal G3 supplied to the gate terminal and the V-phase lower arm switch Q VL The gate control signal G4 is supplied to the gate terminal of the V-phase lower-side gate control signal Q. Furthermore, the gate control signal includes the W-phase upper-side arm switch Q. WH The W-phase upper gate control signal G5 and the W-phase lower arm switch Q are supplied to the gate terminal. WL This includes the W-phase lower gate control signal G6 supplied to the gate terminal. A dead time is inserted into each gate control signal to prevent the upper and lower arm switches of the same phase from being switched on simultaneously.

[0022] Figure 2 schematically illustrates the principle by which a three-phase PWM signal is generated based on a three-phase duty cycle command value. As shown in Figure 2, a triangular wave TW with a predetermined period Tp is generated in the PWM module 12b. Hereafter, the period Tp of the triangular wave TW may be referred to as the PWM period.

[0023] For example, the triangular wave TW is composed of the count value of a PWM timer. In the example shown in Figure 2, during the period from time t1 to time t2, the PWM timer operates in countdown mode, causing the PWM timer's count value to change from the maximum value to the minimum value. Then, during the period from time t2 to time t3, the PWM timer operates in count-up mode, causing the PWM timer's count value to change from the minimum value to the maximum value. The period from time t1 to time t3 corresponds to the period of the triangular wave TW, i.e., the PWM period Tp.

[0024] The countdown period from time t1 to time t2 and the count-up period from time t2 to time t3 each correspond to half the duration of the PWM period Tp. The three-phase duty cycle command value is updated at both the countdown start time t1 and the count-up start time t2. That is, the update period Td of the three-phase duty cycle command value corresponds to half the duration of the PWM period Tp.

[0025] Within the PWM module 12b, a buffer register and an update register are assigned to each of the three duty cycle command values ​​included in the three-phase duty cycle command value. The three-phase duty cycle command value calculated by the MCU core 12a is first stored in the buffer register. Then, when an update timing such as the countdown start time t1 or the count-up start time t2 arrives, the three-phase duty cycle command value stored in the buffer register is transferred to the update register. Thus, "the three-phase duty cycle command value is updated" means that the three-phase duty cycle command value is transferred from the buffer register to the update register at the update timing.

[0026] As described above, the three-phase duty cycle command value calculated by the MCU core 12a needs to be stored in the buffer register before the update timing arrives. Therefore, the MCU core 12a calculates the three-phase duty cycle command value earlier than the update timing. In other words, the MCU core 12a calculates the three-phase duty cycle command value to be updated at the countdown start time t1 earlier than the countdown start time t1 and outputs it to the PWM module 12b. Also, the MCU core 12a calculates the three-phase duty cycle command value to be updated at the countup start time t2 earlier than the countup start time t2 and outputs it to the PWM module 12b. In this way, the MCU core 12a repeats the command value calculation process at the same cycle as the update cycle Td of the three-phase duty cycle command value, but the command value calculation timing is earlier than the update timing.

[0027] As shown in Figure 2, assume that at the countdown start time t1, the U-phase duty command value DU is updated to "DU1", the V-phase duty command value DV is updated to "DV1", and the W-phase duty command value DW is updated to "DW1". The U-phase duty command value DU1 is greater than the V-phase duty command value DV1. The V-phase duty command value DV1 is greater than the W-phase duty command value DW1. "DU1", "DV1", and "DW1" are the values ​​in the update registers assigned to each duty command value as described above.

[0028] During the descent of the triangular wave tweeter (TW), when the triangular wave tweeter reaches the three-phase duty cycle command value, the three-phase PWM signal becomes high. In other words, during the countdown operation of the PWM timer, the three-phase PWM signal becomes high at the timing when the PWM timer's count value matches the three-phase duty cycle command value.

[0029] Therefore, as shown in Figure 2, during the countdown period from time t1 to time t2, the U-phase PWM signal PU becomes high when the PWM timer count value matches the U-phase duty cycle command value DU1. During the countdown period from time t1 to time t2, the V-phase PWM signal PV becomes high when the PWM timer count value matches the V-phase duty cycle command value DV1. During the countdown period from time t1 to time t2, the W-phase PWM signal PW becomes high when the PWM timer count value matches the W-phase duty cycle command value DW1.

[0030] As shown in Figure 2, assume that at the count-up start time t2, the U-phase duty command value DU is updated to "DU2", the V-phase duty command value DV is updated to "DV2", and the W-phase duty command value DW is updated to "DW2". The U-phase duty command value DU2 is greater than the V-phase duty command value DV2. The V-phase duty command value DV2 is greater than the W-phase duty command value DW2. "DU2", "DV2", and "DW2" are the values ​​in the update registers assigned to each duty command value as described above.

[0031] During the rise of the triangular wave TW, when the triangular wave TW reaches the three-phase duty cycle command value, the three-phase PWM signal goes low. In other words, during the count-up operation of the PWM timer, the three-phase PWM signal goes low at the timing when the PWM timer's count value matches the three-phase duty cycle command value.

[0032] Therefore, as shown in Figure 2, during the count-up period from time t2 to time t3, the U-phase PWM signal PU becomes low when the PWM timer count value matches the U-phase duty cycle command value DU2. During the count-up period from time t2 to time t3, the V-phase PWM signal PV becomes low when the PWM timer count value matches the V-phase duty cycle command value DV2. During the count-up period from time t2 to time t3, the W-phase PWM signal PW becomes low when the PWM timer count value matches the W-phase duty cycle command value DW2.

[0033] The operation during the countdown period from time t3 to time t4 is the same as the operation during the countdown period from time t1 to time t2. The operation during the count-up period from time t4 to time t5 is the same as the operation during the count-up period from time t2 to time t3. By repeating the above operation with the update cycle Td of the three-phase duty command value, the duty cycle of the three-phase PWM signal is controlled individually.

[0034] As can be understood from the above explanation, this embodiment illustrates a control mode called asymmetric center alignment mode, in which the rising edge timing and falling edge timing of the PWM signal are controlled individually, in which the duty cycle of the PWM signal is controlled. However, the PWM signal control modes that can be used in the present invention are not limited to asymmetric center alignment mode.

[0035] As shown in Figure 3, for example, if the V-phase duty cycle command value DV and the W-phase duty cycle command value DW are equal among the three-phase duty cycle command values ​​updated at the countdown start time t1, then the rising edge timing of the V-phase PWM signal PV and the rising edge timing of the W-phase PWM signal PW coincide during the countdown period from time t1 to time t2.

[0036] As already mentioned, electrolytic corrosion may occur in the rotor bearing of the three-phase motor 20 due to the potential difference (shaft voltage) between the output shaft of the three-phase motor 20 and the motor case. In the example shown in Figure 3, in the nth PWM control cycle, the on-timing of the V-phase PWM signal PV and the on-timing of the W-phase PWM signal PW coincide. As a result of the inventors' research, it has been found that, as shown in Figure 3, a large instantaneous fluctuation in the shaft voltage at the moment when the switching timings of two phases of the three-phase PWM signal coincide may affect the occurrence of electrolytic corrosion. In the example in Figure 3, for example, when the three-phase motor 20 is in the powering state and the V-phase and W-phase currents are positive (when current flows from the power conversion circuit 11 to the three-phase motor 20), a rapid fluctuation in the shaft voltage occurs when the switching timings of the V-phase PWM signal PV and the W-phase PWM signal PW coincide. On the other hand, under similar conditions, if the V-phase current is positive and the W-phase current is negative, a rapid fluctuation in the shaft voltage occurs when the turn-off of the V-phase high-side coincides with the turn-on of the W-phase low-side, or when the turn-on of the V-phase high-side coincides with the turn-off of the W-phase low-side.

[0037] To solve the above technical problems, the MCU 12 in this embodiment predicts, based on the three-phase duty cycle command value, that voltage fluctuations will occur in the same direction and at the same timing at at least two of the three-phase connection terminals 13u, 13v, and 13w connected to the three-phase motor 20. In this case, the MCU 12 delays the timing of the voltage fluctuation at one of the two connection terminals by 1 hour and advances the timing of the voltage fluctuation at the other connection terminal by 2 hours. The sum of the first and second hours is a predetermined time ΔT during which the timing of voltage fluctuations at the two-phase connection terminals does not overlap. In the following, in order to facilitate understanding of the present invention, the operation of this embodiment will be described in comparison with the technology disclosed in Japanese Patent Application Publication No. 2005-51959.

[0038] The technology disclosed in Japanese Patent Publication No. 2005-51959 is a technology aimed at avoiding simultaneous switching of multiple phases. Hereinafter, the technology disclosed in Japanese Patent Publication No. 2005-51959 will be referred to as the comparative technology. In the comparative technology, when the edge timings of two phases of a three-phase PWM signal match, the rising edge timing and falling edge timing of one of the two phases of the PWM signal are delayed by a predetermined time ΔT.

[0039] For example, as shown in Figure 3, consider a case where the rising edge timing of the V-phase PWM signal PV and the rising edge timing of the W-phase PWM signal PW coincide during the countdown period from time t1 to time t2. In this case, as shown in Figure 4, the comparative technique delays the phase of the W-phase PWM signal PW by a predetermined time ΔT. As a result, the rising edge timing of the W-phase PWM signal PW is delayed by a predetermined time ΔT relative to the rising edge timing of the V-phase PWM signal PV, thus avoiding simultaneous switching of the V-phase and W-phase. Furthermore, since the falling edge timing of the W-phase PWM signal PW is also delayed by a predetermined time ΔT, the duty cycle of the W-phase PWM signal PW does not change during one period of the PWM period Tp.

[0040] Figure 5 is a timing chart showing an example of a three-phase PWM signal generated by this embodiment when the rising edge timing of the V-phase PWM signal and the rising edge timing of the W-phase PWM signal coincide during the countdown period from time t1 to time t2. As shown in Figure 5, in this embodiment, during the countdown period from time t1 to time t2, the MCU 12 delays the rising edge timing of the W-phase PWM signal PW by a first time and advances the rising edge timing of the V-phase PWM signal PV by a second time. As an example, the MCU 12 determines the first and second times to be half of a predetermined time ΔT. As a result, the time difference between the rising edge timing of the V-phase PWM signal PV and the rising edge timing of the W-phase PWM signal PW becomes relatively equal to the predetermined time ΔT, thus avoiding simultaneous switching of the V-phase and W-phase.

[0041] Furthermore, as shown in Figure 5, during the count-up period from time t2 to time t3, the MCU12 delays the falling edge timing of the W-phase PWM signal PW by 1 hour and advances the falling edge timing of the V-phase PWM signal PV by 2 hours. Thus, in this embodiment, the MCU12 performs compensation processing by delaying the rising edge timing of the W-phase PWM signal PW by 1 hour, and then delaying the next falling edge timing by the same 1 hour. Similarly, the MCU12 performs compensation processing by advancing the rising edge timing of the V-phase PWM signal PV by 2 hours, and then advancing the next falling edge timing by the same 2 hours. By performing these compensation processes, the impact on motor control caused by the shift in the switching timing of the V-phase and W-phase can be suppressed. In addition, while the comparative technique shown in Figure 4 shifted the phase of the PWM signal of one phase by ΔT, the technique in Figure 5 sets the phase shift of the PWM signal per phase to be smaller than ΔT, thus further suppressing the impact on motor control caused by the shift in switching timing compared to the comparative technique.

[0042] The operation of the MCU12 in the example shown in Figure 5 will be explained in detail below. The MCU core 12a of the MCU12 performs a command value calculation process before the countdown start time t1, which is the update timing of the three-phase duty command value. Based on the three-phase duty command value calculated by the command value calculation process, it predicts whether the edge timings of two of the three-phase PWM signals will match. For example, if the V-phase duty command value DV and the W-phase duty command value DW are equal among the three-phase duty command values ​​calculated before the countdown start time t1, the MCU core 12a predicts that the rising edge timing of the V-phase PWM signal PV and the rising edge timing of the W-phase PWM signal PW will match during the countdown period from time t1 to time t2.

[0043] If the MCU core 12a predicts that the rising edge timing of the V-phase PWM signal PV and the rising edge timing of the W-phase PWM signal PW will coincide, it performs a correction process by subtracting a value corresponding to the first time ΔT / 2 from the calculated value of the W-phase duty command value DW, and also performs a correction process by adding a value corresponding to the second time ΔT / 2 to the calculated value of the V-phase duty command value DV. The MCU core 12a outputs the U-phase duty command value DU calculated by the command value calculation process, and the corrected V-phase duty command value DV and W-phase duty command value DW to the PWM module 12b.

[0044] As described above, the three-phase duty cycle command value input from the MCU core 12a to the PWM module 12b before the countdown start time t1 is temporarily stored in a buffer register. Then, when the countdown start time t1 arrives, the three-phase duty cycle command value stored in the buffer register is transferred to the update register. In this way, at the countdown start time t1, the contents of the update register are updated with the new three-phase duty cycle command value. As a result, as shown in Figure 5, during the countdown period from time t1 to time t2, the rising edge timing of the W-phase PWM signal PW is delayed by the first time ΔT / 2, and the rising edge timing of the V-phase PWM signal PV is advanced by the second time ΔT / 2.

[0045] The MCU core 12a executes the command value calculation process again before the count-up start time t2, which is the next update timing for the three-phase duty command value. The MCU core 12a performs compensation processing on the duty command values ​​among the three-phase duty command values ​​calculated by the current command value calculation process that were corrected during the previous command value calculation process. For example, the MCU core 12a performs compensation processing by adding a value corresponding to the first time ΔT / 2 to the calculated value of the W-phase duty command value DW among the three-phase duty command values ​​calculated by the current command value calculation process, and by subtracting a value corresponding to the second time ΔT / 2 from the calculated value of the V-phase duty command value DV. The MCU core 12a outputs the U-phase duty command value DU calculated by the current command value calculation process, and the compensated V-phase duty command value DV and W-phase duty command value DW to the PWM module 12b.

[0046] As described above, the three-phase duty cycle command value input from the MCU core 12a to the PWM module 12b before the count-up start time t2 is temporarily stored in a buffer register. Then, when the count-up start time t2 arrives, the three-phase duty cycle command value stored in the buffer register is transferred to the update register. In this way, at the count-up start time t2, the contents of the update register are updated with the new three-phase duty cycle command value. As a result, as shown in Figure 5, during the count-up period from time t2 to time t3, the falling edge timing of the W-phase PWM signal PW is delayed by the first time ΔT / 2, and the falling edge timing of the V-phase PWM signal PV is advanced by the second time ΔT / 2.

[0047] Next, as shown in Figure 6, we consider the case where, during the countdown period from time t1 to time t2, the duty cycles of the V-phase PWM signal PV and the W-phase PWM signal PW are close to 100%, and the rising edge timing of the V-phase PWM signal and the rising edge timing of the W-phase PWM signal coincide. In this case, as shown in Figure 7, if, for example, the phase of the W-phase PWM signal PW is delayed by a predetermined time ΔT based on the comparison technique, the falling edge timing of the W-phase PWM signal PW may exceed the PWM period Tp. Therefore, in this case, the PWM signal cannot be generated by the usual method of generating a PWM signal by comparing the triangular wave TW with the three-phase duty cycle command value, and the program becomes complicated.

[0048] Conversely, as shown in Figure 8, if the phase of the W-phase PWM signal PW is advanced by a predetermined time ΔT, the rising edge timing of the W-phase PWM signal PW may exceed the PWM period Tp. Therefore, even in this case, the usual method of generating a PWM signal by comparing the triangular wave TW with the three-phase duty cycle command value cannot be used, and the program becomes more complex.

[0049] Figure 9 is a timing chart showing an example of a three-phase PWM signal generated by this embodiment when the duty cycles of the V-phase PWM signal and the W-phase PWM signal are close to 100%, and the rising edge timing of the V-phase PWM signal and the rising edge timing of the W-phase PWM signal coincide. As shown in Figure 9, in this embodiment, the MCU 12 sets the duty cycle of the voltage fluctuations of the two-phase connection terminals to 100% or less if the duty cycle of the voltage fluctuations of the two-phase connection terminals, which are predicted to occur in the same direction and at the same timing, falls within the range from the first threshold to 100%.

[0050] Specifically, during the countdown period from time t1 to time t2, the MCU12 delays the rising edge timing of the V-phase PWM signal PV by a first time interval ΔT1, and advances the rising edge timing of the W-phase PWM signal PW by a second time interval ΔT2. The sum of the first time interval ΔT1 and the second time interval ΔT2 is equal to a predetermined time interval ΔT. As a result, the time difference between the rising edge timing of the V-phase PWM signal PV and the rising edge timing of the W-phase PWM signal PW becomes relatively equal to the predetermined time interval ΔT, thus avoiding simultaneous switching of the V-phase and W-phase. Furthermore, even when the duty cycle of the V-phase and W-phase PWM signals is close to 100%, the PWM signal can be generated using the normal method of generating a PWM signal by comparing the triangular wave TW with the three-phase duty cycle command value. Note that the first time ΔT1 and the second time ΔT2 may each be set to half of the predetermined time ΔT, but the first time ΔT1 and the second time ΔT2 may also be adjusted as appropriate so that the triangular wave TW remains on the same slope even after the switching timing is shifted.

[0051] Furthermore, as shown in Figure 9, during the count-up period from time t2 to time t3, the MCU12 delays the falling edge timing of the V-phase PWM signal PV by a first time interval ΔT1, and advances the falling edge timing of the W-phase PWM signal PW by a second time interval ΔT2. Thus, in this embodiment, the MCU12 performs compensation processing to delay the rising edge timing of the V-phase PWM signal PV by a first time interval ΔT1, and then delays the next falling edge timing by the same first time interval ΔT1. Similarly, the MCU12 performs compensation processing to advance the rising edge timing of the W-phase PWM signal PW by a second time interval ΔT2, and then advances the next falling edge timing by the same second time interval ΔT2. By performing these compensation processes, the impact on motor control caused by the shift in the switching timing of the V-phase and W-phase can be suppressed.

[0052] The operation of MCU12 in the example shown in Figure 9 will be explained in detail below. The MCU core 12a of MCU12 performs a command value calculation process before the countdown start time t1, which is the update timing of the three-phase duty command value. Based on the three-phase duty command value calculated by the command value calculation process, it predicts whether the edge timings of two phases of the three-phase PWM signal match. For example, at the start of the countdown... If the V-phase duty cycle command value DV and the W-phase duty cycle command value DW are equal among the three-phase duty cycle command values ​​calculated before time t1, the MCU core 12a predicts that the rising edge timing of the V-phase PWM signal PV and the rising edge timing of the W-phase PWM signal PW will coincide during the countdown period from time t1 to time t2.

[0053] The MCU core 12a predicts that the rising edge timing of the V-phase PWM signal PV and the rising edge timing of the W-phase PWM signal PW coincide, and determines that the duty cycles of the V-phase and W-phase are within the range from the first threshold to 100%, then performs a correction process by subtracting a value corresponding to the first time ΔT1 from the calculated value of the V-phase duty command value DV, and also performs a correction process by adding a value corresponding to the second time ΔT2 to the calculated value of the W-phase duty command value DW. The MCU core 12a outputs the U-phase duty command value DU calculated by the command value calculation process, and the corrected V-phase duty command value DV and W-phase duty command value DW to the PWM module 12b.

[0054] As described above, the three-phase duty cycle command value input from the MCU core 12a to the PWM module 12b before the countdown start time t1 is temporarily stored in a buffer register. Then, when the countdown start time t1 arrives, the three-phase duty cycle command value stored in the buffer register is transferred to the update register. In this way, at the countdown start time t1, the contents of the update register are updated with the new three-phase duty cycle command value. As a result, as shown in Figure 9, during the countdown period from time t1 to time t2, the rising edge timing of the V-phase PWM signal PV is delayed by the first time interval ΔT1, and the rising edge timing of the W-phase PWM signal PW is advanced by the second time interval ΔT2.

[0055] The MCU core 12a executes the command value calculation process again before the count-up start time t2, which is the next update timing for the three-phase duty command value. The MCU core 12a performs compensation processing on the duty command values ​​among the three-phase duty command values ​​calculated by the current command value calculation process that were corrected during the previous command value calculation process. For example, the MCU core 12a performs compensation processing by adding a value corresponding to the first time ΔT1 to the calculated value of the V-phase duty command value DV among the three-phase duty command values ​​calculated by the current command value calculation process, and also performs compensation processing by subtracting a value corresponding to the second time ΔT2 from the calculated value of the W-phase duty command value DW. The MCU core 12a outputs the U-phase duty command value DU calculated by the current command value calculation process, and the compensated V-phase duty command value DV and W-phase duty command value DW to the PWM module 12b.

[0056] As described above, the three-phase duty cycle command value input from the MCU core 12a to the PWM module 12b before the count-up start time t2 is temporarily stored in a buffer register. Then, when the count-up start time t2 arrives, the three-phase duty cycle command value stored in the buffer register is transferred to the update register. In this way, at the count-up start time t2, the contents of the update register are updated with the new three-phase duty cycle command value. As a result, as shown in Figure 9, during the count-up period from time t2 to time t3, the falling edge timing of the V-phase PWM signal PV is delayed by the first time ΔT1, and the falling edge timing of the W-phase PWM signal PW is advanced by the second time ΔT2.

[0057] Next, as shown in Figure 10, we consider the case where, during the countdown period from time t1 to time t2, the duty cycles of the U-phase PWM signal PU and the V-phase PWM signal PV are close to 0%, and the rising edge timing of the U-phase PWM signal PU and the rising edge timing of the V-phase PWM signal PV coincide. In this case, as shown in Figure 11, if, for example, the phase of the V-phase PWM signal PV is delayed by a predetermined time ΔT based on the comparison technique, the rising edge timing of the V-phase PWM signal PV may extend beyond the trough of the triangular wave TW. Therefore, in this case, the usual method of generating a PWM signal by comparing the triangular wave TW with the three-phase duty cycle command value cannot generate the PWM signal, and the program becomes complicated.

[0058] Although not shown in the diagram, conversely, if the phase of the V-phase PWM signal PW is advanced by a predetermined time ΔT, the falling edge timing of the V-phase PWM signal PV may exceed the trough of the triangular wave TW. Therefore, even in this case, the usual method of generating a PWM signal by comparing the triangular wave TW with the three-phase duty cycle command value cannot generate the PWM signal, and the program becomes more complex.

[0059] Figure 12 is a timing chart showing an example of a three-phase PWM signal generated by this embodiment when the duty cycles of the U-phase PWM signal PU and the V-phase PWM signal PV are close to 0%, and the rising edge timing of the U-phase PWM signal PU and the rising edge timing of the V-phase PWM signal PV coincide. As shown in Figure 12, in this embodiment, the MCU 12 sets the duty cycle of the voltage fluctuations of the two-phase connection terminals to 0% or more if the duty cycle of the voltage fluctuations of the two-phase connection terminals, which are predicted to occur in the same direction and at the same timing, falls within the range from the second threshold to 0%.

[0060] Specifically, during the countdown period from time t1 to time t2, the MCU12 delays the rising edge timing of the V-phase PWM signal PV by a first time interval ΔT4, and advances the rising edge timing of the U-phase PWM signal PU by a second time interval ΔT3. The sum of the first time interval ΔT4 and the second time interval ΔT3 is equal to a predetermined time interval ΔT. As a result, the time difference between the rising edge timing of the V-phase PWM signal PV and the rising edge timing of the U-phase PWM signal PU becomes relatively equal to a predetermined time interval ΔT, thus avoiding simultaneous switching of the V-phase and U-phase. Furthermore, even when the duty cycle of the V-phase and U-phase PWM signals is close to 0%, the PWM signal can be generated using the normal method of generating a PWM signal by comparing a triangular wave TW with a three-phase duty cycle command value. Note that the first time ΔT4 and the second time ΔT3 may each be set to half of the predetermined time ΔT, but the first time ΔT4 and the second time ΔT3 may also be adjusted as appropriate so that the triangular wave TW remains on the same slope even after the switching timing is shifted.

[0061] Furthermore, as shown in Figure 12, during the count-up period from time t2 to time t3, the MCU 12 delays the falling edge timing of the V-phase PWM signal PV by a first time interval ΔT4, and advances the falling edge timing of the U-phase PWM signal PU by a second time interval ΔT3. Thus, in this embodiment, the MCU 12 performs compensation processing to delay the rising edge timing of the V-phase PWM signal PV by a first time interval ΔT4, and then delays the next falling edge timing by the same first time interval ΔT4. Similarly, the MCU 12 performs compensation processing to advance the rising edge timing of the U-phase PWM signal PU by a second time interval ΔT3, and then advances the next falling edge timing by the same second time interval ΔT3. By performing these compensation processing, the impact on motor control caused by the shift in the switching timing of the V-phase and U-phase can be suppressed.

[0062] The operation of the MCU12 in the example shown in Figure 12 will be explained in detail below. The MCU core 12a of the MCU12 performs a command value calculation process before the countdown start time t1, which is the update timing of the three-phase duty command value. Based on the three-phase duty command value calculated by the command value calculation process, it predicts whether the edge timings of two of the three-phase PWM signals will match. For example, if the V-phase duty command value DV and the U-phase duty command value DU are equal among the three-phase duty command values ​​calculated before the countdown start time t1, the MCU core 12a predicts that the rising edge timing of the V-phase PWM signal PV and the rising edge timing of the U-phase PWM signal PU will match during the countdown period from time t1 to time t2.

[0063] The MCU core 12a predicts that the rising edge timing of the V-phase PWM signal PV and the rising edge timing of the U-phase PWM signal PU coincide, and determines that the duty cycles of the V-phase and U-phase fall within the range from the second threshold to 0%, then performs a correction process by subtracting a value corresponding to the first time ΔT4 from the calculated value of the V-phase duty command value DV, and also performs a correction process by adding a value corresponding to the second time ΔT3 to the calculated value of the U-phase duty command value DU. The MCU core 12a outputs the W-phase duty command value DW calculated by the command value calculation process, and the corrected V-phase duty command value DV and U-phase duty command value DU to the PWM module 12b.

[0064] As described above, the three-phase duty cycle command value input from the MCU core 12a to the PWM module 12b before the countdown start time t1 is temporarily stored in a buffer register. Then, when the countdown start time t1 arrives, the three-phase duty cycle command value stored in the buffer register is transferred to the update register. In this way, at the countdown start time t1, the contents of the update register are updated with the new three-phase duty cycle command value. As a result, as shown in Figure 12, among the three-phase PWM signals generated by the PWM module 12b during the countdown period from time t1 to time t2, the rising edge timing of the V-phase PWM signal PV is delayed by the first time ΔT4, and the rising edge timing of the U-phase PWM signal PU is advanced by the second time ΔT3.

[0065] The MCU core 12a executes the command value calculation process again before the count-up start time t2, which is the next update timing for the three-phase duty command value. The MCU core 12a performs compensation processing on the duty command values ​​among the three-phase duty command values ​​calculated by the current command value calculation process that were corrected during the previous command value calculation process. For example, the MCU core 12a performs compensation processing by adding a value corresponding to the first time ΔT4 to the calculated value of the V-phase duty command value DV among the three-phase duty command values ​​calculated by the current command value calculation process, and also performs compensation processing by subtracting a value corresponding to the second time ΔT3 from the calculated value of the U-phase duty command value DU. The MCU core 12a outputs the W-phase duty command value DW calculated by the current command value calculation process, and the compensated V-phase duty command value DV and U-phase duty command value DU to the PWM module 12b.

[0066] As described above, the three-phase duty cycle command value input from the MCU core 12a to the PWM module 12b before the count-up start time t2 is temporarily stored in a buffer register. Then, when the count-up start time t2 arrives, the three-phase duty cycle command value stored in the buffer register is transferred to the update register. In this way, at the count-up start time t2, the contents of the update register are updated with the new three-phase duty cycle command value. As a result, as shown in Figure 12, during the count-up period from time t2 to time t3, the falling edge timing of the V-phase PWM signal PV is delayed by the first time ΔT4, and the falling edge timing of the U-phase PWM signal PW is advanced by the second time ΔT3.

[0067] As shown in Figure 13, when the MCU12 predicts that the voltage fluctuations of two phase connection terminals will occur in the rising direction and at the same timing, and the duty cycle of the voltage fluctuation of one connection terminal is increasing while the duty cycle of the voltage fluctuation of the other connection terminal is decreasing, the MCU12 will then determine the rising edge timing of the voltage fluctuation of one connection terminal. The timing of the initial and the next falling edge are delayed by a first time interval ΔT5, while the rising edge timing and the next falling edge timing of the voltage fluctuation at the other connection terminal are advanced by a second time interval ΔT6. The sum of the first time interval ΔT5 and the second time interval ΔT6 is equal to a predetermined time interval ΔT.

[0068] Figure 13 is a timing chart showing an example of a three-phase PWM signal generated by this embodiment when the duty cycle of the V-phase PWM signal PV is increasing and the duty cycle of the W-phase PWM signal PW is decreasing, and the rising edge timing of the V-phase PWM signal PV and the rising edge timing of the W-phase PWM signal PW coincide. In this case, the MCU 12 delays the rising edge timing and the next falling edge timing of the V-phase PWM signal PV by a first time interval ΔT5, and advances the rising edge timing and the next falling edge timing of the W-phase PWM signal PW by a second time interval ΔT6.

[0069] In the example shown in Figure 13, the turn-on timing of the V-phase PWM signal and the turn-on timing of the W-phase PWM signal were originally synchronized. Therefore, at the next turn-off timing, the W-phase is either earlier than the V-phase or at the same timing. In the example shown in Figure 13, by advancing the W-phase and delaying the V-phase, it is possible to avoid the timing of the V-phase and W-phase synchronizing again at the next turn-off timing.

[0070] As shown in Figure 14, when the MCU 12 predicts that the voltage fluctuations of two phase connection terminals will occur in the same direction and at the same timing, and the duty cycle of the voltage fluctuation of one connection terminal is decreasing while the duty cycle of the voltage fluctuation of the other connection terminal is increasing, the MCU 12 delays the falling edge timing and the next rising edge timing of the voltage fluctuation of one connection terminal by a first time ΔT8, and advances the falling edge timing and the next rising edge timing of the voltage fluctuation of the other connection terminal by a second time ΔT7. The sum of the first time ΔT8 and the second time ΔT7 is equal to a predetermined time ΔT.

[0071] Figure 14 is a timing chart showing an example of a three-phase PWM signal generated by this embodiment when the duty cycle of the V-phase PWM signal PV is increasing and the duty cycle of the W-phase PWM signal PW is decreasing, and the falling edge timing of the V-phase PWM signal and the falling edge timing of the W-phase PWM signal coincide. In this case, the MCU 12 delays the falling edge timing of the W-phase PWM signal PW and the next rising edge timing by a first time ΔT8, and advances the falling edge timing of the V-phase PWM signal PV and the next rising edge timing by a second time ΔT7.

[0072] In the example shown in Figure 14, the turn-off timing of the V-phase PWM signal and the W-phase PWM signal were originally synchronized. Therefore, at the next turn-on timing, the V-phase is either earlier than the W-phase or at the same timing. In the example shown in Figure 14, by advancing the V-phase and delaying the W-phase, it is possible to avoid the timing of the V-phase and W-phase synchronizing again at the next turn-on timing.

[0073] In the above explanation, a three-phase PWM signal without considering dead time was used, but a dead time is provided in the gate control signals supplied to each arm switch of the power conversion circuit 11. Figure 15 is a timing chart showing an example of the waveforms of the U-phase upper gate control signal G1, the U-phase lower gate control signal G2, the U-phase terminal voltage Vu, the V-phase upper gate control signal G3, the V-phase lower gate control signal G4, and the V-phase terminal voltage Vv when the direction of the U-phase and V-phase currents is both from the power conversion circuit 11 to the three-phase motor 20. In Figure 15, the U-phase terminal voltage Vu is the voltage at the U-phase connection terminal 13u, and the V-phase terminal voltage Vv is the voltage at the V-phase connection terminal 13v. Also in Figure 15, Vp is the positive potential of the DC power supply 30, and Vn is the negative potential of the DC power supply 30. For the sake of simplicity, the voltage drop when the IGBT and diode conduct is ignored in Figure 15.

[0074] As shown in Figure 15, a dead time TD is inserted between the U-phase upper gate control signal G1 and the U-phase lower gate control signal G2, and also between the V-phase upper gate control signal G3 and the V-phase lower gate control signal G4. When the direction of the currents in both the U-phase and V-phase is from the power conversion circuit 11 to the three-phase motor 20, the U-phase terminal voltage Vu fluctuates in synchronization with the U-phase upper gate control signal G1, and the V-phase terminal voltage Vv fluctuates in synchronization with the V-phase upper gate control signal G3.

[0075] As shown in Figure 15, for example, let's assume that the U-phase upper gate control signal G1 and the V-phase upper gate control signal G3 coincide at their off-timing. In this case, since the U-phase terminal voltage Vu and the V-phase terminal voltage Vv simultaneously fluctuate from the positive potential Vp to the negative potential Vn of the DC power supply 30, the potential fluctuation at the neutral point N of the three-phase motor 20 becomes larger compared to the case where only one phase fluctuates, and consequently the shaft voltage of the three-phase motor 20 also fluctuates significantly, causing noise. To avoid this, in this embodiment, when the off-timing of the U-phase upper gate control signal G1 and the V-phase upper gate control signal G3 are closer than a predetermined time ΔT, that is, when there is a risk that the phase voltage fluctuation timings will coincide due to a delay in the gate driver, the off-timing of the U-phase upper gate control signal G1 and its adjacent on-timing are delayed by a first time ΔT1. Accordingly, the U-phase lower gate control signal G2 is also delayed by a first time ΔT1 in its on-timing and off-timing, which correspond to the U-phase upper gate control signal G1, in order to maintain the dead time TD. As a result, the waveform of the U-phase terminal voltage Vu is also delayed by a first time ΔT1.

[0076] Furthermore, in this embodiment, the off-timing of the V-phase upper gate control signal G3 and its adjacent on-timing are advanced by a second time ΔT2. Accordingly, the V-phase lower gate control signal G4 is also advanced by a second time ΔT2, with its on-timing and off-timing corresponding to the V-phase upper gate control signal G3 being advanced by the second time ΔT2, in order to maintain the dead time TD. As a result, the waveform of the V-phase terminal voltage Vv is also advanced by a second time ΔT2. The sum of the first time ΔT1 and the second time ΔT2 is equal to a predetermined time ΔT. By performing the above operations, it is possible to prevent the two phase voltages from fluctuating simultaneously in the same direction, and as a result, it is possible to suppress large instantaneous fluctuations in the shaft voltage of the three-phase motor 20.

[0077] Figure 16 is a timing chart showing an example of the waveforms of the U-phase upper gate control signal G1, U-phase lower gate control signal G2, U-phase terminal voltage Vu, V-phase upper gate control signal G3, V-phase lower gate control signal G4, and V-phase terminal voltage Vv, when the direction of the U-phase and V-phase currents is both from the three-phase motor 20 to the power conversion circuit 11.

[0078] As shown in Figure 16, a dead time TD is inserted between the U-phase upper gate control signal G1 and the U-phase lower gate control signal G2, and also between the V-phase upper gate control signal G3 and the V-phase lower gate control signal G4. When the direction of the currents in both the U-phase and V-phase is from the three-phase motor 20 to the power conversion circuit 11, the U-phase terminal voltage Vu fluctuates in synchronization with the U-phase lower gate control signal G2, and the V-phase terminal voltage Vv fluctuates in synchronization with the V-phase lower gate control signal G4.

[0079] As shown in Figure 16, for example, let's assume that the U-phase lower gate control signal G2 and the V-phase lower gate control signal G4 coincide in their on-timing. In this case, the U-phase terminal voltage Vu and the V-phase terminal voltage Vv simultaneously fluctuate from the positive potential Vp to the negative potential Vn of the DC power supply 30, causing a large fluctuation in the shaft voltage of the three-phase motor 20 and resulting in noise. To avoid this, in this embodiment, if the off-timings of the U-phase lower gate control signal G2 and the V-phase lower gate control signal G4 are closer than a predetermined time ΔT, the on-timing of the U-phase lower gate control signal G2 and its adjacent off-timing are delayed by a first time ΔT1. Accordingly, the U-phase upper gate control signal G1 is also delayed by a first time ΔT1 in its on-timing and off-timing, which correspond to the U-phase lower gate control signal G2, in order to maintain a dead time TD. As a result, the waveform of the U-phase terminal voltage Vu is also delayed by a first time ΔT1.

[0080] Furthermore, in this embodiment, the on-timing of the V-phase lower gate control signal G4 and its adjacent off-timing are advanced by a second time ΔT2. Accordingly, the on-timing and off-timing of the V-phase upper gate control signal G3 are also advanced by a second time ΔT2 to maintain the dead time TD, corresponding to the V-phase lower gate control signal G4. As a result, the waveform of the V-phase terminal voltage Vv is also advanced by a second time ΔT2. Note that the sum of the first time ΔT1 and the second time ΔT2 is equal to a predetermined time ΔT. By performing the above operations, it is possible to prevent the two phase voltages from fluctuating simultaneously in the same direction, and as a result, it is possible to suppress large instantaneous fluctuations in the shaft voltage of the three-phase motor 20.

[0081] Furthermore, Figure 16 showed the case where both the U-phase current and the V-phase current flow from the three-phase motor 20 to the power conversion circuit 11. Next, we will explain the case where the directions of the two currents are opposite, that is, for example, when the U-phase current flows from the power conversion circuit 11 to the three-phase motor 20, and the V-phase current flows from the three-phase motor 20 to the power conversion circuit 11. In this case, the U-phase terminal voltage Vu fluctuates in synchronization with the U-phase upper gate control signal G1, and the V-phase terminal voltage Vv fluctuates in synchronization with the V-phase lower gate control signal G4. For example, when the off-timing of the U-phase upper gate control signal G1 and the on-timing of the V-phase lower gate control signal G4 coincide, the U-phase terminal voltage Vu and the V-phase terminal voltage Vv simultaneously fluctuate from the positive potential Vp to the negative potential Vn of the DC power supply 30. When the terminal voltages of multiple phases fluctuate simultaneously and in the same direction, the shaft voltage of the three-phase motor 20 also fluctuates significantly, which can cause noise. To suppress this, when the current and on / off timings meet the above conditions, for example, the off timing of the U-phase upper gate control signal G1 is delayed by a first time ΔT1, and the on timing and off timing of the subsequent U-phase lower gate control signal G2, and the on timing of the U-phase upper gate control signal G1 are sequentially delayed by a first time ΔT1. In addition, the on timing of the V-phase lower gate control signal G4 is advanced by a second time ΔT2, and the off timing of the V-phase upper gate control signal G3 immediately preceding it, the off timing of the subsequent V-phase lower gate control signal G4, and the on timing of the V-phase upper gate control signal G3 are sequentially advanced by a second time ΔT2. The sum of the first time ΔT1 and the second time ΔT2 is equal to a predetermined time ΔT. Through these operations, the impact on motor control is minimized while suppressing large instantaneous fluctuations in the shaft voltage of the three-phase motor 20.

[0082] As described above, in this embodiment, when a dead time is provided, it is determined whether the voltage fluctuations of at least two of the three-phase connection terminals 13u, 13v, and 13w occurred in the same direction and at the same timing, taking into consideration (1) whether the terminal voltage fluctuations synchronize with the upper gate control signal or the lower gate control signal change depending on the direction of the current, and (2) whether the turn-on timing is delayed by the amount of the dead time due to the provision of a dead time.

[0083] As described above, according to one embodiment of the present disclosure, voltage fluctuations at at least two of the three-phase connection terminals 13u, 13v, and 13w are prevented from occurring in the same direction and at the same timing, thereby suppressing large instantaneous fluctuations in the shaft voltage of the three-phase motor 20. In other words, according to one embodiment of the present disclosure, noise caused by large instantaneous fluctuations in the shaft voltage can be reduced. It is possible to reduce it. As a result, according to one embodiment of the present disclosure, it is possible to suppress the occurrence of electrolytic corrosion in the rotor bearing of the three-phase motor 20.

[0084] The present invention is not limited to the embodiments described above, and the configurations described herein can be combined as appropriate within the bounds of mutual non-inconsistency. For example, in the above embodiment, a motor control device 10 for controlling a three-phase motor 20 was exemplified, but the motor to be controlled is not limited to a three-phase motor 20, but can be an n-phase motor (where n is an integer of 3 or more). Also, in the above embodiment, IGBTs were exemplified as each arm switch included in the power conversion circuit 11, but each arm switch may be a high-power switching element other than an IGBT, such as a MOS-FET. [Explanation of symbols]

[0085] 10…Motor control device, 11…Power conversion circuit, 12…MCU (control unit), 12a…MCU core, 12b…PWM module, 13u…U-phase connection terminal, 13v…V-phase connection terminal, 13w…W-phase connection terminal, 20…Three-phase motor, 30…DC power supply

Claims

1. A motor control device for controlling an n-phase motor (where n is an integer of 3 or more), A power conversion circuit connected to the aforementioned n-phase motor, which performs mutual conversion between DC power and n-phase AC power, The system includes a control unit that controls the power conversion circuit based on an n-phase duty cycle command value that is updated at a predetermined update cycle, Based on the n-phase duty cycle command value, if the control unit predicts that voltage fluctuations will occur in the same direction and at the same timing at at least two of the n-phase connection terminals connected to the n-phase motor, it delays the timing of the voltage fluctuation at one of the two connection terminals by a first hour and advances the timing of the voltage fluctuation at the other connection terminal by a second hour. A motor control device in which the sum of the first time and the second time is a predetermined time during which the timing of voltage fluctuations at the two-phase connection terminals does not overlap.

2. The motor control device according to claim 1, wherein the control unit determines the first time and the second time to be half the value of the predetermined time, respectively.

3. The motor control device according to claim 1 or 2, wherein the control unit reduces the duty cycle of the voltage fluctuations of the two-phase connection terminals to 100% or less when the duty cycle of the voltage fluctuations of the two-phase connection terminals falls within a range from a first threshold to 100%.

4. The motor control device according to any one of claims 1 to 3, wherein the control unit sets the duty cycle of the voltage fluctuation of the two-phase connection terminals to 0% or more when the duty cycle of the voltage fluctuation of the two-phase connection terminals falls within a range from a second threshold to 0%.

5. The motor control device according to any one of claims 1 to 4, wherein the control unit predicts that the voltage fluctuations of the two-phase connection terminals will occur in the rising direction and at the same timing when the duty cycle of the voltage fluctuation of one connection terminal is increasing and the duty cycle of the voltage fluctuation of the other connection terminal is decreasing, delays the rising edge timing and the next falling edge timing of the voltage fluctuation of one connection terminal by the first time, and advances the rising edge timing and the next falling edge timing of the voltage fluctuation of the other connection terminal by the second time.

6. The motor control device according to any one of claims 1 to 5, wherein the control unit predicts that the voltage fluctuations of the two phases of the connection terminals will occur in the falling direction and at the same timing when the duty cycle of the voltage fluctuation of one connection terminal is decreasing and the duty cycle of the voltage fluctuation of the other connection terminal is increasing, delays the falling edge timing and the next rising edge timing of the voltage fluctuation of one connection terminal by the first time, and advances the falling edge timing and the next rising edge timing of the voltage fluctuation of the other connection terminal by the second time.

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