Motor control device

Abstract

This motor control device obtains three-phase modulation voltage command values obtained by pulse width modulation of three-phase voltage commands for respective phases of a three-phase AC motor, and generates a gate pulse signal used for control of each switching element of an inverter that converts DC power into AC power on the basis of the three-phase modulation voltage command values. The motor control device calculates the three-phase modulation voltage command values by either three-phase modulation control in which the three-phase modulation voltage command values are changed according to the electrical angle of the motor or two-phase modulation control in which one of the three-phase modulation voltage command values is fixed and the other two-phase modulation voltage command values are changed according to the electrical angle, and performs switching between the two-phase modulation control and the three-phase modulation control a plurality of times within one cycle of the electrical angle.

Description

Motor Control Device

[0001] The present invention relates to a device for controlling a motor.

[0002] Conventionally, motors used for driving automobiles and the like have been required to have features such as miniaturization, higher output, and higher efficiency. To achieve these features, motor control devices capable of performing two-phase modulation motor control in addition to ordinary three-phase modulation motor control have been proposed. The two-phase modulation method is a method for driving and controlling a motor by sequentially fixing the voltage level of one phase of the three-phase AC power supplied from an inverter to a three-phase AC motor at a predetermined level, and modulating the remaining two phases of AC power.

[0003] Regarding switching between the two-phase modulation method and the three-phase modulation method, the technology of Patent Document 1 is known. Patent Document 1 describes an inverter control device that switches from the three-phase modulation method to the two-phase modulation method after a predetermined period has elapsed or a predetermined time delay from the time when a slip command value for a three-phase induction motor changes from negative to positive.

[0004] Japanese Patent No. 3395920

[0005] In the technology of Patent Document 1, when the slip command value changes from negative to positive, it is determined that the switching condition for the modulation method is satisfied, and switching from the three-phase modulation method to the two-phase modulation method is performed after a predetermined period elapses or a predetermined time delay from that point. Therefore, there is a delay from when the modulation method switching condition is satisfied until the modulation method is actually switched, and as a result, the loss and torque ripple generated in the motor may not be sufficiently suppressed.

[0006] In order to solve the above problem, a main object of the present invention is to achieve both reduction of loss and suppression of torque ripple in motor control that uses both two-phase modulation and three-phase modulation.

[0007] The motor control device according to the present invention obtains three-phase modulated voltage command values ​​by pulse width modulating the three-phase voltage commands for each phase of a three-phase AC motor, and generates gate pulse signals used to control each switching element of an inverter that converts DC power to AC power based on the three-phase modulated voltage command values. The three-phase modulated voltage command values ​​are calculated by either three-phase modulation control, which changes the three-phase modulated voltage command values ​​according to the electrical angle of the motor, or two-phase modulation control, which fixes the modulated voltage command value of one of the three phases and changes the modulated voltage command values ​​of the other two phases according to the electrical angle, and the two-phase modulation control and the three-phase modulation control are switched multiple times within one cycle of the electrical angle.

[0008] According to the present invention, in motor control using both two-phase modulation and three-phase modulation methods, it is possible to achieve both loss reduction and torque ripple suppression.

[0009] A diagram illustrating the overall configuration of a motor drive system equipped with a motor control device according to one embodiment of the present invention. A block diagram showing the functional configuration of the motor control device according to one embodiment of the present invention. A flowchart showing the processing flow of the motor control device according to one embodiment of the present invention. A flowchart showing the processing flow of the motor control device according to one embodiment of the present invention. A diagram showing an example of the waveform of the AC voltage output from the inverter to the motor.

[0010] Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. In this embodiment, an example of application to a motor drive system used in electric vehicles such as electric vehicles and hybrid vehicles will be described.

[0011] Figure 1 is an overall configuration diagram of a motor drive system equipped with a motor control device according to one embodiment of the present invention. In Figure 1, the motor drive system 100 comprises a motor control device 1, a three-phase AC motor (hereinafter simply referred to as "motor") 2, an inverter 3, a rotational position detector 4, and a high-voltage battery 5.

[0012] The motor control device 1 controls the operation of the inverter 3 based on a torque command T* corresponding to the target torque requested from the vehicle to the motor 2, thereby generating a gate pulse signal to control the drive of the motor 2. The generated gate pulse signal is then output to the inverter 3. The details of the motor control device 1 will be explained later.

[0013] The inverter 3 includes an inverter circuit 31, a gate drive circuit 32, and a smoothing capacitor 33. The gate drive circuit 32 generates gate drive signals to control each switching element in the inverter circuit 31 based on gate pulse signals input from the motor control device 1, and outputs them to the inverter circuit 31. The inverter circuit 31 has switching elements corresponding to the upper and lower arms of the U-phase, V-phase, and W-phase, respectively. By controlling these switching elements according to the gate drive signals input from the gate drive circuit 32, the DC power supplied from the high-voltage battery 5 is converted to AC power and output to the motor 2. The smoothing capacitor 33 smooths the DC power supplied from the high-voltage battery 5 to the inverter circuit 31.

[0014] Motor 2 is a synchronous motor that is rotationally driven by AC power supplied from inverter 3, and has a stator and a rotor. When AC power input from inverter 3 is applied to armature coils Lu, Lv, and Lw provided on the stator, three-phase AC currents Iu, Iv, and Iw conduct in motor 2, and armature magnetic flux is generated in each armature coil. Attraction and repulsion forces are generated between the armature magnetic flux of each armature coil and the magnetic flux of the permanent magnets arranged on the rotor, which generates torque in the rotor and drives the rotor to rotate.

[0015] A rotational position sensor 8 is attached to the motor 2 to detect the rotational position θm of the rotor. The rotational position detector 4 calculates the rotational position θm from the input signal of the rotational position sensor 8. The result of the rotational position θm calculation by the rotational position detector 4 is input to the motor control device 1 and is used in the phase control of the AC power performed by the motor control device 1 in accordance with the phase of the induced voltage of the motor 2.

[0016] Here, a resolver consisting of an iron core and windings is more preferable for the rotational position sensor 8, but a magnetoresistive element such as a GMR sensor or a sensor using a Hall element is also acceptable. Furthermore, the rotational position detector 4 may estimate the rotational position θm using the three-phase AC currents Iu, Iv, Iw flowing through the motor 2 or the three-phase AC voltages Vu, Vv, Vw applied to the motor 2 from the inverter 3, without using the input signal from the rotational position sensor 8.

[0017] A current sensor 7 is positioned between the inverter 3 and the motor 2. The current sensor 7 detects the three-phase alternating currents Iu, Iv, and Iw (U-phase alternating current Iu, V-phase alternating current Iv, and W-phase alternating current Iw) that energize the motor 2. The current sensor 7 is constructed using, for example, a Hall current sensor. The detection results of the three-phase alternating currents Iu, Iv, and Iw by the current sensor 7 are input to the motor control device 1 and are used for phase control of the AC power performed by the motor control device 1, similar to the calculation results of the rotation position θm by the rotation position detector 4. Although Figure 2 shows an example in which the current sensor 7 is composed of three current detectors, the current detector may be made of two current detectors, and the remaining one-phase alternating current may be calculated from the fact that the sum of the three-phase alternating currents Iu, Iv, and Iw is zero. Alternatively, the pulsed DC current flowing from the high-voltage battery 5 to the inverter 3 may be detected by a shunt resistor or the like inserted between the smoothing capacitor 33 and the inverter 3, and the three-phase AC currents Iu, Iv, and Iw may be determined based on this DC current and the three-phase AC voltages Vu, Vv, and Vw applied from the inverter 3 to the motor 2.

[0018] Next, the motor control device 1 will be described in detail. Figure 2 is a block diagram showing the functional configuration of the motor control device 1 according to one embodiment of the present invention. In Figure 2, the motor control device 1 has the following functional blocks: a current command generation unit 10, an electrical angle calculation unit 11, an electrical angle rotation speed calculation unit 12, a UVW / dq conversion unit 13, a current control unit 14, a dq / UVW conversion unit 15, a voltage control unit 16, a dead time compensation unit 17, and a gate pulse signal generation unit 18. The motor control device 1 is configured, for example, by a microcomputer, and these functional blocks can be realized by executing a predetermined program in the microcomputer. Alternatively, some or all of these functional blocks may be realized using hardware circuits such as logic ICs or FPGAs.

[0019] The current command generation unit 10 calculates the d-axis current command Id* and the q-axis current command Iq* based on the input torque command T*. Here, for example, a pre-set current command map or mathematical formula is used to determine the d-axis current command Id* and the q-axis current command Iq* corresponding to the torque command T*.

[0020] The electrical angle calculation unit 11 calculates the electrical angle θe corresponding to the magnetic pole position of the motor 2 based on the rotational position θm obtained by the rotational position detector 4.

[0021] The electrical angular rotation speed calculation unit 12 calculates the electrical angular rotation speed ωe corresponding to the rotational speed of the motor 2 from the time change of the electrical angle θe. Note that the electrical angular rotation speed ωe may be expressed as either angular velocity (rad / s) or rotational speed (rpm). These values ​​may also be converted to and used interchangeably.

[0022] The UVW / dq conversion unit 13 performs a dq conversion based on the electrical angle θe for the U-phase, V-phase, and W-phase AC currents Iu, Iv, and Iw input from the current sensor 7, and calculates the d-axis current value Id and the q-axis current value Iq.

[0023] The current control unit 14 calculates the d-axis voltage command Vd* and q-axis voltage command Vq* corresponding to the torque command T*, based on the deviation between the d-axis current command Id* and q-axis current command Iq* output from the current command generation unit 10 and the d-axis current value Id and q-axis current value Iq output from the UVW / dq conversion unit 13, so that these values ​​match. Here, taking into account the calculation delay corresponding to the electrical angular rotation speed ωe, the d-axis voltage command Vd* corresponding to the deviation between the d-axis current command Id* and the d-axis current value Id, and the q-axis voltage command Vq* corresponding to the deviation between the q-axis current command Iq* and the q-axis current value Iq, are determined at predetermined calculation cycles by current control calculation using a control method such as PI control. Non-interference control may be used as needed.

[0024] The dq / UVW conversion unit 15 performs a three-phase conversion based on the electrical angle θe for the d-axis voltage command Vd* and the q-axis voltage command Vq* to obtain the three-phase voltage commands Vu*, Vv*, and Vw* (U-phase voltage command value Vu*, V-phase voltage command value Vv*, and W-phase voltage command value Vw*).

[0025] The voltage control unit 16 determines the duty cycle command values ​​Du, Dv, and Dw for the U-phase, V-phase, and W-phase based on the three-phase voltage commands Vu*, Vv*, and Vw* obtained by the dq / UVW conversion unit 15. Here, the three-phase modulated voltage command values ​​Vum*, Vvm*, and Vwm* are obtained by pulse width modulating the three-phase voltage commands Vu*, Vv*, and Vw*, respectively, using the carrier signal of the PWM conversion which changes periodically at a predetermined carrier frequency and the voltage Vdc of the high-voltage battery 5. Then, based on the obtained three-phase modulated voltage command values ​​Vum*, Vvm*, and Vwm*, the pulse width of the gate drive signal to be output to each switching element is determined, thereby determining the duty cycle command values ​​Du, Dv, and Dw for the U-phase, V-phase, and W-phase gate pulse signals, respectively. Details of the calculation method of the duty cycle command values ​​Du, Dv, and Dw by the voltage control unit 16 will be described later.

[0026] The dead time compensation unit 17 calculates the dead time compensation amount for each phase duty command value Du, Dv, Dw obtained by the voltage control unit 16, and adds the calculated dead time compensation amount to each phase duty command value Du, Dv, Dw to obtain the duty command value Dcu, Dcv, Dcw after dead time compensation for each phase. Specifically, the dead time compensation unit 17 calculates the dead time compensation amount Dxdt for each phase using, for example, the following equations (1) to (3). Equation (1) is the calculation formula when the phase current Ix is less than or equal to a negative threshold -Ith, equation (2) is the calculation formula when the phase current Ix is between a negative threshold -Ith and a positive threshold Ith, and equation (3) is the calculation formula when the phase current Ix is greater than or equal to a positive threshold Ith. In equations (1) to (3), the subscript x in the dead time compensation amount Dxdt and the phase current Ix is one of u, v, or w, representing the U phase, V phase, and W phase, respectively. Also, Td represents a predetermined dead time, fs represents the carrier frequency, and Ith represents a predetermined absolute threshold (absolute value of the threshold). (When Ix ≤ -Ith) Dxdt = -Td × fs ... (1) (When -Ith < Ix < Ith) Dxdt = -Td × fs × Ix / Ith ... (2) (When Ix ≥ Ith) Dxdt = Td × fs ... (3)

[0027] After calculating the dead time compensation amount Dxdt (x=u,v,w) for each phase using equations (1) to (3) above, the dead time compensation unit 17 calculates the duty cycle command values ​​Dcu, Dcv, and Dcw for each phase after dead time compensation by adding these to the duty cycle command values ​​Du, Dv, and Dw for each phase according to equations (4) to (6) below. Dcu = Du + Dudt ... (4) Dcv = Dv + Dvdt ... (5) Dcw = Dw + Dwdt ... (6)

[0028] The dead time compensation unit 17 performs the calculation processing described above, and if the phase currents of the U-phase, V-phase, and W-phase are positive values, a positive dead time compensation amount is added to the duty command values ​​Du, Dv, and Dw of each phase via feedforward control. If the phase currents are negative values, a negative dead time compensation amount is added to the duty command values ​​Du, Dv, and Dw of each phase, respectively.

[0029] The gate pulse signal generation unit 18 generates gate pulse signals (PWM pulse signals) Gup, Gun, Gvp, Gvn, Gwp, and Gwn for controlling the operation of each switching element of the upper and lower arms of the inverter 3, based on the duty cycle command values ​​Dcu, Dcv, and Dcw after dead time compensation obtained by the dead time compensation unit 17. For example, by converting the duty cycle command values ​​Dcu, Dcv, and Dcw after dead time compensation into predetermined voltage signals, the unit generates gate pulse signals Gup, Gvp, and Gwp for the upper arm of each phase, and also generates gate pulse signals Gun, Gvn, and Gwn for the lower arm that correspond to these gate pulse signals Gup, Gvp, and Gwp. These gate pulse signals generated by the gate pulse signal generation unit 18 are output from the motor control device 1 to the gate drive circuit 32 of the inverter 3, and are converted into gate drive signals by the gate drive circuit 32. This controls the on / off state of each switching element in the upper and lower arms of the inverter circuit 31, thereby adjusting the output voltage of the inverter 3.

[0030] Next, the details of the calculation method for the duty cycle command values ​​Du, Dv, and Dw in the motor control device 1 will be explained. As mentioned above, the voltage control unit 16 obtains three-phase modulated voltage command values ​​Vum*, Vv*, and Vw* by pulse width modulating the three-phase voltage commands Vu*, Vv*, and Vw* respectively, and calculates the duty cycle command values ​​Du, Dv, and Dw based on these.

[0031] Specifically, the voltage control unit 16 first determines the modulation offset voltages to be added to the three-phase voltage commands Vu*, Vv*, and Vw*. At this time, the voltage control unit 16 uses either the offset voltage Vs2 for two-phase modulation or the offset voltage Vs3 for three-phase modulation as the modulation offset voltage Vm for each phase. Details of these offset voltages Vs2 and Vs3 will be described later.

[0032] Next, the voltage control unit 16 calculates the modulation voltage command values ​​Vum*, Vvm*, and Vwm* for each phase by adding the determined modulation offset voltage Vm to the voltage commands Vu*, Vv*, and Vw* for each phase, respectively, according to the following equations (7) to (9): Vum* = Vu* + Vm ... (7) Vvm* = Vv* + Vm ... (8) Vwm* = Vw* + Vm ... (9)

[0033] Finally, the voltage control unit 16 calculates the duty cycle command values ​​Du, Dv, and Dw for each phase based on the modulated voltage command values ​​Vum*, Vvm*, and Vwm* for each phase obtained by the above calculation and the voltage Vdc of the high-voltage battery 5, using the following equations (10) to (12): Du = Vum* / (Vdc / 2) + 50% ... (10) Dv = Vvm* / (Vdc / 2) + 50% ... (11) Dw = Vwm* / (Vdc / 2) + 50% ... (12)

[0034] Next, we will explain the details of the offset voltages Vs2 and Vs3 mentioned above.

[0035] In the motor control device 1 of this embodiment, motor 2 can be controlled by using both three-phase modulation control and two-phase modulation control. Three-phase modulation control is a control method used when the load on motor 2 is relatively small, and is implemented by changing the modulation voltage command values ​​Vum*, Vvm*, and Vwm* of the three phases (U-phase, V-phase, and W-phase) after PWM conversion according to the electrical angle θe of motor 2. On the other hand, two-phase modulation control is a control method used when the load on motor 2 is relatively large, and is implemented by fixing the modulation voltage command value of one of the three-phase modulation voltage command values ​​Vum*, Vvm*, and Vwm* within a predetermined angular range of the electrical angle θe, and changing the modulation voltage command values ​​of the other two phases according to the electrical angle θe of motor 2.

[0036] In the motor control device 1 of this embodiment, switching between three-phase modulation control and two-phase modulation control is performed by changing the value of the modulation offset voltage Vm described above. Specifically, in three-phase modulation control, the offset voltage Vs3 for three-phase modulation obtained by the following equation (13) is used as the modulation offset voltage Vm. On the other hand, in two-phase modulation control, the offset voltage Vs2 for two-phase modulation obtained by the following equation (14) or (15) is used as the modulation offset voltage Vm. In equations (13) to (15), Vmax represents the maximum value of the voltage commands Vu*, Vv*, and Vw* for each phase, and Vmin represents the minimum value of the voltage commands Vu*, Vv*, and Vw* for each phase. Vs3 = -(Vmax + Vmin) / 2 ... (13) (When |Vmax| ≥ |Vmin|) Vs2 = Vdc / 2 - Vmax ... (14) (When |Vmax| < |Vmin|) Vs2 = Vdc / 2 - Vmin ... (15)

[0037] In the voltage control unit 16 of the motor control device 1, the above-mentioned offset voltage Vs3 for three-phase modulation or offset voltage Vs2 for two-phase modulation is used as the modulation offset voltage Vm, and the modulation voltage command values ​​Vum*, Vvm*, and Vwm* for each phase are calculated using the above-mentioned equations (7) to (9). In this way, PWM conversion equivalent to PWM modulation using a carrier signal is performed on the three-phase voltage commands Vu*, Vv*, and Vw*, respectively, and the three-phase modulation voltage command values ​​Vum*, Vvm*, and Vwm* can be obtained.

[0038] In this embodiment, the motor control device 1 alternately uses the offset voltage Vs3 for three-phase modulation and the offset voltage Vs2 for two-phase modulation multiple times within one cycle (360°) of the electrical angle θe of the motor 2. This allows for multiple switching between three-phase modulation control and two-phase modulation control. The specific method will be explained below with reference to Figures 3 and 4.

[0039] Figures 3 and 4 are flowcharts showing the processing flow of a motor control device 1 according to one embodiment of the present invention. The motor control device 1 generates gate pulse signals Gup, Gun, Gvp, Gvn, Gwp, and Gwn by executing processing according to the flowcharts in Figures 3 and 4 at predetermined calculation cycles, and outputs them to the inverter 3. This controls the switching operation of each switching element in the inverter circuit 31 in the inverter 3, thereby controlling the drive of the motor 2.

[0040] In step S10, the current command generation unit 10, electrical angle calculation unit 11, electrical angle rotation speed calculation unit 12, UVW / dq conversion unit 13, current control unit 14, and dq / UVW conversion unit 15 are used to generate three-phase voltage commands Vu*, Vv*, and Vw* corresponding to the torque command T*. The generated three-phase voltage commands Vu*, Vv*, and Vw* are input to the voltage control unit 16.

[0041] In step S20, the voltage control unit 16 performs overmodulation correction on the three-phase voltage commands Vu*, Vv*, and Vw* generated in step S10. Here, for example, the modulation rate is calculated based on the amplitude of the three-phase voltage commands Vu*, Vv*, and Vw*, and if this modulation rate reaches a predetermined upper limit, the three-phase voltage commands Vu*, Vv*, and Vw* are corrected so that the effective values ​​of the modulation rates are equal. Specifically, for example, the relationship between the modulation rate and the correction coefficient is calculated offline in advance, and a table summarizing the calculation results is stored in the motor control device 1. Using this table, the correction coefficient corresponding to the modulation rate calculated based on the three-phase voltage commands Vu*, Vv*, and Vw* is obtained and multiplied by the three-phase voltage commands Vu*, Vv*, and Vw* respectively to perform overmodulation correction.

[0042] In the following explanation, we will not distinguish between the cases where overmodulation correction was performed in step S20 and the cases where it was not, and will proceed with the explanation from step S30 onward. That is, in the following explanation, the three-phase voltage commands Vu*, Vv*, and Vw* represent the corrected three-phase voltage commands Vu*, Vv*, and Vw* if overmodulation correction was performed, and represent the three-phase voltage commands Vu*, Vv*, and Vw* generated in step S10 if overmodulation correction was not performed.

[0043] In step S30, the voltage control unit 16 calculates the offset voltage Vs3 for three-phase modulation by the aforementioned formula (13) using the three-phase voltage commands Vu*, Vv*, Vw*.

[0044] In step S40, the voltage control unit 16 determines whether to perform two-phase modulation control. Here, for example, based on the modulation factor calculated in step S20, if the modulation factor is equal to or greater than a predetermined value, it is determined that two-phase modulation control is to be performed, and the process proceeds to step S50. On the other hand, if the modulation factor is less than the predetermined value, it is determined that three-phase modulation control is to be performed without performing two-phase modulation control, and the process proceeds to step S140. It should be noted that whether to perform two-phase modulation control may be determined by other methods, for example, based on the three-phase voltage commands Vu*, Vv*, Vw*.

[0045] In step S50, the voltage control unit 16 calculates the offset voltage Vs2 for two-phase modulation by the aforementioned formula (14) or formula (15) using the three-phase voltage commands Vu*, Vv*, Vw*.

[0046] In step S60, counting is performed by a timer internally provided in the voltage control unit 16. This timer represents the elapsed time since the start of two-phase modulation control most recently.

[0047] In step S70, the voltage control unit 16 determines whether the current count value of the timer is equal to or greater than a predetermined first threshold value. The first threshold value used in the determination processing of step S70 is a value that defines the execution time of one two-phase modulation control session when two-phase modulation control and three-phase modulation control are alternately implemented, and is set according to the rotation speed of the motor 2 (electrical angular rotation speed ωe), the number of times of switching between two-phase modulation control and three-phase modulation control within one cycle of the electrical angle θe, and the like. If the count value of the timer is equal to or greater than the first threshold value, it is determined that the timing to switch from two-phase modulation control to three-phase modulation control has come, and the process proceeds to step S80; if the count value is less than the first threshold value, it is determined that two-phase modulation control should be continued as it is, and the process proceeds to step S120.

[0048] In step S80, the voltage control unit 16 determines whether the number of consecutive executions after the most recent switching from two-phase modulation control to three-phase modulation control (the number of executions of the processing shown in the flowcharts of FIG. 3 and FIG. 4) is equal to or greater than a predetermined second threshold. The second threshold used in the determination processing of step S80 is a value that defines the execution time per three-phase modulation control when two-phase modulation control and three-phase modulation control are alternately executed, and is set in advance in accordance with the execution cycle of the flowcharts of FIG. 3 and FIG. 4, the number of times of switching between two-phase modulation control and three-phase modulation control within one cycle of the electrical angle θe, and the like. If the number of consecutive executions is equal to or greater than the second threshold, it is determined that the timing to switch from three-phase modulation control to two-phase modulation control has come, and the process proceeds to step S90; if the number of consecutive executions is less than the second threshold, it is determined that three-phase modulation control should be continued as it is, and the process proceeds to step S100.

[0049] In step S90, the voltage control unit 16 resets the count values of the timer and the number of consecutive executions respectively used in the determinations of steps S70 and S80 to 0. Accordingly, in the next processing, a negative determination is made in step S70, so the processing of step S130 described later is executed, and switching from three-phase modulation control to two-phase modulation control is performed.

[0050] In step S100, the voltage control unit 16 increments the value of the number of consecutive executions used in the determination of step S80 by 1.

[0051] After the processing of step S90 or S100 is executed, in the subsequent step S110, the voltage control unit 16 sets the offset voltage Vs3 for three-phase modulation calculated in step S30 as the modulation offset voltage Vm.

[0052] In step S120, the voltage control unit 16 resets the count value of the number of consecutive executions used in the previous determination of step S80 to 0.

[0053] In step S130, the voltage control unit 16 sets the offset voltage Vs2 for two-phase modulation calculated in step S50 as the modulation offset voltage Vm.

[0054] In step S140, the voltage control unit 16 resets the timer and the count value for the number of continuations used in the previous steps S70 and S80 to 0, respectively.

[0055] In step S150, the voltage control unit 16 sets the offset voltage Vs3 for three-phase modulation calculated in step S30 to the modulation offset voltage Vm.

[0056] After executing any of steps S110, S130, or S150 to set the modulation offset voltage Vm to either the offset voltage Vs2 for two-phase modulation or the offset voltage Vs3 for three-phase modulation, the process proceeds to step S160 in Figure 4. In step S160, the voltage control unit 16 uses the modulation offset voltage Vm set by these processes to calculate the modulation voltage command values ​​Vum*, Vvm*, and Vwm* for each phase according to equations (7) to (9) described above.

[0057] In step S170, the voltage control unit 16 imposes upper and lower limits on the modulation voltage command values ​​Vum*, Vvm*, and Vwm* for each phase, which were determined in step S160. Here, because there is a possibility that the modulation voltage command values ​​Vum*, Vvm*, and Vwm* may exceed predetermined upper and lower limits in the overmodulation region, the voltage Vdc of the high-voltage battery 5 is used to limit the modulation voltage command values ​​Vum*, Vvm*, and Vwm* for each phase so that they remain within the range of, for example, 2 / Vdc × maximum modulation rate.

[0058] In the following explanation, we will not distinguish between the cases where upper and lower limit restrictions were implemented in step S170 and the cases where they were not, and will proceed with the explanation from step S180 onward. That is, in the following explanation, the modulation voltage command values ​​Vum*, Vvm*, and Vwm* represent the modulation voltage command values ​​Vum*, Vvm*, and Vwm* after the upper and lower limit restrictions were implemented, and represent the modulation voltage command values ​​Vum*, Vvm*, and Vwm* obtained in step S160, if the upper and lower limit restrictions were not implemented.

[0059] In step S180, the voltage control unit 16 uses the modulated voltage command values ​​Vum*, Vvm*, Vwm* and the voltage Vdc of the high-voltage battery 5 to calculate the duty cycle command values ​​Du, Dv, and Dw for each phase using the aforementioned equations (10) to (12).

[0060] In step S190, the dead time compensation unit 17 performs dead time compensation on the duty command values ​​Du, Dv, and Dw for each phase obtained in step S180. Here, the dead time compensation amount Dxdt is calculated using one of the aforementioned equations (1) to (3), and using this dead time compensation amount Dxdt, the duty command values ​​Dcu, Dcv, and Dcw for each phase after dead time compensation are calculated according to equations (4) to (6).

[0061] In step S200, the gate pulse signal generation unit 18 calculates gate pulse signals Gup, Gun, Gvp, Gvn, Gwp, and Gwn for each switching element of the upper and lower arms of each phase, based on the duty command values ​​Dcu, Dcv, and Dcw after dead time compensation obtained in step S190.

[0062] After executing the process in step S200, the motor control device 1 terminates the process shown in the flowcharts of Figures 3 and 4. The gate pulse signals Gup, Gun, Gvp, Gvn, Gwp, and Gwn calculated in step S200 are output from the motor control device 1 to the gate drive circuit 32 of the inverter 3 and used to control the on / off state of each switching element of the upper and lower arms of the inverter circuit 31.

[0063] Figure 5 shows an example waveform of one of the three-phase AC voltages Vu, Vv, and Vw (for example, the U-phase AC voltage Vu) output from the inverter 3 to the motor 2 when the inverter 3 is controlled by the motor control device 1 of this embodiment. In the waveform examples shown in Figure 5, the waveform 51 shown by the thin solid line shows an example waveform when only three-phase modulation control is performed, and the waveform 52 shown by the thick solid line shows an example waveform when only two-phase modulation control is performed. On the other hand, the waveform 53 shown by the dashed line shows an example waveform when the inverter 3 is controlled by the motor control device 1 of this embodiment according to the processing procedure described in the flowcharts of Figures 3 and 4. In Figure 5, the horizontal axis represents the electrical angle θe of the motor 2, and the vertical axis represents the voltage.

[0064] As shown in Figure 5, in the waveform 52 during two-phase modulation control, the voltage is constant (100V, -100V) in a predetermined angular range T centered at 90° and 270° of the electrical angle θe. On the other hand, in the waveform 53 from the motor control device 1, this angular range T is divided into a section 61 where the voltage is the same as waveform 51 and a section 62 where the voltage is the same as waveform 52. Thus, in the motor control device 1 of this embodiment, by performing the aforementioned control, the switching between two-phase modulation control and three-phase modulation control is performed multiple times within the angular range T.

[0065] The length of section 61 is determined according to the first threshold used in the determination process in step S70 of Figure 3. The length of section 62 is determined according to the second threshold used in the determination process in step S80 of Figure 3. These thresholds may be arbitrarily changed based on the rotational speed of the motor 2 (electrical angular rotation speed ωe) and the three-phase alternating currents Iu, Iv, and Iw flowing through the motor 2.

[0066] For example, in a low-load region where the rotational speed of motor 2 is relatively high and the three-phase AC currents Iu, Iv, and Iw are relatively small, the switching loss of inverter 3 becomes dominant over the copper loss of motor 2 as a loss related to driving motor 2. Therefore, in this case, it is preferable to adjust the first and second thresholds in such a way that the number of switching cycles is reduced as much as possible and switching losses are reduced by increasing the first threshold to lengthen the period of two-phase modulation control, while decreasing the second threshold to shorten the period of three-phase modulation control.

[0067] On the other hand, in the medium-to-high load region where the rotational speed of motor 2 is relatively low and the three-phase AC currents Iu, Iv, and Iw are relatively large, the copper loss of motor 2 becomes dominant as a loss related to driving motor 2, rather than the switching loss of inverter 3. Therefore, in this case, it is preferable to adjust the first and second thresholds so as to increase the number of switching cycles with an emphasis on suppressing vibration of motor 2, by decreasing the first threshold to shorten the period of two-phase modulation control and increasing the second threshold to lengthen the period of three-phase modulation control.

[0068] Furthermore, the angular range T for switching between two-phase modulation control and three-phase modulation control may also be varied based on the rotational speed of motor 2 (electrical angular rotation speed ωe) and the three-phase AC currents Iu, Iv, and Iw flowing through motor 2. However, in this case, since the phase targeted by two-phase modulation control switches every 60° of electrical angle θe, it is necessary to change the angular range T with 60° as the upper limit.

[0069] Furthermore, the number of switching cycles between two-phase modulation control and three-phase modulation control within one period (360°) of the electrical angle θe may be changed according to the pulse width of the gate pulse signals Gup, Gun, Gvp, Gvn, Gwp, and Gwn generated by the gate pulse signal generation unit 18. For example, the values ​​of the first threshold and the second threshold can be adjusted so that the number of switching cycles within one period of the electrical angle θe decreases as the pulse width increases, and conversely, increases as the pulse width decreases. In this way, switching losses can be suppressed in the inverter 3, while vibration components caused by harmonics can be suppressed in the motor 2.

[0070] According to the embodiment of the present invention described above, the following effects are achieved.

[0071] (1) The motor control device 1 generates three-phase voltage commands Vu*, Vv*, and Vw* for each phase of the three-phase AC motor 2 using the current command generation unit 10, the electrical angle calculation unit 11, the electrical angle rotation speed calculation unit 12, the UVW / dq conversion unit 13, the current control unit 14, and the dq / UVW conversion unit 15 (step S10). Then, the voltage control unit 16 obtains three-phase modulated voltage command values ​​Vum*, Vvm*, and Vwm* by pulse width modulating the three-phase voltage commands Vu*, Vv*, and Vw* respectively (steps S20 to S160). Based on these, the voltage control unit 16, the dead time compensation unit 17, and the gate pulse signal generation unit 18 generate gate pulse signals Gup, Gun, Gvp, Gvn, Gwp, and Gwn, which are used to control each switching element of the inverter 3 that converts DC power to AC power (steps S170 to S200). At this time, the three-phase modulation voltage command values ​​Vum*, Vvm*, and Vwm* are calculated by either three-phase modulation control, which changes the three-phase modulation voltage command values ​​Vum*, Vvm*, and Vwm* according to the electrical angle θe of the motor 2, or two-phase modulation control, which fixes the modulation voltage command value of one of the three-phase modulation voltage command values ​​Vum*, Vvm*, and Vwm* and changes the modulation voltage command values ​​of the other two phases according to the electrical angle θe. Furthermore, as shown in Figure 5, switching between two-phase modulation control and three-phase modulation control is performed multiple times within one cycle of the electrical angle θe. In this way, compared to conventional technology, it is possible to achieve both loss reduction and torque ripple suppression in motor control using both two-phase and three-phase modulation methods.

[0072] (2) In two-phase modulation control, the voltage control unit 16 uses the offset voltage Vs2 (first offset voltage) for two-phase modulation, which is obtained by equations (14) and (15) based on the voltage Vdc of the DC power input from the high-voltage battery 5 to the inverter 3, as the modulation offset voltage Vm for each phase, and calculates the three-phase modulation voltage command values ​​Vum*, Vvm*, and Vwm* respectively by equations (7) to (9) (steps S50, S130, S160). In three-phase modulation control, the voltage control unit 16 uses the offset voltage Vs3 (second offset voltage) for three-phase modulation, which is different from the offset voltage Vs2 for two-phase modulation, as the modulation offset voltage Vm for each phase, and calculates the three-phase modulation voltage command values ​​Vum*, Vvm*, and Vwm* respectively by equations (7) to (9) (steps S110, S160). In step S160, within a predetermined angular range T of the electrical angle θe, the offset voltage Vs2 is used (step S70: No), and the offset voltage Vs2 is switched to the offset voltage Vs3 for a predetermined time (step S70: Yes), and the three-phase modulation voltage command values ​​Vum*, Vvm*, and Vwm* are calculated, respectively. In this way, three-phase modulation control can be performed for a predetermined time during the implementation period of two-phase modulation control, making it possible to reliably achieve both loss reduction and torque ripple suppression in the drive control of the motor 2.

[0073] (3) The voltage control unit 16 sets the offset voltage Vs3 for three-phase modulation using equation (13), which is based on the maximum and minimum values ​​of the three-phase voltage commands Vu*, Vv*, and Vw*. The offset voltage Vs3 thus set is used as the modulation offset voltage Vm, and the modulation voltage command values ​​Vum*, Vvm*, and Vwm* are calculated by the calculations in equations (7) to (9), so that three-phase modulation control for the three-phase voltage commands Vu*, Vv*, and Vw* can be realized with a small computational load.

[0074] It should be noted that the present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention.

[0075] 1...Motor control device, 2...Motor, 3...Inverter, 4...Rotational position detector, 5...High-voltage battery, 7...Current sensor, 8...Rotational position sensor, 10...Current command generation unit, 11...Electrical angle calculation unit, 12...Electrical angle rotation speed calculation unit, 13...UVW / dq conversion unit, 14...Current control unit, 15...dq / UVW conversion unit, 16...Voltage control unit, 17...Dead time compensation unit, 18...Gate pulse signal generation unit, 31...Inverter circuit, 32...Gate drive circuit, 33...Smoothing capacitor, 100...Motor drive system

Claims

1. A motor control device that calculates three-phase modulated voltage command values ​​by pulse width modulating each of the three-phase voltage commands for each phase of a three-phase AC motor, and generates gate pulse signals used to control each switching element of an inverter that converts DC power to AC power based on the three-phase modulated voltage command values, wherein the motor control device calculates the three-phase modulated voltage command values ​​by either three-phase modulation control, which changes each of the three-phase modulated voltage command values ​​according to the electrical angle of the motor, or two-phase modulation control, which fixes the modulated voltage command value of one of the three-phase modulated voltage command values ​​and changes the modulated voltage command values ​​of the other two phases according to the electrical angle, and switches between the two-phase modulation control and the three-phase modulation control multiple times within one cycle of the electrical angle.

2. A motor control device according to claim 1, wherein in the two-phase modulation control, the modulation voltage command values ​​of the three phases are calculated using a first offset voltage based on the voltage of the DC power; in the three-phase modulation control, the modulation voltage command values ​​of the three phases are calculated using a second offset voltage different from the first offset voltage; and within a predetermined angular range of the electrical angle, the first offset voltage is used while switching the first offset voltage to the second offset voltage for a predetermined time to calculate the modulation voltage command values ​​of the three phases.

3. A motor control device according to claim 2, wherein the motor control device sets the second offset voltage based on the maximum and minimum values ​​of the three-phase voltage command.

4. A motor control device according to claim 2, wherein the predetermined time is changed based on the rotational speed of the motor and the magnitude of the current flowing through the motor.

5. A motor control device according to claim 2, wherein the motor control device changes the angle range with an upper limit of 60° in the electrical angle.

6. A motor control device according to claim 1, wherein the number of switching operations within one cycle of the electrical angle is changed according to the pulse width of the gate pulse signal.

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