Motor Drive Unit

Abstract

To perform more accurate correction control in a dead time.SOLUTION: A motor drive device comprises a control unit that controls an operation of a plurality of switching elements included in an inverter. The control unit executes dead time correction control of correcting a voltage command value of a motor in such a dead time that switching elements of series-connected upper and lower arms among the plurality of switching elements are simultaneously controlled to be in an OFF state. When executing the dead time correction control, the control unit estimates a phase current of the motor by using a current command value of the motor and decides a correction amount of the voltage command value on the basis of a value of the estimated phase current.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to a motor drive device. [Background technology]

[0002] Patent Document 1 discloses that during a dead time when the switching elements of upper and lower arms connected in series among a plurality of switching elements in an inverter are simultaneously turned off, dead time correction control is executed to correct a voltage command value in order to compensate for a difference between a voltage command value and an actual voltage. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2021 / 171679 Summary of the Invention [Problem to be solved by the invention]

[0004] In the configuration described in Patent Document 1, when generating a command signal for controlling a switching element during dead time correction control, a calculation is performed using three-phase detection currents detected by a current sensor that detects the phase currents of a motor. However, the phase currents of a motor change depending on the torque and rotation speed of the motor. Therefore, there is a risk that accurate correction cannot be performed in dead time correction control using the three-phase detection currents, which are the detected values.

[0005] The present invention has been made in consideration of the above circumstances, and has an object to provide a motor drive device that can perform correction control during dead time more accurately. [Means for solving the problem]

[0006] The present invention is a motor drive device comprising an inverter that drives a motor, and a control unit that controls operation of a plurality of switching elements of the inverter, wherein the control unit executes dead time correction control to correct a voltage command value of the motor during dead time when switching elements of upper and lower arms that are connected in series among the plurality of switching elements are simultaneously in an off state, and is characterized in that, when executing the dead time correction control, the control unit estimates a phase current of the motor using a current command value of the motor, and determines a correction amount of the voltage command value based on the estimated value of the phase current.

[0007] According to this configuration, in the dead time correction control, the correction amount of the voltage command value is determined using a value estimated based on the current command value, so that the voltage command value can be corrected without depending on the torque or rotation speed of the motor.

[0008] In addition, when estimating the phase current of the motor, the control unit may add a current ripple amount calculated by the following equation (1) to a current command value of the motor, and use the added value as an estimated value of the phase current. Current ripple = inverter voltage ÷ motor inductance × (carrier period / 2) (1)

[0009] According to this configuration, when estimating the phase current, it is possible to calculate an estimated value taking into account the current ripple. Therefore, the estimated value of the phase current includes the amount of ripple, and by using the estimated value to determine the amount of correction of the voltage command value, it is possible to perform more accurate dead time correction control. Effect of the Invention

[0010] In the present invention, in the dead time correction control, the correction amount of the voltage command value is determined using the estimated value of the phase current based on the current command value, thereby making it possible to perform more accurate dead time correction control without depending on the torque or rotation speed of the motor. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram illustrating a motor drive device according to an embodiment. [Diagram 2] FIG. 2 is a diagram illustrating a functional configuration of the control unit. [Diagram 3] FIG. 3 is a diagram for explaining a voltage drop caused by a positive current flowing during the dead time. [Figure 4] FIG. 4 is a diagram for explaining a voltage rise caused by a negative current flowing during the dead time. [Diagram 5] FIG. 5 is a diagram showing the relationship between the phase current and the phase voltage when the dead time correction control is performed. [Figure 6] FIG. 6 is a diagram for explaining the estimation of a phase current from a current command value and a current ripple. [Figure 7] FIG. 7 is a diagram showing current waveforms when dead time correction control is performed using estimated values ​​of phase currents. [Figure 8] FIG. 8 is a diagram showing waveforms during dead time correction control in the comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, a motor drive device according to an embodiment of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiment described below.

[0013] 1 is a diagram illustrating a motor drive device according to an embodiment. The motor drive device 1 includes a DC power supply 2, an inverter 3, a motor 4, and a control unit 5. The motor drive device 1 also includes a smoothing capacitor C in its electric circuit.

[0014] The DC power supply 2 is a DC power supply that can be charged and discharged. This DC power supply 2 is formed of, for example, a secondary battery such as a nickel-metal hydride battery or a lithium-ion battery. The DC power supply 2 discharges power to the inverter 3 side, or charges with power supplied from the inverter 3 side. During power running, the power stored in the DC power supply 2 can be supplied to the motor 4. During regeneration, the motor 4 functions as a generator, so that the power generated by the motor 4 can be charged to the DC power supply 2.

[0015] The inverter 3 is a power conversion device that converts DC power supplied from the DC power source 2 into AC power and supplies it to the motor 4. This inverter 3 is composed of an inverter circuit having multiple switching elements so that a three-phase current can be passed through the coil of the motor 4. The inverter circuit has a switching element and a diode for each phase, and the switching elements perform a switching operation to convert the DC power into AC power. The switching operation is to switch the switching elements between ON and OFF. The switching elements are composed of insulated gate bipolar transistors.

[0016] The inverter 3 is composed of six semiconductor element modules constituting upper and lower arms 3a, 3b, and 3c of each phase (U phase, V phase, and W phase). Each of the upper and lower arms 3a, 3b, and 3c of each phase includes two switching elements and two diodes.

[0017] The U-phase upper and lower arms 3a are composed of an upper arm 31 in which a switching element T1 and a diode D1 are connected in parallel, and a lower arm 32 in which a switching element T2 and a diode D2 are connected in parallel. The upper arm 31 and the lower arm 32 are connected in series, and a U-phase coil of the motor 4 is connected to the connection point thereof.

[0018] The V-phase upper and lower arms 3b are composed of an upper arm 33 in which a switching element T3 and a diode D3 are connected in parallel, and a lower arm 34b in which a switching element T4 and a diode D4 are connected in parallel. The upper arm 33 and the lower arm 34 are connected in series, and a V-phase coil of the motor 4 is connected to the connection point between them.

[0019] The W-phase upper and lower arms 3c are configured with an upper arm 35 in which a switching element T5 and a diode D5 are connected in parallel, and a lower arm 36 in which a switching element T6 and a diode D6 are connected in parallel. The upper arm 35 and the lower arm 36 are connected in series, and a W-phase coil of the motor 4 is connected to their connection point.

[0020] The motor 4 is driven by power supplied from the inverter 3. The motor 4 is electrically connected to the DC power supply 2 via the inverter 3. The motor 4 is also electrically connected to the inverter 3 via three-phase coils (coils for U-phase, V-phase, and W-phase). The motor 4 is driven by current flowing through the three-phase coils. The motor 4 also functions as a generator in addition to an electric motor. When the motor 4 is installed in a vehicle, it functions as a power source for driving the vehicle.

[0021] The control unit 5 is composed of an electronic control device that controls the operation of the inverter 3. This electronic control device is composed of a microcomputer equipped with a CPU, RAM, ROM, and an input / output interface. The control unit 5 performs signal processing according to a program previously stored in the ROM. Signals from various sensors are input to the control unit 5. Examples of signals input to the control unit 5 include a phase current from a current sensor that detects a phase current of the motor 4 and a rotation angle from a rotation angle sensor that detects the rotation angle of the motor 4. The control unit 5 then executes various controls based on the signals input from the various sensors. For example, the control unit 5 calculates the electrical angle, electrical angular velocity, and rotation speed of the motor 4 based on the rotation angle of the motor 4 input from the rotation angle sensor.

[0022] Furthermore, when controlling the operation of the inverter 3, the control unit 5 outputs a signal for controlling the switching elements of the inverter 3 to the inverter 3. This signal includes a gate signal for switching between the on state and the off state of the switching element to be controlled among the multiple switching elements. In this manner, the control unit 5 controls the voltage and current to be applied to the motor 4 by controlling the inverter 3. An example of the functional configuration when the control unit 5 generates the gate signal is shown in FIG. 2.

[0023] 2 is a diagram showing a schematic functional configuration of the control unit 5. The control unit 5 controls a d-axis current command value id com and the q-axis current command value iq com Based on this, the control circuit 10 generates voltage command values ​​Vu, Vv, and Vw for each phase, generates gate signals according to the voltage command values, and outputs the gate signals to the inverter (INV) 3.

[0024] The control unit 5 includes a current command generating unit, a three-phase / dq axis conversion unit, a PI control unit, a dq axis / three-phase conversion unit, an adder, a voltage command correcting unit 10, and a PWM signal conversion unit.

[0025] The current command generator generates a d-axis current command value id according to the torque command value. com and the q-axis current command value iq com and outputs it to the PI control unit. The torque command value is calculated based on the accelerator opening and the vehicle speed. For example, the torque command value calculated by another control device is input to the control unit 5.

[0026] The three-phase / dq-axis conversion unit converts the V-phase current iv and W-phase current iw into a d-axis current id and a q-axis current iq based on the electrical angle of the motor 4 and outputs them to the PI control unit. The three-phase / dq-axis conversion unit receives the V-phase current iv and W-phase current iw of the motor 4 detected by a current sensor, as well as the electrical angle of the motor 4 calculated based on the rotation angle of the motor 4 detected by a rotation angle sensor. The three-phase / dq-axis conversion unit functions as a current feedback system.

[0027] The PI control section calculates the d-axis current command value idcom and the deviation between the d-axis current id and the q-axis current command value iq com Depending on the deviation between the q-axis current iq and the d-axis voltage command value Vd com and the q-axis voltage command value Vq com The PI control section receives the d-axis current id and the q-axis current iq as feedback information from the three-phase / dq-axis converter. The PI control section then calculates the deviation of the actual measured value from the current command value, and outputs the d-axis voltage command value Vd com and the q-axis voltage command value Vq com is output to the dq axis / three-phase conversion section.

[0028] The dq axis / three-phase conversion section converts the d axis voltage command value Vd com and the q-axis voltage command value Vq com and the electrical angular velocity of the motor 4. The three-phase voltage command values ​​Vu, Vv, Vw are output from the dq-axis / three-phase conversion unit to an adder.

[0029] The adder adds the correction value input from the voltage command correction unit 10 to the three-phase voltage command values ​​Vu, Vv, Vw input from the dq-axis / three-phase conversion unit, and outputs the result to the PWM signal conversion unit.

[0030] The PWM signal conversion unit generates gate signals for the switching elements of each phase of the inverter 3 based on the three-phase voltage command values ​​Vu, Vv, and Vw input from the adder. Then, the PWM signal conversion unit outputs the gate signals for each phase to the inverter 3.

[0031] The voltage command correction unit 10 is a correction unit that performs dead time correction. In the inverter 3, in order to prevent a short circuit between the upper and lower arms, a period (dead time) is set in which the switching elements constituting the upper and lower arms are simultaneously turned off. The output voltage of the inverter 3 during the dead time is determined by the current flowing through the inverter 3. Therefore, during the dead time, a difference occurs between the voltage command value and the output voltage, as shown in FIG. 3 and FIG. 4. As shown in FIG. 3, when the phase current flows in the positive direction during the dead time, the phase voltage drops with respect to the voltage command value. As shown in FIG. 4, when the phase current flows in the negative direction during the dead time, the phase voltage rises with respect to the voltage command value. In order to correct this, the control unit 5 executes dead time correction control. That is, the control unit 5 executes dead time correction control that corrects the voltage command value during the dead time in which the switching elements of the upper and lower arms connected in series among the multiple switching elements are simultaneously turned off. During the dead time, since the direction of change in the phase voltage is determined according to the direction in which the phase current flows as shown in Figures 3 and 4, the phase voltage can be controlled to an appropriate value (target voltage) by performing correction to increase or decrease the voltage command value according to the direction in which the phase current flows as shown in Figure 5. Figure 5 illustrates, for comparison, a case in which correction is performed and a case in which correction is not performed.

[0032] In the example shown in Figure 5, if no correction is performed, when the "target voltage" indicated by the thin solid line is desired to be obtained as the output voltage, the "target voltage" is used as the voltage command value as is to control the voltage. However, as shown in Figures 3 and 4, during dead time the output voltage deviates from the voltage command value. For this reason, in the uncorrected case, the output voltage is as shown by the dashed line in Figure 5. In this way, a voltage different from the original target is output.

[0033] Therefore, the voltage command correction unit 10 determines the correction amount of the voltage command value according to the direction in which the phase current flows in the dead time correction control. For example, when it is desired to obtain the "target voltage" shown in FIG. 5 as the output voltage, the "corrected voltage command" shown by the thick solid line in FIG. 5 is generated as the voltage command value in consideration of the voltage change during the dead time shown in FIG. 3 and FIG. 4. In the control unit 5, in order to obtain the target voltage as the output voltage during the dead time, when the phase current flows in the positive direction, the corrected voltage command value is corrected to a value larger than the target voltage, and when the phase current flows in the negative direction, the corrected voltage command value is corrected to a value smaller than the target voltage. To achieve this, the voltage command correction unit 10 outputs the correction amount of the voltage command value to the adder. Note that FIG. 3 and FIG. 4 illustrate the contents related to the phase current of the V phase and a state in which both the upper arm 33 and the lower arm 34 of the V phase are OFF.

[0034] Specifically, when the phase current flows in the positive direction during the dead time, the voltage command correction unit 10 determines the correction amount of the voltage command value to be a positive value. Then, the control unit 5 adds the positive correction amount to the voltage command value, so that the voltage command value after correction is greater than that before correction. Also, when the phase current flows in the negative direction during the dead time, the voltage command correction unit 10 determines the correction amount of the voltage command value to be a negative value. Then, the control unit 5 adds the negative correction amount to the voltage command value, so that the voltage command value after correction is smaller than that before correction. As a result, voltage control is performed by the corrected voltage command value shown by the thick solid line in FIG. 5, and the target voltage shown by the thin solid line in FIG. 5 can be obtained as the output voltage. In FIG. 2, the target voltage is shown by a dashed line in the waveform showing the relationship between the corrected voltage command value and the target voltage.

[0035] Thus, in the dead time correction control, it is important to identify the direction of the phase current. When identifying the direction of the phase current, the control unit 5 uses the current direction in the estimated value of the phase current, rather than the current direction in the phase current (sensor value) detected by the current sensor. The phase current depends on the torque and rotation speed of the motor 4. Therefore, when the sensor value is used, it may be difficult to accurately determine the direction of the phase current. Therefore, the control unit 5 identifies the direction of the phase current using the estimated value of the phase current, which is a value that does not depend on the torque and rotation speed of the motor 4. At that time, the control unit 5 estimates the phase current using a current command value. Furthermore, when estimating the phase current, the control unit 5 determines the estimated value of the phase current taking into account the current ripple.

[0036] Specifically, when estimating the phase current of the motor 4, the control unit 5 adds the amount of ripple calculated by the following formula (1) to the phase current command value for the motor 4, and sets the added value as the estimated value of the phase current. Current ripple = inverter voltage ÷ motor inductance × (carrier period / 2) (1)

[0037] The inverter voltage in the above formula (1) is the voltage applied to the inverter 3. The control unit 5 calculates the d-axis voltage command value Vd com and the q-axis voltage command value Vq com and are used to calculate the inverter voltage in the above formula (1). The motor inductance in the above formula (1) is the inductance of the coil in the motor 4. The carrier period in the above formula (1) is the period of the carrier signal. In other words, the carrier period is the period for switching the inverter 3.

[0038] In the dead time correction control, as shown in Fig. 6, the control unit 5 calculates an estimated value of the phase current by adding a current ripple to the phase current command value, and determines a correction amount of the voltage command value based on the estimated value of the phase current. That is, the voltage command correction unit 10 determines a correction amount of the voltage command value based on the estimated value of the phase current. At that time, the voltage command correction unit 10 determines a correction amount of the voltage command value based on the current direction of the estimated phase current. Then, the correction amount determined by the voltage command correction unit 10 is added to the three-phase voltage command values ​​Vu, Vv, and Vw. That is, in the dead time correction control, the control unit 5 determines a correction amount of the voltage command value using the phase current estimated based on the current command value and the ripple amount which is a calculated value, and corrects the voltage command value according to the correction amount.

[0039] As a result, when the control unit 5 performs the dead time correction control, the q-axis current command value iq com and the q-axis current iq, it is possible to reduce the electrical sixth-order vibration of the q-axis current iq. By reducing the electrical sixth-order vibration of the q-axis current iq during the dead time in this way, it is possible to suppress current disturbances near 0 amperes in the phase current waveform. On the other hand, in the dead time correction control of the comparative example as shown in Fig. 8, electrical sixth-order vibrations occur in the q-axis current iq and the d-axis current id, and current disturbances occur near 0 amperes in the phase current.

[0040] In the comparative example illustrated in FIG. 8, when the correction amount of the voltage command value is determined during the dead time correction control, the phase current (sensor value) detected by the current sensor is used as it is. The time change amount of the phase current changes due to the influence of the motor torque and the motor rotation speed. The phase current expressed as a sine wave changes so that the amplitude increases as the motor torque increases, so the change amount per unit time increases. Similarly, the phase current changes so that the period shortens as the motor rotation speed increases, so the change amount per unit time increases. Therefore, when the sensor value of the phase current is used, it is difficult to accurately determine whether the direction in which the phase current flows is positive or negative. In addition, a discrepancy occurs between the current that the microcontroller can recognize and the actual current (with ripple). The microcontroller can recognize the current only when the AD converter is activated, so the microcontroller cannot recognize all the currents. In other words, the current that the microcontroller can recognize is the current while the AD converter is activated, so the microcontroller cannot accurately recognize the actual current (with ripple). Therefore, although the amount of ripple contained in the actual current changes depending on the carrier cycle, motor inductance, and inverter voltage (PCU voltage), this change cannot be recognized by the microcomputer. Therefore, when determining the amount of correction of the voltage command value during dead time correction control, the control unit 5 uses an estimated value of the phase current estimated using the current command value. Therefore, the control unit 5 can determine the amount of dead time correction depending on whether the direction of current flow in the estimated phase current is positive or negative.

[0041] As described above, according to the embodiment, when determining the correction amount of the voltage command value in the dead time correction control, by using the estimated value of the phase current calculated based on the current command value and the current ripple, it is possible to determine the correction amount of the voltage command value without depending on the torque and rotation speed of the motor 4. This makes it possible to perform more accurate dead time correction control.

[0042] Although an example in which the motor drive device 1 controls the inverter 3 has been described, the present invention is not limited to this. In other words, the motor drive device 1 can perform dead time correction control on a power control unit (PCU) including the inverter 3 and a boost converter. [Explanation of symbols]

[0043] 1 Motor drive unit 2 DC power supply 3 Inverter 4 Motors 5. Control section 10 Voltage command correction section C Smoothing capacitor

Claims

[Claim 1] an inverter that drives a motor; A control unit that controls operations of a plurality of switching elements included in the inverter; Equipped with the control unit is a motor drive device that executes dead time correction control to correct a voltage command value of the motor during a dead time when switching elements of upper and lower arms connected in series among the plurality of switching elements are simultaneously in an off state, The control unit is When executing the dead time correction control, a phase current of the motor is estimated using a current command value of the motor, and a correction amount of the voltage command value is determined based on the estimated value of the phase current; When estimating the phase current of the motor, the amount of ripple in the current calculated by the following formula (1) is added to the current command value of the motor, and the sum is regarded as the estimated value of the phase current. A motor drive device comprising: Current ripple = inverter voltage ÷ motor inductance × (carrier period / 2) ... (1)

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