JP2013055852A - Driver of ac motor and vehicle with the same, and control method of ac motor - Google Patents

Abstract

A drive device for an AC motor that switches between modulation PWM control and sinusoidal PWM control to suppress a sudden decrease in torque during an emergency switching operation when the rotational speed of the AC motor changes suddenly.
A vehicle travels when an ECU is controlled by an ECU using PWM control to drive a motor generator. ECU 300 controls inverter 140 by switching a plurality of control modes including sine wave PWM control and overmodulation PWM control. The ECU 300 forcibly switches from the overmodulation PWM control to the sine wave PWM control when the current rapidly increases as the drive wheel 160 changes from the slip state to the grip state during the overmodulation PWM control. The upper limit value of the modulation factor in the sine wave PWM control is relaxed so that a larger torque than that in the normal time can be output in the sine wave PWM control.
[Selection] Figure 1

Description

  The present invention relates to a drive device for an AC motor, a vehicle equipped with the drive device, and a control method for the AC motor, and more specifically, pulse width modulation (PWM) having a sine wave modulation mode and an overmodulation mode. The present invention relates to control of an AC motor to which control is applied.

  In order to drive and control an AC motor using a DC power supply, a driving method using an inverter is generally employed. The inverter is switching-controlled by an inverter drive circuit. For example, a voltage switched according to PWM control is applied to the AC motor.

  Further, in order to improve the voltage utilization factor and obtain a high output in a region where the motor rotation speed is high, the fundamental wave component of the motor applied voltage is higher than that of the sine wave PWM control (hereinafter also referred to as “sine wave modulation mode”). Overmodulation PWM control (hereinafter also simply referred to as “overmodulation mode”) and rectangular wave voltage control are applied as AC motor control using a large modulation method.

  Japanese Patent Application Laid-Open No. 2010-041901 (Patent Document 1) describes switching of a determination value used for switching determination from an overmodulation mode to a sine wave modulation mode in an AC motor control device using an overmodulation mode and a sine wave modulation mode. A configuration that is variably set based on the state is disclosed.

  According to the configuration disclosed in Japanese Patent Laying-Open No. 2010-041901 (Patent Document 1), the number of times of switching in switching the control mode from the overmodulation mode to the sine wave modulation mode during execution of PWM control in the overmodulation mode. Due to the effects of dead time, switching from the overmodulation mode to the sine wave modulation mode is unlikely to occur when chattering in which the switching of the control mode is frequently repeated between the sine wave modulation mode and the overmodulation mode is likely to occur. By setting the modulation factor determination value so that chattering can occur, the occurrence of chattering can be suppressed.

JP 2010-041901 A

  Overmodulation PWM control can output a larger torque than sine wave PWM control, but generates a voltage waveform with a smaller number of pulses than sine wave PWM control. Control response tends to be slightly inferior.

  For this reason, when overmodulation PWM control is performed, if the drive wheel shifts from a slipping state to a gripping state, this control response is generated for the generated power generated by the AC motor due to a sudden increase in deceleration torque. There is a risk that the power conversion operation cannot follow up due to a delay in the characteristics, resulting in an overvoltage state. In order to cope with such a situation, when a sudden speed fluctuation occurs, the control response is delayed by urgently changing the control mode from overmodulation PWM control to responsive sine wave PWM control. In some cases, a technique for avoiding the above (hereinafter referred to as “emergency switching operation”) is employed.

  In general, when such an urgent avoidance control is performed, the control returns to the overmodulation PWM control for a predetermined period so that the control returns to the overmodulation PWM control immediately and no chattering of the control occurs. May be banned.

  However, in sine wave PWM control, control response is superior to overmodulation PWM control, but on the contrary, the torque that can be output is limited compared to overmodulation PWM control. There is a risk of sudden torque drop.

  The present invention has been made to solve such a problem, and an object of the present invention is to provide a rotational speed of an AC motor in an AC motor drive device that switches and controls overmodulation PWM control and sine wave PWM control. This is to suppress a sudden decrease in torque during an emergency switching operation in the case where a sudden change occurs.

  An AC motor drive device according to the present invention includes an inverter and a control device, and uses pulse width modulation control based on a comparison between a sinusoidal voltage command signal and a carrier wave signal for operating the AC motor according to an operation command. Control the inverter and drive the AC motor. In the pulse width modulation control, the control device sets an overmodulation mode for controlling the frequency of the carrier signal to be an integer multiple of the frequency of the voltage command signal, and sets the frequency of the carrier signal regardless of the frequency of the voltage command signal. The inverter is controlled by switching a plurality of control modes including the sine wave modulation mode. The control device has an emergency switching function for forcibly switching from the overmodulation mode to the sine wave modulation mode based on the current flowing through the AC motor during execution of the overmodulation mode. When the control mode is switched from the overmodulation mode to the sine wave modulation mode by the emergency switching function, the control device relaxes an upper limit value for limiting the amplitude of the voltage command signal in the sine wave modulation mode.

  Preferably, when the control mode is switched from the overmodulation mode to the sine wave modulation mode by the emergency switching function, the control device sets a larger upper limit value in the sine wave modulation mode as the frequency of the carrier signal increases.

  Preferably, when the control mode is switched from the overmodulation mode to the sine wave modulation mode by the emergency switching function, the control device sets a larger upper limit value in the sine wave modulation mode as the rotational speed of the AC motor is lower.

  Preferably, when the control device switches the control mode from the overmodulation mode to the sine wave modulation mode by the emergency switching function, the pulse width modulation signal applied to the inverter during one cycle of the voltage command signal is a rectangular wave 1 pulse. Set the upper limit so that it does not occur.

  Preferably, the control device executes the emergency switching function when the q-axis current of the current flowing through the AC motor exceeds a predetermined threshold value of the q-axis current determined based on the d-axis current.

  Preferably, the threshold value is set to a value larger than the q-axis current command value in the sine wave modulation mode.

  Preferably, the control device switches the control mode from the sine wave modulation mode to the overmodulation mode based on a modulation factor determined by an input DC voltage to the inverter and a voltage command value given to the AC motor. The upper limit value is a threshold value for determining switching of the control mode from the sine wave modulation mode to the over modulation mode.

  A vehicle according to the present invention is a vehicle capable of traveling using a driving force generated by an AC motor, and includes an inverter for controlling an applied voltage of the AC motor, and a control device for controlling the inverter. Is provided. The control device controls the inverter using pulse width modulation control based on a comparison between a sinusoidal voltage command signal and a carrier wave signal for operating the AC motor according to the operation command. In the pulse width modulation control, the control device sets an overmodulation mode for controlling the frequency of the carrier signal to be an integer multiple of the frequency of the voltage command signal, and sets the frequency of the carrier signal regardless of the frequency of the voltage command signal. The inverter is controlled by switching a plurality of control modes including the sine wave modulation mode. The control device has an emergency switching function for forcibly switching from the overmodulation mode to the sine wave modulation mode based on the current flowing through the AC motor during execution of the overmodulation mode. When the control mode is switched from the overmodulation mode to the sine wave modulation mode by the emergency switching function, the control device relaxes an upper limit value for limiting the amplitude of the voltage command signal in the sine wave modulation mode.

  The control method for an AC motor according to the present invention is a control method for an AC motor whose applied voltage is controlled by an inverter. A control method includes a step of controlling an inverter using pulse width modulation control based on a comparison between a sinusoidal voltage command signal and a carrier signal for operating an AC motor in accordance with an operation command, and in the pulse width modulation control, a carrier signal A plurality of control modes including an overmodulation mode for controlling the frequency of the signal to be an integral multiple of the frequency of the voltage command signal and a sine wave modulation mode for setting the frequency of the carrier signal independent of the frequency of the voltage command signal. A step of switching and controlling the inverter; a step of executing an emergency switching function forcibly switching from the overmodulation mode to the sine wave modulation mode based on a current flowing through the AC motor during execution of the overmodulation mode; When switching the control mode from overmodulation mode to sine wave modulation mode by function, voltage is applied in sine wave modulation mode. And a step of relaxing the upper limit value for limiting the amplitude of the decree signal.

  ADVANTAGE OF THE INVENTION According to this invention, in the drive device of the alternating current motor which switches and controls overmodulation PWM control and sine wave PWM control, it is possible to suppress the sudden decrease in torque at the time of emergency switching operation when the rotational speed of the alternating current motor changes suddenly. It becomes.

1 is an overall block diagram of a vehicle equipped with an AC motor drive device according to an embodiment of the present invention. It is a figure which illustrates schematically the control mode of the motor generator in this Embodiment. It is a figure for demonstrating the PWM signal in PWM control. FIG. 3 is a diagram for explaining a correspondence relationship between an operation state of a motor generator and a control mode of FIG. 2. It is a figure for demonstrating emergency switching operation | movement. It is a figure for demonstrating the problem in emergency switching operation | movement. It is a figure for demonstrating the outline | summary of the setting of the modulation factor upper limit in this Embodiment. It is a figure for demonstrating the relationship between the modulation factor upper limit at the time of emergency switching operation | movement, and a PWM signal. In this Embodiment, it is a functional block diagram for demonstrating the mode switching control performed by ECU. In this Embodiment, it is a flowchart for demonstrating the detail of the mode switching control process performed by ECU.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, about the same or equivalent part in a figure, the same code | symbol is attached | subjected and the description is not repeated.

[Basic configuration of vehicle]
FIG. 1 is an overall block diagram of a vehicle 100 equipped with an AC motor drive device according to an embodiment of the present invention. In the present embodiment, a configuration in which vehicle 100 is an electric vehicle will be described as an example. However, the configuration of vehicle 100 is not limited to this, and any vehicle that can run with electric power from a power storage device is applicable. Is possible. Vehicle 100 includes, for example, a hybrid vehicle and a fuel cell vehicle in addition to an electric vehicle.

  Referring to FIG. 1, vehicle 100 includes a power storage device 110, a system main relay (SMR) 115, a converter 120, an inverter 130, a motor generator 140, a power transmission gear 150, and driving wheels. 160 and an ECU (Electronic Control Unit) 300.

  The power storage device 110 is a power storage element configured to be chargeable / dischargeable. The power storage device 110 includes, for example, a secondary battery such as a lithium ion battery, a nickel metal hydride battery, or a lead storage battery, and a power storage element such as an electric double layer capacitor.

  Power storage device 110 is connected to converter 120 of converter 120 through power lines PL1 and NL1. Power storage device 110 supplies electric power for driving motor generator 140 to converter 120. Power storage device 110 stores the electric power generated by motor generator 140. The output of power storage device 110 is, for example, about 200V.

  Relays included in SMR 115 are connected to power storage device 110 and power lines PL1, NL1, respectively. SMR 115 is controlled by control signal SE <b> 1 from ECU 300, and switches between power supply and cutoff between power storage device 110 and converter 120.

  Capacitor C1 is connected between power line PL1 and power line NL1. Capacitor C1 reduces voltage fluctuation between power line PL1 and power line NL1.

  Converter 120 includes switching elements Q1, Q2, diodes D1, D2, and a reactor L1.

  Switching elements Q1 and Q2 are connected in series between power lines PL2 and NL1, with the direction from power line PL2 toward power line NL1 as the forward direction. In this embodiment, an IGBT (Insulated Gate Bipolar Transistor) is described as an example of the switching element, but a power MOS (Metal Oxide Semiconductor) transistor or a power bipolar transistor is used instead of the IGBT. Also good.

  Antiparallel diodes D1 and D2 are connected to switching elements Q1 and Q2, respectively. Reactor L1 is provided between a connection node of switching elements Q1 and Q2 and power line PL1. That is, converter 120 forms a chopper circuit.

  Switching elements Q1, Q2 are controlled based on control signal PWC from ECU 300, and perform voltage conversion operation between power lines PL1, NL1 and power lines PL2, NL1.

  Converter 120 is basically controlled such that switching elements Q1 and Q2 are turned on and off in a complementary manner in each switching period. Converter 120 boosts the DC voltage from power storage device 110 during the boosting operation. This boosting operation is performed by supplying the electromagnetic energy accumulated in reactor L1 during the ON period of switching element Q2 to power line PL2 via switching element Q1 and antiparallel diode D1.

  Converter 120 steps down the DC voltage from inverter 130 during the step-down operation. This step-down operation is performed by supplying the electromagnetic energy stored in reactor L1 during the ON period of switching element Q1 to power line NL1 via switching element Q2 and antiparallel diode D2.

  The voltage conversion ratio in these step-up and step-down operations is controlled by the on-period ratio (duty ratio) of the switching elements Q1 and Q2 in the switching period. When the step-up operation and the step-down operation are not required, the voltage conversion ratio = 1.0 (duty ratio = 100) is set by setting the control signal PWC to fix the switching elements Q1 and Q2 to ON and OFF, respectively. %).

  In the present invention, converter 120 is not essential, and the output voltage from power storage device 110 may be directly supplied to inverter 130.

  Capacitor C2 is connected between power lines PL2 and NL1 connecting converter 120 and inverter 130. Capacitor C2 reduces voltage fluctuation between power lines PL2 and NL1. Voltage sensor 170 detects the voltage applied to capacitor C2 and outputs the detected value VH to ECU 300.

  Inverter 130 is connected to converter 120 via power lines PL2 and NL1. Inverter 130 is controlled by control command PWI from ECU 300, and converts DC power output from converter 120 into AC power for driving motor generator 140.

  Inverter 130 includes a U-phase arm 131, a V-phase arm 132, and a W-phase arm 133, which form a three-phase bridge circuit. U-phase arm 131, V-phase arm 132, and W-phase arm 133 are connected in parallel between power line PL2 and power line NL1.

  U-phase arm 131 includes switching elements Q3 and Q4 connected in series between power line PL2 and power line NL1, and diodes D3 and D4 connected in parallel to switching elements Q3 and Q4, respectively. The cathode of diode D3 is connected to the collector of switching element Q3, and the anode of diode D3 is connected to the emitter of switching element Q3. The cathode of diode D4 is connected to the collector of switching element Q4, and the anode of diode D4 is connected to the emitter of switching element Q4.

  V-phase arm 132 includes switching elements Q5 and Q6 connected in series between power line PL2 and power line NL1, and diodes D5 and D6 connected in parallel to switching elements Q5 and Q6, respectively. The cathode of diode D5 is connected to the collector of switching element Q5, and the anode of diode D5 is connected to the emitter of switching element Q5. The cathode of diode D6 is connected to the collector of switching element Q6, and the anode of diode D6 is connected to the emitter of switching element Q6.

  W-phase arm 133 includes switching elements Q7 and Q8 connected in series between power line PL2 and power line NL1, and diodes D7 and D8 connected in parallel to switching elements Q7 and Q8, respectively. The cathode of diode D7 is connected to the collector of switching element Q7, and the anode of diode D7 is connected to the emitter of switching element Q7. The cathode of diode D8 is connected to the collector of switching element Q8, and the anode of diode D8 is connected to the emitter of switching element Q8.

  Motor generator 140 is, for example, a three-phase AC motor generator including a rotor in which permanent magnets are embedded and a stator having a three-phase coil Y-connected at a neutral point. One end of each of the three coils of the U phase, V phase, and W phase is connected to the neutral point, the other end of the U phase coil is connected to the connection node of the switching elements Q3, Q4, and the other end of the V phase coil. One end is connected to a connection node of switching elements Q5 and Q6, and the other end of the W-phase coil is connected to a connection node of switching elements Q7 and Q8.

  The output torque of motor generator 140 is transmitted to drive wheels 160 via power transmission gear 150 constituted by a speed reducer and a power split mechanism, and causes vehicle 100 to travel. The motor generator 140 can generate power by the rotational force of the drive wheels 160 during the regenerative braking operation of the vehicle 100. Then, the generated power is converted into charging power for power storage device 110 by inverter 130.

  Further, in a hybrid vehicle equipped with an engine (not shown) in addition to motor generator 140, necessary engine driving force is generated by operating this engine and motor generator 140 in a coordinated manner. In this case, it is also possible to charge the power storage device 110 using the power generated by the rotation of the engine.

  Although FIG. 1 shows a configuration in which one motor generator and inverter pair is provided, the number of motor generators and inverters is not limited to this, and a configuration in which a plurality of motor generators and inverters are provided may be employed. For example, in the case of a hybrid vehicle including two motor generators, one motor generator is used exclusively as an electric motor for driving the drive wheels 160, and the other motor generator is used exclusively as a generator driven by an engine. May be.

  Current sensor 180 is provided in a power transmission path between inverter 130 and motor generator 140. Since the sum of the currents flowing through the respective phases of motor generator 140 is always zero, it is sufficient that current sensor 180 is provided in at least one of the two phases of the power transmission path. In FIG. 1, for example, current sensor 180 is provided in the U-phase and V-phase power transmission paths, and detected currents Iu and Iv are sent to ECU 300.

  The rotation angle sensor 190 is provided in the motor generator 140. Rotation angle sensor 190 detects rotation angle θ of motor generator 140 and outputs the detected value to ECU 300. ECU 300 calculates the rotational speed or angular speed of motor generator 140 based on rotational angle θ from rotational angle sensor 190.

  ECU 300 includes a CPU (Central Processing Unit), a storage device, and an input / output buffer, all of which are not shown in FIG. 1, and inputs signals from each sensor and the like, and outputs control signals to each device. 100 and each device are controlled. Control in ECU 300 is not limited to processing by software, and processing by dedicated hardware (electronic circuit) is also possible.

  In addition, in FIG. 1, although demonstrated as an example the structure provided with one ECU300 as a control apparatus, the structure of a control apparatus is not limited to this. For example, ECU 300 may have a configuration in which a control device is provided for each device or function.

  ECU 300 receives voltage VB and current IB from power storage device 110. ECU 300 calculates a state of charge (SOC) of the power storage device based on voltage VB and current IB.

[Description of control mode]
Control of motor generator 140 by ECU 300 will be described in further detail. FIG. 2 is a diagram schematically illustrating a control mode of motor generator 140 in the present embodiment.

  As shown in FIG. 2, the AC motor drive device according to the present embodiment uses three control modes by switching motor control 140, that is, power conversion in inverter 130.

  The sine wave PWM control is used as a general PWM control. As shown in FIG. 3, a sine wave voltage command (waveform W11 in FIG. 3) is turned on / off for each phase upper and lower arm elements. And a carrier wave (typically a triangular wave) (waveform W10 in FIG. 3). As a result, for a set of a high level period corresponding to the on period of the upper arm element and a low level period corresponding to the on period of the lower arm element, the duty is set so that the fundamental wave component becomes a sine wave within a certain period. Is controlled. In the sine wave PWM control, asynchronous PWM control is applied, and the carrier frequency of the carrier wave is set regardless of the rotational speed of the motor generator 140. The carrier frequency in the sine wave PWM control is set to a range (for example, about 5 to 10 kHz) that is higher than the audible frequency band and that does not cause excessive switching loss.

  Switching between the sine wave PWM control and the overmodulation PWM control is expressed by a ratio of a fundamental wave component (effective value) of a motor applied voltage (line voltage) to a DC link voltage (that is, a system voltage VH) of the inverter 130. The modulation rate is used. Specifically, when the modulation rate is equal to or lower than the predetermined upper limit value UL, the sine wave PWM control is selected, and when the modulation rate exceeds the upper limit value UL, the overmodulation PWM control is selected.

  In this specification, this modulation factor is obtained when the voltage command value obtained by three-phase to two-phase conversion (dq axis conversion) of the voltage command applied to the motor generator 140 is Vd and Vq. Can be expressed by the following equation (1).

Modulation rate = (Vd ² + Vq ² ) ^1/2 / VH (1)
In the sine wave PWM control, typically, the amplitude of the voltage command of the sine wave is set to be in a range equal to or lower than the carrier wave amplitude, and in this case, the upper limit value UL is set to about 0.61. Also proposed is a control method in which a voltage command is generated by superimposing a 3n-order harmonic component (n: a natural number, typically n = 1 third-harmonic) on a sine wave component in the range below the carrier wave amplitude. In this case, the upper limit value UL is set to about 0.71, for example. In the present specification, even when the amplitude of the sine wave voltage command is larger than the carrier wave amplitude, the case where asynchronous PWM control is performed is referred to as sine wave PWM control.

  On the other hand, in the rectangular wave voltage control, one pulse of a rectangular wave having a ratio of 1: 1 between the high level period and the low level period is applied to the AC motor within the predetermined period. As a result, the modulation rate is increased to 0.78.

  Overmodulation PWM control is used at a modulation factor between sinusoidal PWM control and rectangular wave voltage control. In overmodulation PWM control, synchronous PWM control is applied, and the carrier frequency of the carrier wave is controlled in accordance with the rotational speed of motor generator 140. That is, the carrier wave synchronized with the phase of the voltage command is such that the carrier frequency is an integral multiple of the frequency of the voltage command according to the rotation speed of the motor generator (preferably 3 · (2n−1) times, n: natural number). Generated.

  In general, overmodulation PWM control performs PWM control similar to the sine wave PWM control in the range where the amplitude of the voltage command (sine wave component) is larger than the carrier wave amplitude (waveform W12 in FIG. 3). The fundamental wave component can be increased by distorting the voltage command from the original sine wave waveform (amplitude correction), and the modulation rate can be increased from the maximum modulation rate UL in the sine wave PWM control mode to a range of 0.78. it can. In overmodulation PWM control, since the amplitude of the voltage command (sine wave component) is larger than the carrier wave amplitude, the line voltage applied to the motor generator 140 is not a sine wave but a distorted voltage.

  In the motor generator 140, the induced voltage increases as the rotational speed and output torque increase, so that the required drive voltage (motor required voltage) increases. The boosted voltage by the converter 120, that is, the system voltage VH needs to be set higher than this motor required voltage. On the other hand, there is a limit value (VH maximum voltage) in the boosted voltage by converter 120, that is, system voltage VH.

  Therefore, the PWM control mode by sine wave PWM control or overmodulation PWM control, which controls the amplitude and phase of the motor applied voltage (AC) by feedback of the motor current according to the operating state of the motor generator 140, and the rectangular wave voltage One of the control modes is selectively applied. In the rectangular wave voltage control, since the amplitude of the motor applied voltage is fixed, the torque control is executed by the phase control of the rectangular wave voltage pulse based on the deviation between the actual torque value and the torque command value.

  FIG. 4 shows the correspondence between the operation state of motor generator 140 and the above-described control mode.

  Referring to FIG. 4, sine wave PWM control is generally used in order to reduce torque fluctuation in the low rotational speed range A1, overmodulation PWM control in the middle rotational speed range A2, and in the high rotational speed range A3. Square wave voltage control is applied. In particular, the output of motor generator 140 is improved by applying overmodulation PWM control and rectangular wave voltage control. As described above, which one of the control modes shown in FIG. 2 is used is basically determined within the range of the realizable modulation rate.

[Problems at sudden speed change in overmodulation mode]
When the vehicle travels, for example, when traveling on a snowy road or a wet road surface, the state where the drive wheels slip and the state where the road surface is gripped may be repeated. In this case, when the driving wheel slips, the rotational speed of the motor generator increases rapidly, and when the slipping state changes to the grip state, the rotational speed decreases rapidly. In such a sudden speed change, especially when the driving wheel changes from the slip state to the grip state, the induced torque of the motor generator increases due to a sudden increase in deceleration torque.

  In the overmodulation mode, as described above, a harmonic filter is superimposed on a sinusoidal current waveform to intentionally distort the waveform, and thus a current filter is generally used. Depending on the control period of the current filter (for example, 250 ms (= 400 Hz)), the control period of the current feedback control may be limited and the control response may not be sufficiently improved.

  For this reason, when the grip state is changed from the slip state as described above, the control for suppressing the voltage increase caused by the slip state cannot catch up, and there is a possibility that the overvoltage state may occur.

  To cope with this, when the slip state is changed to the grip state in the overmodulation mode, the overmodulation mode is forcibly switched to the sine wave modulation mode with excellent control response to reduce the voltage with high response. The drive device may be configured to have an emergency switching function.

  This emergency switching operation will be described in more detail with reference to FIG. FIG. 5 shows the current flowing through the motor generator on the dq coordinate axis, where the horizontal axis indicates the field direction component current Id and the vertical axis indicates the torque direction component current Iq.

  Referring to FIG. 5, a curve W30 in FIG. 5 is a curve indicating a current command value in the sine wave modulation mode. In the sine wave modulation mode, for example, a current command indicated by a point P1 on the curve W30 is shown. Current feedback control is executed so as to obtain a value.

  In the overmodulation mode, in order to output a higher torque than in the sine wave modulation mode, for example, as indicated by a point P2 in FIG. Control is executed as follows.

  Then, the emergency switching operation is executed in response to the change from the slip state to the grip state and the Iq current exceeds the switching line indicated by the dashed curve W31, and the control mode is changed from the overmodulation mode to the sine wave modulation. The mode is forcibly switched to mode.

  In the sinusoidal modulation mode, the executable modulation rate is limited as described above, and accordingly, the Iq current is also limited, and the operating point is changed from the point P3 to the point P1 in FIG. Be changed. Then, as a result, the torque direction component current Iq decreases, and as shown by the curve W20 in FIG. 6, the output torque is rapidly reduced by switching to the sine wave modulation mode, and the torque with respect to the torque command value TR is reduced. There may be a shortage.

[Description of Drive Control in Embodiment]
Therefore, in the present embodiment, when the control mode is switched from the overmodulation mode to the sine wave modulation mode by the emergency switching operation, the upper limit value of the modulation factor in the sine wave modulation mode is accordingly accompanied as shown in FIG. The mode switching control for relaxing UL from UL1 to UL2 is executed.

  Thereby, in the sine wave modulation mode, an intermediate Iq current (that is, torque) between the points P1 and P3 in FIG. 5 can be output, so that the control mode is changed from the overmodulation mode by the emergency switching operation. The output torque when the mode is switched to the sine wave modulation mode can be gradually changed, and a sudden decrease in torque can be suppressed.

  At this time, the upper limit value of the modulation rate is preferably relaxed within a range in which at least two pulses in PWM control are included in the half cycle of the voltage command signal, as indicated by a curve W12A in FIG. Middle part of FIG. 8). That is, it is preferable that the PWM signal does not become one pulse of the rectangular wave in the sine wave modulation mode, like the PWM signal shown in the lower part of FIG. 8 in the case of the curve W12B. This is to prevent the control from becoming unstable when the control mode is switched from the sine wave modulation mode to the rectangular wave voltage control described in FIG. More specifically, in the sine wave modulation mode, current feedback control is performed and the voltage phase is not controlled, but in rectangular wave voltage control, only the voltage phase is controlled. Therefore, when the control mode is switched from the rectangular wave control to the rectangular wave voltage control in the sine wave modulation mode, the command is the same rectangular wave, but the voltage phase changes and the control becomes unstable. It is.

  As to the upper limit value of the modulation rate, the condition for preventing such a PWM signal with one pulse of a rectangular wave is that the voltage waveform period and the number of carriers included in the period are as shown in FIG. Dependent. That is, a range in which the upper limit UL of the modulation rate can be relaxed is determined by the rotation speed of the motor generator and the carrier frequency of the carrier wave. Specifically, when the rotation speed is relatively slow or the carrier frequency is high, the number of carrier waves included in one period of the voltage command is relatively large, and therefore, it is difficult to obtain a PWM signal of one rectangular wave pulse. The upper limit value can be set larger.

  FIG. 9 is a functional block diagram for describing mode switching control executed by ECU 300 in the present embodiment. Each functional block described in the functional block diagram illustrated in FIG. 9 is realized by hardware or software processing by the ECU 300.

  Referring to FIG. 1 and FIG. 9, ECU 300 includes modulation factor calculation unit 310, modulation factor upper limit setting unit 320, emergency switching determination unit 330, storage unit 340, mode switching unit 350, and command generation unit 360. Including.

  Modulation factor calculation unit 310 receives voltage command values Vd, Vq and system voltage VH. The modulation factor calculation unit 310 calculates the modulation factor RAT using the above equation (1) using these pieces of information, and outputs the calculated modulation factor RAT to the mode switching unit 350.

  Modulation rate upper limit setting section 320 is output from rotation speed MRN calculated from rotation angle θ of motor generator 140 acquired from rotation angle sensor 190, carrier frequency FCar of the carrier wave, and emergency switching determination section 330 described later. The execution flag FLG of the emergency switching operation is received. The modulation factor upper limit setting unit 320 sets the modulation factor upper limit UL in the sine wave modulation mode to UL1 shown in FIG. 7 when the emergency switching operation is not executed. Further, when the emergency switching operation is being performed, the modulation factor upper limit value UL is set to be larger than UL1 based on the rotational speed MRN and the carrier frequency FCar. Then, modulation factor upper limit setting unit 320 outputs the set modulation factor upper limit value UL to command generation unit 360.

  Emergency switching determination unit 330 receives current values Id and Iq flowing through motor generator 140 on the dq coordinate axes and control mode MOD selected by mode switching unit 350.

  The emergency switching determination unit 330 calculates an emergency switching threshold value Iq_th corresponding to the acquired current value Id using a map as shown in FIG. 5 stored in advance in the storage unit 340. Then, when the control mode MOD indicates the overmodulation mode, the emergency switching determination unit 330 turns on the execution flag FLG for executing the emergency switching operation when the current value Iq exceeds the threshold value Iq_th. It is set and output to modulation factor upper limit setting section 320 and mode switching section 350.

  Mode switching unit 350 receives modulation rate RAT calculated by modulation rate calculation unit 310 and execution flag FLG from emergency switching determination unit 330.

  When the execution flag FLG does not instruct execution of emergency switching, the mode switching unit 350 switches between the overmodulation mode and the sine wave modulation mode based on the modulation rate RAT from the modulation rate calculation unit 310. Further, when execution of emergency switching is instructed, mode switching unit 350 switches the control mode from the overmodulation mode to the sine wave modulation mode regardless of the modulation rate RAT.

  Then, mode switching unit 350 outputs the set current control mode MOD to emergency switching determination unit 330 and command generation unit 360.

  Command generation unit 360 receives modulation factor upper limit value UL set by modulation factor upper limit setting unit 320, control mode MOD from mode switching unit 350, torque command value TR, rotation speed MRN of motor generator 140, and carrier frequency FCar. receive.

  Command generation unit 360 calculates a voltage command value from rotation speed MRN and command torque TR within a range not exceeding modulation factor upper limit value UL. And the PWM control signal PWI to the inverter 130 is produced | generated by comparing the waveform of the calculated voltage command value with the carrier wave of the carrier frequency FCar.

  FIG. 10 is a flowchart for illustrating the details of the mode switching control process executed by ECU 300 in the present embodiment. In the flowchart shown in FIG. 10 and FIG. 11 described below, the processing is realized by a program stored in advance in the ECU 300 being called from the main routine and executed in a predetermined cycle. Alternatively, for some steps, it is also possible to construct dedicated hardware (electronic circuit) and realize processing.

  Referring to FIGS. 1 and 10, ECU 300 performs PWM control in step (hereinafter, step is abbreviated as S) 100 based on modulation rate RAT determined from voltage command values Vq and Vd and system voltage VH. It is determined whether the mode is a sine wave modulation mode or an over modulation mode.

  If the control mode is the PWM control mode (YES in S100), then ECU 300 determines in S110 whether the control mode is an overmodulation mode.

  If it is the overmodulation mode (YES in S110), the process proceeds to S120, and ECU 300 acquires current values Iq and Id. ECU 300 calculates threshold value Iq_th indicating whether or not to perform an emergency switching operation from current value Id acquired in S130, and whether current value Iq acquired in S140 exceeds threshold value Iq_th. Determine whether or not.

  If current value Iq exceeds threshold value Iq_th (YES in S140), ECU 300 determines that an emergency switching operation is necessary, and in S150, the control mode is changed from the overmodulation mode to the sine wave modulation mode. Is switched.

  Thereafter, ECU 300 obtains rotation speed MRN of motor generator 140 and carrier frequency FCar of the carrier wave (S160), calculates upper limit value UL2 using them, and sets UL2 as modulation factor upper limit value UL ( S170).

  In S180, ECU 300 calculates a voltage command value from rotation speed MRN and command torque TR within a range not exceeding the calculated modulation factor upper limit value UL, and calculates the waveform of the calculated voltage command value and the carrier frequency. A control signal PWI to the inverter 130 is generated by comparing the Fcar carrier.

  If current value Iq is equal to or smaller than threshold value Iq_th in S140 (NO in S140), ECU 300 determines that the emergency switching operation is unnecessary and continues the overmodulation mode. Then, ECU 300 advances the process to S175, and sets UL1 as the modulation factor upper limit UL in the sine wave modulation mode. Thereafter, ECU 300 generates control signal PWI to inverter 130 in the overmodulation mode in S180.

  If the sine wave modulation mode is selected at S110 (NO at S110), ECU 300 proceeds to S175, sets UL1 to modulation factor upper limit UL, and at S180, sine wave modulation mode. Thus, the control signal PWI to the inverter 130 is generated.

  When the control mode is the rectangular wave voltage control mode at S100 (NO at S100), the process proceeds to S180, ECU 300 sets the voltage phase according to torque command value TR, and inverter 130 is set. A control signal PWI is generated.

  Although not shown in detail in FIG. 10, when switching from the rectangular wave voltage control mode to the PWM control mode, the necessity of switching is determined based on a comparison between the current phase and a predetermined threshold value. Is done.

  By performing the control according to the above-described process, when a sudden speed change occurs from the slip state to the grip state during execution of the over modulation mode, an emergency switching operation from the over modulation mode to the sine wave modulation mode is performed. It is possible to prevent an overvoltage from occurring, and to suppress a rapid decrease in torque by relaxing the upper limit of the modulation rate. As a result, it is possible to prevent breakage and failure of the device, and to reduce rapid torque fluctuation during traveling.

  Also, when switching to the rectangular wave voltage control mode by relaxing the upper limit of the modulation factor in the emergency switching operation from the overmodulation mode to the sine wave modulation mode within the range that does not become a rectangular wave in the sine wave modulation mode Therefore, it is possible to prevent the voltage phase from becoming unstable and maintain control stability.

  The combination of “inverter 130” and “ECU 300” in the present embodiment corresponds to “AC motor drive device” in the present invention.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  100 vehicle, 110 power storage device, 115 SMR, 120 converter, 130 inverter, 131 U-phase arm, 132 V-phase arm, 133 W-phase arm, 140 motor generator, 150 power transmission gear, 160 drive wheel, 170 voltage sensor, 180 current Sensor, 190 Rotation angle sensor, 300 ECU, 310 Modulation rate calculation unit, 320 Modulation rate upper limit setting unit, 330 Emergency switching determination unit, 340 Storage unit, 350 Mode switching unit, 360 Command generation unit, C1, C2 capacitor, D1 D8 diode, L1 reactor, NL1, PL1, PL2 power line, Q1-Q8 switching element.

Claims (9)

AC motor drive device,
An inverter for controlling the applied voltage of the AC motor;
A control device for controlling the inverter using pulse width modulation control based on a comparison between a sinusoidal voltage command signal and a carrier wave signal for operating the AC motor according to an operation command;
In the pulse width modulation control, the control device controls an overmodulation mode for controlling the frequency of the carrier signal to be an integral multiple of the frequency of the voltage command signal, and the frequency of the carrier signal is set to the frequency of the voltage command signal. Controlling the inverter by switching a plurality of control modes including a sine wave modulation mode set independently of
The control device has an emergency switching function for forcibly switching from the overmodulation mode to the sine wave modulation mode based on a current flowing through the AC motor during execution of the overmodulation mode,
The control device relaxes an upper limit value for limiting an amplitude of the voltage command signal in the sine wave modulation mode when the control mode is switched from the over modulation mode to the sine wave modulation mode by the emergency switching function. , AC motor drive device.   When the control device is switched from the overmodulation mode to the sine wave modulation mode by the emergency switching function, the control device sets the upper limit value in the sine wave modulation mode to be larger as the frequency of the carrier signal is larger. The driving apparatus for an AC motor according to claim 1.   When the control device switches the control mode from the overmodulation mode to the sine wave modulation mode by the emergency switching function, the upper limit value in the sine wave modulation mode is set larger as the rotational speed of the AC motor is lower. The AC motor drive device according to claim 1.   When the control device switches the control mode from the overmodulation mode to the sine wave modulation mode by the emergency switching function, a pulse width modulation signal applied to the inverter during one period of the voltage command signal is a rectangular wave. The AC motor driving apparatus according to claim 2 or 3, wherein the upper limit value is set so as not to be one pulse.   The control device executes the emergency switching function when a q-axis current of a current flowing through the AC motor exceeds a predetermined threshold value of a q-axis current determined based on a d-axis current. The drive device of the alternating current motor described in 1.   6. The AC motor driving apparatus according to claim 5, wherein the threshold value is set to a value larger than a q-axis current command value in the sine wave modulation mode. The control device switches a control mode from the sine wave modulation mode to the overmodulation mode based on a modulation factor determined by an input DC voltage to the inverter and a voltage command value given to the AC motor,
The AC motor driving apparatus according to claim 1, wherein the upper limit value is a threshold value for determining switching of the control mode from the sine wave modulation mode to the overmodulation mode. A vehicle capable of traveling using a driving force generated by an AC motor,
An inverter for controlling the applied voltage of the AC motor;
A control device for controlling the inverter using pulse width modulation control based on a comparison between a sinusoidal voltage command signal and a carrier wave signal for operating the AC motor according to an operation command;
In the pulse width modulation control, the control device controls an overmodulation mode for controlling the frequency of the carrier signal to be an integral multiple of the frequency of the voltage command signal, and the frequency of the carrier signal is set to the frequency of the voltage command signal. Controlling the inverter by switching a plurality of control modes including a sine wave modulation mode set independently of
The control device has an emergency switching function for forcibly switching from the overmodulation mode to the sine wave modulation mode based on a current flowing through the AC motor during execution of the overmodulation mode,
The control device relaxes an upper limit value for limiting an amplitude of the voltage command signal in the sine wave modulation mode when the control mode is switched from the over modulation mode to the sine wave modulation mode by the emergency switching function. ,vehicle. An AC motor control method in which an applied voltage is controlled by an inverter,
Controlling the inverter using pulse width modulation control based on a comparison between a sinusoidal voltage command signal and a carrier signal for operating the AC motor in accordance with an operation command;
In the pulse width modulation control, an overmodulation mode for controlling the frequency of the carrier signal to be an integral multiple of the frequency of the voltage command signal, and setting the frequency of the carrier signal regardless of the frequency of the voltage command signal Switching the plurality of control modes including a sine wave modulation mode to control the inverter;
Executing an emergency switching function for forcibly switching from the overmodulation mode to the sine wave modulation mode based on a current flowing through the AC motor during the overmodulation mode;
Relaxing the upper limit value for limiting the amplitude of the voltage command signal in the sine wave modulation mode when the control mode is switched from the over modulation mode to the sine wave modulation mode by the emergency switching function. AC motor control method.

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