JP5277846B2 - AC motor control system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve feed-forward control for setting a phase of a rectangular wave voltage applied to an AC motor after suppressing a data amount to be previously stored. <P>SOLUTION: Torque values T(4), T(5) sandwiching a torque command value Tqcom therebetween are extracted from among torque values T(1)-T(n) at prescribed voltage phases &theta;(1)-&theta;(n) which are calculated in accordance with a prescribed torque operational expression T including motor variables (&omega;, VH, &theta;). It is possible to calculate a voltage phase &theta;ff corresponding to the torque command value Tqcom and generated by feed-forward control without preparing a map, in which the motor variable are used as arguments, by linear interpolation using the torque values T(4), T(5) and voltage phases &theta;(4), &theta;(5). <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to an AC motor control system, and more particularly to motor control in which a DC voltage is converted into a rectangular wave AC voltage by an inverter and applied to the AC motor.

  A motor control system that drives and controls an AC motor by converting a DC voltage into an AC voltage by an inverter is generally used. In such a motor control system, generally, in order to drive an AC motor with high efficiency, the motor current is controlled according to sinusoidal pulse width modulation (PWM) control based on vector control.

  However, the sinusoidal PWM control has a problem that it is difficult to obtain a high output in a high speed region because the fundamental wave component of the output voltage of the inverter cannot be sufficiently increased and the voltage utilization rate is limited. In view of this point, it has been proposed to adopt a control method capable of outputting a voltage having a larger fundamental wave component than the sine wave PWM control.

  Japanese Patent Laying-Open No. 2006-320039 (Patent Document 1) describes a control system in which a rectangular wave voltage having an amplitude of a voltage variably controlled by a converter is applied to an AC motor. In particular, in Patent Document 1, for torque control using a rectangular wave voltage, while the voltage phase is basically changed according to the torque deviation, when the motor rotation speed changes abruptly, the motor rotation speed change ratio is changed. The voltage command value of the output voltage of the converter is set according to the above. In this way, it is possible to realize motor control that can change the motor applied voltage in response to a sudden change in the motor rotation speed without waiting for torque feedback control that does not have high control response.

Japanese Patent No. 3764337 (Patent Document 2) also discloses a control apparatus for a synchronous motor that performs variable speed driving of a synchronous motor by a power converter, while keeping the amplitude of the output voltage of the power converter constant. It describes changing the phase of the voltage. In particular, feedforward control is described in which the phase of the output voltage is changed according to the current reference value, the voltage amplitude reference value, and the constant of the synchronous motor.
JP 2006-320039 A Japanese Patent No. 3764337 JP 2004-80924 A JP 2006-166499 A

  As described in Patent Document 2, since the control response of the feedback control is not so high in the rectangular wave voltage control, the phase of the rectangular wave voltage is feedforward controlled in accordance with the operation command value of the AC motor, the motor constant, and the like. Is done.

  However, in such feedforward control, in order to obtain an appropriate voltage phase corresponding to the operation command, not only the motor constant of the AC motor, but also the variable (rotation speed, etc.) indicating the operating state of the AC motor and the torque are used. It is necessary to set the voltage phase according to the correspondence. Therefore, if a map for obtaining the voltage phase using the variable and the torque command value as an argument is configured in advance, the storage capacity of the map increases as the number of map points increases by increasing the variable to ensure the accuracy of the feedforward control. Is concerned. In particular, when feedback control and feedforward control are combined, or when control that uses rectangular wave voltage control and PWM control depending on the state of the AC motor is employed, the memory capacity required for the entire motor control increases. Accordingly, it is required to suppress the storage capacity by feedforward control.

  The present invention has been made to solve such a problem, and an object of the present invention is to provide a rectangular wave voltage applied to an AC motor in accordance with a variable and an operation command value in a motion state of the AC motor. The feedforward control for setting the phase is realized while suppressing the amount of data to be stored in advance.

  An AC motor control system according to the present invention includes an inverter that converts a DC voltage into an AC voltage for driving the AC motor, a converter that variably controls the DC voltage input to the inverter according to a voltage command value, and a first motor. And a control unit. The first motor control unit generates an alternating current from the inverter based on at least one motor variable related to the operating state of the AC motor and the torque command value so that the AC motor outputs a torque according to the torque command value. It is comprised so that the voltage phase of the rectangular wave voltage applied to an electric motor may be set. The first motor control unit includes a phase torque characteristic calculation unit and a phase calculation unit. The phase torque characteristic calculation unit has a first phase, which is a voltage phase corresponding to a first torque value lower than the torque command value, and a torque command value according to a torque calculation formula using the motor variable and the voltage phase as variables. A second phase that is a voltage phase at a high second torque value is obtained. The phase calculation unit corresponds to the torque command value based on the ratio between the difference between the first and second torque values and the difference between the first and second phases and one of the first and second phases. It is configured to calculate a voltage phase.

  According to the control system for the AC motor, the calculation according to the torque calculation formula in which the current value of the variable is substituted without referring to the map using the motor variable related to the operation state of the AC motor and the torque command value as arguments. Based on the above, the voltage phase corresponding to the torque command value can be set. Therefore, it is possible to realize feedforward control that sets the voltage phase corresponding to the torque command value while reflecting the operation state of the AC motor without storing a multidimensional map with a plurality of arguments.

  Preferably, the phase torque characteristic calculation unit calculates a plurality of torque values for a plurality of predetermined voltage phases by substituting the current value of the motor variable into a torque calculation formula, and among the plurality of torque values, And setting one of the torque values lower than the torque command value, which has the smallest difference from the torque command value, as the first torque value, and among the torque values higher than the torque command value, The other one having the smallest difference is set as the second torque value.

  By doing this, among the pairs of voltage phase-torque values calculated according to the torque calculation formula, linear interpolation of two sets of torque values-voltage phases that minimize the torque difference across the torque command value, The voltage phase by feedforward control can be obtained with high accuracy.

  More preferably, the first motor control unit further includes a loss estimation unit configured to estimate a torque loss in the AC motor according to the operating state of the AC motor. The phase torque characteristic calculation unit sets the first and second torque values according to the torque calculation formula and the torque loss estimated by the loss estimation unit.

  In this way, since the torque loss estimation according to the current operating state of the AC motor can be reflected in the feedforward control, the voltage phase can be set with higher accuracy.

  More preferably, the first motor control unit further includes a parameter estimation unit configured to correct a constant parameter of the torque calculation equation in accordance with the operating state of the AC motor. Then, the phase torque characteristic calculation unit sets the first and second torque values according to the torque calculation formula to which the constant parameter corrected by the parameter estimation unit is applied.

  In this way, the parameter constant of the torque calculation formula for the feedforward control can be modified according to the operating state of the AC motor, so that the voltage phase setting accuracy can be further improved. Since the parameter constant estimation map can be basically configured as a map for one dimension (typically, motor current), it is possible to avoid an enormous storage capacity.

  Alternatively, preferably, the control system for the AC motor further includes a second motor control unit. The second motor control unit is configured to control the voltage phase of the rectangular wave voltage based on a torque deviation with respect to the torque command value of the AC motor so that the AC motor outputs a torque according to the torque command value. . The voltage phase command value is set according to the sum of the set values by the first and second motor control units.

  In this way, the rectangular wave voltage control can be made highly accurate by combining feedback control based on torque deviation and feedforward control based on a torque calculation formula that reflects a variable related to the operating state of the AC motor. Even in combination, the increase in the amount of data to be stored in advance can be reduced.

  Preferably, the AC motor is configured to be mounted on an electric vehicle and generate a vehicle driving force of the electric vehicle.

  According to the electric vehicle, the rectangular wave voltage control that contributes to improving the output in the high speed region of the AC motor can be realized without excessively occupying the storage region of the electronic control unit (ECU).

  According to the present invention, the feedforward control for setting the phase of the rectangular wave voltage applied to the AC motor in accordance with the variable and the operation command value in the motion state of the AC motor is performed after suppressing the amount of data to be stored in advance. realizable.

  Embodiments of the present invention will be described below in detail with reference to the drawings. In the following, the same or corresponding parts in the drawings are denoted by the same reference numerals, and the description thereof will not be repeated in principle.

(System configuration)
FIG. 1 is an overall configuration diagram of an AC motor control system according to an embodiment of the present invention.

  Referring to FIG. 1, motor control system 100 includes a DC voltage generation unit 10 #, a smoothing capacitor C0, an inverter 14, a control device 30, and an AC motor M1.

  AC motor M1 is a driving motor that generates torque for driving the driving wheels of an electric vehicle such as a hybrid vehicle or an electric vehicle. In other words, in the present embodiment, the electric vehicle includes all vehicles equipped with a motor for generating wheel driving force, including an electric vehicle not equipped with an engine. Note that AC motor M1 is generally configured to have both functions of an electric motor and a generator. Further, this AC motor M1 may be configured to have a function of a generator driven by an engine in a hybrid vehicle. Further, AC electric motor M1 may operate as an electric motor for the engine, and may be incorporated in a hybrid vehicle as one that can start the engine, for example.

  DC voltage generation unit 10 # includes a DC power supply B, system relays SR1 and SR2, a smoothing capacitor C1, and a step-up / down converter 12.

  The DC power source B is composed of a secondary battery such as nickel metal hydride or lithium ion, a fuel cell, an electric double layer capacitor, or a combination thereof. The DC voltage Vb output from the DC power source B is detected by the voltage sensor 10. Voltage sensor 10 outputs detected DC voltage Vb to control device 30.

  System relay SR 1 is connected between the positive terminal of DC power supply B and power line 6, and system relay SR 2 is connected between the negative terminal of DC power supply B and ground line 5. System relays SR1 and SR2 are turned on / off by signal SE from control device 30. Smoothing capacitor C <b> 1 is connected between power line 6 and ground line 5.

  Buck-boost converter 12 includes a reactor L1, power semiconductor switching elements Q1, Q2, and diodes D1, D2.

  Power switching elements Q <b> 1 and Q <b> 2 are connected in series between power line 7 and ground line 5. On / off of power switching elements Q1 and Q2 is controlled by switching control signals S1 and S2 from control device 30.

In the embodiment of the present invention, as a power semiconductor switching element (hereinafter, simply referred to as “switching element”), an IGBT (Insulated Gate Bipolar Transistor),
A power MOS (Metal Oxide Semiconductor) transistor, a power bipolar transistor, or the like can be used. Anti-parallel diodes D1, D2 are arranged for switching elements Q1, Q2.

  Reactor L1 is connected between a connection node of switching elements Q1 and Q2 and power line 6. Further, the smoothing capacitor C 0 is connected between the power line 7 and the ground line 5.

  Inverter 14 includes a U-phase arm 15, a V-phase arm 16, and a W-phase arm 17 provided in parallel between power line 7 and ground line 5. Each phase arm is composed of a switching element connected in series between the power line 7 and the ground line 5. For example, U-phase arm 15 includes switching elements Q3 and Q4, V-phase arm 16 includes switching elements Q5 and Q6, and W-phase arm 17 includes switching elements Q7 and Q8. Further, antiparallel diodes D3 to D8 are connected to switching elements Q3 to Q8, respectively. Switching elements Q3 to Q8 are turned on / off by switching control signals S3 to S8 from control device 30.

  An intermediate point of each phase arm is connected to each phase end of each phase coil of AC electric motor M1. Typically, AC electric motor M1 is a three-phase permanent magnet motor, and is configured such that one end of three coils of U, V, and W phases are commonly connected to a midpoint. Furthermore, the other end of each phase coil is connected to the midpoint of the switching elements of each phase arm 15-17.

  During the boosting operation, the step-up / step-down converter 12 boosts a DC voltage obtained by boosting the DC voltage Vb supplied from the DC power supply B (this DC voltage corresponding to the input voltage to the inverter 14 is hereinafter also referred to as “system voltage”) VH. Supply to the inverter 14. Further, during the step-down operation, the step-up / down converter 12 steps down the DC voltage (system voltage) supplied from the inverter 14 via the smoothing capacitor C0 and charges the DC power source B. During the step-up operation and the step-down operation, on / off of switching elements Q1, Q2 is controlled in response to switching control signals S1, S2 from control device 30, respectively. If switching elements Q1 and Q2 are fixed to ON and OFF, respectively, VH = Vb (voltage ratio = 1.0) can be obtained.

  Smoothing capacitor C0 smoothes the DC voltage from step-up / down converter 12, and supplies the smoothed DC voltage to inverter 14. The voltage sensor 13 detects the voltage across the smoothing capacitor C 0, that is, the system voltage VH, and outputs the detected voltage to the control device 30.

  When the torque command value of AC motor M1 is positive (Tqcom> 0), inverter 14 responds to switching control signals S3 to S8 from control device 30 when a DC voltage is supplied from smoothing capacitor C0. The AC motor M1 is driven so as to output a positive torque by converting the DC voltage into an appropriate motor applied voltage (AC voltage) by the switching operation of the elements Q3 to Q8. Further, when the torque command value of the AC motor M1 is zero (Tqcom = 0), the inverter 14 converts the DC voltage to an appropriate motor applied voltage (AC voltage) by a switching operation in response to the switching control signals S3 to S8. The AC electric motor M1 is driven so that the torque becomes zero by converting to. Thus, AC electric motor M1 is driven to generate zero or positive torque designated by torque command value Tqcom.

  Further, during regenerative braking of an electric vehicle equipped with motor control system 100, torque command value Tqcom of AC electric motor M1 is set to be negative (Tqcom <0). In this case, the inverter 14 converts the AC voltage generated by the AC motor M1 into a DC voltage by a switching operation in response to the switching control signals S3 to S8, and converts the converted DC voltage (system voltage) to the smoothing capacitor C0. To the step-up / down converter 12. The regenerative braking here refers to braking with regenerative power generation when the driver operating the electric vehicle performs a footbrake operation, or regenerative braking by turning off the accelerator pedal while driving, although the footbrake is not operated. This includes decelerating (or stopping acceleration) the vehicle while generating electricity.

  Current sensor 24 detects a motor current flowing through AC electric motor M <b> 1 and outputs the detected motor current to control device 30. Since the sum of instantaneous values of the three-phase currents iu, iv, and iw is zero, the current sensor 24 has a motor current for two phases (for example, a V-phase current iv and a W-phase current iw) as shown in FIG. It is sufficient to arrange it so as to detect.

  The rotation angle sensor (resolver) 25 detects the rotor rotation angle ANG of the AC electric motor M1 and sends the detected rotation angle ANG to the control device 30. The control device 30 can calculate the rotational speed (represented by the rotational speed per unit time (typically rpm)) and the angular speed ω (rad / s) based on the rotational angle ANG. Note that the rotation angle sensor 25 may be omitted by directly calculating the rotation angle ANG from the motor voltage or current in the control device 30.

  The control device 30 is configured by a CPU (Central Processing Unit) (not shown) and an electronic control unit (ECU) with a built-in memory, and based on a map and a program stored in the memory, an operation using a detection value by each sensor. Perform processing. The control device 30 controls the operation of the motor control system 100 by such arithmetic processing so that the AC motor M1 is operated according to the operation command from the host ECU. Note that a part of the control device 30 may be configured to execute predetermined numerical / logical operation processing by hardware such as an electronic circuit.

  Specifically, the control device 30 determines the torque command value Tqcom, the battery voltage Vb detected by the voltage sensor 10, the system voltage VH detected by the voltage sensor 13, the motor currents iv and iw from the current sensor 24, and the rotation angle. Based on the rotation angle ANG from the sensor 25, the operations of the step-up / down converter 12 and the inverter 14 are controlled so that the AC motor M1 outputs a torque according to the torque command value Tqcom by a method described later. That is, the switching control signals S1 to S8 for controlling the buck-boost converter 12 and the inverter 14 as described above are generated and output to the buck-boost converter 12 and the inverter 14.

  During the step-up operation of the step-up / down converter 12, the control device 30 feedback-controls the output voltage VH of the smoothing capacitor C0, and generates the switching control signals S1 and S2 so that the output voltage VH becomes a voltage command value.

  In addition, when control device 30 receives signal RGE indicating that the electric vehicle has entered the regenerative braking mode from the host ECU, switching control signal S <b> 3 to convert the AC voltage generated by AC motor M <b> 1 into a DC voltage. S8 is generated and output to the inverter 14. Thereby, the inverter 14 converts the AC voltage generated by the AC motor M <b> 1 into a DC voltage and supplies it to the step-up / down converter 12.

  Further, when receiving a signal RGE indicating that the electric vehicle has entered the regenerative braking mode from the external ECU, control device 30 generates switching control signals S1 and S2 so as to step down the DC voltage supplied from inverter 14. , Output to the step-up / down converter 12. As a result, the AC voltage generated by AC motor M1 is converted to a DC voltage, stepped down, and supplied to DC power supply B. Furthermore, control device 30 generates signal SE for turning on / off system relays SR1, SR2 and outputs the signal SE to system relays SR1, SR2.

(Control configuration)
Next, power conversion in the inverter 14 controlled by the control device 30 will be described in detail.

  As shown in FIG. 2, in motor control system 100 according to the embodiment of the present invention, three control modes are switched and used for power conversion in inverter 14.

  The sine wave PWM control is used as a general PWM control, and the switching elements in each phase arm are turned on / off according to a voltage comparison between a sine wave voltage command value and a carrier wave (typically a triangular wave). Control. 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. The ratio is controlled. As is well known, in the sine wave PWM control, this fundamental wave component (effective value) can be increased only to about 0.61 times the inverter input voltage. Hereinafter, in this specification, the ratio of the fundamental wave component of the voltage applied to AC motor M1 (hereinafter also simply referred to as “motor applied voltage”) to the DC link voltage of inverter 14 (that is, system voltage VH) is referred to as “modulation rate”. ".

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

  The overmodulation PWM control performs PWM control similar to the sine wave PWM control in a range where the amplitude of the voltage command is larger than the carrier wave amplitude. In particular, the fundamental wave component can be increased by distorting the voltage command from the original sine wave waveform, and the modulation rate can be increased from the maximum modulation rate in the sine wave PWM control mode to a range of 0.78.

  In the AC motor M1, 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 12, that is, the system voltage VH needs to be set higher than the required voltage of the motor. On the other hand, there is a limit value (VH maximum voltage) in the boosted voltage by converter 12, that is, system voltage VH.

  Therefore, a PWM control mode by sine wave PWM control or overmodulation PWM control that controls the amplitude and phase of the motor applied voltage (AC) by feedback of the motor current according to the operating state of AC motor M1, and 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. 3 shows the correspondence between the operating state of AC electric motor M1 and the control mode described above.
Referring to FIG. 3, schematically, sinusoidal PWM control is used in order to reduce torque fluctuation in the low speed range A1, overmodulation PWM control in the medium speed range A2, and rectangular wave in the high speed range A3. Voltage control is applied. In particular, application of overmodulation PWM control and rectangular wave voltage control can improve the output of AC electric motor M1. 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.

Next, details of PWM control and rectangular wave voltage control will be described.
FIG. 4 is a control block diagram in the sine wave PWM control and overmodulation PWM control executed by the control device 30. Each block in FIG. 4 is realized by a predetermined program executed by the control device 30 and / or control arithmetic processing by an electronic circuit in the control device 30.

  Referring to FIG. 4, PWM control unit 200 includes a current command generation unit 210, coordinate conversion units 220 and 250, a PI calculation unit 240, and a PWM signal generation unit 260.

  Current command generation unit 210 generates a d-axis current command value Idcom and a q-axis current command value Iqcom corresponding to torque command value Tqcom of AC electric motor M1 according to a table created in advance.

  The coordinate conversion unit 220 performs the v-phase current iv and the W-phase current detected by the current sensor 24 by coordinate conversion (3 phase → 2 phase) using the rotation angle ANG of the AC motor M1 detected by the rotation angle sensor 25. Based on iv, a d-axis current Id and a q-axis current Iq are calculated.

  A deviation ΔId (ΔId = Idcom−Id) with respect to the command value of the d-axis current and a deviation ΔIq (ΔIq = Iqcom−Iq) with respect to the command value of the q-axis current are input to the PI calculation unit 240. PI calculating section 240 performs PI calculation with a predetermined gain for each of d-axis current deviation ΔId and q-axis current deviation ΔIq to obtain a control deviation, and d-axis voltage command value Vd # and q-axis corresponding to this control deviation Voltage command value Vq # is generated.

  The coordinate conversion unit 250 converts the d-axis voltage command value Vd # and the q-axis voltage command value Vq # into the U-phase, V-phase, W-phase by coordinate conversion (2 phase → 3 phase) using the rotation angle ANG of the AC motor M1. Each phase voltage command value Vu, Vv, Vw of the phase is converted. The system voltage VH is also reflected in the conversion from the d-axis and q-axis voltage command values Vd # and Vq # to the phase voltage command values Vu, Vv and Vw.

  The PWM signal generation unit 260 generates the switching control signals S3 to S8 shown in FIG. 1 based on the comparison between the voltage command values Vu, Vv, Vw in each phase and a predetermined carrier wave. The inverter 14 is subjected to switching control according to the switching control signals S3 to S8 generated by the PWM control unit 200, whereby an AC voltage for outputting torque according to the torque command value Tqcom is applied to the AC motor M1. The

  During overmodulation PWM control, the amplitude of the AC voltage command corresponding to the fundamental component of the motor applied voltage, that is, the voltage command values Vd # and Vq # converted from the two-phase to three-phase, is expressed by the inverter input voltage. It becomes a state larger than (system voltage VH). However, since a voltage exceeding the system voltage VH cannot be applied from the inverter 14 to the AC motor M1, depending on the PWM control according to the original voltage command values Vd # and Vq #, the voltage command values Vd # and Vq #. The original modulation rate corresponding to the above cannot be secured.

  For this reason, during overmodulation PWM control, amplitude correction processing for expanding the voltage amplitude (× k times, k> 1) so that the voltage application interval is increased with respect to the AC voltage command based on the voltage command values Vd # and Vq #. By performing the above, it becomes possible to secure the original modulation rate based on the voltage command values Vd # and Vq #. In the configuration example of FIG. 4, it is assumed that the coordinate conversion unit 250 also executes amplitude correction processing when applying overmodulation PWM control.

  Furthermore, a control mode determination unit 300 and a VH command value generation unit 310 are provided. Control mode determination unit 300 calculates a modulation factor using system voltage VH, d-axis voltage command value Vd #, and q-axis voltage command value Vq #, and performs sine wave PWM control and overmodulation PWM control according to the calculated modulation rate. Select one of the following. For example, the modulation factor can be calculated by the following equation (a).

FM = (Vd # ² + Vq # ² ) ^1/2 / VH (a)
VH command value generation unit 310 generates control command value VH # (hereinafter also referred to as voltage command value VH #) of system voltage VH according to torque command value Tqcom and rotational speed Nm of AC electric motor M1.

  The PWM signal generation unit 350 follows the predetermined PWM control so that the output voltage of the buck-boost converter 12 becomes the voltage command value VH # based on the battery voltage Vb detected by the voltage sensor 10 and the current system voltage VH. Switching control signals S1 and S2 are generated.

  With the above configuration, during PWM control, feedback control of the motor current (Id, Iq) is performed so that the output torque of AC electric motor M1 matches torque command value Tqcom.

(Rectangular wave voltage control according to this embodiment)
Next, the control operation in the rectangular wave voltage control according to the embodiment of the present invention will be described with reference to FIGS. As will become apparent from the following description, the control system for an AC motor according to the present embodiment has a characteristic point in the control configuration of rectangular wave voltage control, particularly feedforward control. That is, it is described in a positive manner that a known control configuration can be arbitrarily applied to portions other than the feedforward control of the rectangular wave voltage control.

  Referring to FIG. 5, rectangular wave voltage control unit 400 includes power calculation unit 410, torque calculation unit 420 and PI calculation unit 430, feedforward control unit 440, addition unit 450, and rectangular wave generator 460. And a signal generation unit 470. Feed forward control unit 440 includes a phase / torque characteristic calculation unit 442 and an FF (feed forward) phase calculation unit 445.

  Note that each block in FIG. 5 is also realized by a control program executed by a predetermined program executed by the control device 30 and / or an electronic circuit (hardware) in the control device 30.

  The power calculation unit 410 uses the phase currents obtained from the V-phase current iv and the W-phase current iw by the current sensor 24 and the voltages (u-phase, v-phase, w-phase) voltages Vu, Vv, Vw as follows ( 1) Calculate the power supplied to the motor (motor power) Pmt according to the equation (1).

Pmt = iu · Vu + iv · Vv + iw · Vw (1)
The torque calculation unit 420 uses the motor power Pmt obtained by the power calculation unit 410 and the angular velocity ω calculated from the rotation angle ANG of the AC electric motor M1 detected by the rotation angle sensor 25, according to the following equation (2). Estimated value Tq is calculated.

Tq = Pmt / ω (2)
Note that the estimated torque value Tq is not limited to the estimation method by the power calculation unit 410 and the torque calculation unit 420, but a point that can be obtained by an arbitrary method will be described. Alternatively, the estimated torque value Tq may be obtained by arranging a torque sensor instead of the power calculation unit 410 and the torque calculation unit 420.

  Torque deviation ΔTq (ΔTq = Tqcom−Tq) with respect to torque command value Tqcom is input to PI calculation unit 430. PI operation unit 430 performs PI operation with a predetermined gain on torque deviation ΔTq to obtain a control deviation, and calculates voltage phase θfb according to the obtained control deviation.

  Specifically, as shown in FIG. 6, when positive torque is generated (Tqcom> 0), the voltage phase θv is advanced when torque is insufficient, while the voltage phase θv is delayed when torque is excessive and negative torque is generated (Tqcom). <0) When the torque is insufficient, the PI calculation unit 430 calculates the voltage phase θfb by feedback control based on the torque deviation ΔTq so that the voltage phase θv is delayed when the torque is insufficient and the voltage phase θv is advanced when the torque is excessive.

  Thus, the rectangular wave voltage phase set by the feedback control based on the torque deviation is obtained. That is, feedback control based on the torque deviation is executed by power calculation unit 410, torque calculation unit 420, and PI calculation unit 430. That is, the electric power calculation unit 410, the torque calculation unit 420, and the PI calculation unit 430 constitute a “second motor control unit” for feedback control.

  However, since the operation amount of the motor applied voltage is only the phase in the rectangular wave voltage control, the control responsiveness is relatively lowered as compared with the PWM control in which the amplitude and phase of the motor applied voltage can be the operation amount. Further, in the power calculation (equation (1)) in the power calculation unit 410, filter processing for removing noise and the like from the detected motor current value is unavoidable. It becomes difficult to ensure sufficient control response.

  Feedforward control unit 440 performs feedforward control according to motor rotation speed Nm and system voltage VH as variables related to the operating state of AC electric motor M1 (hereinafter also referred to as motor variables) and torque command value Tqcom. Sets the voltage phase θff. That is, the feedforward control unit 440 corresponds to a “first motor control unit”.

  The rotation speed Nm can be calculated from the rotation angle ANG of the AC motor M1 detected by the rotation angle sensor 25. As for system voltage VH, voltage command value VH # may be used instead of the voltage detected by voltage sensor 13.

  Adder 450 adds voltage phase φv corresponding to a rectangular wave voltage phase command according to the addition of voltage phase φfb by feedback control set by PI calculator 430 and voltage phase φff set by feedforward controller 440. Set.

  The rectangular wave generator 460 generates each phase voltage command value (rectangular wave pulse) Vu, Vv, Vw according to the voltage phase φv set in the adding unit 450. The signal generator 470 generates switching control signals S3 to S8 according to the phase voltage command values Vu, Vv, and Vw. When inverter 14 performs a switching operation according to switching control signals S3 to S8, a rectangular wave voltage according to voltage phase φv is applied as each phase voltage of the motor.

  With this configuration, the torque of AC electric motor M1 is covered by the combination of feedforward control and feedback control so that the control responsiveness of the feedback control described above is covered and the offset steady-state deviation is eliminated by feedback control. Can be controlled.

  In the feedforward control, it is necessary to determine the voltage phase φff corresponding to the torque command value Tqcom after grasping the voltage phase-torque characteristic relationship in advance. However, as shown in FIG. 7, it is known that the voltage phase-torque characteristic relationship changes according to the operating state of the AC motor.

  Referring to FIG. 7, the output torque of AC electric motor M1 varies depending on the combination of voltage phase φv, motor rotation speed Nm, and system voltage VH (that is, the amplitude of the rectangular wave voltage).

  For example, FIG. 7A shows output torque characteristics corresponding to changes in voltage phase φv and system voltage VH when rotational speed Nm = N1. Similarly, FIG. 7B shows the characteristics of the output torque corresponding to the voltage phase φv and the system voltage VH when the rotational speed Nm = N2 is higher than that.

  Schematically, for the same voltage phase, the output torque increases as the system voltage VH (rectangular wave voltage amplitude) increases, while the output torque decreases as the rotational speed increases. 7 (a) and 7 (b) show the characteristics of the power running region in FIG. 6. Similarly, in the regenerative region (not shown), the system voltage rises with respect to the same voltage phase. The absolute value of the output torque increases as the rotational speed increases, while the absolute value of the output torque decreases as the rotational speed increases.

  That is, in order to ensure the accuracy of the feedforward control, the voltage phase θff is set according to the voltage phase-torque characteristics reflecting the current values of the motor variables (typically, Nm and VH) indicating the operation state. There is a need to. The reflection of the motor variable can be realized by creating a map including the motor variable as an argument based on the measurement experiment result of the voltage phase-torque characteristic under various operating conditions. However, since this map uses torque command values and motor variables as arguments, it is necessarily a multidimensional map. In order to improve the control accuracy, it is necessary to increase the number of map points. Therefore, there is a concern that the map data becomes enormous and excessively occupies the storage area of the ECU.

  In particular, in the control configuration in which the combination with the feedback control in the rectangular wave voltage control or the combination with the PWM control is performed as in the present embodiment, the storage capacity of data, programs, etc. required for other controls This will increase the above concerns.

  Therefore, in the present embodiment, by configuring the feedforward control unit 440 as follows, the torque calculation equation according to the voltage equation (dq axis) of the motor is stored without storing a huge amount of map data. Based on the calculation, the voltage phase θff by feedforward control is calculated.

  First, the derivation of a torque calculation expression indicating the voltage phase-torque characteristic relationship used for feedforward control will be described. As is generally known, voltage equations and torque equations on d-axis and q-axis in a permanent magnet type synchronous motor are expressed by the following equations (3) to (5).

  In the equations (3) and (4), Ra represents the armature winding resistance, ψ represents the number of armature linkage fluxes of the permanent magnet, and P represents the number of pole pairs of the AC motor M1. Further, ω represents the electrical angular velocity of the AC motor M1. The electrical angular velocity ω can be obtained by ω = 2π · (Nm / 60) · P) using the motor rotation speed Nm (rpm).

  The voltage component depending on the winding resistance contributes in a very low speed region, and other components become dominant as the rotational speed increases. For this reason, when the rectangular wave voltage control is applied in the high speed region (FIG. 2), the winding resistance component in the equations (3) and (4) can be ignored. Therefore, the above equations (4) and (5) are expressed by the following equations (6) and (7) when the rectangular wave voltage control is applied.

  Furthermore, when the rectangular wave voltage control is performed, considering that the fundamental wave component amplitude of the motor applied voltage indicated by the d-axis voltage and the q-axis voltage is 0.78 times the system voltage VH, Equations (6) and (7 ) Expression is applied to the above expression (3), the torque calculation expression (8) indicating the relationship between the voltage phase θ of the rectangular wave voltage and the output torque T of the AC motor M1 can be obtained.

  As understood from the equation (8), the relationship between the voltage phase θ and the torque T in the current operation state is referred to the map by substituting the motor variables VH and ω (Nm) into the torque calculation equation. Instead, it is obtained by calculation. In the equation (8), ψ represents a counter electromotive voltage coefficient of the AC motor M1. Since the constant terms Ka and Kb are fixed in advance, the above equation (8) can be transformed into the following equation (9). That is, the equations (8) and (9) are torque calculation equations using the motor variables VH and ω and the voltage phase θ as variables.

  Since each of the constants Ka and Kb in the formula (9) can be obtained in advance as one constant, it can be stored in the control device 30 (ECU).

  Next, a method for setting the voltage phase θff by feedforward control according to the torque calculation formula (8) will be described.

  Referring to FIG. 8, phase / torque characteristic calculation unit 442 (FIG. 6) uses AC motor M1 for a plurality (n, n: an integer of 3 or more) of voltage phases θ (1) to θ (n). By substituting the current electrical angular velocity ω and the system voltage VH into the equation (8), the corresponding torque values T (1) to T (n) are respectively calculated. For example, the voltage phases θ (1) to θ (n) are predetermined voltage phases set in advance at equal intervals.

  The torque values T (1) to T (n) include a torque value T (k) lower than the torque command value Tqcom and a torque value T (k + 1) higher than the torque command value Tqcom, that is, the torque command value Tqcom. Two sandwiched torque values are included. Preferably, the torque value T (k) is a torque value having a minimum difference from the torque command value Tqcom among torque values lower than the torque command value Tqcom, and the torque value T (k + 1) is a torque command value. Among the torque values higher than Tqcom, the torque value having the smallest difference from the torque command value Tqcom is set. In the example of FIG. 9, T (4) and T (5) correspond to two adjacent torque values sandwiching the torque command value Tqcom with respect to the torque command value Tqcom.

  The phase / torque characteristic calculation unit 442 extracts two torque values T (k) and T (k + 1) and voltage phases θ (k) and θ (k + 1) sandwiching the torque command value Tqcom, and calculates the FF phase. It outputs to the part 445 (FIG. 6).

  The FF phase calculation unit 445 performs voltage interpolation θff corresponding to the torque command value Tqcom by linear interpolation using the extracted torque values T (k) and T (k + 1) and the voltage phases θ (k) and θ (k + 1). Is calculated. In the example of FIG. 8, the voltage phase θff corresponding to the torque command value Tqcom is calculated by linear interpolation using the torque values T (4) and T (5) and the voltage phases θ (4) and θ (5). Is done.

  Next, a processing procedure of rectangular wave voltage control in the AC motor control system according to the embodiment of the present invention will be described with reference to FIGS. A program for executing the processing procedure according to the flowcharts shown in FIGS. 9 and 10 is stored in advance in the control device 30, and is executed at a predetermined cycle by the CPU in the control device when the rectangular wave voltage control is applied. .

  Referring to FIG. 10, when rectangular wave voltage control is applied, control device 30 calculates voltage phase θfb (feed forward term) by feedback control based on torque deviation in step S100. The processing in step S100 corresponds to the functions of the power calculation unit 410, torque calculation unit 420, and PI calculation unit 430 shown in FIG.

  Further, in step S120, control device 30 calculates voltage phase θff (feedforward term) by feedforward control based on motor variable (VH, ω) and torque command value Tqcom. The processing in step S120 corresponds to the function of the feedforward control unit 440 shown in FIG.

  In step S150, control device 30 further calculates voltage phase φv of the rectangular wave voltage according to the sum of feedforward term θff and feedback term θfb. The processing in step S150 corresponds to the function of the adding unit 450 shown in FIG.

  FIG. 10 is a flowchart for explaining in detail the processing procedure in the feedforward control in step S120 of FIG.

  Referring to FIG. 10, in step S <b> 125, control device 30 determines a plurality of voltages at Δθ intervals according to equation (8) in which the current motor variables (typically system voltage VH and electrical angular velocity ω) are substituted. Torque values T (1) to T (n) for the phases θ (1) to θ (n) are calculated.

  Further, in step S126, control device 30 determines two torque values T (k) and T (k + 1) sandwiching torque command value Tqcom from torque values T (1) to T (n) obtained in step S125. Then, voltage phases θ (k) and θ (k + 1) corresponding to the respective torque values are extracted. That is, the processing in steps S125 and S126 corresponds to the function of the phase / torque characteristic calculation unit 442 in FIG.

  In step S127, the controller 30 determines the gradient Δθ / ΔT between the torque values T (k) and T (k + 1) and the voltage phases θ (k) and θ (k + 1) extracted in step S126, that is, the gradient: (Θ (k + 1) −θ (k)) / (T (k + 1) −T (k)) is calculated. In the example of FIG. 8, Δθ / ΔT = (θ (5) −θ (4)) / (T (5) −T (4)).

  Then, in step S128, control device 30 calculates voltage phase θff by using one of voltage phases θ (k) and θ (k + 1) and gradient Δθ / ΔT. For example, using the voltage phase θ (k), a calculation formula of θff = θ (k) + {Tqcom−T (k)} · (Δθ / ΔT) can be applied.

  As described above, according to the rectangular wave voltage control in the control system for an AC motor according to the present embodiment, the map using the motor variable and the torque command value related to the operating state of the AC motor as arguments is not referred to. The voltage phase (feed forward term) corresponding to the torque command value Tqcom can be set based on the calculation according to the torque calculation formula (Equation (8)) into which the current value of the motor variable is substituted. Therefore, it is possible to realize feedforward control that sets the voltage phase corresponding to the torque command value while reflecting the operation state of the AC motor without storing a multidimensional map with a plurality of arguments.

(Variation 1 of rectangular wave voltage control)
FIG. 11 is a block diagram illustrating a control configuration of rectangular wave voltage control according to the first modification of the present embodiment.

  Compared to FIG. 11, in the rectangular wave voltage control unit 400 according to the first modification of the present embodiment, the feedforward control unit 440 includes the phase / torque characteristic calculation unit 442 and the FF phase calculation unit 445. The torque loss estimating unit 446 is further included.

  The torque loss estimation unit 446 estimates the torque loss Tloss in the AC motor M1 based on the current motor state, typically the rotational speed Nm.

  FIG. 12 shows a relationship between the motor rotation speed Nm and the torque loss Tloss in the AC motor M1 as a representative example of the torque loss characteristic with respect to the motor state. The torque loss Tloss corresponds to the amount of torque reduction caused by the loss due to the rotor rotation resistance or the like in the AC motor M1. The torque loss Tloss shows a characteristic that monotonously increases as the motor rotation speed Nm increases. For this reason, even if a map using the motor state as an argument is used, a torque loss estimation unit that reflects the characteristics of FIG. 12 by a one-dimensional map (motor rotational speed-torque loss) that does not increase the map storage capacity so much. 446 can be configured.

  Referring to FIG. 11 again, the phase / torque characteristic calculation unit 442 uses the following equation (10) in which the torque loss Tloss estimated by the torque loss estimation unit 446 is added to the above equation (8). The same function as in FIG. 5 is executed.

  The phase / torque characteristic calculation unit 442 follows the torque calculation formula including the torque loss Tloss in the same manner as in FIG. 5, and torque values T (1) to T (1) to a plurality of predetermined voltage phases θ (1) to θ (n). While calculating T (n), two torque values T (k), T (k + 1) and corresponding voltage phases θ (k), θ (k + 1) sandwiching the torque command value Tqcom are extracted.

  Calculation of voltage phase (feedforward term) θff by FF phase calculation unit 445 and control configuration other than feedforward control unit 440 are the same as in FIG. 5, and therefore detailed description will not be repeated.

  FIG. 13 is a flowchart for explaining the processing procedure of the feedforward control of the rectangular wave voltage control according to the first modification of the present embodiment.

  Compared with FIG. 10, in the feedforward control of the rectangular wave voltage control according to the first modification of the present embodiment, the control device 30 performs the step S <b> 121 according to the current motor state (motor rotational speed Nm), The torque loss Tloss is estimated according to the characteristics shown in FIG.

  Then, in step S125, the control device 30 obtains a predetermined voltage phase θ (1) by equation (10), which is a torque calculation equation reflecting the torque loss Tloss obtained in step S121, as in step S125 of FIG. Torque values T (1) to T (n) for .about..theta. (N) are calculated. Since the subsequent steps S126 to S128 are the same as those in FIG. 10, the description thereof will not be repeated.

  According to the rectangular wave voltage control according to the first modification of the present embodiment, the feedforward control can be executed by further reflecting the torque loss according to the motor state (rotational speed), so that the control accuracy can be improved.

(Variation 2 of rectangular wave voltage control)
FIG. 14 is a block diagram showing a control configuration of rectangular wave voltage control according to the second modification of the present embodiment.

  Compared to FIG. 5, in the rectangular wave voltage control unit 400 according to the second modification of the present embodiment, the feedforward control unit 440 is added to the phase / torque characteristic calculation unit 442 and the FF phase calculation unit 445. The parameter correction unit 448 is further included.

  The parameter correction unit 448 corrects the motor constant parameter in the torque calculation formula (8) based on the current motor state, typically the motor currents Id and Iq.

  FIG. 15 shows the relationship between the d-axis and q-axis inductances Ld and Lq with respect to the d-axis current Id and the q-axis current Iq as a representative example of the change characteristic of the motor constant parameter with respect to the motor state. As shown in the figure, the inductances Ld and Lq have characteristics that monotonously decrease as the motor currents Id and Iq increase. For this reason, even if a map having the motor state as an argument is used, the parameter correction unit 448 reflecting the characteristics of FIG. 15 is configured by a one-dimensional map (motor current-inductance) that does not increase the map storage capacity so much. can do.

  Referring to FIG. 14 again, the phase / torque characteristic calculation unit 442 includes a predetermined voltage according to the set torque calculation formula in which the motor constant parameters (inductances Ld and Lq) in the formula (8) are variably set by the parameter correction unit 448. Calculation of torque values T (1) to T (n) for the phases θ (1) to θ (n) is executed. Then, two torque values T (k), T (k + 1) and corresponding voltage phases θ (k), θ (k + 1) sandwiching the torque command value Tqcom are extracted.

  The calculation of voltage phase (feedforward term) θff by FF phase calculation unit 445 and the control configuration other than feedforward control unit 440 are the same as in FIG. 8, and therefore detailed description will not be repeated.

  FIG. 16 is a flowchart for explaining the processing procedure of the feedforward control of the rectangular wave voltage control according to the second modification of the present embodiment.

  FIG. 16 is compared with FIG. 10, in the feedforward control of the rectangular wave voltage control according to the second modification of the present embodiment, the control device 30 responds to the current motor state (motor currents Id and Iq) in step S122. , (8) Motor constant parameters in equation are corrected. Then, in step S125, control device 30 performs torque value T (for a predetermined voltage phase θ (1) to θ (n) according to equation (8) in which the motor constant parameter is corrected based on the processing in step S122. 1) to T (n) are calculated. Subsequent steps S126 to S128 are the same as those in FIG. 10, and detailed description thereof will not be repeated.

  According to the rectangular wave voltage control according to the second modification of the present embodiment, it is possible to improve the accuracy of the torque calculation formula by reflecting the change in the motor constant parameter corresponding to the motor state (motor rotation speed). As a result, the control accuracy of the feedforward control of the rectangular wave voltage control can be improved.

  In the feedforward control of the rectangular wave voltage control according to the present embodiment, two torque values T (k) sandwiching the torque command value Tqcom by the phase / torque characteristic calculation unit 442 (FIGS. 5, 11, and 14) are used. ) And T (k + 1) extraction are not limited to the above examples. For example, the predetermined voltage phases θ (1) to θ (n) are not necessarily equal intervals.

  In the present embodiment, as a preferable configuration example, DC voltage generation unit 10 # of the motor control system includes buck-boost converter 12 so that the input voltage (system voltage VH) to inverter 14 can be variably controlled. However, as long as the input voltage to inverter 14 can be variably controlled, DC voltage generation unit 10 # is not limited to the configuration exemplified in this embodiment. Further, it is not always indispensable that the inverter input voltage is variable, and the present invention is also applied to a configuration in which the output voltage of the DC power supply B is directly input to the inverter 14 (for example, a configuration in which the step-up / down converter 12 is omitted). The invention can be applied. Further, the motor variable reflected in the torque calculation formula is not limited to the above description (Nm and VH).

  Further, with regard to the AC motor serving as a load of the motor control system, in the present embodiment, a permanent magnet motor mounted for driving a vehicle on an electric vehicle (hybrid vehicle, electric vehicle, etc.) is assumed. The present invention can also be applied to a configuration in which an arbitrary AC motor used in the above is used as a load.

  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.

1 is an overall configuration diagram of an AC motor control system according to an embodiment of the present invention. FIG. It is a conceptual diagram explaining the control system used for the power conversion in the inverter in the motor control system shown in FIG. It is a conceptual diagram which shows the rough relationship between the driving | running state of an alternating current motor, and control mode. It is a control block diagram of sine wave PWM control and overmodulation PWM control. It is a block diagram which shows the control structure of the rectangular wave voltage control by this Embodiment. It is a conceptual diagram which shows the correspondence of the voltage phase and torque in rectangular wave voltage control. It is an extension figure explaining the change of the voltage phase-torque characteristic with respect to the driving | running state of an alternating current motor. It is a conceptual diagram explaining the setting method of the voltage phase by the feedforward control of the rectangular wave voltage control by this Embodiment. It is a flowchart explaining the process sequence of the rectangular wave voltage control by this Embodiment. It is a flowchart explaining the processing procedure of the feedforward control of the rectangular wave voltage control by this Embodiment. It is a block diagram which shows the control structure of the rectangular wave voltage control by the modification 1 of this Embodiment. It is a conceptual diagram which shows the torque loss characteristic with respect to a motor state. It is a flowchart explaining the processing procedure of the feedforward control of the rectangular wave voltage control by the modification 1 of this Embodiment. It is a block diagram which shows the control structure of the rectangular wave voltage control by the modification 2 of this Embodiment. It is a conceptual diagram which shows an example of the change characteristic of the motor constant with respect to an electric motor state. It is a flowchart explaining the process sequence of the feedforward control of the rectangular wave voltage control by the modification 2 of this Embodiment.

Explanation of symbols

  5 Ground wire, 6, 7 Power line, 10, 13 Voltage sensor, 10 # DC voltage generator, 12 Buck-boost converter, 13 Voltage sensor, 14 Inverter, 15-17 Each phase arm (U, V, W), 24 Current Sensor, 25 rotation angle sensor, 30 control unit (ECU), 100 motor control system, 200 PWM control unit, 210 current command generation unit, 220, 250 coordinate conversion unit, 240 PI calculation unit, 260, 350 PWM signal generation unit, 300 control mode determination unit, 310 command value generation unit, 400 rectangular wave voltage control unit, 410 power calculation unit, 420 torque calculation unit, 430 PI calculation unit, 440 feedforward control unit, 442 phase / torque characteristic calculation unit, 445 FF Phase calculation unit, 446 torque loss estimation unit, 448 parameter correction unit, 450 addition Unit, 460 rectangular wave generator, 470 signal generation unit, ANG rotation angle, B DC power supply, C0, C1 smoothing capacitor, D1-D8 antiparallel diode, Id, Iq Motor current (d axis, q axis), Idcom, Iqcom Current command value (d axis, q axis), iu, iv, iw Motor current (each phase current), L1 reactor, M1 AC motor, Nm motor rotational speed, Pmt motor power, Q1-Q8 switching element for power, S1- S8 switching control signal, SR1, SR2 system relay, T (1) to T (n) torque value, Tloss torque loss, Tq torque estimated value, Tqcom torque command value, Vb DC voltage (battery voltage), Vd # d-axis voltage Command value, VH DC voltage (system voltage), VH # voltage command value, Vq # q-axis voltage command value, Vu, Vv Vw Each phase voltage command value, ΔId, ΔIq Current deviation (d axis, q axis), ΔTq Torque deviation, θ (1) to θ (n) voltage phase, θff voltage phase (feed forward term), θv voltage phase (rectangular) Wave voltage), φfb voltage phase (feedback term), ω electrical angular velocity.

Claims (6)

An inverter that converts a DC voltage into an AC voltage for driving an AC motor;
A converter that variably controls the DC voltage input to the inverter according to a voltage command value;
Application from the inverter to the AC motor based on at least one motor variable related to the operating state of the AC motor and the torque command value so that the AC motor outputs a torque according to a torque command value A first motor controller configured to set a voltage phase of the rectangular wave voltage to be
The first motor control unit includes:
In accordance with a torque calculation formula using the motor variable and the voltage phase as variables, a first phase that is the voltage phase corresponding to a first torque value that is lower than the torque command value, and a first phase that is higher than the torque command value. A phase torque characteristic calculator configured to obtain a second phase that is the voltage phase at a torque value of 2,
Based on the ratio between the difference between the first and second torque values and the difference between the first and second phases, and one of the first and second phases, the torque command value corresponds to the torque command value. A control system for an AC motor, comprising: a phase calculation unit configured to calculate a voltage phase.   The phase torque characteristic calculation unit calculates a plurality of torque values for a plurality of predetermined voltage phases by substituting a current value of the motor variable into the torque calculation formula, and among the plurality of torque values, Among the torque values lower than the torque command value, one that has the smallest difference from the torque command value is set as the first torque value, and among the torque values higher than the torque command value, 2. The control system for an AC motor according to claim 1, wherein the second torque value is set to the other one having the smallest difference from the torque command value. The first motor control unit includes:
A loss estimation unit configured to estimate torque loss in the AC motor according to an operating state of the AC motor;
3. The AC motor according to claim 1, wherein the phase torque characteristic calculation unit sets the first and second torque values according to the torque calculation formula and the torque loss estimated by the loss estimation unit. Control system. The first motor control unit includes:
A parameter estimation unit configured to correct a constant parameter of the torque calculation equation according to an operating state of the AC motor;
The AC according to claim 1 or 2, wherein the phase torque characteristic calculation unit sets the first and second torque values according to the torque calculation formula to which the constant parameter corrected by the parameter estimation unit is applied. Electric motor control system. A second phase control unit configured to control a voltage phase of the rectangular wave voltage based on a torque deviation of the AC motor with respect to the torque command value so that the AC motor outputs a torque according to the torque command value. A motor control unit;
2. The AC motor control system according to claim 1, wherein the voltage phase command value is set according to a sum of set values by the first and second motor control units.   The control system for an AC motor according to claim 1, wherein the AC motor is configured to be mounted on an electric vehicle and generate a vehicle driving force of the electric vehicle.

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