JP5482574B2 - AC motor control system - Google Patents

Description

  The present invention relates to an AC motor control system, and more particularly to an AC motor control in which a control mode is switched between rectangular wave control and pulse width modulation control (PWM control).

  In order to drive and control an AC motor using a DC power supply, a drive system 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.

  In addition to PWM control, rectangular wave control in which a one-pulse switching waveform is applied to the AC motor according to the electrical angle is also applied. In the rectangular wave control, since the fundamental wave component of the motor applied voltage is larger than that in the PWM control, a high output can be obtained particularly in a region where the motor rotation speed is high.

  Japanese Patent Laying-Open No. 2006-320039 (Patent Document 1) describes AC motor control that selectively applies PWM control and rectangular wave control. For PWM control, in addition to sine wave PWM control, overmodulation PWM control in which the amplitude of the AC voltage command is larger than that of sine wave PWM control is further used.

  In particular, Patent Document 1 considers that the control response of rectangular wave control is not so high, and improves the controllability of the motor current by changing the motor applied voltage in response to a sudden change in the motor rotation speed. Is described.

  Japanese Patent Laying-Open No. 2010-81660 (Patent Document 2) describes that control mode switching from rectangular wave control to PWM control (overmodulation PWM control) is determined based on an actual current phase. . In particular, Patent Document 2 discloses that the current phase of the instantaneous current itself is added to the control mode switching corresponding to the steady operation state based on the current phase of the smoothed current obtained by filtering the harmonic component of the instantaneous current. It is described that control mode switching corresponding to a transient operation state based on the above is performed.

JP 2006-320039 A JP 2010-81660 A

  As described in Patent Document 1, since only the phase of the voltage pulse can be controlled by the rectangular wave control, the control responsiveness is lower than the PWM control that can control both the amplitude and the phase of the AC voltage. Further, in the rectangular wave control, the frequency of the voltage pulse corresponds to the rotational frequency of the AC motor, and therefore a control cycle is provided corresponding to the electrical angle of the AC motor. For this reason, compared with the control period in PWM control corresponding to the period of the carrier signal, the control period in rectangular wave control tends to be longer. In particular, when the rectangular wave control is applied in the low rotation speed region, the control cycle may be further prolonged, and the control responsiveness may be reduced.

  According to Patent Document 2, overcurrent and overvoltage are improved by improving controllability by switching from rectangular wave control to PWM control (overmodulation PWM) by transient control mode switching based on the current phase of instantaneous current. It is expected to prevent. However, at the low rotation speed, the control mode switching determination cycle becomes longer as well as the control cycle, and there is a possibility that the control mode switching from the rectangular wave control to the PWM control cannot be executed effectively.

  The present invention has been made to solve such problems, and the object of the present invention is to prevent the occurrence of overcurrent and overvoltage even if a control disturbance occurs in the AC motor when rectangular wave control is applied. It is to be.

  According to an aspect of the present invention, an AC motor control system includes an inverter, a rectangular wave control unit, a pulse width modulation control unit, and a control mode selection unit. The inverter controls the voltage applied to the AC motor that is electrically connected between the DC power source and the AC motor. The rectangular wave control unit generates a control command for the inverter according to rectangular wave control for controlling the voltage phase of the rectangular wave voltage applied to the AC motor so that the AC motor is operated according to the operation command. The pulse width modulation control unit generates an inverter control command by pulse width modulation control based on a comparison between a carrier wave and an AC voltage command for operating the AC motor according to the operation command. The control mode selection unit selects one of the rectangular wave control and the pulse width modulation control. When the rectangular wave control is selected and the operation area of the AC motor is within the predetermined area, the control mode selection unit sets the control mode to the rectangular wave control according to the change in the rotational speed of the AC motor. To pulse width modulation control.

  Preferably, when the rectangular wave control is selected and the operation region of the AC motor is outside the predetermined region, the control mode selection unit according to the phase of the current flowing between the inverter and the AC motor. The control mode is switched from rectangular wave control to pulse width modulation control.

  More preferably, the predetermined region includes a region where the rotational speed of the AC motor is lower than a predetermined value.

  More preferably, the predetermined region includes a region where the rotational speed of the AC motor is lower than a predetermined value and the torque of the AC motor is higher than a predetermined value.

  Preferably, the AC motor is configured to generate a driving torque of driving wheels of the electric vehicle. When the rectangular wave control is selected and the operation region of the AC motor is within the predetermined region, the control mode selection unit detects the slip or grip of the drive wheel when the AC motor is detected. A change in rotational speed is detected, and the control mode is switched from rectangular wave control to pulse width modulation control.

  According to this invention, even if a control disturbance occurs in the AC motor when the rectangular wave control is applied, it is possible to prevent the occurrence of an overcurrent or an overvoltage.

1 is an overall configuration diagram of an AC motor control system according to an embodiment of the present invention. FIG. It is a figure which illustrates roughly the control mode in the control system of the alternating current motor by embodiment of this invention. It is a conceptual diagram explaining the rough correspondence of the driving | running area | region of AC motor, and control mode. It is a wave form diagram explaining the example of generation | occurrence | production of the overcurrent at the time of rectangular wave control application. It is a functional block diagram which shows the control structure of the AC motor by embodiment of this invention. FIG. 6 is a functional block diagram illustrating in detail a configuration example of a PWM control unit illustrated in FIG. 5. FIG. 6 is a functional block diagram illustrating in detail a configuration example of a rectangular wave control unit illustrated in FIG. 5. It is a flowchart which shows the process sequence of the switching process of the control mode between PWM control and rectangular wave control in embodiment of this invention. It is a conceptual diagram explaining the control mode switching from the rectangular wave control in a specific driving | operation area | region. It is a conceptual diagram explaining the control mode switching determination from rectangular wave control to PWM control based on the current phase.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description, 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.

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, and a control device 30.

  AC electric motor M1 is, for example, for traveling for generating driving torque of driving wheels of an electric vehicle (referred to as a vehicle that generates vehicle driving force by electric energy such as a hybrid vehicle, an electric vehicle, and a fuel cell vehicle). It is a motor. Alternatively, AC electric motor M1 may be configured to have a function of a generator driven by an engine, or may be configured to have both functions of an electric motor and a generator. Further, AC electric motor M1 may operate as an electric motor for the engine, and may be incorporated in a hybrid vehicle so as to have a starter function for starting the engine, for example. That is, in the present embodiment, the “AC motor” includes an AC drive motor, a generator, and a motor generator (motor generator).

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

  The DC power supply B is typically configured by a secondary battery (such as nickel metal hydride or lithium ion) or a power storage device of a power storage device. The DC voltage Vb output from the DC power supply B and the input / output DC current Ib are detected by the voltage sensor 10 and the current sensor 11, respectively.

  System relay SR 1 is connected between the positive terminal of DC power supply B and power line 6, and system relay SR 1 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 a signal SE from control device 30.

  Converter 12 includes a reactor L1, power semiconductor switching elements Q1, Q2, and diodes D1, D2. Power semiconductor switching elements Q 1 and Q 2 are connected in series between power line 7 and ground line 5. On / off of power semiconductor switching elements Q 1 and Q 2 is controlled by switching control signals S 1 and S 2 from control device 30.

  In this embodiment, power semiconductor switching elements (hereinafter simply referred to as “switching elements”) include IGBTs (Insulated Gate Bipolar Transistors), power MOS (Metal Oxide Semiconductor) transistors, or power bipolar transistors. 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.

  Smoothing capacitor C 0 is connected between power line 7 and ground line 5. Voltage sensor 13 detects the voltage across smoothing capacitor C 0, that is, DC voltage VH of power line 7, and outputs the detected value to control device 30. Hereinafter, the DC voltage VH corresponding to the DC side voltage of the inverter 14 is also referred to as a system voltage VH.

  Inverter 14 is electrically connected between DC voltage generating unit 10 # and AC electric motor M1. Inverter 14 includes a U-phase upper and lower arm 15, a V-phase upper and lower arm 16, and a W-phase upper and lower arm 17 provided in parallel between power line 7 and ground line 5. Each phase upper and lower arm is constituted by a switching element connected in series between the power line 7 and the ground line 5. For example, the U-phase upper and lower arms 15 are composed of switching elements Q3 and Q4, the V-phase upper and lower arms 16 are composed of switching elements Q5 and Q6, and the W-phase upper and lower arms 17 are composed of 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.

  Typically, AC motor M1 is a three-phase permanent magnet type synchronous motor, and is configured by commonly connecting one end of three U, V, and W-phase stator coils to a neutral point. Furthermore, the other end of each phase coil is connected to the midpoint of the switching elements of the upper and lower arms 15 to 17 of each phase.

  Converter 12 is configured to perform bidirectional DC voltage conversion between DC voltages Vb and VH by on / off control of switching elements Q1 and / or Q2. The voltage conversion ratio (VH / Vb) by converter 12 is controlled according to the duty ratio of switching elements Q1, Q2. Specifically, voltage command value VHr is set according to the state of AC electric motor M1, and the duty ratio in converter 12 is controlled based on the detected values of DC voltages VH and Vb. When it is not necessary to boost DC voltage VH from DC voltage Vb, VH = Vb (voltage conversion ratio = 1.0) is set by fixing switching elements Q1 and Q2 to ON and OFF, respectively. You can also.

  In converter 12, basically, switching elements Q1 and Q2 are controlled to be turned on and off in a complementary manner in each switching period. In this way, the DC voltage VH can be controlled to the voltage command value VHr in accordance with both charging and discharging of the DC power supply B without switching the control operation in particular according to the current direction of the converter 12. .

  Current sensor 24 detects a motor current (phase 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 to detect

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

  The control device 30 is composed of an electronic control unit (ECU), and performs motor processing by executing software stored in advance by a CPU (Central Processing Unit) (not shown) and / or hardware processing by a dedicated electronic circuit. The operation of the control system 100 is controlled.

  Specifically, control device 30 controls inverter 14 and converter 12 such that AC electric motor M1 operates in accordance with torque command value Trqcom. Control device 30 includes torque command value Trqcom, DC voltage Vb detected by voltage sensor 10, system voltage VH detected by voltage sensor 13, motor currents iu and iw detected by current sensor 24, and a rotation angle sensor. The rotation angle θ from 25 is input. Based on these input signals, control device 30 controls switching control signals S1 and S2 for controlling DC voltage conversion by converter 12 and switching control signals S3 to S3 for controlling DC / AC voltage conversion by inverter 14. S8 is generated.

  In the electric vehicle, the torque command value Trqcom of AC electric motor M1 is set as part of the traveling control for controlling the traveling of the electric vehicle so that acceleration or deceleration according to the accelerator operation and the brake operation of the user is realized. For example, when AC electric motor M1 is a traveling motor, Trqcom> 0 is set during vehicle acceleration, while Trqcom <0 is set during regenerative braking. 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. When charging of DC power supply B is prohibited, Trqcom = 0 is set so that regenerative power is not generated even during deceleration.

  When the torque command value is positive (Trqcom> 0), inverter 14 converts the DC voltage from smoothing capacitor C0 into an AC voltage by switching operations of switching elements Q3 to Q8 in response to switching control signals S3 to S8. Then, AC motor M1 is driven so as to output a positive torque.

  Further, when the torque command value is zero (Trqcom = 0), the inverter 14 generates a rotating magnetic field that makes the output torque of the AC motor M1 zero by switching operation in response to the switching control signals S3 to S8. Is controlled to occur.

  Further, when the torque command value is negative (Trqcom <0), inverter 14 converts the AC voltage generated by AC electric motor M1 into a DC voltage by a switching operation in response to switching control signals S3 to S8. The converted DC voltage (system voltage) is supplied to the converter 12 via the smoothing capacitor C0.

  Converter 12 controls system voltage VH to voltage command value VHr by switching control (duty control) of switching elements Q1, Q2 in response to switching control signals S1, S2. Through this voltage control, the DC power source B is charged according to the surplus power in the power line 7 and the DC power source B is discharged according to the insufficient power in the power line 7.

(Description of control mode)
The control of AC motor M1 by control device 30 will be described in further detail.

  FIG. 2 is a diagram schematically illustrating a control mode in the AC motor control system according to the embodiment of the present invention.

  As shown in FIG. 2, in the motor control system 100 according to the embodiment of the present invention, three control modes are switched and used for control of the AC motor M1, that is, power conversion in the inverter.

  As shown in FIG. 2, in the motor control system 100 according to the embodiment of the present invention, three control modes are switched and used for control of the AC motor M1, that is, power conversion in the inverter.

  The sine wave PWM control is used as general PWM control, and controls on / off of each phase upper and lower arm elements according to a voltage comparison between a sine wave voltage command and a carrier wave (typically a triangular wave). 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.

  As is well known, in the sinusoidal PWM control in which the amplitude of the sinusoidal voltage command is limited to a range below the carrier wave amplitude, the fundamental wave of the applied voltage to the AC motor M1 (hereinafter also simply referred to as “motor applied voltage”). The component can only be increased to about 0.61 times the DC link voltage of the inverter. Hereinafter, in this specification, the ratio of the fundamental component (effective value) of the motor applied voltage (line voltage) to the DC link voltage (that is, the system voltage VH) of the inverter 14 is referred to as “modulation rate”. In the sine wave PWM control, since the amplitude of the voltage command of the sine wave is in the range below the carrier wave amplitude, the line voltage applied to the AC motor M1 becomes a sine wave.

  On the other hand, in the rectangular wave control, one pulse of the rectangular wave with 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.

  The overmodulation PWM control performs PWM control similar to the sine wave PWM control in a range where the amplitude of the voltage command (sine wave component) 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 (amplitude correction), and the modulation rate can be increased from the maximum modulation rate in the sine wave PWM control to a range of 0.78. it can. In overmodulation PWM control, since the amplitude of the voltage command (sine wave component) is greater than the carrier wave amplitude, the line voltage applied to AC motor M1 is not a sine wave but a distorted voltage.

  In the AC motor M1, the induced voltage increases as the rotational speed and the output torque increase, so 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, either PWM control (sine wave PWM control or overmodulation PWM control) or rectangular wave control is selectively applied according to the state of AC electric motor M1. The selection of the control mode shown in FIG. 2, that is, the control mode switching determination will be described in detail later.

  In the rectangular wave control, since the amplitude of the motor applied voltage is fixed, the only controllable parameter is the phase of the motor applied voltage. Further, since the control cycle is determined according to the electrical angle of AC electric motor M1, the control cycle becomes longer as the rotational speed decreases. In rectangular wave control, when executing torque feedback control that directly controls the phase of the rectangular wave voltage pulse based on the deviation between the target torque command value and the actual torque value, and in the same way as PWM control, The phase of the motor applied voltage may be controlled by feedback.

  FIG. 3 is a conceptual diagram illustrating a schematic correspondence relationship between the operation range of the AC motor and the control mode.

  Referring to FIG. 3, the operating range of AC electric motor M1 is indicated by a combination of rotational speed and torque. The output (power) of AC electric motor M1 is represented by the product of rotational speed and torque. Schematically, rectangular wave control is used in the high output region.

  Here, an electric vehicle equipped with AC electric motor M1 as a traveling motor is assumed. When both the accelerator pedal and the brake pedal are operated at a low rotational speed of the AC motor M1, the AC motor M1 operates at the operating point P1. The operating point P1 is originally located in a relatively low rotational speed and high torque region in an operating region where rectangular wave control is applied.

  As a result, since the rectangular wave control is applied at a low rotational speed, the control responsiveness may be reduced. Under such conditions, if a control disturbance such as a sudden change in the rotational speed of the AC motor M1 due to the occurrence of slip or grip occurs, the actual output torque deviates from the torque command value even if the torque command value is constant. There is a risk of it. As a result, as shown in FIG. 4, the phase current of AC electric motor M <b> 1 increases, and an overcurrent that exceeds the specified value Imax may occur.

  On the other hand, when the vehicle decelerates from the operating point P1, that is, when the rotational speed of the AC motor M1 further decreases, the control mode is switched from rectangular wave control to PWM control (overmodulation PWM). When PWM control (overmodulation PWM) is applied, it is expected to prevent overcurrent and overvoltage by improving controllability. However, when the rectangular wave control is applied at a low rotational speed, there is a concern that the cycle for determining whether or not the control mode switching is necessary becomes longer as well as the control cycle. For this reason, in the determination of the control mode switching based on the actual current phase as in Patent Document 2, the switching from the rectangular wave control to the PWM control (overmodulation PWM) is delayed, so that the inverter and / or the AC motor is overloaded. There is a risk of current and overvoltage.

  Therefore, in the motor control system 100 according to the embodiment of the present invention, the control mode is switched so as not to cause such a problem at the low rotational speed.

  FIG. 5 is a functional block diagram showing a control configuration of the AC motor according to the embodiment of the present invention.

  Referring to FIG. 5, control device 30 includes a PWM control unit 200, a control mode selection unit 300, and a rectangular wave control unit 400. In PWM control unit 200, sine wave PWM control and overmodulation PWM control are selectively executed.

  FIG. 6 is a functional block diagram showing in detail a configuration example of the PWM control unit 200 shown in FIG.

  Referring to FIG. 6, PWM control unit 200 includes a current command generation unit 210 and a feedback control unit 290. Feedback control unit 290 includes coordinate conversion units 220 and 250, voltage command generation unit 240, and PWM modulation unit 260.

  Current command generation unit 210 generates a d-axis current command value Idcom and a q-axis current command value Iqcom according to torque command value Trqcom 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 θ of the AC motor M1 detected by the rotation angle sensor 25. From each phase current calculated from iw, a d-axis current value Id and a q-axis current value Iq in the dq-axis plane are calculated. At this time, a filtering process for removing harmonic components of the current may be combined.

  The voltage command generator 240 receives the d-axis current deviation ΔId (ΔId = Idcomf−Id) and the q-axis current deviation ΔIq (ΔIq = Iqcomf−Iq) relative to the q-axis current command value. The In voltage command generation unit 240, for each of deviations ΔId and ΔIq, a PI (proportional integration) operation with a predetermined gain is performed to obtain a control deviation. Voltage command generation unit 240 generates a d-axis voltage command value Vd # and a q-axis voltage command value Vq # according to the control deviation.

  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 θ of the AC motor M1. Each phase voltage command Vu, Vv, Vw of the phase is converted.

  The PWM modulation unit 260 controls on / off of the upper and lower arm elements of each phase of the inverter 14 based on a comparison between a carrier wave having a fixed period (not shown) and an AC voltage command (which comprehensively indicates Vu, Vv, Vw). Switching control signals S3 to S8 are generated.

  When the inverter 14 is subjected to switching control according to the switching control signals S3 to S8, an AC voltage (pseudo sine wave voltage) for outputting torque according to the torque command value Trqcom is applied to the AC motor M1.

  When the sine wave PWM control is selected, the PWM control unit 200 outputs a voltage according to the torque command value Trqcom by the feedback control of the d-axis current and the q-axis current shown in FIG. Command values Vd # and Vq # are generated. When overmodulation PWM control is selected, a function for correcting voltage amplitude is added to the feedback loop shown in FIG. Thereby, the voltage commands Vu, Vv, Vw of each phase are corrected to be larger than the amplitude according to the voltage command values Vd #, Vq #. As a result, the fundamental wave component of the voltage command value can thereby be increased, and a larger output than the sine wave PWM control can be generated.

  FIG. 7 is a functional block diagram showing in detail a configuration example of the rectangular wave control unit 400 shown in FIG.

  Referring to FIG. 7, rectangular wave control unit 400 includes power calculation unit 410, torque calculation unit 420, PI calculation unit 430, rectangular wave generator 440, signal generation unit 450, and coordinate conversion unit 460. including.

  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

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 θ 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)
Torque deviation ΔTq (ΔTq = Trqcom−Tq) with respect to torque command value Trqcom is input to PI calculation unit 430. PI calculation unit 430 performs PI calculation with a predetermined gain on torque deviation ΔTq to obtain a control deviation, and sets phase φv of the rectangular wave voltage according to the obtained control deviation. Specifically, when positive torque is generated (Trqcom> 0), the voltage phase is advanced when torque is insufficient, while when the torque is excessive, the voltage phase is delayed, and when negative torque is generated (Trqcom <0), the voltage phase is increased when torque is insufficient. While delaying, the voltage phase is advanced when the torque is excessive.

  The rectangular wave generator 440 generates each phase voltage command (rectangular wave pulse) Vu, Vv, Vw according to the voltage phase φv set by the PI calculation unit 430. The signal generator 450 generates switching control signals S3 to S8 according to the phase voltage commands Vu, Vv, and Vw. When inverter 14 performs a switching operation according to switching control signals S3 to S8, a rectangular wave pulse according to voltage phase φv is applied as each phase voltage of AC electric motor M1.

  The rectangular wave control unit 400 can control the torque of the AC motor M <b> 1 by torque (power) feedback control. Note that, in the power calculation (equation (1)) in the power calculation unit 410, a filter process for removing distortion components from the detected motor current (iv, iw) is also executed. Alternatively, the torque deviation ΔTq may be obtained based on the detection value of the torque sensor by arranging a torque sensor instead of the power calculation unit 410 and the torque calculation unit 420.

  The coordinate conversion unit 460 performs coordinate conversion (3 phase → 2 phase) based on each phase current obtained from the V phase current iv and W phase current iw by the current sensor 24 and the rotation angle θ of the AC motor M1. , D-axis current Id and q-axis current Iq are calculated. Then, the coordinate conversion unit 460 outputs the d-axis current Id and the q-axis current Iq to the control mode selection unit 300. Note that the function of the coordinate conversion unit 460 can also be realized by operating the coordinate conversion unit 220 of the PWM control unit 200 during the rectangular wave control.

  Again referring to FIG. 5, control mode selection unit 300 includes system voltage VH, voltage command values Vd # and Vq # (from PWM control unit 200), and d-axis currents Id and Iq (rectangular wave control unit). 400) and the rotational speed Nm and torque Trq of AC electric motor M1 are input. The rotation speed Nm can be obtained from the output of the rotation angle sensor 25. For the torque Trq, a torque command value Trqcom may be used. As described later, control mode selection unit 300 performs control mode switching determination from PWM control to rectangular wave control based on the modulation factor calculated from system voltage VH and voltage command values Vd # and Vq #. Further, the control mode selection unit 300 performs control mode switching determination from the rectangular wave control to the PWM control based on the current phase φi obtained from the d-axis current Id and the q-axis current Iq during the rectangular wave control.

  When the control mode selection unit 300 selects the rectangular wave control, the switching control signals S <b> 3 to S <b> 8 generated by the rectangular wave control unit 400 are supplied to the inverter 14. On the other hand, when the control mode selection unit 300 selects PWM control, the switching control signals S <b> 3 to S <b> 8 generated by the PWM control unit 200 are supplied to the inverter 14.

  Next, selection of a control mode by the control mode selection unit 300 will be described in detail with reference to FIG. Each step in the flowchart shown in FIG. 8 is realized by executing a program stored in advance in the control device 30 at a predetermined cycle. Alternatively, for some steps, it is also possible to implement processing by constructing dedicated hardware (electronic circuit). The control process shown in FIG. 8 is executed for each control cycle.

  Referring to FIG. 8, control device 30 determines in step S100 whether the current control mode is a rectangular wave control mode. When the current control mode is PWM control (NO determination in S100), control device 30 executes control mode switching determination from PWM control to rectangular wave control in steps S110 to S130. On the other hand, when the current control mode is rectangular wave control (when YES is determined in S100), control device 30 executes control mode switching determination from rectangular wave control to PWM control in steps S210 to S240.

  First, the control mode switching determination from PWM control to rectangular wave control will be described. In step S110, control device 30 calculates voltage command values Vd # and Vq # by a control calculation according to the feedback control shown in FIG. In step S120, control device 30 converts system voltage VH into an AC voltage applied to AC motor M1 based on voltage command values Vd #, Vq # and system voltage VH calculated in step S110. The modulation factor is calculated.

For example, the modulation rate FM is calculated by the following equation (3).
FM = {(Vd # ² + Vq # ² ) ^1/2 } / VH (3)
In step S130, the control device 30 determines whether or not the modulation factor obtained in step S120 is 0.78 or more. When modulation rate ≧ 0.78 (when S130 is YES), control device 30 cannot generate an appropriate AC voltage in PWM control, and therefore proceeds to step S200 to perform rectangular wave control. Switch the control mode to select. On the other hand, when modulation factor <0.78 (NO in S130), control device 30 proceeds to step S300 and continuously selects PWM control. When PWM control is selected, control device 30 determines whether to use sine wave PWM control or overmodulation PWM control in step S310. Note that overmodulation PWM is applied in the first control cycle when the rectangular wave control mode is switched to the PWM control mode. Thereafter, in step S310, depending on whether the modulation rate based on the voltage command values Vd # and Vq # belongs to the modulation rate range in each of the sine wave PWM control and the overmodulation PWM control shown in FIG. Thus, one of the sine wave PWM and the overmodulation PWM is selected.

  Next, control mode switching determination from rectangular wave control to PWM control will be described. In the rectangular wave control, since the voltage amplitude is constant, control mode switching cannot be determined based on the modulation rate. Therefore, basically, control mode switching is determined based on the current phase.

  When the rectangular wave control is selected (YES in S100), control device 30 proceeds to step S210 to determine whether or not AC electric motor M1 is operating in a predetermined operating region.

  Referring to FIG. 9, the predetermined area 330 used for the determination in step S <b> 210 is a “low speed area” in which the rotation speed is lower than a predetermined threshold value Nth. Alternatively, the predetermined region 330 is a “low speed and high torque region” where the rotational speed <Mth and the torque> Tth.

  The rotation speed threshold value Nth can be determined experimentally based on the correspondence between the control period in rectangular wave control and the decrease in control responsiveness. On the other hand, the torque threshold Tth can be set in correspondence with a torque region that leads to an overcurrent or overvoltage when the control responsiveness decreases.

  Referring to FIG. 8 again, control device 30 sets the current phase in steps S220 and S230 when NO is determined in step S210, that is, when the operating range of AC electric motor M1 is outside predetermined region 330 (FIG. 9). Based on the normal switching judgment based on this.

  Here, a normal control mode switching determination from the rectangular wave control to the PWM control based on the current phase will be described with reference to FIG.

  Referring to FIG. 10, the current phase of AC electric motor M1 is defined by the following equation (4) according to the ratio of d-axis current Id and q-axis current Iq.

φi = tan ⁻¹ (Iq / Id) (4)
When current phase φi changes beyond the preset switching line 320 to the retard side, control mode switching from rectangular wave control to PWM control is instructed. The switching line 320 is set on the retard side with respect to the maximum efficiency phase line 310 corresponding to a set of current phases where the torque is maximum for the same current amplitude.

  As shown in Patent Document 2, it is preferable to calculate the current phase φi compared with the switching line 320 based on the current value after filtering for removing the harmonic current. In this case, in addition to the switching line 320, it is preferable to further provide an emergency switching line 325 that is compared with the current phase of the instantaneous current before filtering. The switching line 320 corresponds to the stationary switching line in Patent Document 2, and the switching line 325 corresponds to the transient switching reference line in Patent Document 2.

  Referring to FIG. 8 again, in step S220, control device 30 calculates current phase φi according to equation (4) based on d-axis current Id and q-axis current Iq. Further, in step S230, control device 30 determines whether or not current phase φi calculated in step S220 is more retarded than switching line 320 (FIG. 10).

  Then, when current phase φi is retarded from switching line 320 (when YES is determined in S230), control device 30 proceeds to step S300 to instruct control mode switching to PWM control. . On the other hand, when current phase φi is not retarded from switching line 320 (when NO is determined in S230), control device 30 proceeds to step S300 and continuously selects rectangular wave control.

  In contrast, when the operating range of AC motor M1 is within predetermined region 330 (FIG. 9) (when YES is determined in S210), control device 30 causes a sudden change in the rotational speed of AC motor M1 in step S240. Determine whether you are doing.

  When AC electric motor M1 is a motor for driving an electric vehicle, the result of slip detection or grip detection in the electric vehicle can be commonly used for the determination in step S240. That is, when slip or grip is detected in the electric vehicle, S240 can be determined as YES. Alternatively, the determination in step S240 may be executed by comparing the amount of change in rotational speed per unit time (for example, per control cycle) with a predetermined determination value.

  When the rotational speed of the AC motor is changing suddenly (YES in S240), control device 30 proceeds to step S300 and switches the control mode to PWM control regardless of the determination based on the current phase. . On the other hand, when there is no sudden change in the rotational speed (NO determination in S240), control device 30 executes normal control mode switching determination based on the current phase in steps S220 and S230.

  Thus, in the AC motor control system according to the present embodiment, in the rectangular wave control in the predetermined region of the low rotation speed, when a control disturbance typified by the rotation speed change of the AC motor M1 occurs, immediately, PWM control with high control response can be applied. As a result, even when a control disturbance occurs in a state in which controllability is concerned because rectangular wave control is applied at a relatively low rotational speed, it is possible to prevent occurrence of overcurrent and overvoltage.

  Note that the predetermined region 330 in FIG. 9 can be determined in accordance with the rotational speed (Nm <Nth) from the viewpoint of control response of the rectangular wave control. However, since the current and voltage are relatively small in the low torque region, there is a low possibility that overcurrent or overvoltage will occur even if the control responsiveness decreases. Therefore, from the viewpoint of minimizing the execution of the forced control mode switching determination away from the normal control mode switching determination, as shown in FIG. 9, in the low rotation speed region (Nm <Nth) The predetermined region 330 is preferably set only in the high torque region (T> Tth).

  In the present embodiment, a three-phase motor is exemplified as AC motor M1, but when control using selective use of rectangular wave control and PWM control is applied, for a multi-phase motor other than three-phase motor The control mode switching according to the present invention can also be applied. Further, when the PWM control is configured only by the sine wave PWM control without including the overmodulation PWM control, the control mode switching according to the present invention can be similarly applied.

  Further, in FIG. 1, as a preferable configuration example, a configuration is shown in which DC voltage generation unit 10 # of the motor drive system includes converter 12 so that the input voltage (system voltage VH) to inverter 14 can be variably controlled. DC voltage generation unit 10 # is not limited to the configuration exemplified in the present embodiment. That is, it is not essential 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 converter 12 is omitted). Is possible.

  Further, with regard to the AC motor serving as the load of the motor drive system, in the present embodiment, a permanent magnet motor mounted as a running motor in 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.

  The present invention can be applied to AC motor control in which the control mode is switched between rectangular wave control and pulse width modulation control (PWM control).

  5 Ground wire, 6, 7 Power line, 10 Voltage sensor, 10 # DC voltage generator, 11, 24 Current sensor, 12 Converter, 13 Voltage sensor, 14 Inverter, 15-17 Upper and lower arms for each phase, 25 Rotation angle sensor, 30 Control device (ECU), 100 motor control system, 200 PWM control unit, 210 current command generation unit, 220, 250, 460 coordinate conversion unit, 240 voltage command generation unit, 260 PWM modulation unit, 290 feedback control unit, 300 control mode Selection unit, 310 maximum efficiency phase line, 320, 325 switching line, 330 predetermined region, 400 rectangular wave control unit, 410 power calculation unit, 420 torque calculation unit, 430 calculation unit, 440 rectangular wave generator, 450 signal generation unit, 495 Current storage unit, B DC power supply, C0, C1 smoothing capacitor , D1 to D8 Anti-parallel diode, Ib DC current, Id d-axis current value, Idcom, Iqcom Current command value (d-axis, q-axis), Imax specified value, Iq q-axis current value, L1 reactor, M1 AC motor, Nm Rotational speed (AC motor), Nth, Tth threshold, P1 operating point (AC motor), Q1-Q8 power semiconductor switching element, S1-S8 switching control signal, SE signal, SR1, SR2 system relay, Tq torque estimated value, Trqcom Torque command value, Vb DC voltage, VH DC voltage (system voltage), Vd d-axis voltage command value, Vq q-axis voltage command value, Vu, Vv, Vw Each phase voltage command, iu, iv, iw Motor current (phase Current).

Claims (4)

An inverter for controlling an applied voltage to the AC motor, electrically connected between the DC power source and the AC motor;
A rectangular wave control unit for generating a control command for the inverter according to a rectangular wave control for controlling a voltage phase of a rectangular wave voltage applied to the AC motor so as to operate the AC motor according to an operation command;
A pulse width modulation control unit for generating a control command for the inverter by pulse width modulation control based on a comparison between a carrier wave and an AC voltage command for operating the AC motor according to the operation command;
A control mode selection unit for selecting one of the control modes of the rectangular wave control and the pulse width modulation control;
When the rectangular wave control is selected and the operation region of the AC motor is within a predetermined region, the control mode selection unit changes the control mode according to a change in the rotational speed of the AC motor. switching example from the rectangular wave control to the pulse width modulation control,
The control system for an AC motor , wherein the predetermined region is a region where the rotational speed of the AC motor is lower than a predetermined value . An inverter for controlling an applied voltage to the AC motor, electrically connected between the DC power source and the AC motor;
A rectangular wave control unit for generating a control command for the inverter according to a rectangular wave control for controlling a voltage phase of a rectangular wave voltage applied to the AC motor so as to operate the AC motor according to an operation command;
A pulse width modulation control unit for generating a control command for the inverter by pulse width modulation control based on a comparison between a carrier wave and an AC voltage command for operating the AC motor according to the operation command;
A control mode selection unit for selecting one of the control modes of the rectangular wave control and the pulse width modulation control;
When the rectangular wave control is selected and the operation region of the AC motor is within a predetermined region, the control mode selection unit changes the control mode according to a change in the rotational speed of the AC motor. switching example from the rectangular wave control to the pulse width modulation control,
The control system for an AC motor , wherein the predetermined region is a region where the rotational speed of the AC motor is lower than a predetermined value and the torque of the AC motor is higher than a predetermined value . When the rectangular wave control is selected and the operation region of the AC motor is outside the predetermined region, the control mode selection unit has a phase of a current flowing between the inverter and the AC motor. The control system for an AC motor according to claim 1 or 2 , wherein the control mode is switched from the rectangular wave control to the pulse width modulation control according to the control. The AC motor is configured to generate a driving torque of driving wheels of an electric vehicle,
When the rectangular wave control is selected and the operation region of the AC motor is within a predetermined region, the control mode selection unit, when slip or grip of the drive wheel is detected, The control system for an AC motor according to any one of claims 1 to 3 , wherein a change in rotational speed of the AC motor is detected, and the control mode is switched from the rectangular wave control to the pulse width modulation control.

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