JP2010119201A - Controller for ac motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To secure stability in control, in AC motor control where third harmonics are superposed on an AC voltage command by PWM control in overmodulation mode. <P>SOLUTION: A voltage command generator 240 generates voltage commands Vd# and Vq#, based on deviations ΔId and ΔIq between currents on d- and q-axis. The voltage commands Vd# and Vq# are converted into each phase of voltage commands Vu, Vv, and Vw by a coordinate converter 250 after being corrected for increasing the amplitude of a voltage to be applied to a motor by a voltage amplitude corrector 270. A PWM modulator 260 generates switching control signals S3-S8 for an inverter 14, according to each phase of voltage commands Vu#, Vv# and Vw# where third harmonics are superposed by a harmonic superposition processor 255#. The harmonic superposition processor 255# sets the amplitude of third harmonic components, so that an inflection point caused by the third harmonic components may not occur any more, in addition to the inflection point caused by fundamental wave components (voltage commands Vu, Vv and Vw), in the waveform at the apex of the voltage command. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an AC motor control apparatus, and more particularly to control of an AC motor to which pulse width modulation (PWM) control having a sine wave modulation mode and an overmodulation mode is applied.

  In order to drive and control an AC motor using a DC power source, a driving method using an inverter is 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 particular, Japanese Patent Laid-Open No. 2008-11682 (Patent Document 1) discloses that, as a control mode of an AC motor, overmodulation PWM control is applied in addition to sinusoidal PWM control, and third harmonics are used in these PWM control. It is described that the applied voltage is controlled to include.

Similarly, Japanese Patent Application Laid-Open No. 2007-259688 (Patent Document 2), Japanese Patent Application Laid-Open No. 2007-244066 (Patent Document 3), and Japanese Patent Application Laid-Open No. 2007-116862 (Patent Document 4) also perform PWM control on an AC motor. In this case, a control configuration is described in which the third harmonic is superimposed on the sine wave command.
JP 2008-11682 A JP 2007-259688 A JP 2007-244066 A JP 2007-116862 A

  As described in Patent Documents 1 to 4, it is known that the application range of PWM control can be expanded by superimposing the third harmonic on the voltage command. However, unless the amplitude of the superimposed harmonic component is made appropriate, there is a concern that the stability of PWM control, particularly PWM control in the overmodulation mode, may be impaired.

  The present invention has been made to solve such problems, and the object of the present invention is to control an AC motor that superimposes a third harmonic on an AC voltage command by PWM control in an overmodulation mode. It is to ensure control stability.

  An AC motor control apparatus according to the present invention is an AC motor control apparatus in which an applied voltage is controlled by an inverter, and includes a current detector and a pulse width modulation control unit. A current flowing between the current detector, the inverter and the AC motor is detected. The pulse width modulation control unit generates an inverter control command by pulse width modulation control based on a comparison between an AC voltage command for operating the AC motor in accordance with the operation command and a carrier wave. The pulse width modulation control unit includes a sine wave modulation control unit and an overmodulation control unit. The sine wave modulation control unit generates a control command according to a deviation between the motor current detected by the current detector and the current command corresponding to the operation command in accordance with the sine wave pulse width modulation method. The overmodulation control unit outputs a control command according to the motor current and the current deviation of the current command according to the overmodulation pulse width modulation method for outputting an applied voltage having a larger amplitude of the fundamental wave component than the sine wave pulse width modulation method. appear. The overmodulation control unit includes a first calculation unit, an amplitude correction unit, a first command conversion unit, a first harmonic superimposition unit, and a first modulation unit. The first calculation unit calculates a current deviation based on the motor current and the current command, and calculates a control value indicating the AC voltage command according to the calculated current deviation. The amplitude correction unit performs correction calculation for expanding the amplitude of the AC voltage command with respect to the calculated control value. The first command conversion unit converts the correction-calculated control value into a sine wave voltage command. The first harmonic superimposing unit generates an AC voltage command by superimposing a 3n-order harmonic component on the sine wave voltage command converted by the first command conversion unit. The first modulation unit generates a control command based on a comparison between the generated AC voltage command and a carrier wave. Further, the first harmonic superimposing unit limits the amplitude of the 3n-order harmonic component to a range in which no inflection point due to the 3n-order harmonic component occurs in the AC voltage command in which the 3n-order harmonic component is superimposed. To do.

  According to the AC motor control apparatus described above, in the overmodulation mode PWM control in which the number of on / off operations of the switching elements constituting the inverter is relatively reduced because the amplitude of the AC voltage command is large, the alternating current is generated by superimposing the third harmonic. It is possible to prevent a new inflection point from occurring in the voltage command. As a result, it is possible to prevent the waveform from becoming asymmetric between the positive / negative voltages of the motor applied voltage corresponding to each half cycle of the electrical angle (0 to 180 degrees / 180 to 360 degrees). Stability can be increased.

  Preferably, the sine wave modulation control unit includes a second calculation unit, a second command conversion unit, a second harmonic superimposition unit, and a second modulation unit. The second calculation unit calculates a current deviation based on the motor current and the current command, and calculates a control value indicating the AC voltage command according to the calculated current deviation. The second command conversion unit converts the control value calculated by the second calculation unit into a sine wave voltage command. The second harmonic superimposing unit generates an AC voltage command by superimposing the 3n-order harmonic component on the sine wave voltage command converted by the second command conversion unit. The second modulator generates a control command based on a comparison between the AC voltage command generated by the second harmonic superimposing unit and the carrier wave. The amplitude of the 3n-order harmonic component superimposed by the second harmonic superimposing unit with respect to the sine wave voltage command having the same amplitude is the same as that of the 3n-order harmonic component superimposed by the first harmonic superimposing unit. It is equivalent to the amplitude.

  In this way, the amplitude ratio of the third harmonic component to the fundamental wave component can be made the same between the sine wave modulation mode and the over modulation mode, so switching between the sine wave modulation mode and the over modulation mode is possible. Control stability at the time can be further enhanced.

  Preferably, the sine wave modulation control unit includes a second calculation unit, a second command conversion unit, a second harmonic superposition unit, and a second modulation unit. The second calculation unit calculates a current deviation based on the motor current and the current command, and calculates a control value indicating the AC voltage command according to the calculated current deviation. The second command conversion unit converts the control value calculated by the second calculation unit into a sine wave voltage command. The second harmonic superimposing unit generates an AC voltage command by superimposing the 3n-order harmonic component on the sine wave voltage command converted by the second command conversion unit. The second modulator generates a control command based on a comparison between the AC voltage command generated by the second harmonic superimposing unit and the carrier wave. The amplitude of the 3n-order harmonic component superimposed by the second harmonic superimposing unit with respect to the sine wave voltage command having the same amplitude is the same as that of the 3n-order harmonic component superimposed by the first harmonic superimposing unit. Greater than amplitude.

  In this way, the application range of the PWM control in the sine wave modulation mode can be expanded by the superposition of the third harmonic, while the control stability of the PWM control when the over modulation mode cannot be covered by the sine wave modulation mode. The amplitude of the third harmonic component can be set so as to increase

  According to the present invention, control stability can be ensured in AC motor control in which the third harmonic is superimposed on the AC voltage command by PWM control in the overmodulation mode.

  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.

(General configuration of motor control)
FIG. 1 is an overall configuration diagram of a motor drive control system to which an AC motor control device according to an embodiment of the present invention is applied.

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

  For example, AC electric motor M1 generates torque for driving drive 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). This is an electric motor for driving. 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 as one that can start 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 constituted by a secondary battery such as nickel metal hydride or lithium ion, or a power storage device such as an electric double layer capacitor. 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 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 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 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 coils of U, V, and W phases 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.

  During the boosting operation, the converter 12 converts the DC voltage VH 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”) to the inverter 14. To supply. More specifically, in response to switching control signals S1 and S2 from controller 30, switching element Q1 is turned on and switching element Q2 is turned on (or both switching elements Q1 and Q2 are turned off). ) Are alternately provided, and the step-up ratio is in accordance with the ratio of these ON periods. Alternatively, if switching elements Q1 and Q2 are fixed to ON and OFF, respectively, VH = Vb (step-up ratio = 1.0) can be obtained.

  In the step-down operation, converter 12 steps down DC voltage VH (system voltage) supplied from inverter 14 through smoothing capacitor C0 and charges DC power supply B. More specifically, in response to switching control signals S1 and S2 from control device 30, only switching element Q1 is turned on and both switching elements Q1 and Q2 are turned off (or Q2 of the switching element). Of the ON period) are alternately provided, and the step-down ratio is in accordance with the duty ratio of the ON period.

  Smoothing capacitor C 0 smoothes the DC voltage from 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 value to the control device 30.

  When the torque command value of AC motor M1 is positive (Trqcom> 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. AC motor M1 is driven so as to output a positive torque by converting a DC voltage into an AC voltage by switching operation of elements Q3 to Q8. Further, when the torque command value of AC electric motor M1 is zero (Trqcom = 0), inverter 14 converts the DC voltage to the AC voltage by the switching operation in response to switching control signals S3 to S8, and the torque is zero. The AC motor M1 is driven so that Thus, AC electric motor M1 is driven to generate zero or positive torque designated by torque command value Trqcom.

  Further, during regenerative braking of an electric vehicle equipped with motor drive control system 100, torque command value Trqcom of AC electric motor M1 is set to a negative value (Trqcom <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 converter 12 via 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 motor current MCRT 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 θ of the AC electric motor M 1 and sends the detected rotation angle θ to the control device 30. Control device 30 can calculate the rotational speed (rotational speed) and angular speed ω (rad / s) of AC electric motor M1 based on 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 configured by an electronic control unit (ECU), and performs software processing by executing a program stored in advance by a CPU (not shown) and / or hardware processing by a dedicated electronic circuit. Control the behavior.

  As a representative function, the control device 30 includes the input torque command value Trqcom, the DC voltage Vb detected by the voltage sensor 10, the DC current Ib detected by the current sensor 11, and the system voltage detected by the voltage sensor 13. Based on VH, motor currents iv and iw from current sensor 24, rotation angle θ from rotation angle sensor 25, etc., AC motor M1 outputs torque according to torque command value Trqcom by a control method described later. The operations of the converter 12 and the inverter 14 are controlled. That is, switching control signals S1 to S8 for controlling converter 12 and inverter 14 as described above are generated and output to converter 12 and inverter 14.

  During the boost operation of converter 12, control device 30 performs feedback control of system voltage VH, and generates switching control signals S1 and S2 so that system voltage VH matches the voltage command value.

  In addition, when control device 30 receives signal RGE indicating that the electric vehicle has entered the regenerative braking mode from an external ECU, switching control signal S3-3 converts AC voltage generated by AC motor M1 into 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 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. And output to the 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.

(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 of AC electric motor M1 in the motor drive system according to the embodiment of the present invention.

  As shown in FIG. 2, in the motor drive 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 a 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. In addition, a control method has been proposed in which a voltage command is generated by superimposing a 3n-order harmonic component (n: a natural number, typically n = 1 third-harmonic) on a sine wave component in a range below the carrier wave amplitude. ing. This control method makes it possible to increase the upper limit value of the modulation rate to which the sine wave PWM control can be applied, from 0.61.

  By superimposing harmonics, a period in which the voltage command is higher than the carrier wave amplitude occurs even in sinusoidal PWM control, but the 3n-order harmonic component superimposed on each phase is canceled between lines. The line voltage maintains a sine wave. In the present embodiment, this control method is also included in the sine wave PWM control.

  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 (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 is increased from the maximum modulation rate in the sine wave PWM control mode to a range of 0.78. Can do. 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. Even in the overmodulation PWM control, by superimposing the 3n-order harmonic component on the sine wave component, the fluctuation of the voltage command at the time of switching to the sine wave PWM control is suppressed.

  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 the torque fluctuation in the low rotational speed range A1, overmodulation PWM control in the intermediate rotational speed range A2, and in the high rotational speed range A3. Square wave 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 of the control modes shown in FIG. 2 is used is basically determined within the range of the modulation rate that can be realized.

(Description of control configuration in each control mode)
FIG. 4 is a block diagram illustrating a motor control configuration based on sinusoidal PWM control, which is a basic control configuration by the AC motor control apparatus according to the embodiment of the present invention. Each functional block for motor control described in the block diagrams described below including FIG. 4 is realized by hardware or software processing by the control device 30.

  Referring to FIG. 4, sine wave PWM control unit 200 switches switching control signals S <b> 3 to S <b> 3 of inverter 14 such that AC motor M <b> 1 outputs torque according to torque command value Trqcom when sine wave PWM control mode is selected. S8 is generated.

  The sine wave PWM control unit 200 includes a current command generation unit 210, coordinate conversion units 220 and 250, a voltage command generation unit 240, and a 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. Based on iw, a d-axis current Id and a q-axis current Iq are calculated.

  Deviation ΔId (ΔId = Idcom−Id) relative to the command value of the d-axis current and deviation ΔIq (ΔIq = Iqcom−Iq) relative to the command value of the q-axis current are input to the voltage command generation unit 240. The voltage command generation unit 240 obtains a control deviation by performing PI (proportional integration) calculation with a predetermined gain for each of the d-axis current deviation ΔId and the q-axis current deviation ΔIq, and a d-axis voltage command value corresponding to the control deviation. Vd # and q-axis voltage command value Vq # are 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 θ of the AC motor M1. Each phase voltage command Vu, Vv, Vw of the phase is converted.

  The harmonic superimposition processing unit 255 superimposes the 3n-order harmonic component on the U-phase, V-phase, and W-phase voltage commands Vu, Vv, and Vw calculated by the coordinate conversion unit 250.

  Here, the 3n-order harmonic can be an arbitrary frequency as long as it is a harmonic having a frequency 3 · n times (n: a natural number) with respect to the fundamental frequency, but is typically a third-order harmonic. It will be referred to as a wave (n = 1). That is, the third harmonic in the following is equivalent to the meaning of the third nth harmonic.

  Harmonic superposition processing section 255 generates voltage command Vu # in which the third-order harmonic component is superimposed on U-phase voltage command Vu (Vu = Va · sin ωt) according to the following equation (1). In the equation (1), the coefficient k1 defines the amplitude of the third harmonic component superimposed during the sinusoidal PWM control by the ratio to the amplitude of the fundamental wave component.

Vu # = Vu + Va · k1 · sin3ωt (1)
Then, the harmonic superposition processing unit 255 generates voltage commands Vv # and Vw # in which the third-order harmonics are superimposed on the V-phase and W-phase voltage commands Vv and Vw as in the U-phase.

  As shown in FIG. 5, the PWM modulation unit 260 controls the on / off of the upper and lower arm elements of each phase of the inverter 14 based on the comparison between the carrier wave 262 and the AC voltage command 264. A pseudo sine wave voltage is generated for each phase. The carrier wave 262 is constituted by a triangular wave or a sawtooth wave having a predetermined frequency. The AC voltage command 264 comprehensively indicates the phase voltage commands Vu #, Vv #, and Vw # shown in FIG. 4 and is omitted in FIG. It is superimposed.

  In the PWM modulation for inverter control, the amplitude of the carrier wave 262 corresponds to the input DC voltage (system voltage VH) of the inverter 14. However, the amplitude of the carrier wave 262 used in the PWM modulator 260 can be fixed by converting the amplitude of the AC voltage command 264 to be PWM-modulated into one obtained by dividing the original amplitude of each phase voltage command by the system voltage VH.

  Referring to FIG. 4 again, the inverter 14 is subjected to switching control according to the switching control signals S3 to S8 generated by the PWM control unit 200, so that torque according to the torque command value Trqcom is output to the AC motor M1. AC voltage is applied to

  FIG. 6 is a block diagram illustrating a general example of a motor control configuration based on overmodulation PWM control.

  Referring to FIG. 6, overmodulation PWM control unit 201 includes a current filter 230 and a voltage amplitude correction unit 270 in addition to the configuration of sine wave PWM control unit 200 shown in FIG. 4. Further, a harmonic superposition processing unit 255 # is provided instead of the harmonic superposition processing unit 255.

  The current filter 230 executes a process of smoothing the d-axis current Id and the q-axis current Iq calculated by the coordinate conversion unit 220 in the time axis direction. Thereby, the actual currents Id and Iq based on the sensor detection values are converted into the filtered currents Idf and Iqf.

  In the overmodulation PWM control unit 201, the current deviations ΔId and ΔIq are calculated using the filtered currents Idf and Iqf. That is, ΔId = Idcom−Idf and ΔIq = Iqcom−Iqf.

  Voltage amplitude correction unit 270 performs correction processing for expanding the amplitude of the motor applied voltage with respect to original d-axis voltage command value Vd # and q-axis voltage command value Vq # calculated by voltage command generation unit 240. Execute.

  When overmodulation PWM control is applied, the amplitude of each phase voltage command (fundamental wave component) obtained by converting the voltage command values Vd # and Vq # into two-phase to three-phase is larger than the inverter input voltage (system voltage VH). Become. This state corresponds to a state in which the amplitude of the AC voltage command 264 is larger than the amplitude of the carrier wave 262 in the waveform diagram shown in FIG. In this case, since the inverter 14 cannot apply a voltage exceeding the system voltage VH to the AC motor M1, the PWM according to each phase voltage command signal according to the original voltage command values Vd # and Vq #. Depending on the control, the original modulation rate corresponding to the voltage command values Vd # and Vq # cannot be secured.

  Therefore, with respect to the AC voltage command based on the voltage command values Vd # and Vq #, the voltage command is corrected by expanding the voltage amplitude (× m times, m> 1) so that the voltage application interval is increased. The original modulation rate based on the values Vd # and Vq # can be secured. The voltage amplitude expansion ratio m in the voltage amplitude correction unit 270 can be theoretically derived based on this original modulation rate.

  The coordinate conversion unit 250 converts the voltage command that has been corrected by the voltage amplitude correction unit 270 into the phase voltage commands Vu, Vv, and Vw.

  Harmonic superposition processing section 255 # generates voltage command Vu # in which the third-order harmonic component is superimposed on U-phase voltage command Vu (Vu = Va · sin ωt) according to the following equation (2). In the equation (2), the coefficient k2 defines the amplitude of the third-order harmonic component superimposed during overmodulation PWM control as a ratio to the amplitude of the fundamental wave component.

Vu # = Vu + Va · k2 · sin3ωt (2)
Then, harmonic superposition processing section 255 # generates voltage commands Vv # and Vw # in which the third-order harmonics are superimposed on V-phase and W-phase voltage commands Vv and Vw as in the U-phase.

  PWM modulation unit 260 generates switching control signals S3 to S8 for inverter 14 in accordance with each phase voltage command Vu #, Vv #, Vw # on which the third harmonic is superimposed by harmonic superimposition processing unit 255 #.

  Here, coefficient k2 indicating the amplitude ratio of the harmonic component in harmonic superposition processing section 255 # is set as described below.

  FIG. 7 shows an operation waveform when a third harmonic component is superimposed on the voltage command for the purpose of expanding the application range of the sine wave PWM control.

  In this case, in order to expand the application range of the sine wave PWM, the waveform at the apex portion of the AC voltage command 264 has irregularities, that is, a change caused by the third harmonic component in addition to the inflection point due to the fundamental wave component. The coefficient (amplitude ratio) k1 is made relatively large so that more poles are generated. As a result, the sinusoidal PWM control can be applied even to a region where the modulation factor exceeds 0.61.

  On the other hand, the sine wave PWM control is applied to the region where the modulation factor = 0.78 to which the rectangular wave voltage control is applied even by the sine wave PWM control in which the third harmonic component is superimposed as shown in FIG. It is difficult. Therefore, overmodulation PWM control is required in the modulation rate region that is between the two.

  FIG. 8 shows an operation waveform in the comparative example of the overmodulation PWM control in which the third harmonic component is superimposed on the voltage command.

  FIG. 8 shows an operation waveform when the amplitude ratio k2 of the third harmonic component in the overmodulation PWM control is the same as the amplitude ratio k1 in FIG. As a result, as in FIG. 7, irregularities (inflection points due to the third harmonic component) occur in the waveform of the apex portion of the AC voltage command 264.

  In this way, in the voltage comparison between the carrier wave 262 and the AC voltage command 264, the number of times of switching at the apex portion of the AC voltage command 264 is between half a cycle of the electrical angle (0 to 180 degrees / 180 to 360 degrees). A different phenomenon may occur. For example, as indicated by a dotted line in FIG. 8, the switching element is turned on / off during the positive voltage application period (electrical angle 0 to 180 degrees), whereas the negative voltage application period (electrical period) In the angle 180 to 360 degrees), the switching element is not turned on / off at the corresponding portion where the phase is shifted by 180 degrees from the above. As a result, the motor applied voltage becomes asymmetric between the positive and negative voltages. When such a phenomenon occurs, the motor current is disturbed.

  Therefore, in the motor drive system according to the present embodiment, as shown in FIG. 9, when overmodulation PWM control is applied, amplitude ratio k2 of the third harmonic component by harmonic superimposition processing unit 255 # is set to the third harmonic. The waveform is limited to a range where no irregularities (inflection points due to the third harmonic component) are generated in the waveform of the apex portion of the AC voltage command 264 on which the wave is superimposed.

  When the amplitude ratio k2 is set in this way, the motor applied voltage controlled by turning on / off the switching element of the inverter 14 based on the comparison between the carrier wave 262 and the AC voltage command 264 is within one electrical cycle (electrical angle 360 degrees). Since the positive / negative voltage waveform can be made symmetrical, it is possible to prevent disturbance of the motor current and stably control the AC motor.

  In the motor drive system according to the present embodiment, sinusoidal PWM control is performed with respect to amplitude ratio k2 (harmonic superposition processing unit 255 #) of the third harmonic component in overmodulation PWM control set as described above. It is preferable to set k1 = k2 for the amplitude ratio k1 (harmonic superposition processing unit 255) of the third harmonic component in FIG. If it does in this way, in addition to said effect, the control stability at the time of switching between a sine wave modulation mode and an overmodulation mode can further be improved. Also, the application area of the sine wave PWM control can be expanded as compared with the case where the third harmonic is not superimposed.

  Alternatively, the amplitude ratio k1 in the sine wave PWM control may be set to a value larger than the amplitude ratio k2 in the overmodulation PWM control. In this way, the application range of the sine wave PWM control can be expanded as compared with the case of k1 = k2, while the amplitude of the third harmonic component can be set so as to improve the stability of the overmodulation PWM control. .

  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 a motor drive control system to which an AC motor control device according to an embodiment of the present invention is applied. It is a figure which illustrates schematically the control mode of the AC motor in the motor drive system by embodiment of this invention. The correspondence relationship between the operating state of the AC motor and the control mode shown in FIG. 2 is shown. It is a block diagram explaining the motor control structure by the sine wave PWM control in the control apparatus of the alternating current motor by embodiment of this invention. FIG. 5 is a waveform diagram for explaining the operation of the PWM modulation unit in FIG. 4. It is a block diagram explaining the motor control structure by the overmodulation PWM control in the control apparatus of the alternating current motor by embodiment of this invention. It is an operation | movement waveform diagram of the sine wave PWM control which superimposed the 3rd harmonic. It is an operation | movement waveform diagram of the overmodulation PWM control (comparative example) which superimposed the 3rd harmonic. It is an operation | movement waveform diagram of the overmodulation PWM control which superimposed the 3rd harmonic in the motor drive system by this Embodiment.

Explanation of symbols

  5 Ground wire, 6, 7 Power line, 10, 13 Voltage sensor, 10 # DC voltage generator, 11, 24 Current sensor, 12 Converter, 14 Inverter, 15 U phase upper and lower arm, 16 V phase upper and lower arm, 17 W phase upper and lower Arm, 25 rotation angle sensor, 30 control unit (ECU), 100 motor drive control system, 200 sine wave PWM control unit, 201 overmodulation PWM control unit, 210 current command generation unit, 220, 250 coordinate conversion unit, 230 current filter , 240 Voltage command generation unit, 255, 255 # harmonic superimposition processing unit, 260 PWM modulation unit, 262 carrier wave, 264 AC voltage command, 270 voltage amplitude correction unit, B DC power supply, C0, C1 smoothing capacitor, D1-D8 reverse Parallel diode, Ib DC current, Id d-axis current, Idcom, Iqcom Command value, Idf, Iqf current (filter processing), Iq q-axis current, iu, iv, iw three-phase current, k1, k2 coefficient (amplitude ratio), L1 reactor, M1 AC motor, MCRT motor current, Q1-Q8 power Semiconductor switching element, SR1, SR2 system relay, Trqcom torque command value, Vb DC voltage, Vd #, Vq # voltage command value (d, q axis), VH DC voltage (system voltage), Vu #, Vv #, Vw # Voltage command (after superimposing third harmonics), Vu, Vv, Vw Voltage command (before superimposing third harmonics), ΔId, ΔIq Current deviation, θ rotor rotation angle, ω angular velocity.

Claims (3)

An AC motor control device in which an applied voltage is controlled by an inverter,
A current detector for detecting a current flowing between the inverter and the AC motor;
A pulse width modulation control unit that generates a control command for the inverter by pulse width modulation control based on a comparison between an AC voltage command and a carrier wave for operating the AC motor according to an operation command;
The pulse width modulation control unit
A sine wave modulation control unit that generates the control command according to a deviation between the motor current detected by the current detector and a current command corresponding to the operation command according to a sine wave pulse width modulation method,
The control command is generated according to the motor current and the current deviation of the current command according to an overmodulation pulse width modulation method for outputting an applied voltage having a larger amplitude of the fundamental wave component than the sine wave pulse width modulation method. Including an overmodulation control unit,
The overmodulation control unit
A first arithmetic unit that calculates the current deviation based on the motor current and the current command, and calculates a control value indicating the AC voltage command according to the obtained current deviation;
An amplitude correction unit that performs a correction calculation for expanding the amplitude of the AC voltage command with respect to the calculated control value;
A first command conversion unit that converts the control value that has been subjected to the correction calculation into a sine wave voltage command;
A first harmonic superimposing unit that generates the AC voltage command by superimposing a 3n-order harmonic component on the sine wave voltage command converted by the first command conversion unit;
A first modulation unit that generates the control command based on a comparison between the generated AC voltage command and the carrier wave;
The first harmonic superimposing unit is configured such that an inflection point due to the 3n-order harmonic component does not occur in the AC voltage command in which the 3n-order harmonic component is superimposed on the amplitude of the 3n-order harmonic component. A control device for an AC motor that is restricted within. The sine wave modulation controller is
A second arithmetic unit that calculates the current deviation based on the motor current and the current command, and calculates a control value indicating the AC voltage command according to the calculated current deviation;
A second command conversion unit that converts the control value calculated by the second calculation unit into a sine wave voltage command;
A second harmonic superimposing unit that generates the AC voltage command by superimposing a 3n-order harmonic component on the sine wave voltage command converted by the second command conversion unit;
A second modulation unit that generates the control command based on a comparison between the AC voltage command generated by the second harmonic superimposing unit and the carrier wave;
For the sine wave voltage command having the same amplitude, the amplitude of the 3n-order harmonic component superimposed by the second harmonic superimposing unit is the 3n-order harmonic superimposed by the first harmonic superimposing unit. The control device for an AC motor according to claim 1, wherein the control device is equivalent to an amplitude of a wave component. The sine wave modulation controller is
A second arithmetic unit that calculates the current deviation based on the motor current and the current command, and calculates a control value indicating the AC voltage command according to the calculated current deviation;
A second command conversion unit that converts the control value calculated by the second calculation unit into a sine wave voltage command;
A second harmonic superimposing unit that generates the AC voltage command by superimposing a 3n-order harmonic component on the sine wave voltage command converted by the second command conversion unit;
A second modulation unit that generates the control command based on a comparison between the AC voltage command generated by the second harmonic superimposing unit and the carrier wave;
For the sine wave voltage command having the same amplitude, the amplitude of the 3n-order harmonic component superimposed by the second harmonic superimposing unit is the 3n-order harmonic superimposed by the first harmonic superimposing unit. The control device for an AC motor according to claim 1, wherein the control device is larger than the amplitude of the wave component.

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