JP5375679B2 - Control device for motor drive system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To smoothly perform the determination of switching to rectangular voltage wave control from PWM control during AC electric motor control which selectively employs rectangular wave control and PWM control. <P>SOLUTION: In this motor drive system using an inverter, in pulse-width modulation (PWM) control, the inverter is controlled by the voltage comparison of an AC voltage command for operating an AC electric motor in accordance with an operation command and a carrier wave represented by a triangle wave. At PWM control selection, switching to rectangular wave control from PWM control is commanded when an instantaneous value of the AC voltage command is larger than an amplitude of the carrier wave at each of timings corresponding to two points closest to the timings at which the positive and negative of the voltage command are inverted among apexes of the carrier wave. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a control device for a motor drive system, and more particularly to AC motor control for switching a control mode between rectangular wave control and pulse width modulation (PWM) control.

  In order to drive an AC motor using a DC power source, a motor drive system using an inverter is used. The inverter performs DC / AC power conversion by switching control by an inverter drive circuit. For example, based on a comparison between a sinusoidal voltage command and a carrier wave (triangular wave), a pseudo-AC voltage that is obtained by switching a DC voltage and is pulse-width modulated is output from the inverter and applied to the AC motor.

  In addition, in order to expand the amplitude of the fundamental wave component of the voltage applied to the AC motor, overmodulation PWM control in which the amplitude of the sine wave voltage command exceeds the amplitude of the carrier wave, or a square wave voltage with one positive and negative pulse synchronized with the rotation frequency There is known a rectangular wave control for applying a voltage.

  For example, Japanese Patent Application Laid-Open No. 2008-31420 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2009-100588 (Patent Document 2) selectively apply PWM control including overmodulation PWM control and rectangular wave control. AC motor control is described.

JP 2008-31420 A JP 2009-100588 A

  When the PWM control and the rectangular wave control are selectively applied, it is necessary to determine whether to switch between these control modes. For example, in Patent Document 1 (paragraph 0046), the necessity of switching from the PWM control mode to the rectangular wave control mode is determined by comparing the required voltage amplitude obtained from the voltage command with the absolute value of the peak value of the carrier wave (triangular wave). Is determined.

  Further, in Patent Document 2, in order to prevent the occurrence of torque vibration when switching from the PWM control mode to the rectangular wave control mode, according to the switching timing in the first cycle after switching to the rectangular wave control mode, It is described that the control mode is switched on and off.

  However, in the switching region between PWM control (especially overmodulation PWM control) and rectangular wave control, due to the influence of dead time and control calculation error due to sensor error, in the motor state that should be switched to the rectangular wave control mode originally There is a case where switching to the rectangular wave control mode is erroneously required even though there is not.

  If such a situation occurs, immediately after switching to the rectangular wave control mode, a result of requesting switching to the PWM control mode again is caused, so that switching between both control modes may occur frequently. is there. Furthermore, since the voltage applied to the AC motor is discontinuous, the current may increase in a surge manner.

  The present invention has been made in order to solve such problems, and an object of the present invention is to provide a rectangular voltage wave from PWM control in AC motor control that selectively applies rectangular wave control and PWM control. Smooth switching determination to control is to be performed.

  In one aspect of the present invention, a control device for a motor drive control system including a current detector for detecting a motor current flowing between an inverter and an AC motor includes a carrier wave having a predetermined amplitude and a predetermined frequency, and an AC motor. Means for generating an inverter control command by pulse width modulation control based on comparison with an AC voltage command for operation according to the operation command, and a rectangular wave voltage applied to the AC motor when selecting pulse width modulation control Determining means for determining whether or not switching to the rectangular wave control for controlling the voltage phase of the signal is necessary. The determination means determines the pulse width when the instantaneous value of the AC voltage command is larger than the amplitude of the carrier wave at each of the timings corresponding to the two points closest to the timing at which the positive / negative of the voltage command is reversed. Means for instructing switching from modulation control to rectangular wave control is included.

  According to the present invention, an object of the present invention is to smoothly perform switching determination from PWM control to rectangular voltage wave control in AC motor control that selectively applies rectangular wave control and PWM control.

1 is an overall configuration diagram of a motor drive system according to an embodiment of the present invention. It is a conceptual diagram explaining the control mode of the alternating current motor in the motor drive system by embodiment of this invention. It is a wave form diagram explaining control operation of PWM control. It is a wave form diagram explaining synchronous PWM control. It is a conceptual diagram explaining the example of control mode switching based on the modulation factor according to a voltage command amplitude. It is a wave form diagram explaining the operation example when the switching determination from PWM control mode to rectangular wave control mode is not normal. It is a flowchart explaining the control processing of the switching determination from PWM control mode to rectangular wave control mode in the motor drive system by embodiment of this invention. It is a wave form diagram explaining the operation example determined to be the switching necessity from PWM control mode to a rectangular wave control mode. It is a wave form diagram explaining the operation example determined to be the switching unnecessary from PWM control mode to a rectangular wave control mode.

FIG. 1 is an overall configuration diagram of a motor drive system according to an embodiment of the present invention.
Referring to FIG. 1, motor drive 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 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 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.

  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 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.

  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 it so as 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. 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, and controls the operation of the motor drive system 100 by software processing by executing a program stored in advance by a CPU (not shown) and / or hardware processing by a dedicated electronic circuit. .

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

  As shown in FIG. 2, in motor drive system 100 according to the embodiment of the present invention, three control modes are switched and used for control of AC electric motor M <b> 1, that is, power conversion in inverter 14.

  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 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.

  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, the 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 control One of the modes is selectively applied. Which one of the control modes shown in FIG. 2 is used is basically determined so as to be within the range of a realizable modulation rate.

  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. 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.

The operation of PWM control will be further described with reference to FIGS.
Referring to FIG. 3, in PWM control, each phase of AC motor M <b> 1 is pseudo-sine by controlling on / off of the switching element of each phase of inverter 14 based on voltage comparison between carrier wave 160 and voltage command 170. A pulse width modulation voltage 180 as a wave voltage is applied. The carrier wave 160 can be configured by a triangular wave or a sawtooth wave having a predetermined frequency. Below, a triangular wave is illustrated.

  In asynchronous PWM, the frequency of the carrier wave 160 (hereinafter referred to as the carrier wave frequency) does not change in synchronization with the rotational speed (rotational frequency) of the AC motor M1, and is fixed at a relatively high predetermined frequency at which electromagnetic noise is difficult to detect. Is done.

  On the other hand, as shown in FIG. 4, in synchronous PWM, the rotational frequency (rotational frequency) of AC electric motor M <b> 1 is synchronized with k times the rotational frequency of AC electric motor M <b> 1 (k: an integer equal to or greater than 2). In addition, the carrier frequency is controlled. As a result, in the synchronous PWM, the number of carriers of the carrier wave 160 included in the electrical angle 360 degrees (one cycle) of the AC motor M1 is controlled to a constant value k. In the present embodiment, synchronous PWM is applied in distinction from so-called rectangular wave control in which a rectangular wave voltage of one positive and negative pulse is applied in synchronization with the rotation frequency of AC electric motor M1, so that k is used as described above. ≧ 2.

  Since phase voltage command 170 is also synchronized with the rotational frequency of AC electric motor M1, as a result, the frequency ratio between carrier wave 160 and phase voltage command 170 is also k: 1.

  In synchronous PWM, the positive / negative symmetry of the pulse width modulation voltage 180 (FIG. 2) can be ensured even if the number of carriers per electrical angle period (360 degrees) is reduced. For this reason, in overmodulation control in which the number of on / off switching operations is reduced because the amplitude of the voltage command is large, application of synchronous PWM is preferable.

Next, control mode switching determination in the PWM control mode will be described.
Generally, as shown in Patent Document 1, the transition from the PWM control mode including the overmodulation PWM control to the rectangular wave control mode depends on the relationship between the amplitude of the voltage command and the input DC voltage of the inverter. Is determined.

  For example, when the modulation rate reaches the determination value F0 (for example, F0 = 0.78) based on the modulation rate obtained from the voltage command amplitude by PWM control defined as described above, the PWM control mode Switching to the rectangular wave control mode can be instructed.

  Referring to FIG. 5, before time ta, the PWM control mode is selected, and the modulation rate increases as the amplitude of the voltage command increases due to the feedback control for increasing the output torque. As can be understood from FIG. 2, when the modulation rate exceeds about 0.61, overmodulation PWM control is applied.

  When the voltage command amplitude further increases and the modulation factor reaches 0.78 at time ta, it is determined that switching to the rectangular wave control mode is necessary. After time ta, rectangular wave control is applied and the voltage amplitude is fixed, so that the modulation rate is also fixed at 0.78.

  However, in the control mode switching determination based on the modulation factor calculated from the voltage command amplitude as shown in FIG. 5, an accurate switching determination can be made in the vicinity of the switching region due to the control error due to the influence of the dead time and sensor error. There is a possibility of disappearing. FIG. 6 shows an operation example when the switching determination to the rectangular wave control mode is not normal.

  Referring to FIG. 6, in the rectangular wave control mode, AC inverter M1 in which normal inverter output voltage Vinv is switched between a high level period and a low level period at time t0, which is a zero cross point where the sign of voltage command 170 is inverted. A square wave voltage of 1 pulse of positive and negative synchronized with the rotation frequency of (see the lower part of FIG. 6). That is, in the region where it is determined that switching to the rectangular wave voltage mode is necessary, it is necessary that the voltage command value | Vcp | is always higher than the carrier voltage | Vcw |.

  However, in the control mode determination based on the modulation factor calculated from the voltage command amplitude including the control error, the voltage command value | Vcp | is actually higher than the carrier voltage | Vcw | as shown in the upper part of FIG. There is a risk that it is determined that the switching from the PWM control mode to the rectangular wave control mode is necessary in spite of a state in which there is a period during which the period becomes smaller.

  In such a situation, the switching from the rectangular wave control mode to the PWM control mode is again instructed by the voltage command 170 calculated immediately after the feedback control, as shown in the middle stage of FIG. The output voltage Vinv becomes a pulse width modulation voltage according to the voltage comparison between the carrier wave 160 and the voltage command 170. As a result, the motor applied voltage becomes discontinuous, and the current of the AC motor M1 may increase in a surge state due to the discontinuous voltage transition.

  Therefore, in the motor drive system according to the embodiment of the present invention, switching determination from the PWM control mode to the rectangular wave control mode is executed according to the flowchart shown in FIG.

  Referring to FIG. 7, control device 30 determines in step S100 whether the PWM control mode is being selected. That is, step S100 is determined to be YES when sine wave PWM control or overmodulation PWM control is applied. In the case of the rectangular wave control in which the PWM control mode is not selected (NO in S100), the determination of switching from the PWM control mode to the rectangular wave control mode is not necessary, so the following steps S105 to S180 are skipped. The

  While selecting PWM control mode (when YES is determined in S100), control device 30 advances the process to step S105 to operate AC electric motor M1 according to torque command value Trqcom by feedback control of AC electric motor M1. The voltage command 170 (FIG. 4) for each phase is calculated.

  Further, in step S110, control device 30 determines whether or not synchronous PWM is applied. As described above, as a preferred mode, synchronous PWM is applied in accordance with selection of overmodulation PWM control in a region with a high modulation rate that becomes a boundary with the rectangular wave control mode. When synchronous PWM is applied (YES determination in S110), control device 30 advances the process to step S150 to determine whether or not the carrier vertex timing is closest to the zero cross point of voltage command 170.

  Referring to FIG. 8, time t0 corresponds to a zero cross point at which the positive / negative of voltage command 170 is reversed. The carrier vertex timing corresponding to each vertex of the carrier wave 160 includes two times t1 and t2, which are the two closest to the zero cross point (time t0). That is, times t1 and t2 correspond to “carrier vertex timing closest to zero cross point”.

  As described above, in synchronous PWM, since the number of carriers (k) in one electric cycle (360 degrees) of AC motor M1 is determined in advance, the “carrier vertex timing nearest to the zero cross point” is set to the value of AC motor M1. It can be grasped in advance based on the rotation angle θ. Therefore, when applying synchronous PWM, the determination in step S150 can be easily performed based on the rotation angle θ.

  Then, at the carrier vertex timing closest to the zero cross point (when YES is determined in S150), control device 30 determines that absolute value | Vp # | of voltage command 170 and absolute value | Vcw | Compare As shown in FIG. 8, when | Vp # |> | Vcw | is satisfied (YES in S160), voltage command (AC voltage) 170 is higher than the voltage at each vertex of carrier wave 160, that is, Therefore, it is determined that the voltage command value | Vcp | is always higher than the carrier voltage | Vcw |. For this reason, control device 30 determines that switching from PWM control mode to rectangular wave control mode is necessary, and instructs switching from PWM control mode to rectangular wave control mode in step S170.

  On the other hand, as shown in FIG. 9, when | Vp # | ≦ | Vcw | is satisfied (at the time of NO determination in S160) at the carrier vertex timing closest to the zero cross point, switching to the rectangular wave voltage mode has been described with reference to FIG. Since a problem may occur, it is determined that switching from the PWM control mode to the rectangular wave control mode is unnecessary. That is, control device 30 proceeds to step S180 to maintain the PWM control mode.

  When synchronous PWM is not applied (NO determination in S110), control device 30 proceeds to step S120 and calculates the modulation factor based on the voltage command value calculated in step S105. And control device 30 performs switching judgment (Drawing 5) based on the modulation factor computed at Step S120 by Step S130. As described above, when the asynchronous PWM is applied to the sine wave PWM control and the synchronous PWM is applied to the overmodulation PWM, the modulation factor is relatively small in the non-application region of the synchronous PWM, and the rectangular wave control mode. Therefore, even if the switching determination is based on the modulation rate, the possibility that the problem described in FIG. 6 occurs is low.

  As described above, in the motor drive device according to the embodiment of the present invention, the rectangular wave control is performed from the PWM control mode on condition that the voltage command (AC voltage) for the PWM control calculation is higher than the voltage at each vertex of the carrier wave. Instruct to switch to mode. Accordingly, the control voltage is erroneously switched from PWM control to rectangular wave control due to the error of the modulation factor calculated from the voltage command amplitude including the control error, so that the applied voltage to the AC motor M1 is discontinuous. Thus, the current can be prevented from increasing in a surge state.

  Then, by comparing the voltage of the carrier wave 160 and the voltage command 170 at the carrier vertex timing closest to the zero cross point, the voltage command (AC voltage) for the PWM control calculation is changed to the carrier wave particularly when the synchronous PWM control is applied. It can be easily determined whether or not the voltage is higher than the voltage at each vertex.

  However, even when the asynchronous PWM is applied, the calculation is complicated, but it is possible to grasp the carrier vertex timing closest to the zero cross point in advance, so steps S110 to S130 are omitted, and step S150 is always performed. The determination may determine whether or not switching from the PWM control mode to the rectangular wave control mode is necessary. Alternatively, at each vertex timing of the carrier wave 160, the absolute value | Vp # | of the voltage command 170 is compared with the absolute value | Vcw | (ie, amplitude) of the carrier wave 160, and | Vp # |> | Vcw | When the period (for example, the electrical angle of AC motor M1 is 180 degrees or 360 degrees) continues, it may be determined that switching from the PWM control mode to the rectangular wave control mode is necessary.

  In the present embodiment, a three-phase motor is illustrated as the AC motor M1, but the current sampling process according to the present invention can be applied to a multiphase motor other than the three-phase motor.

  In FIG. 1, as a preferred 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 a load of the motor drive system, in the present embodiment, a permanent magnet motor mounted for driving a vehicle 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 control of an AC motor that performs control mode switching between rectangular wave control and pulse width modulation control.

  5 ground wire, 6, 7 power line, 10, 13 voltage sensor, 10 # DC voltage generator, 11, 24 current sensor, 12 converter, 14 inverter, 15-17 upper and lower arms for each phase, 25 rotation angle sensor, 30 control device , 100 motor drive system, 160 carrier wave, 170 voltage command, 180 pulse width modulation voltage, B DC power supply, C0, C1 smoothing capacitor, D1-D8 antiparallel diode, Ib DC current, L1 reactor, M1 AC motor, Q1-Q8 Power semiconductor switching element, S to S8 switching control signal, SE signal, SR1, SR2, SR1 system relay, Trqcom torque command value, VH, Vb DC voltage, VHr voltage command value, Vinv inverter output voltage, iu, iv, iw Motor current (phase current).

Claims (1)

A control device of a motor drive control system comprising an inverter, an AC motor whose applied voltage is controlled by the inverter, and a current detector for detecting a motor current flowing between the inverter and the AC motor,
Means for generating a control command for the inverter by pulse width modulation control based on a comparison between a carrier wave having a predetermined amplitude and a predetermined frequency and an AC voltage command for operating the AC motor according to an operation command;
Determination means for determining whether or not to switch to rectangular wave control for controlling the voltage phase of the rectangular wave voltage applied to the AC motor when selecting the pulse width modulation control;
The determination means has an instantaneous value of the AC voltage command larger than an amplitude of the carrier wave at each of timings corresponding to two points closest to a timing at which the positive / negative of the voltage command is inverted among the vertexes of the carrier wave. A control device for a motor drive system including means for instructing switching from the pulse width modulation control to the rectangular wave control.

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