JP2011019302A - Controller for motor driving system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately detect the abnormality of an inverter in a motor driving system which has an AC motor capable of switching its control mode.SOLUTION: An offset F/B processor 300 corrects each phase voltage command, based on an offset correction computed from each phase motor current. A control mode determiner 260 performs switching between a PWM control mode and a rectangular-wave voltage control mode, according to the operating conditions of an AC motor M1. An abnormality detector 400 determines whether a state that an offset F/B integration term computed by PI calculation with the offset F/B processor 300 exceeding threshold has continued for a specified time. When it is determined that the state of the interval over the threshold has continued over a specified interval, the detector detects that an inverter 14 is abnormal. The abnormality detector 400 corrects the threshold in the direction of increase, when it is determined that the changeover of the control mode is required, as well as when the change in torque or the change in revolution at a specified value or over is detected in the AC motor M1.

Description

  The present invention relates to a technique for detecting an abnormality of an inverter, and more particularly to a technique for detecting that one phase of each phase arm of an inverter has an open failure.

  In recent years, an increasing number of vehicles use electric motors to drive electric vehicles such as electric vehicles and hybrid vehicles. In general, an inverter is used to drive such a motor.

  Japanese Patent Laid-Open No. 2006-320176 (Patent Document 1) discloses a DC power source and two semiconductor switching elements connected in series to form upper and lower arms for each phase, and the power of the DC power source is changed to a variable voltage / variable frequency AC. An electric vehicle control comprising: an inverter for converting the inverter; a smoothing capacitor connected between the DC terminals of the inverter; an AC motor supplied with the output AC of the inverter to generate a vehicle driving force; and a control means for controlling the inverter In the apparatus diagnosis device, a series connection of two resistors is connected between the DC terminals of the inverter, and this series connection point is connected to the connection point of the upper and lower arms of either phase of the inverter to form a diagnosis point A configuration for diagnosing a short fault and an open fault by comparing the potential at the diagnostic point with a predetermined reference value is disclosed.

  Japanese Patent Laid-Open No. 2009-017665 (Patent Document 2) discloses an abnormality detection apparatus for detecting abnormality of an inverter including first to n-th (n is a natural number) switching circuits. switching is performed when an overcurrent exceeding a predetermined threshold is detected within a first predetermined time when the first switching element of the switching circuit of a natural number less than n) is turned on for the first predetermined time. A configuration for determining that a second switching element of a circuit is short-circuited is disclosed.

JP 2006-320176 A JP 2009-017665 A

  By the way, the structure which switches conventionally the control system of an AC motor between a pulse width modulation (PWM) control system and a rectangular wave voltage control system according to the driving | running | working area | region of an AC motor is known. In such a configuration, in order to drive the motor with high efficiency, the motor current is generally controlled according to PWM based on vector control. However, in PWM control, there is a limit to securing the line fundamental wave voltage, Applying a rectangular wave voltage with the PWM duty fixed to the maximum value to the motor and controlling the output torque by phase control of the rectangular wave voltage (rectangular wave voltage control method) and a normal PWM control method There has been proposed a configuration in which switching is applied accordingly.

  However, in such a configuration, there is a possibility that the motor current is greatly disturbed by the unstable control operation at the switching point of the control method. As a result, in the configuration that detects the abnormality of the inverter based on the potential of the diagnostic point and the current flowing through the inverter as described above, the error is detected by detecting the fluctuation of the potential and the current that occurs when the control method is switched. May be judged as an inverter malfunction.

  Therefore, the present invention has been made to solve such a problem, and an object of the present invention is to provide a control device capable of accurately detecting an abnormality of an inverter in a motor drive system having an AC motor capable of switching a control mode. Is to provide.

  A control device for a motor drive system according to the present invention is a control device for a motor drive system including a DC power source and an inverter that converts a DC voltage output from the DC power source into an AC voltage for driving an AC motor. The control device includes a first control mode in which a rectangular wave voltage is applied to the AC motor and a second control mode in which the applied voltage to the AC motor is controlled in accordance with pulse width modulation control according to the operating condition of the AC motor. A control mode determination unit that determines whether or not switching is necessary, an offset correction unit that performs feedback control for correcting an offset amount of a motor current flowing through each phase of the AC motor, and an offset correction unit that is calculated based on the offset amount. And an abnormality detection unit that detects that the inverter is abnormal by monitoring the offset feedback amount. The abnormality detection unit determines whether or not the state in which the offset feedback amount exceeds the threshold value has continued for a predetermined time, and detects that the inverter is abnormal when determining that the state in which the offset feedback amount has exceeded the threshold value has continued for a predetermined time A detecting means, a change detecting means for detecting that a torque change or a rotational speed change of a predetermined value or more has occurred in the AC motor, and a change detecting means detecting the occurrence of a torque change or a rotational speed change of a predetermined value or more. Then, when the control mode determination unit determines that switching between the first and second control modes is necessary, it includes correction means for correcting the threshold value so as to increase the threshold value.

  Preferably, the inverter includes a plurality of arms each corresponding to each phase of the AC motor, and each of the plurality of arms includes two switching elements connected in series. When the abnormality detection means determines that the state exceeding the threshold value has continued for a predetermined time, it indicates that one switching element included in any one of the plurality of arms is an open failure in which the switching element is always in an OFF state. To detect.

  According to the present invention, in a motor drive system having an AC motor capable of switching the control mode, it is possible to accurately detect an abnormality occurring in the inverter.

1 is an overall configuration diagram of a motor drive system according to an embodiment of the present invention. It is a figure which illustrates schematically the control mode of AC motor M1 in the motor drive system by an embodiment of the invention. It is a flowchart explaining the selection system of a control mode. It is a figure which shows the correspondence of the operation state of an AC motor, and the control mode shown in FIG. It is a block diagram explaining the motor control structure by the motor drive system by embodiment of this invention. It is a timing chart explaining the abnormality detection method in an abnormality detection part. It is a flowchart explaining the abnormality detection method in an abnormality detection part. It is a timing chart explaining the abnormality detection method by the abnormality detection part when a motor rotation speed changes suddenly. It is a flowchart explaining the setting method of the threshold value for the abnormality detection in an abnormality detection part.

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

(General configuration of motor control)
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 motor M1 generates torque for driving the 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). This is an electric motor for driving. Alternatively, AC 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. Furthermore, AC motor M1 may operate as an electric motor for the engine, and may be incorporated in a hybrid vehicle so that the engine can be started, for example.

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

  The DC power 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.

  Buck-boost 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, an IGBT (Insulated Gate Bipolar Transistor), a power MOS (Metal Oxide Semiconductor) transistor, or a power bipolar transistor is used as a power semiconductor switching element (hereinafter simply referred to as “switching element”). Etc. 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 one end of three U, V, and W phase coils is commonly connected 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.

  In the step-up / down converter 12, 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”) during the boosting operation. Supply to the inverter 14. 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.

  Further, during the step-down operation, the step-up / down converter 12 steps down the DC voltage VH (system voltage) supplied from the inverter 14 via the smoothing capacitor C0 and charges the 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 C0 smoothes the DC voltage from step-up / down converter 12, and supplies the smoothed DC voltage to inverter 14. The voltage sensor 13 detects the voltage across the smoothing capacitor C 0, that is, the system voltage VH, and outputs the detected value to the control device 30.

  When the torque command value of AC motor M1 is positive (Trqcom> 0), inverter 14 is switched in response to switching control signals S3 to S8 from control device 30 when a DC voltage is supplied from smoothing capacitor C0. The AC motor M1 is driven so as to convert a DC voltage into an AC voltage and output a positive torque by the switching operation of the elements Q3 to Q8. Further, when the torque command value of AC 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 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 system 100, torque command value Trqcom of AC motor M1 is set to be negative (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 step-up / down converter 12. The regenerative braking here refers to braking with regenerative power generation when the driver operating the electric vehicle performs a footbrake operation, or regenerative braking by turning off the accelerator pedal while driving, although the footbrake is not operated. This includes decelerating (or stopping acceleration) the vehicle while generating electricity.

  Current sensor 24 detects motor current MCRT flowing through AC 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 two phases of motor current (for example, V-phase current Iv and W-phase current Iiw) 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 motor M1, and sends the detected rotation angle θ to the control device 30. The control device 30 can calculate the rotational speed (rotational speed) Nmt 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 operates the motor drive system 100 by software processing by executing a pre-stored program by a CPU (not shown) and / or hardware processing by a dedicated electronic circuit. To control.

  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, the motor currents Iv and Iw from the current sensor 24, the rotation angle θ from the rotation angle sensor 25, etc., the AC motor M1 outputs torque according to the torque command value Trqcom by a control method described later. The operation of the step-up / down converter 12 and the inverter 14 is controlled. That is, the switching control signals S1 to S8 for controlling the buck-boost converter 12 and the inverter 14 as described above are generated and output to the buck-boost converter 12 and the inverter 14.

  During the step-up operation of buck-boost 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.

  When control device 30 receives a signal RGE indicating that the electric vehicle has entered the regenerative braking mode from an external ECU, switching control signals S3 to S3 convert the AC voltage generated by AC motor M1 into a DC voltage. S8 is generated and output to the inverter 14. Thereby, the inverter 14 converts the AC voltage generated by the AC motor M <b> 1 into a DC voltage and supplies it to the step-up / down converter 12.

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

(Description of control mode)
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 motor M1 in motor drive system 100 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 motor M <b> 1, that is, power conversion in inverter 14.

  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 sine wave 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 sine wave voltage command is in the range of the carrier wave amplitude or less, the line voltage applied to the AC motor M1 becomes a sine wave. Also proposed is a control method in which a voltage command is generated by superimposing a 3n-order harmonic component (n: a natural number, typically n = 1 third-harmonic) on a sine wave component in the range below the carrier wave amplitude. ing. In this control method, a period in which the voltage command becomes higher than the carrier wave amplitude occurs due to the harmonic component. However, since the 3n-order harmonic component superimposed on each phase is canceled between lines, the line voltage is a sine wave. It will be maintained. 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, one pulse of a rectangular wave having a ratio of 1: 1 between the high level period and the low level period is applied to the AC motor M1 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 larger 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 step-up / down converter 12, that is, the system voltage VH needs to be set higher than this motor required voltage. On the other hand, there is a limit value (VH maximum voltage) in the boosted voltage by the buck-boost converter 12, that is, the 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 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 is a flowchart illustrating a control mode selection method.
As shown in the flowchart of FIG. 3, upon receiving a torque command value Trqcom of AC motor M <b> 1 (step S <b> 100) calculated by a host ECU (not shown) based on a required vehicle output according to the accelerator opening, etc., control device 30. Calculates the required motor voltage (induced voltage) from the torque command value Trqcom and the rotational speed of AC motor M1 based on a preset map or the like (step S110), and further calculates the required motor voltage and system voltage VH. According to the relationship with the maximum value (VH maximum value), it is determined whether to perform motor control by applying either the rectangular wave voltage control mode or the PWM control mode (step S120). Whether to use the sine wave PWM control or the overmodulation PWM control when applying the PWM control mode is determined according to the modulation rate range of the voltage command value according to the vector control. According to the control flow, an appropriate control mode is applied from among the plurality of control modes shown in FIG. 2 according to the operating conditions of AC motor M1.

FIG. 4 shows a correspondence relationship between the operation state of AC motor M1 and the above-described control mode.
Referring to FIG. 4, sine wave PWM control is generally used to reduce torque fluctuation in the low rotation speed range A1, overmodulation PWM control in the middle rotation speed range A2, and in the high rotation speed range A3. Square wave voltage control is applied. In particular, the output of AC motor M1 is improved by applying overmodulation PWM control and rectangular wave voltage control. 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.

  FIG. 5 is a block diagram illustrating a motor control configuration by the motor drive system according to the embodiment of the present invention. Each functional block for motor control shown in FIG. 5 can be realized by hardware or software processing by the control device 30.

  Referring to FIG. 5, PWM control unit 200 and offset F / B (feedback) processing unit 300 pulse so that AC motor M1 outputs a torque according to torque command value Trqcom when PWM control mode is selected. Switching control signals S3 to S8 of the inverter 14 are generated in accordance with width modulation (PWM) control. Although illustration is omitted, the control device 30 performs torque control by voltage phase control of the rectangular wave pulse based on the deviation between the estimated torque value and the torque command value when the rectangular wave voltage control mode is selected. A rectangular wave voltage control unit is further provided.

  Specifically, the PWM control unit 200 includes a current command generation unit 210, coordinate conversion units 220 and 240, a PI calculation unit 230, a PWM signal generation unit 250, and a control mode determination unit 260.

  Current command generation unit 210 generates a d-axis current command value Idcom and a q-axis current command value Iqcom corresponding to torque command value Trqcom according to a predetermined table or the like.

  The coordinate conversion unit 220 performs a V-phase current iv and a 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.

  The PI calculation unit 230 receives a deviation ΔId (ΔId = Idcom−Id) with respect to the command value of the d-axis current and a deviation ΔIq (ΔIq = Iqcom−Iq) with respect to the command value of the q-axis current. PI calculation unit 230 performs a PI calculation with a predetermined gain on d-axis current deviation ΔId and q-axis current deviation ΔIq to obtain a control deviation, and d-axis voltage command value Vd # and q-axis voltage command value corresponding to the control deviation. Vq # is generated.

  The coordinate conversion unit 240 converts the d-axis voltage command value Vd # and the q-axis voltage command value Vq # to 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 value Vu #, Vv #, Vw # is converted. The system voltage VH is also reflected in the conversion from the d-axis and q-axis voltage command values Vd # and Vq # to the phase voltage command values Vu #, Vv # and Vw #.

  Offset correction values ΔVu #, ΔVv #, ΔVw # generated by the offset F / B processing unit 300 are added to the phase voltage command values Vu #, Vv #, Vw # converted by the coordinate conversion unit 240. Is done. The values obtained by adding the offset correction values ΔVu #, ΔVv #, ΔVw # to the phase voltage command values Vu #, Vv #, Vw # are the final phase voltage command values Vu *, Vv *, Vw *. The signal is supplied to the PWM signal generation unit 250.

  Specifically, offset F / B processing unit 300 calculates an offset correction value from the motor current flowing in AC motor M1, and based on the calculated offset correction value, each phase voltage command value Vu #, Vv #, Vw #. Correct. Specifically, the offset F / B processing unit 300 includes an offset calculation unit 310, a PI calculation unit 320, and a limiter 330.

  The offset calculation unit 310 calculates an offset amount included in the motor currents iu, iv, iw detected by the current sensor 24. Specifically, the offset calculation unit 310 detects the average value of the target motor current (target value of each phase motor current corresponding to the d-axis and q-axis current command values) at that time by the current sensor 24. The deviations Δiu, Δiv, Δiw are subtracted from the average values of the currents iu, iv, iw and supplied to the PI calculation unit 320 as offset amounts.

  The PI operation unit 320 calculates a P feedback value by multiplying the offset amounts Δiu, Δiv, Δiw by the P gain, and calculates an I Ford back value by multiplying the offset amounts Δiu, Δiv, Δiw by the I gain, These are added to calculate the offset correction values ΔVu, ΔVv, ΔVw of each phase voltage command value. Hereinafter, the P feedback value calculated by the PI calculation unit 320 is also referred to as an “offset F / B integral term”.

  The limiter 330 limits the range that can be corrected by the offset F / B process. Specifically, limiter 330 prevents offset correction values ΔVu, ΔVv, and ΔVw supplied from PI calculation unit 320 from exceeding an upper limit value (hereinafter also referred to as “control limiter”) of a predetermined correction range. Limit to.

  The offset correction value is limited in this way because, for example, when the current sensor 24 is abnormal and the sensor error becomes large, the offset amount also increases. Therefore, the voltage command value is set according to the offset amount. This is because the normal control cannot be performed by correcting.

  Therefore, the limiter 330 uses the control limiter to limit the offset correction values ΔVu, ΔVv, ΔVw from the PI calculation unit 320, and outputs the final offset correction values ΔVu #, ΔVv #, ΔVw #. The offset correction values ΔVu #, ΔVv #, ΔVw # are added to the U-phase, V-phase, and W-phase voltage command values Vu #, Vv #, Vw #, respectively. Voltage command values Vu *, Vv *, Vw * are generated.

  The PWM signal generation unit 250 generates the switching control signals S3 to S8 based on the comparison between the voltage command values Vu *, Vv *, and Vw * of each phase and a predetermined carrier wave. The inverter 14 is subjected to switching control according to the switching control signals S3 to S8 generated by the PWM control unit 200, whereby an AC voltage for outputting torque according to the torque command value Trqcom input to the current command generation unit 210 is obtained. Applied.

  As described above, a closed loop for controlling the motor current to the current command value (Idcom, Iqcom) corresponding to the torque command value Trqcom is configured, whereby the output torque of the AC motor M1 is controlled according to the torque command value Trqcom.

  When the PWM control mode (sine wave PWM control / overmodulation PWM control) is selected according to the flowchart shown in FIG. 3, the control mode determination unit 260 performs sine wave PWM control and overmodulation according to the following modulation factor calculation. Select one of the PWMs.

  Control mode determination unit 260 uses line d voltage command value Vd # and q axis voltage command value Vq # generated by PI operation unit 230 to calculate line voltage amplitude Vamp according to the following equations (1) and (2). calculate.

Vamp = | Vd # | .cosφ + | Vq # | .sinφ (1)
tan φ = Vq # / Vd # (2)
Furthermore, the control mode determination unit 260 calculates the modulation factor Kmd, which is the ratio of the line voltage amplitude Vamp by the above calculation to the system voltage VH, that is, according to the following equation (3).

Kmd = Vamp / VH # (3)
Control mode determination unit 260 selects one of sine wave PWM control and overmodulation PWM control according to modulation factor Kmd obtained by the above calculation. As described above, the selection of the control method by the control mode determination unit 260 is reflected in the carrier wave switching in the PWM signal generation unit 250. That is, at the time of overmodulation PWM control, the carrier wave used at the time of PWM modulation in the PWM signal generation unit 250 is switched from the general one at the time of sine wave PWM control.

  Alternatively, when the modulation factor Kmd obtained by Equation (3) exceeds the range that can be realized by the PWM control mode, the control mode determination unit 260 outputs the output that prompts the change to the rectangular wave voltage control mode. It is sent to an ECU (not shown). The control mode switching determination result in the control mode determination unit 260 is also sent to the abnormality detection unit 400 described below.

(Inverter abnormality detection)
Here, during execution of the PWM control mode or the rectangular wave voltage control, one of the phase arms 15 to 17 of the inverter 14 has an open failure (a failure in which one of the switching elements Q3 to Q8 is always off). In such a case, the half wave of the motor current of the failed phase does not flow, and on average, an offset current flows to the AC motor M1. Due to the influence of the offset current, an overcurrent is generated in the rotor of the AC motor M1, and the rotor generates heat. Therefore, a secondary failure occurs in which the magnetic force of the rotor decreases and the output of the AC motor M1 decreases.

  Therefore, in motor drive system 100 according to the present embodiment, control device 30 further includes an abnormality detection unit 400 for detecting an open failure of inverter 14.

  As shown in FIG. 5, the abnormality detection unit 400 detects an open failure of the inverter 14 by monitoring the offset F / B integral term in the offset F / B processing unit 300.

  FIG. 6 is a timing chart for explaining an abnormality detection method in the abnormality detection unit 400. FIG. 6 shows the U-phase current iu when the U-phase upper arm (switching element Q3) of the inverter 14 has an open failure during PWM control, the offset amount included in the U-phase current iu, and the offset amount based on the offset amount. A time change of the integral term for offset F / B calculated in the F / B processing unit 300 is shown.

  Referring to FIG. 6, in the normal state up to time t1 when the U-phase upper arm is open-failed, the U-phase current iu flows normally, so the offset amount Δiu of the U-phase current is substantially zero. . Therefore, the offset F / B integral term calculated by the offset F / B processing unit 300 (FIG. 5) also shows substantially zero.

  If the U-phase upper arm fails at time t1, the upper half of the U-phase current iu does not flow as shown in FIG. 6, and an offset current flows to the AC motor M1 on average. After this time t1, the offset amount Δiu of the U-phase current increases in the direction of decreasing the current reflecting the waveform of the U-phase current iu.

  When the offset amount Δiu increases, the offset F / B processing unit 300 performs a process for generating an offset correction value for the voltage command value. As a result, the offset F / B integral term (= offset amount × P gain) calculated by the offset F / B processing unit 300 also increases.

  The abnormality detection unit 400 monitors the offset F / B integral term, and when the offset F / B integral term exceeds the threshold value at time t3, the abnormality count addition processing is executed. This threshold is set, for example, in the control limiter. Then, when the abnormality count reaches a preset abnormality confirmation time at time t4, the abnormality detection unit 400 determines that an open failure has occurred and sets an abnormality confirmation flag.

FIG. 7 is a flowchart for explaining an abnormality detection method in the abnormality detection unit 400.
Referring to FIG. 7, when abnormality detection unit 400 receives an offset F / B integral term from PI calculation unit 320 and receives a control limiter from limiter 330, whether or not the offset F / B integral term exceeds the control limiter. Is determined (step S01). If the offset F / B integral term exceeds the control limiter (YES in step S01), an abnormal count is added (step S02), and if the abnormal count is equal to or longer than a predetermined abnormal determination time (step If YES in S03), it is determined that an open state has occurred (step S04). If the abnormality counter has not reached the abnormality confirmation time (NO in step S03), the process returns to S01 again.

  On the other hand, when the offset F / B integral term is equal to or less than the control limiter (NO in step S01), abnormality detection unit 400 determines that the open state does not cause a normal state (step S05). At this time, the abnormal count is reset.

  As described above, the abnormality detection unit 400 detects the open failure of the inverter 14 by monitoring the offset F / B integral term in the offset F / B processing unit 300.

  However, the current offset as shown in FIG. 6 occurs not only when an open failure occurs, but also when the control mode of the AC motor M1 described above is switched between the PWM control mode and the rectangular wave voltage control mode. . This is because a difference in switching timing of the inverter 14 due to a difference in control mode or a difference in waveform applied to the AC motor M1 occurs. Therefore, the offset F / B integral term increases even when the control mode of AC motor M1 is switched. As a result, when the offset F / B integral term exceeds the control limiter, there is a possibility that the abnormality detection unit 400 may erroneously determine that the open state is an abnormal state.

  Therefore, in order to prevent such erroneous detection of abnormality, abnormality detection unit 400 according to the present embodiment, according to information regarding the operating condition (torque and rotation speed) of AC motor M1 and the switching state of the control mode, A configuration is adopted in which a threshold for abnormality determination is variably set.

  FIG. 8 is a timing chart for explaining an abnormality detection method by the abnormality detection unit 400 when the motor rotation speed changes suddenly.

  Referring to FIG. 8, when the upper arm has an open failure at time t11, the current in the upper half of U-phase current iu stops flowing, and an offset current flows to AC motor M1 on average. Therefore, after time t11, the offset amount ΔIu of the U-phase current increases, and accordingly, the offset F / B integral term also increases.

  Here, at time t13 after time t11, it is assumed that the rotational speed of AC motor M1 has suddenly changed due to slippage of the drive wheels. At this time, if the rotational speed is included in the high rotational speed range (corresponding to A2 in FIG. 4), the required motor voltage (induced voltage) calculated based on the torque command value Trqcom and the rotational speed is the VH maximum voltage. Will reach. Therefore, the control mode determination unit 260 switches from the PWM control mode to the rectangular wave voltage control mode.

  When the control mode of AC motor M1 is switched, the above-described current offset occurs at the time of switching. Therefore, as shown in FIG. 8, offset amount ΔIu of U-phase current iu further increases.

  At this time, the abnormality detection unit 400 corrects the threshold for detecting the abnormality of the inverter 14 to a value larger than that of the control limiter when a sudden change in the motor rotation speed and control mode switching are detected. .

  This threshold value is set based on the error of the current sensor 24 and the current offset amount when switching the control mode. For example, under an operating condition in which the motor rotation speed does not change suddenly, the threshold value is set equal to the control limiter in the limiter 330. And in the driving | running condition where the motor rotation speed changes suddenly, a threshold value is set to the value which exceeds the amount of current offset at the time of control mode switching.

  As described above, the abnormality detection unit 400 has corrected the offset F / B integral term beyond the corrected threshold value at time t14 by correcting the threshold value for abnormality detection in the increasing direction according to the sudden change in the motor rotation speed. Sometimes, an abnormal count addition process is executed. When the abnormality count reaches the preset abnormality confirmation time at time t15, the abnormality detection unit 400 determines that the open state has occurred and sets an abnormality confirmation flag.

  FIG. 9 is a flowchart for explaining a threshold value setting method for abnormality detection in the abnormality detection unit 400.

  Referring to FIG. 9, abnormality detection unit 400 determines whether or not the rotational speed of AC motor M1 has suddenly changed (step S11), and if the rotational speed has suddenly changed (YES in step S11), further It is determined whether or not control mode switching has occurred (step S12). Note that the determination in step S11 is performed based on, for example, whether or not a change in the rotational speed greater than or equal to a predetermined value has occurred in a certain period.

  When the control mode is switched (YES in step S12), abnormality detection unit 400 increases the threshold for abnormality detection (step S13). On the other hand, when the rotational speed of AC motor M1 is not changing suddenly (NO in step S11), or when the control mode is not switched even if the rotational speed is changing suddenly (NO in step S12), The abnormality detection unit 400 sets the threshold value to an initial value (for example, a control limiter) (step S14).

  8 and 9, the case where the rotational speed suddenly changes as the operating condition of the AC motor M1 has been described. However, even when the torque of the AC motor M1 changes suddenly, the threshold value is corrected according to the switching of the control mode. The In other words, abnormality detection unit 400 detects an occurrence of torque change or rotation speed change greater than or equal to a predetermined value in AC motor M1, and if it is determined that control mode switching is required, an abnormality is detected. The threshold value is corrected so as to increase the threshold value for detection.

  As described above, in the present embodiment, the open failure of the inverter 14 is detected by monitoring the offset F / B integral term based on the offset amount of each phase motor current. At this time, the threshold value is variably set according to information regarding the operating condition of AC motor M1 and the switching state of the control mode. As a result, when the control mode is switched due to a sudden change in the rotational speed of the AC motor M1, the threshold is corrected in the increasing direction in accordance with the current offset amount at the time of switching. It is possible to prevent an open failure from being erroneously determined from the relationship with the term. As a result, in the motor drive system having an AC motor that can switch the control mode, it is possible to accurately detect an abnormality of the inverter.

  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.

  5 Ground wire, 6, 7 Power line, 10 # DC voltage generator, 10, 13 Voltage sensor, 11, 24 Current sensor, 12 Buck-boost converter, 14 Inverter, 15 U-phase arm, 16 V-phase arm, 17 W-phase arm , 25 rotation angle sensor, 30 control device, 100 motor drive system, 200 PWM control unit, 210 current command generation unit, 220, 240 coordinate conversion, 230, 320 PI calculation unit, 250 PWM signal generation unit, 260 control mode determination unit , 300 Offset F / B processing unit, 310 Offset calculation unit, 330 Limiter, 400 Abnormality detection unit, B DC power supply, C0, C1 smoothing capacitor, D1-D8 Anti-parallel diode, L1 reactor, M1 AC motor, Q1-Q8 power Semiconductor switching element, SR1, SR2 system Over.

Claims (2)

A motor drive system control device comprising a DC power supply and an inverter that converts a DC voltage output from the DC power supply into an AC voltage for driving an AC motor,
Switching between a first control mode for applying a rectangular wave voltage to the AC motor and a second control mode for controlling the applied voltage to the AC motor according to pulse width modulation control according to the operating conditions of the AC motor A control mode determination unit for determining whether it is necessary,
An offset correction unit for performing feedback control for correcting an offset amount of a motor current flowing through each phase of the AC motor;
An abnormality detection unit that detects that the inverter is abnormal by monitoring an offset feedback amount calculated based on the offset amount by the offset correction unit;
The abnormality detection unit
Abnormality detection that detects whether or not the state where the offset feedback amount exceeds the threshold continues for a predetermined time, and detects that the inverter is abnormal when it is determined that the state where the offset feedback amount exceeds the threshold continues for the predetermined time Means,
A change detecting means for detecting that a torque change or a rotational speed change of a predetermined value or more has occurred in the AC motor;
When the change detection means detects the occurrence of torque change or rotation speed change greater than the predetermined value, the control mode determination unit needs to switch between the first and second control modes. And a correction unit that corrects the threshold value so as to increase the threshold value. The inverter includes a plurality of arms each corresponding to each phase of the AC motor, and each of the plurality of arms includes two switching elements connected in series,
When the abnormality detection unit determines that the state exceeding the threshold value has continued for the predetermined time, an open failure in which one switching element included in any one of the plurality of arms is always in an OFF state. The control device for a motor drive system according to claim 1, wherein the controller is detected.

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