JP2010124662A - Motor drive system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a motor drive system capable of securing controllability of a voltage conversion device. <P>SOLUTION: The motor drive system 100 includes: an AC electric motor M1; an inverter 14, which drives and controls the motor M1; a step-up converter 12, which varies an input voltage VH to the inverter 14; and a controller 30, which performs feedback control on the input voltage VH according to a deviation of the input voltage VH to a voltage command value. The controller 30 predicts a variable frequency of the input voltage VH from the operation state of the motor M1 and changes either a control gain in the feedback control or control responsiveness in the drive control of the motor M1 when the fluctuation of the input voltage VH at the predicted variable frequency is estimated to be larger in comparison with the frequency characteristics of the control gain in the feedback control. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a motor drive system, and more particularly to a motor drive system including a voltage converter that varies an input voltage of an inverter.

As a kind of motor drive system applied to a hybrid vehicle, for example, Japanese Patent Application Laid-Open No. 2007-159367 (Patent Document 1) boosts a DC voltage supplied from a DC power source with a voltage converter and boosts the DC voltage. A configuration is disclosed in which (this DC voltage corresponding to the input voltage to the inverter is also referred to as “system voltage” hereinafter) is supplied to the inverter. In such a configuration, the voltage converter uses feedback control for controlling the boosting operation in the voltage converter according to the difference between the voltage command value and the system voltage. In this feedback control, PI (proportional integral) control or the like is often used.
JP 2007-159367 A JP 2007-143303 A JP 2007-159368 A JP 2007-252144 A

  However, in the feedback control described above, the feedback gain may have a characteristic that varies depending on the frequency due to the influence of the frequency characteristic of the voltage converter. When the feedback gain changes, the system voltage as the control target voltage changes up and down around the voltage command value, that is, the fluctuation of the system voltage increases. As a result, there arises a problem that the controllability of the voltage converter is deteriorated.

  Therefore, the present invention has been made to solve such a problem, and an object thereof is to provide a motor drive system capable of ensuring controllability of the voltage converter.

  A motor drive system according to the present invention includes a motor, a drive circuit that controls the drive of the motor, a voltage conversion device that varies the input voltage to the drive circuit, and feedback of the input voltage according to the deviation of the input voltage with respect to the voltage command value. And a control device for controlling. The control device estimates the fluctuation frequency of the input voltage from the operating state of the motor, and when the fluctuation of the input voltage at the estimated fluctuation frequency is predicted to be large in light of the frequency characteristics of the control gain in the feedback control. Any one of the control gain in the feedback control and the control responsiveness in the motor drive control is changed.

  According to the present invention, it is possible to ensure controllability of the voltage converter.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same reference numerals indicate the same or corresponding parts.

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 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 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.

  In the step-up operation, the step-up / down converter 12 boosts a 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”). 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), and the step-down ratio corresponds to 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 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 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 step-up / down converter 12. Regenerative braking here refers to braking involving regenerative power generation when the driver operating the electric vehicle performs a foot brake operation, or turning off the accelerator pedal while driving, although the foot brake is not operated. This includes decelerating the vehicle (or stopping acceleration) while generating regenerative power.

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

  The rotation angle sensor (resolver) 25 detects the rotor rotation angle 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 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, 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 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.

  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 step-up / down converter 12.

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

(Control structure)
The control of the buck-boost converter 12 by the control device 30 will be described in further detail.

  FIG. 2 is a block diagram showing a control structure of buck-boost converter 12 in control device 30 according to the embodiment of the present invention.

  Referring to FIG. 2, control device 30 includes subtraction units 302 and 306, a proportional control unit (PI) 304, a modulation unit (MOD) 308, and a gain control unit 310.

Subtraction unit 302 receives voltage command value VH ^* from a target value determination unit (not shown), and receives system voltage VH from voltage sensor 13. Voltage command value VH ^* is determined by calculating a required voltage of inverter 14 based on torque command value Trqcom and rotation speed target value. The subtraction unit 302 calculates a voltage deviation from the difference between the voltage command value VH ^* and the system voltage VH, and outputs the voltage deviation to the proportional control unit (PI) 304.

  The proportional control unit 304 includes at least a PI control gain (proportional gain and integral gain), and outputs an operation signal corresponding to the input voltage deviation to the subtraction unit 306.

The subtracting unit 306 inverts the operation signal output from the proportional control unit 304 and adds the DC voltage Vb / voltage command value VH ^* (reciprocal of the theoretical step-up ratio in the step-up / down converter 12) of the DC power source B to obtain the duty ratio. Outputs the ratio command. This duty ratio command is a control command that defines the on-duty of the switching element Q1 of the buck-boost converter 12.

  Modulating section 308 compares the carrier wave (carrier wave) generated by an oscillating section (not shown) with the duty ratio command, generates switching control signals S1 and S2, and controls buck-boost converter 12.

  Gain control unit 310 changes a feedback gain (PI control gain) used for a series of feedback control of system voltage VH according to the operating state of AC electric motor M1. As a result, as described below, it is possible to suppress deterioration of the controllability of the system voltage VH, which is the voltage to be controlled, under the influence of fluctuations in the output power generated in the AC motor M1.

  Hereinafter, the PI control gain changing operation by gain control section 310 according to the present embodiment will be described.

  As a control configuration of AC electric motor M1 by motor drive system 100 shown in FIG. 1, control device 30 has AC motor M1 set to torque command value Trqcom by feedback control based on detection values from current sensor 24 and rotation angle sensor 25. The inverter 14 is controlled so as to output the corresponding torque.

  However, in such a control configuration, an error may be superimposed on the detection value output from the sensor due to the assembly accuracy of the current sensor 24 and the rotation angle sensor 25. For example, the detection error of the rotation angle sensor 25 causes a phase change in the voltage vector input to the AC motor M1, and the current flowing through each phase coil of the AC motor M1 is changed. And this current fluctuation becomes a factor which produces the fluctuation | variation of output power in AC electric motor M1.

When the power fluctuation of the AC motor M1 occurs due to the detection error in this way, in the buck-boost converter 12, the system voltage VH that is the voltage to be controlled changes up and down around the voltage command value VH ^* , that is, the system voltage. VH fluctuations are caused. As a result, the controllability of the buck-boost converter 12 is deteriorated.

  On the other hand, some PI control gains in the feedback control system of the buck-boost converter 12 have a frequency characteristic as shown in FIG. 3, for example.

  Specifically, referring to FIG. 3, the PI control gain exceeds “1” that is the reference value in the vicinity of the frequency f1 [Hz]. For this reason, the feedback control system tends to oscillate easily in a predetermined frequency range including the frequency f1, and therefore, when the power fluctuation of the AC motor M1 described above occurs in the predetermined frequency range, the influence is affected. As a result, the fluctuation of the system voltage VH may become remarkable as compared with other frequency ranges.

  In order to suppress the influence of the power fluctuation of the AC motor M1, the fluctuation frequency of the power fluctuation is actually detected, and the detected fluctuation frequency is compared with the frequency characteristic of the PI control gain so that the PI control gain is constant. It is effective to change the PI control gain so that However, detecting the frequency of power fluctuations of AC electric motor M1 increases the processing load of the ECU that constitutes control device 30, and therefore a high-performance ECU may be required.

  Therefore, in the motor drive system according to the present embodiment, as a configuration for ensuring the controllability of buck-boost converter 12 more simply, gain control unit 310 uses a system voltage that is a control target voltage from the operating state of AC electric motor M1. Estimate the fluctuation frequency of VH. As an example, in the present embodiment, gain control unit 310 estimates the fluctuation frequency of the control target voltage from the motor rotation speed of AC electric motor M1.

  Specifically, when an error is superimposed on the detection value of the rotation angle sensor 25, the actual rotation speed calculated from the detection value is a deviation that fluctuates with a period proportional to the rotation period with respect to the average rotation speed. Is included. This rotation period corresponds to the time required for the rotor to rotate 360 degrees and is defined by the detection value of the rotation angle sensor 25. For example, when the detection value of the rotation angle sensor 25 includes a 1.0-order error, the actual rotation number calculated from the detection value is 1 for one cycle of the detection value of the rotation angle sensor 25. It fluctuates at the rate of the period.

  And the fluctuation | variation of this real rotation speed fluctuates the output power of AC electric motor M1 with the period proportional to a rotation period. Therefore, when the motor speed of the AC motor M1 is A [rpm], the AC motor M1 has a fluctuation cycle (= 1 / fluctuation frequency f) determined by the detected value of the rotation angle sensor 25 and the number of pole pairs of the AC motor M1. When the power fluctuation occurs, it is predicted that the system voltage VH is likely to fluctuate at the fluctuation frequency f in the buck-boost converter 12 due to the influence of the power fluctuation. That is, it is possible to estimate at what fluctuation frequency the system voltage VH fluctuates at what motor rotation speed, based on the influence of the detection error of the sensor on the motor control and the number of pole pairs of the AC motor M1.

  Then, when the fluctuation frequency f of the system voltage VH is estimated in this way, the gain controller 310 determines the system voltage VH at the estimated fluctuation frequency f in light of the frequency characteristic of the PI control gain shown in FIG. It is determined whether or not the fluctuation (that is, the deterioration of controllability) becomes significant. When it is determined that the fluctuation of the system voltage VH becomes significant, the gain control unit 310 changes (decreases) the PI control gain so as to obtain a constant gain. Thereby, it can suppress that the controllability of the buck-boost converter 12 deteriorates under the influence of the power fluctuation which generate | occur | produces in AC electric motor M1.

(Example of change)
In the above-described embodiment, when it is determined that the fluctuation of the system voltage VH becomes significant, the PI control gain in the buck-boost converter 12 is changed. However, the control response of motor control is reduced. Even in the configuration, the same effect can be obtained.

  Specifically, the power fluctuation of the AC motor M1 caused by the detection error is suppressed by changing the feedback gain in the motor control or by removing the detection error by filtering the detection value of the current sensor 24. be able to. As a result, fluctuations in system voltage VH can be suppressed, so that the controllability of buck-boost converter 12 can be suppressed from deteriorating.

  As described above, according to the embodiment of the present invention, the fluctuation frequency of the control target voltage of the buck-boost converter is estimated from the operating state of the AC motor, and the control is performed in light of the frequency characteristics of the feedback gain in the buck-boost converter. By changing the feedback gain in the frequency range where the fluctuation of the target voltage is judged to be significant, or changing the control response of the motor control, the controllability of the buck-boost converter deteriorates with a simple device configuration Can be suppressed.

  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 system according to an embodiment of the present invention. It is a block diagram which shows the control structure of the buck-boost converter in the control apparatus by embodiment of this invention. It is a figure which shows an example of the frequency characteristic of PI control gain in the feedback control system of a buck-boost converter.

Explanation of symbols

  5 Ground wire, 6, 7 Power line, 10 # DC voltage generator, 10 Voltage sensor, 11, 24 Current sensor, 12 Buck-boost converter, 13 Voltage sensor, 14 Inverter, 15 U phase upper and lower arm, 16 V phase upper and lower arm, 17 W-phase upper / lower arm, 25 rotation angle sensor, 30 control device, 100 motor drive system, 302, 306 subtraction unit, 304 proportional control unit, 308 modulation unit, 310 gain control unit, C0, C1 smoothing capacitor, D1-D3 reverse Parallel diode, L1 reactor, M1 AC motor, Q1-Q8 power semiconductor switching element, SR1, SR2 system relay.

Claims (1)

A motor,
A drive circuit for driving and controlling the motor;
A voltage converter that varies an input voltage to the drive circuit;
A control device that feedback-controls the input voltage according to a deviation of the input voltage with respect to a voltage command value;
The control device estimates the fluctuation frequency of the input voltage from the operating state of the motor and predicts that the fluctuation of the input voltage at the estimated fluctuation frequency is large in light of the frequency characteristic of the control gain in the feedback control. If so, a motor drive system that changes either the control gain in the feedback control or the control responsiveness in the drive control of the motor.

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