JP2010252496A - Motor drive system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform accurate motor-neutral-point current control by correctly estimating a motor input power. <P>SOLUTION: The power from a capacitor 30 is supplied to a motor 22 via an inverter 24, and a DC power supply 32 is connected to the neutral point of the motor 22. An electronic control unit 40 determines a motor input power Pm, based on the expression: Pm=IdVd<SP>*</SP>+IqVq<SP>*</SP>(where a d-axis voltage command is Vd<SP>*</SP>, a q-axis voltage command is Vq<SP>*</SP>, a d-axis current is Id and q-axis current is Iq). By using the motor input power, the switching of the inverter 24 is controlled. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a motor drive system for connecting a DC power source to a neutral point of a motor and controlling the operation of the inverter to adjust the capacitor voltage on the input side of the inverter and to drive the motor with a current from the inverter.

  2. Description of the Related Art Conventionally, a system that drives a motor by converting DC power from a battery into a predetermined AC current using an inverter has been widely used. In such a system, when changing the output torque of the motor, it is preferable to change the inverter input voltage. Therefore, a motor system has been proposed in which a battery is connected to the neutral point of the motor, a capacitor is connected to the inverter input side, and power is exchanged between the battery and the capacitor by driving the inverter to change the inverter input voltage. ing. In this system, the inverter input voltage can be controlled in accordance with the output torque of the motor, and there is an advantage that a sufficient inverter input voltage can be obtained while the battery voltage is kept relatively low.

  Such a motor system is disclosed in Patent Documents 1 and 2, for example.

JP 2002-291256 A Japanese Patent Laid-Open No. 2000-50686

  Here, the inverter input voltage (capacitor voltage) as described above is controlled by the neutral point current from the battery. Therefore, it is preferable to accurately estimate the motor input power and control the inverter switching to control the neutral point current.

The present invention includes a motor having a star-connected multi-phase motor coil, a DC power source connected to a neutral point of the motor coil, an inverter whose output side is connected to the motor coil, and supplies current to the motor coil. And a capacitor connected to the input side of the inverter, and controls the operation of the inverter, thereby adjusting the capacitor voltage and controlling the current supplied to the motor coil to drive the motor. Based on the d-axis voltage command Vd ^* and the q-axis voltage command Vq ^* and the d-axis current Id and the q-axis current Iq obtained from the detected values of the motor phase currents, It is characterized by seeking.
Pm = IdVd ^* + IqVq ^*

  According to the present invention, the motor input power can be estimated relatively easily and accurately, and accordingly, the neutral point current can be accurately controlled and the capacitor voltage can be accurately controlled.

It is a figure which shows the whole structure of a system. It is a figure which shows the structure of the switching command production | generation in the case of PWM control. It is a figure which shows the structure of the switching command generation | occurrence | production in the case of drive wave control.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of a motor system 20 according to an embodiment of the present invention. The motor system 20 includes a motor 22 that is rotationally driven by three-phase AC, an inverter circuit 24 that can convert DC power into three-phase AC power and supply the motor 22, and a positive bus 26 and a negative bus 28 of the inverter circuit 24. , A DC power source 32 connected to the negative electrode bus 28 of the inverter circuit 24 and the neutral point of the motor 22, and an electronic control unit 40 for controlling the entire apparatus.

  As the motor 22, for example, a PM-type synchronous generator motor capable of generating power is used which includes a rotor having a permanent magnet attached to the outer surface and a stator around which a three-phase coil is wound. The rotating shaft of the motor 22 is an output shaft, and power is output from this rotating shaft. Further, the motor 22 can generate electric power when power is input to its rotating shaft.

  The inverter circuit 24 is composed of six transistors T1 to T6 and six diodes D1 to D6. Two transistors T1 to T6 are arranged in pairs so as to be on the source side and the sink side with respect to the positive electrode bus 26 and the negative electrode bus 28, respectively, and at the connection point, three-phase coils (u, Each of v, w) is connected. Therefore, by switching the transistors T1 to T6, a rotating magnetic field is formed by the three-phase coil of the motor 22, and the motor 22 can be rotationally driven.

  The DC power source 32 is constituted by, for example, a nickel hydride or lithium ion chargeable / dischargeable secondary battery.

  The electronic control unit 40 is configured as a microprocessor, and at each phase current Iu, Iv, Iw from the current sensors 42 to 46 attached to each phase of the three-phase coil of the motor 22 and the neutral point of the motor 22. The neutral point current In from the attached current sensor 48, the rotation angle θ of the rotor from the rotation angle sensor 38 attached to the rotation shaft of the motor 22, and the terminal voltage Vc from the voltage sensor 34 attached to the capacitor 30. The voltage Vb between the terminals from the voltage sensor 36 attached to the DC power source 32, a command value related to motor operation (for example, a motor output torque command value) and the like are input. The electronic control unit 40 outputs a control signal for performing switching control of the transistors T1 to T6 of the inverter circuit 24.

  In such a motor system 20, electric power can be exchanged between the capacitor 30 and the DC power supply 32 via the motor 22 and the inverter circuit 24. That is, by controlling the ratio of the ON periods of the upper transistors T1, T3, T5 and the lower transistors T2, T4, T6 in the inverter circuit 24, power is exchanged between the capacitor 30 and the DC power supply 32. To control. Therefore, the motor 22 can be driven by controlling the output voltage of the capacitor 30 to an appropriate value in accordance with a motor output torque command or the like.

  That is, the electronic control unit 40 generates a switching control signal for the inverter circuit 24 from the output torque command value, the rotational speed of the motor 22, the motor phase currents, etc., and controls the output torque of the motor. The power is moved by controlling the duty ratio of the transistor. Further, the inverter input voltage (the voltage of the capacitor 30) is determined according to the motor output torque command value, the motor rotation speed, etc., and controlled to that voltage.

  Here, regarding the inverter input voltage, the motor output torque control at that time will be described on the assumption that the inverter input voltage is set to the target voltage.

FIG. 2 shows generation of a PWM control signal (PWM signal for controlling switching of the transistors T1 to T6) in the electronic control unit 40. A target excitation current Id ^* , a target torque current Iq ^* , and a target inverter input voltage (capacitor voltage) Vc ^* are calculated from the target torque (motor output torque command value), the motor speed, and the like. These target values are input to the subtracters 50d, 50q, and 50c, the difference is calculated, and the PI control units 52d, 52q, and 52c convert them into command values in PI control according to the target deviation. Here, the deviation with respect to the target neutral point current, which is the output of the PI control unit 52c, is input to the adder 54, where Pm / Vb is added to obtain the target neutral point current In ^* .

In the present embodiment, the motor input power Pm, d-axis voltage command ^Vd *, the q-axis voltage command ^Vq *, d-axis current Id, based on the q-axis current Iq,
Pm = IdVd ^* + IqVq ^*
Ask for. The d-axis current Id and the q-axis current Iq are obtained from the detected values of the motor phase currents.

  Each phase current of the motor is a value that can be detected in real time. From this, the d-axis and q-axis currents can be easily obtained. On the other hand, since each axis voltage command can be obtained immediately from a torque command or the like, the motor input power Pm in the above equation can be obtained by a relatively simple calculation.

Conventionally, in order to calculate the motor input power, a motor shaft output calculated as in the following equation has been used. Here, τ ^* is the torque command value, and ω is the current motor angular velocity.
Pm = τ ^* ω

  However, in Pm calculated in this way, there is an error without considering the loss (copper loss, iron loss, etc.) inside the motor. Therefore, the loss under each operating condition (angular velocity, torque) of the motor to be controlled is measured in advance and stored in a memory as a two-dimensional map, and the loss is read from the map according to the driving situation. The motor input voltage was calculated by adding to the motor shaft output calculated by the above formula.

However, with this conventional method,
(1) The accuracy decreases due to an error in the loss map data. (2) The memory capacity required for map storage increases. (3) The calculation amount required for referring to the two-dimensional map increases. In particular, in the transient state where division is necessary (4), there is a problem that an amount of change in magnetic energy cannot be taken into account and an error occurs.

  According to this embodiment, since the power is calculated from the voltage and current actually required by the motor, the correct motor input power at that time can be accurately calculated. Further, since the calculation can be performed by only two multiplications and one addition, the calculation amount can be reduced.

Thus, assuming that the obtained motor input power Pm is covered by the DC power supply 32, the neutral point current required at that time is estimated by dividing by the voltage Vb. That is, the motor drive current is supplied from the DC power supply 32 as a neutral point current, and the neutral point current is added to the amount of current corresponding to the deviation of the capacitor voltage from the PI control unit 52c, so that the motor drive and A target neutral point current In ^* determined for both control of the capacitor voltage is determined.

The target neutral point current In ^* , which is the output of the adder 54, is input to the subtractor 56, where the neutral point current In actually measured is subtracted, and the difference is supplied to the PI control unit 58. Here, the target value (neutral point voltage command) Vn ^{* of the} neutral point voltage is determined.

  Here, in the above description, the actual current flowing through the lead line from the neutral point is referred to as neutral point current In. On the other hand, I0 of currents Id, Iq, and I0 obtained by coordinate conversion from three-phase (u, v, w) currents Iu, Iv, and Iw is called a zero-phase current.

  Since the output of the PI control unit 52c is Vn *, it is necessary to convert it to V0 *. However, this conversion is simply multiplied by a coefficient √3, and is simply expressed as Vn * hereinafter. If this conversion is included in the gains kp (differential gain) and ki (integral gain) in the PI control unit 52c, the output Vn * of the PI control unit 52c is V0 *.

In this way, the target excitation voltage (d-axis voltage command) Vd ^* , target torque voltage (q-axis voltage command) Vq ^* , and target zero-phase voltage (zero-phase voltage command) Vn obtained by the PI control units 52d and 52q. ^* Is input to the dq0 inverse converter 62, where it is converted into a voltage command value for the uvw phase. The obtained voltage command value is compared with the PWM carrier in the PWM modulation unit 64 to obtain the PWM control signal of each switching element, which is the control terminal of each transistor T1 to T6 of the inverter circuit 24 (if the transistor is IGBT) Gate) and these are switched. In this way, neutral point current and motor drive current can be controlled. The PWM modulator 64 is also supplied with Vb / Vc ^* as a PWM center value, and the neutral point current is controlled based on this.

That is, the neutral point voltage is determined by the duty ratio of the upper transistor and the lower transistor. On the other hand, the duty ratio of the upper transistor and the lower transistor is determined by Vb / Vc ^* . If Vb / Vc ^* = 0.5, the duty ratio indicating the ratio of the ON period of the upper transistor to the ON period of the upper and lower transistors is 50%. If Vb / Vc ^* = 1/3, the upper transistor The duty ratio indicating the ON period is 33%. Therefore, the PWM modulator adds the duty ratio for compensation corresponding to the output from the PI control unit 58 to the basic Vb / Vc ^* to determine the duty ratio.

  Thus, in this embodiment, since the motor input power Pm is accurately detected, the neutral point current can be accurately controlled and the capacitor voltage can be accurately controlled.

FIG. 3 shows a configuration for voltage control when rectangular wave control is performed. A torque command τm ^* for the motor output torque is supplied to the subtractor 70. The subtracter 70 receives an estimated value (torque estimated value) of an actual motor torque output. The estimated torque value may be detected from the motor input current, but may be measured by means such as torque measurement on the output shaft. An error of the output torque is obtained by the subtractor 70, which is input to the PI control unit 72, and a command value Ψ ^* for error compensation for the input voltage phase angle of the motor is output. The input voltage phase of the motor is a phase of the input voltage with respect to the magnet position of the rotor. The output Ψ ^* of the PI control unit 72 is supplied to the adder 74. The adder 74 is input with the measured rotation angle θe of the motor, and the adder 74 calculates a command value of the input voltage phase angle, which is converted by the first-order lag filter 76 to change the phase angle command. Is supplied to the switching pattern generation means 78 as the rotation angle command value θes ^* . The first-order lag filter 76 is a filter having a transfer function of 1 / (Ts + 1), T is a time constant, and s is a Laplace operator.

On the other hand, the calculation of the command value Vn ^* for the duty ratio for controlling the neutral point current is the same as in FIG. 2, and the subtracter 50c, the PI control unit 52c, the adders 54 and 56, and the PI control unit 58. And a zero-phase voltage command Vn ^* is output from the PI control unit 58. Here, since PWM control is performed in FIG. 2, Vb / Vc is added in the adder 60. However, in the configuration of FIG. 3, the zero-phase voltage command Vn ^* is input to the calculator 80. In addition to Vn ^* from the PI control unit 58, Vc ^* and Vb are supplied to this computing unit 80. From these, θd ^* = (Vb + Vn ^* ) / 2Vc ^* is calculated and θd ^* is output. To do. Here, θd ^* indicates a switching timing phase between the ON period of the upper transistor and the ON period of the lower transistor. 2Vc ^* corresponds to 2π, and Vb / 2Vc ^* represents the capacitor voltage Vc at that time. Vn ^* / Vc ^* is a correction term from the error.

  Then, the switching pattern generation means 78 generates switching patterns Su, Sv, Sw of the phases of the transistors T1 to T6 in the inverter circuit 24 from the input signal, and thereby the switching of the transistors T1 to T6 is controlled.

Also in this embodiment, since the Pm / Vb obtained as described above is used when calculating the zero-phase voltage command Vn ^* , effective neutral point current control is performed in the same manner as described above. be able to.

  In addition, since the whole rectangular wave control can employ | adopt what is described in Unexamined-Japanese-Patent No. 2002-84758 etc., description is abbreviate | omitted here.

  20 Motor system, 22 Motor, 24 Inverter circuit, 26 Positive bus, 28 Negative bus, 30 Capacitor, 32 DC power supply, 34, 36 Voltage sensor, 38 Rotation angle sensor, 40 Electronic control unit, 42, 44, 46, 48 Current Sensor, 50d, 50q, 50c, 56, 70 Subtractor, 52d, 52q, 52c, 58, 72 PI control unit, 54, 74 Adder, 62 dq0 inverse conversion unit, 64 PWM modulation unit, 76 First order lag filter, 78 Switching pattern generation means, 80 arithmetic unit.

Claims (1)

A motor having a multi-phase motor coil connected in a star shape;
A DC power source connected to the neutral point of the motor coil;
An inverter whose output side is connected to the motor coil and supplies current to the motor coil;
A capacitor connected to the input side of the inverter;
And adjusting the capacitor voltage by controlling the operation of the inverter, and controlling the current supplied to the motor coil to drive the motor,
The motor input power Pm is obtained by the following equation based on the d-axis voltage command Vd ^* and the q-axis voltage command Vq ^* and the d-axis current Id and the q-axis current Iq obtained from the detected values of the respective phase currents of the motor. A motor drive system characterized by that.
Pm = IdVd ^* + IqVq ^*

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