JP2005130638A - Power conversion device for electric vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power conversion device for electric vehicles, wherein excitation current command is adjusted according to the state of operation and the system efficiency is improved. <P>SOLUTION: The power conversion device for electric vehicles comprises a direct-current power supply 1, an inverter 32 that converts the output of the direct-current power supply 1 into an alternating-current output for driving an alternating-current motor 4 via a smoothing capacitor 31, and a control means 33 that controls the inverter 32. The control means 33 separates the current of the alternating-current motor into an exciting current and a torque current orthogonal to the exciting current, by vector control or sensorless vector control and then controls them. The control means is so constituted that it has a changing means that selectively changes the command value for exciting current, according to the operation mode, powering or regeneration of the alternating-current motor 4. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a power converter for an electric vehicle with improved system efficiency.

  A conventional electric vehicle drive system has a configuration in which a DC input supplied from a DC power source such as a battery is converted into AC by an inverter, and an AC motor is driven by the converted AC output.

  As the control of the inverter, so-called vector control in which torque current and excitation current are separately controlled is used, and sensorless vector control without using a speed sensor is also used. Further, pulse width modulation (PWM) control is usually employed for the inverter.

  The electric vehicle drive performs constant torque control up to the rated speed and controls the excitation current to be constant, but performs so-called field weakening control that decreases the excitation current approximately in inverse proportion to the speed when the speed exceeds the rated speed.

  Also, during deceleration or downhill, regenerative operation is performed to charge the battery with surplus energy.

  In the electric vehicle drive system, when compared with the power running mode, the regenerative mode charges the battery, so the DC voltage becomes higher. Accordingly, as shown in FIG. 5A, the torque current can be increased in the regenerative mode than in the power running mode (the torque current in FIG. 5A is displayed as an absolute value). However, when the regenerative maximum torque is generated with the excitation current having the same value as the efficient excitation current command id * during power running, the phase relationship between the exciting current and the torque current (current phase) as shown in FIG. θT) is broken. That is, only the torque current is increased, and the efficiency of the electric motor is lowered. Therefore, the system efficiency, which is an important index for an electric vehicle, is lowered.

  Further, in the conventional electric vehicle power converter, as shown in FIG. 5B, the excitation current command id * is set to be the same regardless of the power running and the regenerative mode, so that the rotation shifts to the aforementioned field weakening control. The number becomes the same rotation speed n in the power running mode and the regeneration mode, and the system efficiency is also lowered.

As a countermeasure against these problems, a proposal has been made to obtain an excitation current that minimizes the loss in accordance with the torque command by calculation based on a predetermined transfer function to improve efficiency (see, for example, Patent Document 1). .
JP-A-7-67397 (page 3-8, FIG. 1)

  The method for improving the efficiency of the system according to Patent Document 1 has a problem that the control system is complicated and it is necessary to set motor constants in advance, which is troublesome.

  The present invention has been made in view of the above problems, and an object thereof is to provide a power conversion device for an electric vehicle in which an excitation current command is adjusted according to an operation state with a simple control circuit configuration, and system efficiency is improved. To do.

  In order to achieve the above object, a power converter for an electric vehicle according to the present invention includes a DC power supply, an inverter for converting the output of the DC power supply to an AC output for driving an AC motor through a smoothing capacitor, and the inverter. The control means is configured to control the current of the AC motor separately into an excitation current and a torque current orthogonal to the excitation current by vector control or sensorless vector control. It is characterized by having a switching means for selectively switching the command value of the exciting current according to the power running or regenerative operation mode.

  According to the present invention, it is possible to adjust the excitation current according to the operation mode of the regenerative mode and the power running mode only by adding a relatively simple control circuit, and to provide a power converter for an electric vehicle with improved system efficiency. can do.

  Embodiments of the present invention will be described below with reference to the drawings.

  A first embodiment of a power converter for an electric vehicle according to the present invention will be described with reference to FIGS. FIG. 1 is a circuit configuration diagram of a power converter for an electric vehicle according to the present invention.

  A DC power source 1 supplies DC power to an inverter 3 for driving an AC motor 4 via a switch 2. The inverter 3 includes a capacitor 31 for smoothing DC, main circuit elements 32u, 32v, 32w, 32x, 32y, and an inverter circuit 32 configured by bridge connection, and a control circuit 33 for controlling the inverter circuit 32. I have. A current detector 34 for detecting a direct current is attached to the inverter 3. The AC motor 4 is provided with a rotation speed detector 5 for detecting the rotation speed.

  The configuration of the control circuit 33 is as follows. A given torque current (q-axis current) command iq *, an excitation current (d-axis current) command id * obtained by a method to be described later, a torque current (q-axis current) iq and an excitation current (d-axis) calculated by feedback calculation The current) id is compared and calculated by the operational amplifier 331 and the operational amplifier 332, and the respective outputs are set as the q-axis voltage command vq * and the d-axis voltage command vd *. The q-axis voltage command vq * and the d-axis voltage command vd * are converted into a three-phase voltage reference by the coordinate converter 333 and converted into a pulse by the PWM controller 334, thereby obtaining a gate signal of the inverter circuit 32. ing.

  The q-axis current iq and the d-axis current id described above detect an arbitrary two-phase output current of the inverter 3, for example, a U-phase current iu and a W-phase current iw, and these are detected by the coordinate converter 335 from 2 to 2 It is calculated by converting to a phase. Here, the reference phase of the coordinate converter 335 is the slip frequency obtained by calculation from the phase angle θr obtained by integrating the rotational speed n detected by the rotational speed detector 5, the torque current command iq *, and the excitation current command id *. A phase angle θ obtained by adding a phase angle θs obtained by integrating fs is used. Similarly, the phase angle θ is used for the reference phase of the coordinate converter 333 described above.

  The excitation current (d-axis current) command id * is obtained by the following method. That is, if the polarity of the current detected by the current detector 34 is positive, the output of the powering excitation current setting device 336 is selected. Conversely, if the polarity is negative, the regenerative excitation current setting device 337 is selected. Select an output. As shown in FIG. 2, the power running excitation current setting device 336 and the regeneration excitation current setting device 337 are set as functions of the torque current command iq * and the rotation speed n, respectively.

  Note that the determination of the power running or regenerative operation mode is not necessarily performed based on the polarity of the direct current obtained by the current detector 34 of the present embodiment, and may be performed by, for example, determining the polarity of the torque current command iq *.

  FIG. 2A shows the principle of adjusting the excitation current command id * according to the absolute value of the torque current command iq *. The rated excitation current id * 1 is the maximum excitation current during power running, but during regeneration, the torque current command iq * can be set larger than that during power running as described above, and the maximum excitation current at this time is id *. 2. Note that, as described above, keeping the current phase θT constant maintains the maximum efficiency of the electric motor, so the excitation current id * is changed according to the change of the torque current command iq *.

  FIG. 2B shows the number of rotations for switching from constant torque operation to constant power operation. As shown in FIG. 2B, in the power running operation, the field weakening control is performed at the rotational speed n1 or more, but in the regenerative operation, the field weakening control is performed at the rotational speed n2 larger than the rotational speed n1, thereby improving the system efficiency. To do.

  As described above, according to the first embodiment of the present invention, the excitation current that maximizes the motor efficiency can be automatically selected according to the operation mode of the power running operation and the regenerative operation. With the configuration, it is possible to provide a power converter for an electric vehicle with improved system efficiency.

  In the above explanation, it has been explained that the excitation current reference is set so that the efficiency at the time of maximum torque generation during power running is the best, but conversely, the excitation current reference is set from the maximum efficiency condition during regeneration. You may do it.

  FIG. 3 is a circuit configuration diagram of the electric power converter for an electric vehicle according to the second embodiment of the present invention. The same parts of the second embodiment as those of the electric power converter for an electric vehicle according to the first embodiment shown in FIG. The second embodiment is different from the first embodiment in that a DC voltage detector 35 of the inverter 3 is provided instead of the current detector 6 in FIG. 1, and in the power running excitation current setting device 336 and the regeneration time in FIG. Instead of the excitation current setting device 337, an hour excitation current setting device 338 and an excitation current adjuster 339 are provided.

  The operation of the excitation current setting device 338 is basically the same as the operation of the excitation current setting device 336 or the excitation current setting device 337 during regeneration in FIG. The operation of the excitation current adjuster 338 will be described below with reference to FIG.

  As shown in FIG. 4A, the excitation current command id * is changed according to the detected voltage of the DC voltage detector 35, and the weight is multiplied by the excitation current command value id *. Under normal conditions, a regenerative operation is performed when the DC voltage is high, and a power running operation is performed when the DC voltage is low. The voltage range changes depending on the state of charge of the battery and aging. When the relationship between the exciting current and torque current that is efficient at point a in FIG. 4A is set to the current phase θT, as shown in FIG. 4B, when the DC voltage is high, the torque current increases. Accordingly, the excitation current is increased, and control is performed so as to maintain the current phase θT at the maximum efficiency a. When the DC voltage is low, the excitation current is reduced as the torque current is reduced, and control is performed so as to maintain the phase θT of the current at the point of maximum efficiency a. As a result, efficient operation becomes possible. If the excitation current is not adjusted, as shown in FIG. 4 (c), the current phase θT1> θT when the DC voltage is high, and θT2 <θT when the DC voltage is low.

As explained above. According to the second embodiment of the present invention, it is possible to provide a power converter for an electric vehicle with improved system efficiency with a simple control circuit configuration.

  In the description of each embodiment of the present invention, the AC motor 4 is described as an induction motor having a slip frequency fs as an example. However, the present invention can be applied even to a synchronous motor having a slip frequency fs of zero. is there.

The circuit block diagram of the power converter device for electric vehicles which concerns on Example 1 of this invention. Explanatory drawing of the exciting current and torque command of Example 1 of this invention. The circuit block diagram of the power converter device for electric vehicles which concerns on Example 2 of this invention. Explanatory drawing of the excitation current and torque command of Example 2 of this invention. Explanatory drawing of the conventional excitation current and torque command.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 DC power supply 2 Switch 3 Inverter 4 AC motor 5 Current detector 6 Rotation speed detector 7 Voltage detector 31 DC capacitor 32 Inverter circuit 33 Control circuit 331 Operational amplifier 332 Operational amplifier 333 Coordinate converter (2 phase / 3 phase)
334 PWM controller 335 Coordinate converter (3 phase / 2 phase)
336 Power running excitation current setting device 337 Regenerative excitation current setting device 338 Excitation current setting device 339 Excitation current controller

Claims (6)

DC power supply,
An inverter that converts the output of the DC power source into an AC output for driving an AC motor through a smoothing capacitor;
And a control means for controlling the inverter,
The control means includes
The current of the AC motor is separated and controlled into an excitation current and a torque current orthogonal to the excitation current by vector control or sensorless vector control,
A power converter for an electric vehicle, comprising switching means for selectively switching the command value of the exciting current according to the power running or regenerative operation mode of the AC motor.   The electric power converter for an electric vehicle according to claim 1, wherein the determination of the power running or regenerative operation mode of the AC motor is based on the polarity of the DC current of the inverter circuit.   The command value of the excitation current is changed substantially in proportion to the command value of the torque current, and the command value of the excitation current in the regeneration mode is made larger than the command value of the excitation current in the power running mode. Item 4. A power converter for an electric vehicle according to Item 1. The command value of the excitation current in the power running mode is reduced approximately in inverse proportion to the rotational speed when the rotational speed of the AC motor is equal to or higher than the first predetermined value,
The command value of the excitation current in the regenerative mode is reduced substantially in inverse proportion to the rotational speed when the rotational speed of the AC motor becomes equal to or greater than a second predetermined value that is greater than the first predetermined value. The electric power converter for electric vehicles according to claim 1 characterized by things. DC power supply,
An inverter that converts the output of the DC power source into an AC output for driving an AC motor through a smoothing capacitor;
Consists of a control means for controlling the inverter and a voltage detector for detecting a DC voltage of the inverter,
The control means includes
The current of the AC motor is separated and controlled into an excitation current and a torque current orthogonal to the excitation current by vector control or sensorless vector control,
A power converter for an electric vehicle, characterized in that a command value of the exciting current is changed in accordance with a DC voltage detected by the voltage detector. The command value of the excitation current is
6. The electric power converter for an electric vehicle according to claim 5, wherein the power converter is changed substantially in proportion to the DC voltage, and an upper limit and a lower limit are provided.

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