JP2009194949A - Pwm inverter system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To use a PWM inverter low in its carrier frequency to obtain high response output. <P>SOLUTION: In phase arms to apply voltage to the U, V, W-phases of an AC motor Motor, the output ends of the cell units U1 to U3, V1 to V3, W1 to W3 of an inverter single unit constitution are multi-connected in series respectively, and the AC power supplies of the cell units U1 to U3, V1 to V3, W1 to W3 are taken in from the secondary wirings of a common input transformer TR to supply the AC current for variable speed drive to the AC motor Motor. The cell units U1 to U3, V1 to V3, W1 to W3 of the same arm are shifted in the phases of the respective carrier frequencies to obtain a PWM inverter output (high response output) having an equivalently high carrier frequency. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a PWM inverter device that drives an AC motor at a variable speed, and more particularly to a device that obtains a high response to torque control or speed control of an AC motor.

  The PWM inverter device, for example, PWM-controls the rotational speed and output torque of an AC motor for a dynamometer, and enables a running resistance test of a test vehicle and an output torque test of an engine.

In such a device, when the high-speed variable speed operation of the motor or the resonance operation of the motor and the mechanical system is reproduced, high response control of the inverter device is required. As a method of obtaining a high response to the PWM inverter device, there is a method of increasing the frequency of a triangular wave carrier signal to be compared with a sine wave signal having a frequency corresponding to a speed command. Furthermore, there are a method for suppressing electromagnetic noise in addition to high response control by increasing the carrier frequency, and a method for switching the carrier frequency according to the load state (for example, see Patent Document 1).
JP 2006-217776 A

  FIG. 4 shows a main circuit configuration of a two-level inverter with a regenerative converter. In this PWM inverter device, the upper limit of the carrier frequency is about 8 to 15 kHz in consideration of the switching loss and switching speed of the IGBT that becomes the main circuit switching element and the output voltage accuracy, and the upper limit of the carrier frequency is the current. It also becomes the upper limit of the control response.

  For this reason, when it is desired to perform vibration control at a high frequency (rotation speed) as in the dynamo inverter, the specification cannot be satisfied due to the upper limit of the carrier frequency.

  An object of the present invention is to provide a PWM inverter device capable of obtaining a high response output using a PWM inverter having a low carrier frequency.

  In order to solve the above-mentioned problem, the present invention has a phase configuration in which cell units of a PWM inverter having a low carrier frequency are connected in series, and each cell unit in the same phase is equivalent by setting carrier signals to different phases. Therefore, a PWM inverter output having a high carrier frequency can be obtained, and has the following configuration.

(1) A PWM inverter device for driving an AC motor at a variable speed,
The U, V, and W phase phase arms that supply alternating current for variable speed drive to the AC motor are connected in series to the output terminals of the cell unit of the single inverter configuration. A feature is that a PWM voltage output is obtained by shifting the phase of the signal to realize a high carrier.

  As described above, according to the present invention, a phase configuration in which cell units of a PWM inverter having a low carrier frequency are connected in series, and each cell unit in the same phase has a carrier signal different from each other, equivalently. Since a PWM inverter output with a high carrier frequency is obtained, a high response output can be obtained using a PWM inverter with a low carrier frequency.

  FIG. 1 is a configuration diagram of a PWM inverter device showing an embodiment of the present invention, where (a) shows the overall configuration and (b) shows the configuration of a cell unit.

  In FIG. 1, each phase arm that applies voltage to the U, V, and W phases of the AC motor Motor is connected in series with the output terminals of the cell units U <b> 1 to U <b> 3, V <b> 1 to V <b> 3, and W <b> 1 to W <b> 3. The AC power supplies of the cell units U1 to U3, V1 to V3, and W1 to W3 are taken in from the secondary windings of the common input transformer TR, and supply AC current of variable speed drive to the AC motor Motor.

  In this series multiple inverter configuration, in this embodiment, the cell units U1 to U3, V1 to V3, and W1 to W3 of the same arm shift the carrier frequency phase from each other to equivalently output a PWM inverter output with a high carrier frequency ( High response control).

  The configuration of the three-phase serial multiplex PWM inverter device of FIG. 1 can obtain a high voltage output by making the phase of the carrier signal the same in the cell units of the same arm. Furthermore, the carrier phase control makes it possible to obtain uniform switching between units, between phases, and within phases (see, for example, JP-A-2005-278266).

  In this regard, in the present embodiment, the carrier signals are set to have different phases, thereby obtaining a PWM inverter output having an equivalently high carrier frequency.

  FIG. 2 shows the relationship between the carrier and output voltage of the two-level inverter. The gate signal (output phase voltage) of the PWM inverter is generated by comparing the voltage command of the PWM inverter with the carrier signal, and this ON period becomes the PWM output voltage waveform.

  FIG. 3 shows the relationship between the carrier and output voltage of the three serial multiplexing system according to the present embodiment. The figure shows that the output carriers C1 to C3 of each phase have a phase difference of 60 degrees from each other, so that the output phase voltage of the U phase cell units U1 to U3 is combined with the carrier frequency of one cell unit × The PWM waveform of the number of stages is obtained, and the output voltage update timing is three times that of the two-level inverter.

  For example, when configuring a 690V inverter, the DC voltage of the cell unit is about 200V, and a 690V output inverter can be obtained by using a three-stage configuration. When the carrier frequency of each cell is 8 kHz, 8 kHz × 3 = 24 kHz final carrier frequency.

  Therefore, according to the present embodiment, a PWM inverter device having an equivalently higher carrier frequency is realized as the number of serial multiple connection stages is increased, and high response control can be performed. In addition, the following effects can be obtained by increasing the carrier frequency.

  (A) Since the output PWM ripple decreases, it is effective for applications such as dynamometers and elevators where it is desired to reduce torque ripple due to PWM ripple.

  (B) By using the serial multiplexing method, switching loss determined by the carrier frequency can be dispersed, and the capacity can be easily increased.

  (C) By increasing the carrier frequency, it is possible to control up to a high speed. Conventionally, in order to realize high-speed control, it has been necessary to employ a synchronous PWM method that synchronizes PWM and output frequency. However, by using a higher carrier frequency, control at high speed is possible even with asynchronous PWM methods. Is possible.

  In addition, although the case of a 3 phase series 3 multiplex PWM inverter apparatus is shown in embodiment, it can apply to a multiphase series multiplex PWM inverter apparatus, such as a 6 phase series 3 multiplex PWM inverter apparatus, and can obtain an equivalent effect.

  Although the carrier frequency is described as being fixed, switching loss can be reduced by switching or continuously changing the carrier frequency according to the load.

The block diagram of the PWM inverter apparatus which shows embodiment of this invention. The relationship figure of the carrier of 2 level inverter and output voltage. FIG. 3 is a diagram showing the relationship between the carrier and output voltage of the 3 serial multiplexing system. The main circuit block diagram of the 2 level inverter with a regenerative converter.

Explanation of symbols

Motor AC motor U1-U3, V1-V3, W1-W3 Cell unit TR Input transformer

Claims (1)

A PWM inverter device that drives an AC motor at a variable speed,
The U, V, and W phase phase arms that supply AC current for variable speed drive to the AC motor are connected in series to the output terminals of the cell unit of the inverter unit, and the cell units of the same phase are connected to each other by PWM carriers. A PWM inverter device characterized in that a PWM voltage output is obtained by shifting the phase of a signal and a high carrier can be realized.

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