JP2006174532A - Pwm inverter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique for controlling the output voltage from a PWM inverter stably while increasing the frequency. <P>SOLUTION: The PWM inverter comprises a power converter for outputting a voltage of predetermined frequency and magnitude by performing pulse width modulation of a DC voltage source depending on an inputted switching signal, a current controller for detecting the output current from the power converter every sample period and outputting such a voltage command as it follows up a current command, and a voltage controller outputting such a switching signal as the output voltage from the power converter follows the voltage command wherein the reciprocal of integer times of the frequency of output voltage from the power converter is employed as the sample period of the current controller. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a PWM inverter that converts a DC voltage into an AC voltage by pulse width modulation, and particularly proposes a technique for stable control when outputting a high-frequency voltage.

FIG. 2 shows a PWM inverter as an example, and the prior art will be described based on this figure.
The current controller 1 inputs the output current of the power converter 3 and its current command at a constant sampling period, and outputs a voltage command such that the output current follows the current command. The voltage controller 2 inputs a voltage command and outputs a switching signal such that the output voltage of the power converter 3 is in accordance with the voltage command. The power converter 3 inputs a switching signal, and outputs a voltage having a predetermined frequency and magnitude to the load 5 by performing pulse width modulation of the DC voltage source according to the switching signal. The current detector 4 detects the output current of the power converter 3.

JP 10-201246 A

FIG. 3 shows an example of conventional current detection. As the frequency of the current output from the power converter 3 increases, the number of samples for one cycle of the current decreases due to the performance limit of the samples of the current controller 1 and the like. When the sampling period Ts for detecting the output current is a constant value irrespective of the frequency fo of the output voltage of the power converter 3, as is apparent from FIG. 3, the current sampled by the current controller 1 is
・ The current waveform may be asymmetric in positive and negative.
-The amplitude may be smaller than the actual current waveform.
・ The actual current waveform may be out of phase.
Problems arise. Such a problem has an adverse effect that at least current control becomes unstable.

  In order to solve the above problems, an object of the present invention is to provide a PWM inverter that stabilizes current control by synchronizing the sampling period Ts for detecting the output current and the frequency fo of the output voltage of the power converter 3.

  In order to solve the above-described problems, a power converter that outputs a voltage of a predetermined frequency and magnitude by pulse width modulation of a DC voltage source according to an input switching signal, and the power conversion for each sampling period A current controller that detects the output current of the converter and outputs a voltage command that follows the current command; and a voltage that outputs the switching signal such that the output voltage of the power converter is in accordance with the voltage command. In the PWM inverter comprising a controller, the reciprocal of an integer multiple of the frequency of the voltage output from the power converter is used as the sampling period of the current controller.

  The integer value is a multiple of 6.

  According to the present invention, accurate current detection can be performed in a PWM inverter that outputs a high-frequency voltage.

  Even when the output voltage of the PWM inverter was high frequency, the detected current waveform was positive and negative symmetrical and could be made substantially the same as the actual output current waveform.

FIG. 1 is a block diagram of one embodiment of the present invention.
The current controller 1 ′ is different from the prior art. In the present invention, the current controller 1 '

Ts = 1 / (6Nfo) (1)

The sampling period Ts for detecting the output current of the power converter 3 is determined so that Here, N is an integer.

FIG. 4 shows an example of current detection according to the present invention. In the formula (1), N is 1, and the output voltage of the power converter 3 is three-phase. The detected current waveform is subject to positive and negative, and has the same magnitude and no phase shift. Furthermore, by setting the sample period Ts to an inverse of 6N times the frequency fo of the output voltage, the current waveform of each phase is positive and negative symmetric, and current detection can be performed with the same current phase for each phase.

  According to the present invention, since an accurate current can be detected even if the output voltage of the PWM inverter is increased, there is a great possibility of industrial use.

It is explanatory drawing which showed the Example of this invention. It is explanatory drawing which showed the prior art of the PWM inverter. It is explanatory drawing which showed an example of the conventional electric current detection. It is explanatory drawing which showed an example of the electric current detection of this invention.

Explanation of symbols

1, 1 'current controller 2 voltage controller 3 power converter 4 current detector 5 load

Claims (2)

A power converter that outputs a voltage having a predetermined frequency and magnitude by performing pulse width modulation on a DC voltage source according to the input switching signal, and detecting an output current of the power converter for each sampling period. In a PWM inverter comprising a current controller that outputs a voltage command that follows the current command and a voltage controller that outputs the switching signal such that the output voltage of the power converter is in accordance with the voltage command,
A PWM inverter characterized in that a reciprocal of an integer multiple of the frequency of the voltage output from the power converter is used as a sampling period of the current controller.   2. The PWM inverter according to claim 1, wherein the integer value is a multiple of six.

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