JPH0667174B2 - Inverter control device for electric equipment - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an inverter control device in a motor drive of an electric device by an inverter, and particularly to measurement of a power supply frequency.

<Prior Art> Conventionally, in an inverter control type refrigerating vehicle or an air conditioner, a DC power source is switched by switching a power transistor via a transistor drive circuit by a waveform signal output from a PWM (pulse width modulation) control circuit. It was converted into a pseudo AC power source to drive the three-phase AC motor of the compressor. In this inverter-controlled electric device, if the commercial power supply voltage changes or the load of connected electric devices such as a compressor changes, check whether the control circuit such as the microcomputer is operating normally. It is necessary to inspect in advance on the production line. That is, in the above case, the control circuit needs to check whether the waveform signal corresponding to the specified frequency is output to the power transistor of the inverter.

Generally, the voltage waveform of the pseudo AC power supply obtained by switching the power transistor is a rectangular wave as shown in FIG. It is not easy to measure the frequency from such a rectangular wave. In other words, when trying to measure the power supply frequency outside the control circuit, the waveform signal outside the control circuit simply outputs a large number of pulses in which the current is turned on and off repeatedly. It is not possible to distinguish which is the first pulse and which is the last pulse, so the period cannot be specified and the frequency is unknown.

In order to solve the above problems when trying to measure the power supply frequency outside the control circuit, a Fourier transform device is provided at the output part of the inverter, and the waveform signal from the inverter is Fourier transformed to decompose the waveform. You can see the cycle with
The frequency to the motor can be determined.

However, it is necessary to add a Fourier transform device to the inverter control device, the circuit configuration becomes complicated, and it is extremely difficult to accurately obtain the Fourier transform analysis accuracy. In addition, there are cases where the design cannot be achieved due to variations in the precision of circuit components in the PWM control circuit.

Also, when the waveform signal from the inverter changes from the positive level to the negative level, the direction of the current flowing through the motor changes, so the operating frequency of the motor can also be measured by measuring the cycle of polarity switching. . Therefore, it is conceivable to add a device that detects the direction of the current to the output part of the inverter, but in this case, the detection device must detect the current while the high voltage is present during polarity switching. The load is applied to the device, and the inverter control device becomes complicated.

<Purpose> Therefore, in the present invention, when the waveform data is output from the control circuit by utilizing the fact that the pulse to be output to the inverter and the timing of switching the polarity thereof are known in the control circuit using the microcomputer, With the purpose of providing an inverter control device for electric equipment, by separately outputting a pulse signal synchronized with the inverter power supply frequency, the frequency can be easily measured and it can be checked whether or not the control circuit such as a microcomputer is operating normally. There is.

<Embodiment> Hereinafter, one embodiment of the present invention will be described with reference to the drawings in order to convert an inverter unit 1 for converting a DC power supply into a pseudo AC power supply and a power supply frequency output from the inverter unit 1. And a control circuit 2 for outputting the waveform signal of
The control circuit 2 is configured to output a pulse signal synchronized with 1 / N (N is an integer) of the power supply frequency, and the pulse signal output from the control circuit 2 is input to measure the power supply frequency. The circuit 4 is provided.

FIG. 1 is a circuit diagram of a control device. The control circuit 2 is configured to output a waveform signal from the output ports A1 to A6 based on a temperature input signal such as the temperature inside the refrigerator.
The signals from A6 to A6 are output to the transistor drive circuit 3 of the inverter unit 1, and the drive circuit 3 outputs PWM (pulse width modulation waveform) to the base side of the power transistors Tr1 to Tr6. The DC power supply 4a is connected to the emitter side and the collector side of the power transistors Tr1 to Tr6 of the inverter unit 1.

The control circuit 2 has an output port A7 that outputs a pulse signal synchronized with 1 / N (N is an integer) of the power supply frequency, and the frequency measuring circuit 4 is composed of a frequency counter.

Fig. 2 (a) shows U- of the three-phase power supply terminals U, V, W of the motor 5.
FIG. 2 shows a waveform between V and the pulse output from the output port A7 of the control circuit 2 in accordance with the polarity switching of this waveform.
It is reversed as shown in (b). Figure 2 (c) shows the output port A7.
Shows an example in which a pulse signal is output at twice the basic frequency. In this case, if the value of the frequency counter of the frequency measuring circuit 4 is halved, the basic frequency can be measured.

In addition, it is known that in the case of a three-phase power supply, one-sixth of one cycle of data can be output for one cycle in the method of creating the inverter waveform. Therefore, even if the output port A7 of the control circuit 2 is set to the positive level when the first 1/6 data is output and the remaining 5/6 data is output to the negative level as shown in FIG. It becomes possible to measure. In this case, the ON / OFF frequency is the fundamental frequency.

FIG. 3 shows a flow chart for the pulse output shown in FIG. 2 (b). First, the control circuit 2 is initialized, and then the temperature such as the internal temperature is input to the control circuit 2 while the operation switch is in the ON state to determine the frequency. Then, output from the output ports A1 to A6 to the transistor drive circuit 3, drive the power transistors Tr1 to Tr6, and supply the three-phase power supply to the motor 5
Supply to. At the same time, the control circuit 2 determines whether or not the waveform data between U and V has a positive timing. When the waveform data is positive, a pulse signal is output from the output port A7 at a positive level, and when it is negative, a pulse signal is output at a negative level. Output. As a result, the frequency measuring circuit 4 can measure the frequency of the three-phase power supply without connecting the inverter 1 to the motor 5.

<Effect> Since the inverter control device for electric equipment of the present invention is configured as described above, it is only necessary to connect the frequency counter to the terminals of the control circuit without connecting a load such as a motor to the inverter section. Therefore, the power supply frequency can be easily measured.

Therefore, it is not necessary to add a Fourier transform device or a device for detecting the direction of the current to the control circuit, and it is possible to inspect whether or not the control circuit such as the micro computer is operating normally by a simple frequency counter. .

[Brief description of drawings]

FIG. 1 is a circuit diagram of a control device showing an embodiment of the present invention, and FIG.
FIGS. 3A to 3D are waveform diagrams showing waveform data between the same three-phase power source U and V and pulse output from the output port of the control circuit.
The figure is a control flowchart. 1: Inverter, 2: Control circuit, 3: Transistor drive circuit, 4: Frequency measurement circuit.

Claims (1)

[Claims] 1. An inverter unit for converting a DC power supply into a pseudo AC power supply, and a control circuit for outputting a waveform signal for converting a power supply frequency output from the inverter unit,
The control circuit has a determining unit that determines the power supply frequency based on an input signal from the outside, and an output unit that outputs the waveform signal matching the power supply frequency to the inverter unit. A frequency counter for measuring the power supply frequency by inputting and counting the pulse signal output from the terminal is provided, which is provided with a terminal that outputs a pulse signal synchronized with the timing of 1 / N of the power supply frequency determined by the determining means. An inverter control device for electric equipment, characterized in that a power supply frequency can be measured without providing a detection signal from the load by connecting a load to the inverter section.