JPH04222470A - Controlling circuit for pulse width modulation-controlled inverter - Google Patents

Abstract

PURPOSE:To eliminate an AC voltage detecting device by simulating the AC output voltage by a combination of the voltage at the DC side and an actuating signal of an upper semiconductor switch element or lower semiconductor switch element. CONSTITUTION:In a power converting device in which a magnetic flux is controlled by pulse width modulation control, the AC output voltage is required to be detected in view of control. Then, the titled circuit is so configured that a simulation value of the AC output voltage of the power converting device may be detected by a combination of an actuating signal of a semiconductor switch element of an upper arm and the voltage at the DC side when current flows in the load direction from a bridge connection circuit of the semiconductor switch element which constitutes the power converting device and the simulation value may be detected by a combination of an actuating signal of a semiconductor switch element of a lower arm and the voltage at the DC side when current flows in the reverse direction.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control circuit for a pulse width modulation controlled inverter which can omit voltage detection means provided on the AC output side of a power conversion means.

0002

2. Description of the Related Art FIG. 4 is a circuit diagram showing a conventional example of a circuit for controlling a pulse width modulation controlled inverter.

In FIG. 4, AC power from an AC power supply 2 is converted into smooth DC power by a rectifier 3 and a smoothing capacitor 4, and then a transistor as a power conversion means constituted by a transistor as a semiconductor switch element is used. Since the inverter 5 converts the AC power into variable voltage/variable frequency AC power, the AC motor 6, which is the load, can be operated at a desired speed.

This AC motor 6 is controlled by pulse width modulation control.
When operating at variable speed, torque pulsation and magnetic noise can be reduced by performing magnetic flux control. This effect is particularly noticeable when the AC motor 6 is operated at low speed. Therefore, as shown in FIG. 4, a voltage transformer 11 detects the AC voltage output from the transistor inverter 5, and a magnetic flux detector 12 and an isolation amplifier 13 obtain an isolated magnetic flux detection value.

On the other hand, since the magnetic flux setter 14 has set the magnetic flux target value, when the deviation between this magnetic flux target value and the above-mentioned magnetic flux detected value is input to the magnetic flux adjuster 15, this magnetic flux adjuster 1
5 outputs a control signal that makes the input deviation zero. Therefore, this control signal is converted into a pulse width modulation circuit (hereinafter referred to as PWM).
A pulse width modulated pulse signal is extracted from this PWM circuit 16, and this is applied to the transistor inverter 5, so that the voltage and frequency output by the transistor inverter 5 can be set to desired values. is controlled.

[0006]

[Problems to be Solved by the Invention] As mentioned above, the power conversion means that attempts to obtain an AC of a desired voltage and frequency by magnetic flux control needs to detect the AC output voltage of this power conversion means. Since the device must be equipped with a device to detect alternating current voltage, the entire device has the disadvantage of being large and expensive.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to make it possible to omit the voltage detection means that is required to be installed on the AC output side of the inverter.

[0008]

[Means for Solving the Problems] In order to achieve the above object, the control circuit of the present invention includes a power conversion means configured to convert direct current to alternating current by a bridge connection circuit of semiconductor switching elements, and a power conversion means configured to convert direct current to alternating current by a bridge connection circuit of semiconductor switching elements. Voltage detecting means for detecting an output AC voltage, magnetic flux detecting means for converting this AC output voltage into a magnetic flux detected value, and magnetic flux adjusting means for outputting a control signal to make this magnetic flux detected value match a separately set magnetic flux target value. and a pulse width modulation means for outputting a pulse width modulated pulse signal for operating the semiconductor switch element based on the control signal, the DC side of the power conversion means voltage and
output voltage simulating means for inputting the pulse signal outputted by the pulse width modulating means and outputting a value simulating the AC output voltage of the power converting means; It is given to

[0009]

[Operation] In power conversion means that performs pulse width modulation control, even if the DC side voltage is constant, the AC output voltage corresponds to the width of the pulse for operating the semiconductor switching element that constitutes the power conversion means. and change. Therefore, the DC side voltage of the power conversion means inverter, the on/off signal given to the bridge-connected upper arm semiconductor switch element, and the on/off signal given to the lower arm semiconductor switch element.
The purpose is to detect voltage information corresponding to the AC output voltage of this power conversion means from the off signal.

0010

[Embodiment] FIG. 1 is a circuit diagram showing a first embodiment of the present invention. In the embodiment circuit shown in FIG. After converting it into smooth DC power, the transistor inverter 5 as a power conversion means converts it into AC power with variable voltage and variable frequency, and drives the AC motor 6, which is the load, at a desired speed, as shown in FIG. This is the same as the case of the conventional circuit described above. Also, the magnetic flux adjuster 15 outputs a control signal to make the deviation between the two zero by comparing the magnetic flux target value set by the magnetic flux setting device 14 and the magnetic flux detection value output from the magnetic flux detector 12. , which is the same as in the conventional circuit shown in FIG.

In the present invention, the DC input voltage of the transistor inverter 5, ie, the terminal voltage of the smoothing capacitor 4, is isolated and detected by the DC voltage detector 21, and this detected voltage is applied to the output voltage simulation circuit 22. On the other hand, the PWM circuit 16 that provides an on/off pulse signal to the transistor inverter 5 also provides this pulse signal to the output voltage simulation circuit 22.

As mentioned above, the output voltage simulation circuit 22 has the following functions:
The DC input voltage of the transistor inverter 5 and the pulse width modulated pulse signal for operating the transistor inverter 5 are input, and voltage information simulating the AC output voltage of the transistor inverter 5 is output. Therefore, the output signal of this output voltage simulation circuit 22 may be given to the magnetic flux detector 12 instead of the AC side voltage signal of the transistor inverter 5.

FIG. 2 is a circuit diagram showing the configuration of one phase of a transistor inverter for explaining the second embodiment of the present invention, and FIG. 3 is a circuit diagram showing a pulse width modulation for explaining the second embodiment of the present invention. 3 is an operation waveform diagram showing the operation of the control inverter, where A in FIG. 3 is a PWM signal waveform, B in FIG. 3 is an operation signal waveform of upper arm transistor 5P, and C in FIG. 3 is an operation signal of lower arm transistor 5N. Waveform D in FIG. 3 represents the voltage waveform when the output current is in the positive direction, and E in FIG. 3 represents the voltage waveform when the output current is in the negative direction. Note that Td shown in FIG. 3 is a waiting time to prevent arm short circuit.

The PWM signal has a waveform shown in FIG. 3A,
To prevent arm short circuit, upper arm transistor 5P
A waiting time of Td is provided from when the lower arm transistor 5N turns off to when the lower arm transistor 5N turns on, and from when the lower arm transistor 5N turns off until the upper arm transistor 5P turns on. Therefore, the operating signal applied to the upper arm transistor 5P has the waveform shown in FIG. 3B, and the operating signal waveform applied to the lower arm transistor 5N has the waveform shown in FIG. 3C.

As shown in FIG. 2, when the output current flows from the arm toward the load as a positive direction, the voltage waveform at that time is a combination of the DC side voltage and the operating signal of the upper arm transistor 5P, as shown in FIG. 3D. It can be obtained from Further, the voltage waveform when the output current flows in the opposite direction to that described above, that is, from the load to the arm direction, can be obtained from the DC side voltage and the operation signal of the lower arm transistor 5N, as shown in FIG. 3E.

[0016]

According to the present invention, when the current is in the positive direction, the AC output voltage of the magnetic flux control type power conversion means that performs pulse width modulation control is changed to the operating signal of the upper arm semiconductor switching element and the DC side voltage. Also, when the current is in the negative direction, it can be simulated by the operation signal of the lower arm semiconductor switching element and the DC side voltage, so it is necessary to install voltage detection means on the AC side of the power conversion means. Since the circuit is eliminated, the circuit can be simplified, and the device can be made smaller and lighter, and the cost can be reduced.

[Brief explanation of the drawing]

[Fig. 1] A circuit diagram showing a first embodiment of the present invention.

[Figure 2
]A circuit diagram showing the configuration of one phase of a transistor inverter for explaining a second embodiment of the present invention.

FIG. 3 is an operation waveform diagram showing the operation of the pulse width modulation control inverter for explaining the second embodiment of the present invention.

[Figure 4] A circuit diagram showing a conventional example of a circuit that controls a pulse width modulation control inverter.

[Explanation of symbols]

5 Transistor inverter 5N as power conversion means Lower arm transistor 5P Upper arm transistor 11 Voltage transformer 12 Magnetic flux detector 14 Magnetic flux setting device 15 Magnetic flux regulator 16 PWM circuit 21 DC voltage detector 22 Output voltage simulation circuit

Claims (2)

[Claims] 1. Power converting means configured to convert direct current to alternating current by a bridge connection circuit of semiconductor switch elements, voltage detecting means for detecting an alternating current voltage output from the power converting means, and magnetic flux detection of the alternating current output voltage. a magnetic flux detecting means for converting the detected magnetic flux value into a magnetic flux target value, a magnetic flux adjusting means for outputting a control signal to match the detected magnetic flux value with a separately set magnetic flux target value, and a magnetic flux adjusting means for outputting a control signal for making the detected magnetic flux value match a separately set magnetic flux target value; In a control circuit for a pulse width modulation control inverter, the control circuit includes a pulse width modulation means for outputting a pulse signal, and the DC side voltage of the power conversion means and the pulse signal output from the pulse width modulation means are input. A control circuit for a pulse width modulation control inverter, comprising an output voltage simulating means for outputting a value simulating an AC output voltage of the power converting means, and an output of the output voltage simulating means is applied to the magnetic flux detecting means. 2. Power converting means configured to convert direct current to alternating current by a bridge connection circuit of semiconductor switch elements, voltage detecting means for detecting an alternating current voltage output from the power converting means, and magnetic flux detection of the alternating current output voltage. magnetic flux detection means for converting the detected magnetic flux value into a magnetic flux target value that is set separately; In a control circuit for a pulse width modulation control inverter comprising pulse width modulation means for outputting a pulse signal, when current flows from the bridge connection circuit toward the load, the upper arm semiconductor switching element of the bridge connection circuit is turned on.・The voltage obtained from the off signal and the DC side voltage, and when the current flows in the opposite direction to the above,
The voltage obtained from the on/off signal of the lower arm semiconductor switch element of the bridge connection circuit and the DC side voltage,
A control circuit for a pulse width modulation control inverter, characterized in that the AC output voltage simulated value of the power conversion means is supplied to the magnetic flux detection means.