JPH0746072Y2 - Inverter output voltage compensation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to an improvement of an output voltage compensation circuit of an inverter that compensates the output voltage for fluctuations in the power supply of the inverter circuit.

[Prior art and its problems]

FIG. 4 shows a main configuration of an inverter having an output voltage compensating function of a conventional example. 1 is a rectifier circuit, 2 is a smoothing reactor, 3 is a smoothing capacitor, 4 is a bridge-connected diode D and a diode D. The inverter circuit 5 composed of the self-extinguishing element S connected in anti-parallel is an induction motor. Here, the inverter circuit 4 includes the self-extinguishing element S
Are shown as an example of a transistor.

Further, 6 is a control circuit, 7 is a base drive circuit for driving the self-extinguishing element S of the inverter circuit 4, 8 is a DC voltage detector, and 9 is a voltage detection circuit.

That is, FIG. 4 shows an example of a typical transistor inverter having output voltage compensation for fluctuations in power supply voltage,
Since the function of such a device is well known, only the output voltage compensation function will be described as follows.

In FIG. 4, an AC input 101 of a commercial three-phase AC power supply (hereinafter simply referred to as an AC power supply) is converted into a DC by a rectifier circuit 1 to obtain a DC input 102 smoothed by a smoothing reactor 2 and a smoothing capacitor 3, and then an inverter. The AC output 103 of the circuit 4 is supplied to the induction motor 5. Therefore, if this is a transistor inverter using the well-known pulse width modulation method (PWM control) by the switching operation of the self-extinguishing element S of the inverter circuit 4, the inverter circuit driven by the control circuit 6 and the base drive circuit 7 is used. The AC output 103 is obtained by the PWM control based on 4.

Here, as is apparent from the connection configuration shown in FIG. 4, the DC voltage that determines the peak value of the output voltage of the AC output 103 is uniquely determined by the power supply voltage. When it fluctuates, it directly appears as a change in the output voltage.

Therefore, the DC voltage detector 8 detects the DC voltage, obtains the DC voltage detection signal 104, and the voltage detection circuit 9 outputs the compensation signal 1
By applying 05 to the control circuit 6, output voltage compensation is performed as follows with respect to fluctuations in the power supply voltage.

Here, the compensation circuit 61 in the control circuit 6 receives the input M of the modulation degree command and generates the output M.

If the modulation degree of the PWM waveform in the PWM control is M ′, the DC voltage when the power supply voltage is rated is V _DC , and the modulation degree at that time is M, M ′ = (V _DC / V _DC ′) · M ...... By compensating with the compensation circuit 61 according to the equation (1),
A constant output voltage can be supplied even if the power supply voltage changes. However, V _DC ′ is a DC voltage detected by the DC voltage detection signal 104.

However, with such a conventional output voltage compensating method, it is possible to obtain good compensation characteristics against power supply fluctuations in the case of no load, but self-erasing in the case of actual load and fluctuations. Since the turn-off time of the arc element S (transistor) has an essential property of being rapidly shortened when the load is changed from no load to the actual load, there is a drawback that the output voltage cannot be compensated.

[Means for solving problems and actions]

The present invention has been made by paying attention to the above points.By detecting the load current and applying a function generator output having a gain above a certain output current value, not only the fluctuation of the power supply but also the load It is intended to provide a device having a simple structure capable of compensating for an output voltage even with a fluctuation of Therefore, the present invention provides an inverter device with a DC voltage detector and an output current detector, and connects a rectifier circuit and a function generator to the output of the output current detector so that the DC voltage detection value and a certain output current constant value or more. This is based on the idea of obtaining a compensation signal for compensating the output voltage from the difference between the output of the function generator that generates the gain. Hereinafter, the present invention will be described with reference to the drawings.

〔Example〕

FIG. 1 shows a main part configuration of an embodiment of the present invention represented in a manner similar to FIG. 4, 10 is a current detector, 11 is a rectifier circuit, 12
Is a function generator and 13 is a differential amplifier. In the figure, the same reference numerals as those in FIG. 4 indicate the same components.

That is, in the connection configuration shown in FIG.
A current detector 10 for detecting the current of 103 is provided, and an output current detection signal 107 is obtained via a rectifying circuit 11 that converts the output signal 106 of the current detector 10 into a voltage. Further, a function generator 12 that receives the output current detection signal 107 and a differential amplifier 13 that outputs a difference signal between the compensation signal 108 and the compensation signal 105 at the output of the function generator 12 are provided. The output compensation signal 109 is provided to the compensation circuit 61 in the control circuit 6 as the compensation signal V _DC ′.

Here, in order to facilitate understanding of the present invention, the output voltage compensation characteristic will be described in advance with reference to FIG.

FIGS. 2 (a) and 2 (b) show the AC output characteristics with and without the load fluctuation compensation function, respectively. The high frequency F ₁ of the inverter frequency, the medium frequency F ₂ ,
A typical characteristic example of the low frequency F ₃ is shown.

As described above, when the induction motor 5 is operated without load, only the exciting current flows, and since the exciting current is delayed in phase by about 90 ° with respect to the output voltage of the AC output 103, the self-extinguishing element S hardly flows. It flows through the free-wheeling diode D. Therefore, since the self-extinguishing element S is in an unloaded state,
As shown in FIG. 6A, the output voltage is constant from the load open state to the unloaded state operating point Z ₁ . When a load is applied to the induction motor 5 from this state, an in-phase component appears in the output current component and flows through the self-extinguishing element S, so that the turn-off time is shortened as described above. Here, as shown by the characteristics in Fig. 2 that exceeds the no-load operation Z ₁ , the output voltage sharply decreases when the excitation current value is exceeded, and the load operating point
It will be further reduced from Z ₁ according to the load.

Therefore, when the amplitude of the output current becomes larger than the exciting current value in the equation (1) shown above, the DC voltage is detected, and the function generator 12 is caused to operate according to the load current to generate the compensation signal 109. Therefore, the change in the output voltage due to the change in the load current as shown in FIG. 2B can be compensated.

Next, the function of the connection configuration shown in FIG. 1 will be described in detail.

In FIG. 1, the differential amplifier 13 performs a differential operation using the compensation signal 105 output from the voltage detection circuit 9 as one input and the compensation signal 108 output from the function generator 12 as the other input. Here, the amplitude of the output current of the inverter circuit 4 is the current detector 10
Is detected by the rectifier circuit 11 and full-wave rectified by the function generator.
Given to twelve. Here, the function generator 12 has an input / output characteristic as shown in FIG.

3 (a) and 3 (b) show one characteristic example and another characteristic example of the function generator, which are shown in FIG. 2 (a) and
As is clear from the explanation of the output voltage compensation function shown in (b), the characteristic line W ₁ has a high gain from the no-load operating point Z ₁ to the loaded operating point Z ₂ and has a further load characteristic. It has a corresponding low gain, and the characteristic line W ₂ does not have a gradual gain like the characteristic line W ₁ , but has an appropriate constant gain.

As a result, in FIG.
A difference voltage between 105 and 108 is obtained, a new compensation signal 109 of the output of the differential amplifier 13 is given to the control circuit 6, and as described above, the inverter output is specially generated by the equation (1). Therefore, it is possible to cope with the change in the turn-off time of the main transistor due to the change in the output current, and it is obvious that a constant output voltage can be generated for both the power supply change and the load change. Incidentally, in order to obtain the characteristic lines W ₁ and W ₂ as shown in FIG. 3, it is needless to say that a variable resistor is used as the resistance portion which determines the output generation point and the gain, so that various self-extinguishing elements can be supported.

[Effect of device]

As described above, according to the present invention, an output voltage compensating circuit for an inverter having a simple structure capable of compensating the output voltage with respect to load fluctuations and capable of coping with the characteristics of various self-extinguishing elements such as power transistors. Can be provided.

[Brief description of drawings]

FIG. 1 is a block diagram showing a main part configuration of an embodiment of the present invention, FIG. 2 is a diagram showing an output voltage compensation characteristic shown for explanation of FIG. 1, and FIG. 3 is an example of characteristic of a function generator. FIG. 4 and FIG. 4 are block diagrams showing the main configuration of an inverter having an output voltage compensation function of a conventional example. 1, 11 rectifier circuit, 4 inverter circuit, 5 induction motor, 6 control circuit, 7 base drive circuit, 8
...... DC voltage detector, 9 …… Voltage detection circuit, 10 …… Current detector, 12 …… Function generator, 13 …… Differential amplifier, 105,10
8,109 …… Compensation signal, W ₁ , W ₂ …… Characteristic line of the function generator 12.

Claims (1)

[Scope of utility model registration request] 1. A direct-current voltage detector for detecting a direct-current voltage in an inverter circuit formed by bridge-connecting self-extinguishing elements in which diodes are connected in anti-parallel, the output voltage of the inverter circuit being determined by the output of the direct-current voltage detector. In an output voltage compensation circuit of an inverter for compensation, a current detection circuit for detecting an output current of the inverter circuit, a function generator having a gain when the output value of the current detection circuit is input, and having a gain when an input value is a certain value or more, An output voltage of the inverter, comprising: a differential amplifier that outputs a difference between the function generator output signal and the DC voltage detector output signal, and the output voltage of the inverter is compensated by the differential amplifier output signal. Compensation circuit.