JPH05300746A - Output voltage waveform distortion compensator for pwm inverter - Google Patents

Abstract

PURPOSE:To surely compensate the distortion of output voltage regardless of load condition by judging whether the load of an inverter is a linear load, a capacitor input type load, or a hybrid of both loads from the current width of a load current and a peak value ratio, and selecting distortion compensating waveform, according to the judgment, so as to control it. CONSTITUTION:A load condition judging circuit 20 judges whether the load 4 is a linear load or a hybrid load where the capacitor input type load becomes both load conditions from the current width detection signal IW from a current width detector 16 and the peak value detection signal Ip/Irms from a peak value comparator and detector 19, and controls the amplitude of the output waveform of a distortion compensative wave generating circuit 21 from this comparison result. The distortion compensative wave generating circuit 21 has distortion compensators 21a, 21b, and 21c which generate distortion compensative waves geared to load condition, and outputs the output, changing over it with changeover switch 21SW, and adds it to the sine wave signals from the sine wave signal generator 51, and the adder 14 outputs it as the output voltage compensating signal of an inverter.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an output voltage waveform distortion compensator for a PWM inverter.

[0002]

2. Description of the Related Art A PWM inverter applied to an uninterruptible power supply or the like obtains a pulse width modulation wave by comparing a sine wave and a carrier wave (triangular wave), and the modulation wave turns on / off a switching element of an inverter main circuit. In many cases, by controlling the output voltage, an output voltage similar to a sine wave is obtained.

FIG. 3 shows a triangular wave comparison type PWM inverter. The inverter main circuit 1 uses a transistor as a switching element, obtains a single-phase PWM waveform output from the DC power supply 2, removes harmonics by the LC filter 3, and supplies the load 4 with AC power approximate to a sine wave.

The PWM control circuit 5 includes a sine wave generator 5 ₁ whose voltage and frequency are controlled, a triangular wave generator 5 ₂ which generates a carrier wave, and a comparator 5 ₃ which compares the levels of the output waveforms of both generators. And a PWM waveform is obtained from the output of the comparator 5 ₃ and used as the gate signal of the inverter main circuit 1.

FIG. 4 shows a waveform diagram of the PWM inverter.
By comparing the levels of the sine wave and the triangular wave shown in (a), the transistors T _{r1 to} T _r4 are on / off controlled by the modulated waves shown in (c) and (d), respectively, to obtain the inverter output voltage waveform shown in (b). .. The output voltage waveform is shaped into an output voltage approximate to a sine wave by removing the carrier component from the LC filter 3.

[0006]

In the conventional PWM inverter, when a non-linear load such as a capacitor input type rectifier is connected to the load 4, a resistor or a reactor load of an induction machine is connected, and further, There are cases where a plurality of loads are connected in parallel and the load condition changes from a non-linear load state to a linear load state depending on the load operating state.

Among such load conditions, the output voltage waveform of the inverter becomes a distorted waveform which is trapezoidally suppressed at the peak portion of the nonlinear load, and this voltage distortion may adversely affect other loads. ..

In order to solve this problem, the control voltage 5 of the PWM inverter is changed to a modified sine wave signal in which the peak portion is protruded by the compensation amount in the control circuit 5 of the PWM inverter for the non-linear load. The applicant of the present application has already proposed a method of compensating for distortion (Japanese Patent Laid-Open No. 3-2939).
No. 70).

The above-mentioned compensation method is effective when the load is a non-linear load and the load current is constant. On the contrary, it causes distortion.

It is an object of the present invention to provide a compensator that surely compensates for output voltage distortion regardless of changes in load conditions.

[0011]

In order to solve the above problems, the present invention provides a PWM inverter that obtains a PWM waveform according to a sine wave signal and obtains a PWM voltage output at the output of an inverter main circuit. Load type discriminating circuit that discriminates the load of the inverter as a linear load, a capacitor input type load, and a mixed molding load of both loads based on the flow width and peak value ratio of the inverter; A distortion compensating waveform that generates a distortion compensating waveform and generates a spike-shaped distortion compensating waveform in which the peak portion of the sine wave signal is centered and the amplitude is controlled by the peak value ratio is used to distinguish between a capacitor input type load and a mixed molding load. A sine wave signal for obtaining a PWM waveform by adding the generation circuit and the distortion compensation waveform from the distortion compensation waveform generation circuit to the sine wave signal. Characterized by comprising an adder, a.

[0012]

[Function] The inverter load type is determined from the flow width of the load current and the peak value ratio, and the linear load type is uncompensated to eliminate waveform distortion due to compensation, and a sine wave is applied to the capacitor input type load or the mixed molding load. The distortion generated by the capacitor input type load is compensated by adding the spike-shaped distortion compensation wave component generated at the peak portion to the sine wave signal. The amplitude of the distortion compensation waveform at this time is controlled according to the peak value ratio to obtain compensation according to the weight of the load.

[0013]

FIG. 1 is a PWM control circuit diagram showing an embodiment of the present invention. In supplying power from the inverter main circuit 1 to the load 4 via the LC filter 3 with a sinusoidal voltage,
The output voltage V _{out of the} inverter is detected by the transformer 11,
The voltage control amplifier 12 is matched with the voltage command V _set.
Voltage control calculation (PI calculation) is performed.

This voltage control signal V _a adjusts the amplitude of the sine wave signal V _b which is the other input of the multiplier 13, and the multiplier 1
A PWM gate signal modulated by the comparator 5 ₃ is obtained from the output of 3 and the output of the triangular wave generator 5 ₂ .

The sine wave signal V _b to the multiplier 13 is taken out from the output signal of the frequency-controlled sine wave generator 5 ₁ via an adder 14, and the adder 14 distorts the load signal according to the conditions of the load 4. The compensation signal V _c is added to the sine wave signal.

The distortion compensation signal V _c is generated in accordance with the type of load by detecting the flow width, peak value and effective value of the load current. The circuit for generating the distortion compensation signal V _c will be described in detail below.

The current transformer 15 detects a load current waveform from the inverter 1 to the load 4. The flow width detector 16 detects the flow width with respect to the cycle of the inverter operating frequency from this load current waveform by zero-xcess detection or the like. The peak value detector 17 detects the peak value of the load current waveform. The effective value detector 18 detects the effective value of the load current waveform. The peak value ratio detection circuit 19 detects the peak value of the load current, that is, the peak value ratio, from the peak value of the peak value detector 17 and the effective value of the effective value detector 18.

The load condition discriminating circuit 20 comprises a flow width detector 16
It is determined whether the load 4 is a linear load, a capacitor input type load, or a mixed load satisfying both load conditions from the flow width detection signal I _w from the peak value ratio signal I _p / I _rms from the peak value ratio detector 19. ..

This load condition is determined according to the following conditional expression.

[0020] (1) wide linear load conditions through flow I _w ≒ T _INV peak ratio I _p / I _rms ≦ 2 ^1/2 However, T _INV is equivalent to the period of the inverter operating frequency, for example, 50H _Z operation Then, the half cycle is set to 10 ms and compared with the flow width I _W between the load current half cycles.

(2) Capacitor input type load condition Flow width I _W ≦ T _INV /3.3 Peak value ratio I _p / I _rms > 2 ^1/2 (3) Mixed molding load condition Flow width I _W > T _INV / 3.3 Peak value ratio I _p / I _rms > 2 ^{1/2 From the} judgment result according to the above judgment conditions, the load condition judgment circuit 2
0 selects the output waveform of the distortion compensation waveform generation circuit 21 and controls the amplitude. The distortion compensation waveform generation circuit 21 is a distortion compensation waveform generator 21a, 21 which generates a distortion compensation waveform according to a load condition.
b, 21c and, and a changeover switch 21sw to its output as a compensation signal V _c is switched, the distortion compensation waveform generator in accordance with the peak value ratio with the change-over switch 21sw is switched by the load condition determining circuit 20 21a,
21b and 21c have a ROM configuration having, for example, a distortion compensation waveform as a data string, and generate a distortion compensation waveform whose amplitude is controlled by D / A conversion of the data string. This occurrence is a sine wave generator and synchronous control of the sine wave generator 5 _1, the distortion compensation waveform occurs around the peak position of the sine wave, varying the amplification degree of the distortion compensation waveform in accordance with the peak value ratio.

FIG. 2 shows each distortion compensation waveform together with the sine wave of the sine wave generator 5 ₁ and the load current waveform (broken line). The distortion compensating waveform generator 21a generates a compensating waveform under the linear load condition, and its output is set to zero because the load current has no cause of distortion. The distortion compensating waveform generator 21b generates a compensating waveform in the case of a capacitor input type load condition, and the output thereof produces a spike-like load current at the peak portion of the sine wave, so that a waveform similar to the load current peaks at that portion. It occurs with an amplitude according to the value ratio. The distortion compensating waveform generator 21c generates a compensating waveform under the mixed load condition, and the load current becomes a waveform in which a spike current is superimposed on the peak portion of the sine wave, and the waveform for compensating the spike current portion is set to the peak value ratio. It occurs with a corresponding amplitude, and the compensation value is made larger than in the case of 21b.

The distortion-compensated waveform output from the distortion-compensated waveform generating circuit 21 is input to the adder 14 as a signal V _c , added to the sine-wave signal from the sine-wave generator 5 ₁ , and then added from the adder 14. The output voltage of the inverter is output as a signal V _b which has been subjected to distortion compensation.

Therefore, according to this embodiment, the linear load, the capacitor input type load, and the mixed molding load are discriminated from the flow width and peak value ratio of the load current of the PWM inverter.
A distortion compensation waveform is selected and its amplitude is controlled according to this load type.

As a result, the load of the inverter becomes uncompensated when the load is linear, so that distortion is not generated due to distortion compensation, and distortion compensation can be obtained at a capacitor input type load or a mixed load, and the type of load can be reduced. The distortion of the inverter output voltage can be reduced by the corresponding distortion compensation.

In the embodiment, the distortion compensation waveform generation circuit is configured to control in accordance with the flow width detection signal during the spike-shaped waveform generation period, so that the distortion compensation can be further ensured. For example, for the capacitor input type load, the timing of the flow width detection signal is used as the output period control signal of the distortion compensation waveform generator 21b. Further, the spike-shaped waveform period at that time is detected by using the effective value detection signal as the flow width detection reference for the mixed molding load, and at this timing, it is used as the output period control signal of the distortion compensation waveform generator 21c.

Further, in the embodiment, the PWM of the triangular wave comparison system is used.
The case of an inverter is shown, but PWM is performed according to a sine wave signal.
The same operation and effect can be obtained by applying it to a PWM inverter of another method for obtaining a waveform.

[0028]

As described above, according to the present invention, the PWM
Since the load type is discriminated from the flow width of the load current of the inverter and the peak value ratio, and the distortion compensation waveform is selected and controlled according to this discrimination, the waveform distortion of the output voltage can be detected regardless of the load type and light weight. The output voltage waveform distortion can be reduced by obtaining appropriate distortion compensation in accordance with various load conditions such as an inverter that can switch the load and a load that is repeatedly operated and stopped.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a distortion compensation waveform diagram in the example.

FIG. 3 is a configuration diagram of a PWM inverter.

FIG. 4 is a waveform diagram of a PWM inverter.

[Explanation of symbols]

1 ... Inverter main circuit 3 ... Filter 4 ... Load 5 ₁ ... Sine wave generator 5 ₂ ... Triangle wave generator 13 ... Multiplier 16 ... Current width detector 17 ... Peak value detector 18 ... Effective value detector 19 ... Peak Value ratio detector 20 ... Load condition determination circuit 21 ... Distortion compensation waveform generation circuit

Claims (1)

[Claims] 1. A PWM inverter that obtains a PWM waveform according to a sine wave signal to obtain a PWM voltage output at an output of an inverter main circuit, wherein a load of the inverter is a linear load based on a flow width and a peak value ratio of an output current of the inverter. A load type discrimination circuit that discriminates between a capacitor input type load and a mixed molding load of both loads, and generates a zero voltage distortion compensation waveform when the discrimination circuit discriminates a linear load, and Distortion compensation waveform generation circuit for generating a spike-shaped distortion compensation waveform centered on the peak portion of the sine wave signal and controlling the amplitude by the peak value ratio, and the distortion compensation waveform from the distortion compensation waveform generation circuit. A PWM inverter having a sine wave signal for adding to the sine wave signal to obtain a PWM waveform. Data of the output voltage waveform distortion compensation apparatus.