JPH0690569A - Biased magnetism preventing circuit of output transformer of three-phase inverter - Google Patents

Abstract

PURPOSE:To prevent at a biased magnetism and the saturation of an output transformer by installing an adder which changes a zero potential of a modulated signal generater due to the output of a dc component detector. CONSTITUTION:The output current of each phase of a three-phase switching circuit 3 which is detected by an output current detector 11a is a sine wave ac containing a ripple of a frequency of a chopping wave Er as a carrier signal. Therefore, if a cut-off frequency of a low-path filter 11b is made very much smaller than the frequency of that sine wave, the dc voltage proportional to a dc component of the output current can be output from the low-path filter 11b. An adder 12 inverses the dc voltage from a dc component detector 11 and adds it up to the output of a modulated signal generator 8 to change a zero potential of a modulated signal. Therefore, such a PWM signal can be obtained as to remove a dc component of the output current of each phase of the three-phase switching circuit 3. By this method, a dc component can be removed from the output current of each phase of the three-phase switching circuit 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anti-bias circuit for an output transformer of a three-phase inverter, more specifically, by removing a DC component of an output transformer connected to the output side of the inverter. , A circuit for preventing magnetic bias of the transformer.

[0002]

2. Description of the Related Art In a three-phase inverter for converting a direct current into a three-phase alternating current, a three-phase output is provided by interposing an output transformer on the alternating current output side in order to insulate between the direct current input side and the three-phase alternating current output side. There are things I tried to get.

A conventional example of such a three-phase inverter is shown in FIG.
Will be described.

In FIG. 2, 1 is a DC power supply, 2 is a DC filter connected to this DC power supply, 3 is a series-connected switching element U ₁ , U ₂ , V ₁ , V ₂ , W ₁ , W ₂
A three-phase switching circuit consisting of 4 is a connection point of the switching elements U ₁ and U ₂ in series, a switching element V ₁ ,
An AC filter connected between the series connection point of V _{2 and} the series connection point of the switching elements W ₁ and W ₂ and the ground, 5 is an output transformer connected to the output side of the AC filter, and 6 is the output It is a load connected to the secondary side of the transformer.

When a three-phase sine wave alternating current is to be obtained at the output side by the three-phase inverter having the above-mentioned structure, the switching elements U ₁ , U ₂ , V ₁ , V ₂ , W
_A PWM signal is applied to ₁ and W _2, and the switching elements U ₁ , U ₂ , V ₁ , V ₂ , W ₁ and W ₂ are turned on and off by this signal.

In the PWM signal, the output of each phase of the output transformer 5 and the reference sine wave corresponding to each phase obtained from the reference sine wave generator 7 are compared by the modulation signal generator 8 and output as a modulation signal. The modulated signal is further compared with the triangular wave from the carrier signal generator 9 by the PWM control circuit 10 to obtain the modulated signal.

[0007]

In the above three-phase inverter, the zero potential of the sine waves Csu, Csv, Csw as the modulation signal obtained from the modulation signal generator 8 and the triangular wave Er obtained from the carrier signal generator 9 are obtained. The zero potential is not absolute, and the comparison between the sine waves Csu, Csv, Csw and the triangular wave Er is relative.

Further, the zero potential of each output of the three-phase switching circuit 3 fluctuates due to the difference in ON resistance between the switching elements and the difference in switching speed, so that a current containing a DC component flows through the AC filter 4. It will be.

As a result, the iron core of the output transformer 5 may be demagnetized or saturated, which may cause overcurrent to flow into the switching element, resulting in destruction.

[0010]

In order to solve the above problems, the present invention provides a DC power supply, a three-phase switching circuit for switching DC power from the DC power supply to obtain a three-phase output, and the three-phase switching. An output transformer connected to the output side of the circuit, a modulation signal generator that compares the output of each phase of this output transformer with the reference sine wave of each phase to obtain a modulation signal, and this modulation signal as a carrier signal. A PWM control circuit for converting the carrier signal from the generator into a PWM signal for controlling the pulse width of the switching circuit, and detecting the DC component of the output current of each phase of the switching circuit, A DC component detector that obtains a DC voltage proportional to this DC component and an adder that changes the zero potential of the modulation signal generator by the output of this DC component detector are provided. It is characterized in that to prevent the DC magnetic deviation of the output transformer.

[0011]

As described above, the present invention detects the DC component of the output current of each phase of the three-phase switching circuit and changes the zero potential of the modulation signal generator by the DC voltage proportional to this DC component. Since the direct current component is removed, it is possible to prevent the magnetic deviation and saturation of the iron core of the output transformer.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit diagram in which an eccentricity prevention circuit for an output transformer of a three-phase inverter of the present invention is provided, and parts having the same functions as in FIG.

The feature of the present invention is that the circuit of FIG. 2 is provided with a DC component detector 11 to detect the DC component of the output current of each phase of the three-phase switching circuit 3, and the DC voltage proportional to this DC component is added. The zero potential of the modulation signal is changed by adding it to the modulation signal from the modulation signal generator 8 by the device 12.

The DC component detector 11 includes an output current detector 11a for detecting the output current of each phase of the three-phase switching circuit 3 and a low pass filter 11b for detecting the DC component of the detected value of the output current detector 11a. And a buffer 11c for impedance-converting the DC component output from the low-pass filter 11b and converting it into a DC voltage proportional to the DC component.

The adder 12 is the DC component detector 1
The zero potential of the modulation signal is changed by inverting the DC voltage from 1 and adding it to the output of the modulation signal generator 8.

That is, since the output current of each phase of the three-phase switching circuit 3 detected by the output current detector 11a is a sine wave alternating current containing a ripple of the frequency of the triangular wave Er as a carrier signal, it is a low pass filter. If the cutoff frequency of 11b is made sufficiently smaller than the frequency of the sine wave, it is possible to output a DC voltage proportional to the DC component in the output current from the low pass filter 11b.

Therefore, by changing the zero potential of the modulation signal by this DC voltage, it is possible to obtain a PWM signal capable of removing the DC component of the output current of each phase of the three-phase switching circuit 3.

[0018]

As described above, the present invention provides
Since it is possible to remove the DC component from the output current of each phase of the three-phase switching circuit, it is possible to prevent the magnetism and saturation of the iron core of the output transformer, which can cause overcurrent or damage to the switching element. It is possible to eliminate the conventional drawbacks such as the above. Therefore, the margin of the magnetic flux density of the output transformer can be reduced, and the size of the output transformer can be reduced.

Further, the present invention can be applied regardless of the method of connecting the output transformer.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a bias prevention circuit for an output transformer of a three-phase inverter according to the present invention.

FIG. 2 is a circuit diagram of a conventional anti-bias circuit for an output transformer of a three-phase inverter.

[Explanation of symbols]

 3 Three-phase switching circuit 5 Output transformer 7 Reference sine wave generator 8 Modulation signal generator 9 Carrier signal generator 10 PWM control circuit 11 DC component detector 12 Adder

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[Procedure amendment]

[Submission date] August 31, 1993

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Change

[Correction content]

[Figure 1]

[Fig. 2]

Claims (1)

[Claims] 1. A DC power supply, a three-phase switching circuit for switching DC power from the DC power supply to obtain a three-phase output, an output transformer connected to the output side of the three-phase switching circuit, and this output. A modulation signal generator that obtains a modulation signal by comparing the output of each phase of the transformer and the reference sine wave of each phase, and compares the modulation signal with the carrier signal from the carrier signal generator to pulse the switching circuit. A PWM control circuit for converting into a PWM signal for width control, and a DC component detector for detecting the DC component of the output current of each phase of the switching circuit and obtaining a DC voltage proportional to this DC component; And an adder for changing the zero potential of the modulation signal generator by the output of the DC component detector to prevent the output transformer from being biased by the DC component. Bias prevention circuit for inverter output transformer.