JP2990867B2 - Forward converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a forward converter for obtaining voltage-controlled DC power from AC power.

[0002]

2. Description of the Related Art FIG. 3 shows a conventional forward converter, and shows a circuit diagram of a boost chopper system. The AC current from the AC power supply 1 through the LC filter 2 is rectified by a diode bridge 3 serving as a rectifier circuit, and this DC current is boosted by a boost chopper circuit 4 and taken out as a DC output.
The boost chopper circuit 4 supplies a short-circuit current to the DC reactor DCL when the transistor TR is turned on, and supplies the current of the DC reactor DCL to the smoothing capacitor Co and the load side through the diode _{DF when} the transistor TR is turned off. The control circuit 5 controls the on / off ratio of the transistor TR by feedback control based on a comparison between the detection voltage Vdet of the voltage detector 6 and the set voltage Vset.

As another conventional forward conversion device, there is a device in which the diode bridge 3 has a bridge structure of a semiconductor element with a control electrode such as a thyristor or a GTO, or a device in which the chopper circuit 4 is a step-down chopper circuit.

[0004]

A conventional forward conversion device is
With the diode bridge 3 and the boost chopper circuit 4 shown in the figure, only a DC voltage higher than the rectified voltage of the diode bridge 3 can be output, and it cannot be used as a DC power supply that continuously varies the DC voltage from zero volts to a voltage higher than the rectified voltage.

[0005] In addition, since a current cutoff when a short-circuit accident occurs on the load side cannot be performed in a circuit configuration, a dedicated overcurrent protection circuit is required. Further, when the AC power supply 1 is turned on, a rush current flows through the capacitor Co, and thus a prevention circuit is required.

In this respect, a forward converter having a bridge circuit of a semiconductor element can cut off a short-circuit current and suppress an inrush current. However, a DC power supply having a rectified voltage higher than that of the AC power supply 1 needs to be combined with a boost chopper circuit. And make the apparatus complicated and expensive.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a forward conversion device in which overcurrent protection and inrush current are eliminated while continuously varying a DC voltage from zero volts to a voltage exceeding a rectified voltage.

[0008]

According to the present invention, in order to solve the above problems, a series circuit of an AC switch circuit and an AC reactor is connected from an AC power supply via an AC filter, and both ends of the AC reactor are connected to an AC input. connect the rectifier circuit that end, the control unit of the AC switch circuit, said rectifier times
Between the output voltage set value of the circuit and the output voltage detection value of the rectifier circuit.
A voltage control amplifier for proportionally integrating the deviation; and
Positive value obtained by multiplying the amplitude of the voltage waveform by the coefficient of the output of the voltage control amplifier
A multiplier for obtaining a sinusoidal voltage waveform;
Detection that the current detection value has reached the output level of the multiplier
And the current detection value of the AC reactor is zero.
A zero detector for detecting a decrease in the vicinity, and the zero
Set by detector detection, reset by comparator output
A flip-flop to be activated,
Turn on the AC switch only during the period from set to reset.
And a gate circuit for turning on the path .

[0009]

According to the present invention having the above-mentioned structure, a short-circuit current flows through the AC reactor by controlling the AC switch circuit to be turned on, and when the current reaches the voltage control level, the AC switch circuit is controlled to be turned off. The DC output of the boost chopper control is taken out from the reactor to the rectifier circuit, and this chopper control is made into a voltage waveform of an AC power supply to make a rectified current that matches the AC voltage waveform. Further, the DC output voltage is controlled by multiplying the AC voltage waveform by the voltage control system signal.

[0010]

FIG. 1 is a circuit diagram showing an embodiment of the present invention. The alternating current flowing from the AC power supply 1 through the balanced LC filter 2 is applied to a transistor T as a semiconductor element with a control pole.
A diode bridge 3 via an AC switch circuit 7 including diodes D1 and D2 connected in anti-parallel with R1 and TR2.
Of the AC input. An AC reactor 8 is provided at an AC input terminal of the diode bridge 3, and a smoothing capacitor 9 is provided at a DC output terminal.

The transistor TR of the AC switch circuit 7
1, TR2 is subjected to AC chopper control by gate outputs G1, G2 of the control device 10. The control device 10 calculates a deviation between the set voltage Vset and the detection voltage Vdet of the voltage detector 6 by a proportional integral (PI) operation, and a voltage waveform (sine wave) of the AC power supply 1 using the operation result as a multiplier. Vin
, A comparator 13 for comparing a sine wave resulting from the multiplication with the current waveform I _OUt of the AC reactor 8, a zero detector 14 for detecting a zero point of the current waveform I _OUt , An RS flip-flop 15 which is set at the zero point detection timing and reset by the output of the comparator 13 and a gate circuit 16 which obtains the gate outputs of the transistors TR1 and TR2 only during the set period of the flip-flop 15 are provided.

The voltage waveform of AC power supply 1 is detected by transformer 17, and current I _OUt of AC reactor 8 is detected by current transformer 1.
8 is detected. The set and reset signals for the flip-flop 15 are transmitted to the zero point detector 14 and the comparator 13.
Are provided as single-shot pulses having respective output timings.

The operation of the main circuit in the above configuration will be described below. Transistors TR1 and T of AC switch circuit 7
R2 is turned on / off by chopper control. By this on / off control, for example, when the voltage of the AC power supply 1 is in a positive period, the transistor TR1 performs the same operation as the diode D1, and the transistor TR2 performs chopping of the AC current. With this chopping, transistor TR
In the ON period of 2, filter 2 → transistor TR1 / diode D1 → AC reactor 8 → transistor TR2
→ Current starts to flow through the path of the filter 2.

When this current reaches a control level to be described later, the transistor TR2 is turned off, and the AC current is cut off. As a result, the current of the AC reactor 8 performs boost charging of the capacitor 9 and power supply to the load through the diode bridge 3. Similarly, during the negative period of the AC power supply 1, a boosting chopper operation is obtained by chopping the transistor TR1.

Next, the operation of the control device 10 will be described with reference to FIG. First, the output of the multiplier 12 becomes a sine wave voltage waveform obtained by multiplying the amplitude of the sine wave voltage waveform Vin by a coefficient by the output of the voltage control amplifier 11.

In response to the voltage waveform Vin, the transistor T
R2 ON current I _OUT of the (time t ₁₎ by AC reactor 8 is started to increase linearly, when said current level I _OUT reaches the voltage waveform Vin level (time t _2), comparator 1
3 is inverted to reset the flip-flop 15.

By this reset, the output of the gate circuit 16 controls off of both the transistors TR1 and TR2.
After this OFF control, the AC reactor 8 starts to flow toward the diode bridge 3 and decreases toward the current zero point.

When the current of the AC reactor 8 reaches the zero point (time t ₃ ), the flip-flop 15 is set by the detection of the zero point detector 14. With this set, the transistors TR1, TR1
2 is turned on again, and current supply to the AC reactor 8 is started. Hereinafter, the same repetition is performed.

Therefore, the current waveform I of the AC reactor 8 is
_OUt becomes a triangular wave, and the current I to the AC switch circuit 7 is
The half-wave period of the current _IOUt is _reached , and the input current Iin from the AC power supply 1 becomes a sine waveform _enclosing the current I by the filter 2, and the power factor 1 is controlled. FIG. 2 shows only the positive period of the alternating current, but the same applies to the negative period. Further, the DC output level is controlled by the set voltage Vset from zero volts to a level exceeding the rectified voltage of the AC power supply 1 by the multiplier input control to the multiplier 12 by the voltage control amplifier 11.

Further, in this embodiment, since the AC switch circuit 7 is interposed between the AC power supply 1 and the load side, interruption of the fault current on the load side can be performed by turning off the switch circuit 7.
Further, the rush current when the AC power is turned on can be suppressed.

In this embodiment, if the flip-flop 15 is not set to zero current and is set to a level lower than the command value Vin, the AC switch circuit 7 starts to be turned on before the current _IOUt reaches the zero point. The AC reactor 8 can be operated by a sinusoidal current having a ripple.

Although the embodiment is shown by a single-phase circuit, it can be realized by a similar configuration in a three-phase circuit.

[0023]

As described above, according to the present invention, a series circuit of a filter, an AC switch circuit, and an AC reactor is provided between an AC power supply and a rectifier circuit, and a rectifier circuit having both ends of the AC reactor as AC input terminals. And the chopper control of the AC switch circuit is performed by comparing the signal obtained by multiplying the AC voltage waveform by the output of the voltage control amplifier with the current value of the AC reactor.

(1) A step-up chopper control for the AC voltage waveform enables a continuous variable voltage from a DC output of zero volts to a voltage obtained by boosting the AC voltage to be obtained.

(2) Since an AC switch circuit is interposed between the AC power supply and the rectifier circuit, overcurrent protection can be performed by the AC switch circuit against a short circuit on the load side, and a dedicated protection circuit is not required.

(3) Since an AC switch circuit is interposed between the AC power supply and the rectifier circuit, no rush current is generated when the AC power supply is turned on.

(4) The AC current input and the voltage have the same phase, and the device has a power factor of 1, and there is no adverse effect on the AC power supply.

(5) The configuration of the AC switch circuit is simplified.

[Brief description of the drawings]

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

FIG. 2 is a waveform diagram of a main part in the embodiment.

FIG. 3 is a conventional circuit diagram.

[Explanation of symbols]

2 ... AC filter, 7 ... AC switch circuit. 8 ... AC reactor, 10 ... Control device, 11 ... Voltage control amplifier, 1
2 Multiplier, 13 Comparator, 14 Zero detector, 16
Gate circuit.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H02M 7/12 H02M 7/12 Q

Claims (1)

(57) [Claims] An AC switch circuit connected to a series circuit of an AC reactor from an AC power supply via an AC filter, a rectifier circuit having both ends of the AC reactor connected to an AC input terminal, and a control device for the AC switch circuit. Is the output voltage set value of the rectifier circuit and the output voltage of the rectifier circuit
A voltage control amplifier for proportionally integrating the deviation from the detected value, and an output of the voltage control amplifier for controlling the amplitude of the voltage waveform of the AC power supply.
A multiplier for obtaining a sinusoidal voltage waveform multiplied by a coefficient in the multiplier;
A comparator that detects that the bell has been reached, and the current detection value of the AC reactor has decreased near zero.
A zero detector for detecting that the output of the comparator is set by the detection of the zero detector.
Flip-flop reset in a period of time from set to reset of the flip-flop
And a gate circuit for turning on the AC switch circuit.
Forward conversion device characterized by comprising.