JPH1032980A - Voltage conversion apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an isolation-type AC voltage conversion apparatus which is used as a substitute for a commercial transformer and which is small and lightweight. SOLUTION: In an isolation-type AC voltage conversion apparatus, a commercial power supply 9 alternately turns on and off bidirectional semiconductor switches 5, 6 at an input-part frequency conversion circuit 1 in a short cycle under the control of a control circuit 4, and it is converted into a high-frequency AC voltage. The AC voltage is converted into a voltage according to a turn ratio by using a high-frequency insulating transformer 2. An output-part frequency conversion circuit 3 alternately turns on and off switches 7, 8 in synchronization with the input-part frequency conversion circuit 1, a commercial AC voltage in which a voltage is converted according to the turn ratio is outputted from an output filter 10. In addition, when the switching phase of both frequency conversion circuits is controlled, a constant voltage, a constant current and an input power-factor improvement effect are obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage converter, and more particularly, to a small and lightweight insulated voltage converter which can be used as a substitute for a commercial transformer.

[0002]

2. Description of the Related Art Conventionally, a commercial transformer is generally used for voltage conversion of a commercial AC power supply. When each function of output constant voltage, output constant current, and input power factor improvement is required, a constant voltage transformer is used. Furthermore, in order to reduce the size, weight and improve controllability, the converter and inverter are used to convert power in the order of AC → DC → AC, and output constant voltage, output constant current, and input power factor improvement functions. A power supply device having the following is also used.

[0003]

In the conventional voltage conversion system as described above, a commercial transformer operates at a commercial frequency (50/60 Hz) and cannot be downsized.
There was a problem that the weight had to be heavy.
In the case of a constant voltage transformer as well, there is a problem that the size and the weight cannot be reduced. In addition, a power supply unit that combines a converter and an inverter has an output constant voltage, output constant current,
Although it has the functions of improving the input power factor and can achieve a reduction in size and weight, there is a problem that the conversion efficiency is reduced and the control circuit is complicated because there are two power conversion units. Was.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art and to directly convert an AC power supply into an AC having any different voltage by using a high-frequency insulating transformer. An object of the present invention is to provide a small and lightweight insulated voltage converter that can also have each function of current and input power factor improvement.

[0005]

In order to achieve the above object, the present invention provides a voltage converter, comprising: first switching means for switching an input current; and a primary winding connected to an output of the first switching means. , A second switching means connected to a secondary winding of the transformer means, a smoothing means connected to an output of the second switching means, a first switching means and a second switching means. Control means for turning on and off the switching means at a predetermined frequency.

According to the present invention, the input current is switched and converted to a high-frequency current by the above-described configuration, converted to an arbitrary voltage by a high-frequency insulating transformer, and again converted to the same input current by the second switching means. Since the direction current is reproduced (rectified), the same function as that of a commercial transformer can be achieved, and a compact, lightweight, highly efficient, and inexpensive voltage converter can be obtained.

Further, by controlling the phase difference between the operations of the first switching means and the second switching means,
It is possible to control the output voltage. Accordingly, by detecting output voltage, output current, input power factor, and the like, and controlling the phase difference based on the detection result, each function of output constant voltage, output constant current, and input power factor improvement is achieved. Can also.

[0008]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the first embodiment which also serves as an explanatory diagram of the principle of the present invention. The input-portion frequency conversion circuit 1 as the first switching means and the output-portion frequency conversion circuit 3 as the second switching means are respectively composed of two switches 5, 6, 7 and 8, and each of the switches 5, 6 , 7, 8
For example, a bidirectional semiconductor switch capable of high-speed switching based on a control signal from the control circuit 4 can be used.
FIG. 2 is a circuit diagram illustrating a circuit configuration example of the switches 5 to 8. In this example, two parallel circuits of IGBTs 15 and 16 and bypass diodes 17 and 18 are connected in series in the opposite direction. As the semiconductor switch element, for example, besides the IGBT shown in the figure, for example, BJT, FE
Elements such as T and GTO can be used.

Returning to FIG. 1, the high-frequency insulating transformer 2
The secondary winding and the secondary winding each have a center tap,
In addition, the primary winding and the secondary winding are designed such that the winding ratio is equal to the ratio between the voltage Ei of the commercial power supply 9 and the output voltage Eo to be applied to the load 11. An output filter (smoothing circuit) 10 is provided on the output side. This filter passes, for example, the frequency of a commercial power supply, and the switching frequency (for example, several hundred kHz) of the switches 5 to 8 controlled by the control circuit 4 is It has a low-pass (or band-pass) filter characteristic of blocking. The control circuit 4 has, for example, a frequency of several hundred kHz and a duty ratio of 50%.
4 corresponding to each square wave oscillation circuit and each of switches 5 to 8
The switches 5 and 7 are driven in the same phase and the switches 6 and 8 are driven in the opposite phase to the switches 5 and 7. Control circuit 4
Can be configured as shown in FIG. 3 described later.

FIG. 4A is a waveform chart showing waveforms at various parts in the embodiment of FIG. In the example of this figure, the turns ratio of the transformer is 1: 1 and the switching frequency of each switch is lower than the actual one for ease of illustration. The input voltage Ei from the commercial power supply is switched in the opposite phase by the switches 5 and 6 of the input unit frequency conversion circuit 1, and a high-frequency current whose direction is reversed at the switching frequency flows through the primary winding of the transformer 2.

The transformer 2 transforms a high-frequency current in accordance with the winding ratio, and a voltage Em as shown in FIG. Since the switches 7 and 8 of the output section frequency conversion circuit 3 are switched in phase with the switches of the input section, the voltage waveform of the input terminal of the output filter 10 has the same direction of the high-frequency current Em as Eo ′. In addition, the waveform becomes close to the original input power supply waveform. As shown, the output waveform Eo of the output filter 10 is a waveform obtained by multiplying the input waveform by the winding ratio of the transformer 2.

Therefore, in the configuration shown in FIG. 1, the input AC voltage can be directly converted to an arbitrary voltage by determining the winding ratio of the transformer 2 according to the voltage required for the load. Also, since the transformer 2 is a high-frequency transformer, it is smaller and lighter than a commercial transformer, has no elements that consume a large amount of power, has high conversion efficiency, has a simple circuit configuration, and can be manufactured at low cost.

FIG. 3 is a block diagram showing a circuit configuration of the second embodiment. In this embodiment, a filter 20 is also provided in the input section of the first embodiment shown in FIG. 1 to realize a bidirectional voltage conversion function. Note that the same components as those in FIG. 1 are given the same numbers. The input-side filter 20 has a low-pass (or band-pass) having the same configuration as the output-side filter.
It is a filter (smoothing circuit).

Signal generation circuit 27 constituting control circuit 4
Is, for example, a frequency of several hundred kHz and a duty ratio of 50
% Square wave oscillation circuit. And each switch 5-8
Are connected directly to the signal generation circuit 27 via the inverter circuits 25 and 26, respectively, of the drivers 21 and 23 among the four driver circuits 21 to 24 corresponding to. Thus, switches 5 and 7 are driven in the same phase and switches 6 and 8 are driven in the opposite phase to switches 5 and 7. Therefore, as in the case of FIG. 1, if an AC power supply is connected to the input terminal A, the output terminal B
The transformed AC is obtained on the side.

Here, looking at the entire circuit of FIG. 3, the input terminal A side and the output terminal B side have a left-right symmetrical circuit configuration with the transformer 2 as a center. Therefore, even if a power supply is connected to the output terminal B and a load is connected to the input terminal A,
From the power supply to A, and a bidirectional voltage conversion function is realized. For example, when the winding ratio of the transformer 2 is 1: n, FIG.
If the voltage converter shown in (1) is provided, it is possible to obtain a voltage which is n times the power supply voltage or 1 / n by selecting the terminal to be connected. Furthermore, it can be used for a system in which the power transmission direction is reversed between daytime and nighttime, such as a solar power generation system connected to a commercial power supply.

FIG. 5 is a block diagram showing a circuit configuration of the third embodiment. The third embodiment is different from the first embodiment shown in FIG. 1 in that a phase shift circuit 43 for changing the drive phase of the output side switch with respect to the phase of the input side switch, and a circuit for controlling the phase shift circuit 43 Is added to the output constant voltage, the output constant current, and the input power factor improving function.

In FIG. 5, a current detecting transformer CT3
Numerals 0 and 36 respectively output the input and output current waveforms as voltage signals. The voltage detection transformers 31 and 39 output voltages obtained by transforming (level converting) the input voltage and the output voltage at a predetermined ratio. The full-wave rectifier circuits 32 and 34 each include, for example, a diode bridge rectifier circuit,
A smoothing circuit is not provided, and a full-wave rectified waveform signal is output as it is. In addition, the effective value circuits 33, 37, and 40 perform full-wave rectification on the input signals, extract a DC component through a smoothing circuit, and output as an effective value.

The power factor control circuit 35 includes a full-wave rectifier circuit 32,
34. Based on the output signal of the effective value circuit 33, a phase shift control signal for improving the input power factor is generated. Note that the input power factor improvement referred to here means that the shape of the current waveform should be as small as possible when the current suddenly flows only near the voltage peak, such as a rectifier circuit having a capacitor input smoothing circuit. This refers to correcting the shape to a shape close to a sine curve.

The constant current control circuit 38 receives the output signal of the effective value circuit 37 and generates a control signal for obtaining an output constant current characteristic. The constant voltage control circuit 41 receives an output signal of the effective value circuit 40 and generates a control signal for obtaining an output constant voltage characteristic. The low value selection circuit 42 includes, among the control signals output from the three control circuits 35, 38, 41,
The signal with the lowest value is selected and output as the voltage Vcon.

FIG. 6 shows three control circuits 35, 38, 41
4 is a circuit diagram showing a circuit configuration example of a low value selection circuit 42. FIG. All the ones indicated by triangles in the figure are operational amplifiers (op-amps). Further, the multiplication circuit 50 is also configured by an operational amplifier. First, the power factor control circuit 35 will be described. The output signal of the effective value circuit 33 and the output signal of the full-wave rectifier circuit 32 are input to the multiplication circuit 50.
A signal K as shown in FIG. 9 is output. The signal J shown in FIG. 9 is input from the full-wave rectifier circuit 34, and a (K
−J) is output. A is a subtractor 5
The gain is 1.

The next two operational amplifiers 52 and 54 constitute an adder and a buffer, respectively. The adder 52 adds the output signal of the first-stage subtractor 51 and the power factor improvement reference voltage PFref. Therefore, as an output signal of the power factor control circuit 35, a signal corresponding to [PFref + a (K−J)] is output with reference to the power factor improvement reference voltage PFref. In the vicinity, a voltage lower than PFref is output. As the reference voltage source 53, for example, a semi-fixed resistor having both ends connected to a power supply and ground may be used (the same applies to other reference voltage sources).

The constant current control circuit 38 and the constant voltage control circuit 41 have the same circuit configuration.
0 and 70 take the difference between the reference voltages Iref and Vref and the input signal, and b (Iref-Ir.ms) and c (Vre
f-Vr.ms). Here, b and c are the gains of the respective subtracters. The second operational amplifiers 61 and 71 and the third operational amplifiers 62 and 72 are adders and buffers having the same configuration as the power factor control circuit 35, respectively.
And the values of the reference voltage sources Vref 63 and Iref 73 are added and output. Therefore, the constant current control circuit 38 and the constant voltage control circuit 41 output a lower voltage as the output current and the effective value of the output voltage increase, respectively.

The low value selection circuit 42 includes operational amplifiers 81 to 8
3 is composed of three voltage follower circuits. Since a diode is inserted in the output terminal of each voltage follower circuit, when the voltage of the output terminal of the low value selection circuit 42 is higher than the voltage of the non-inverting input terminal of the operational amplifier, the diode is turned on, The output terminal voltage drops to the voltage of the non-inverting input terminal. As a result, the lowest voltage among the voltages output from the three control circuits 35, 38, 41 is output to the output terminal of the low value selection circuit 42 as Vcon. Therefore, based on the way of setting the reference voltage and the gain of each of the control circuits 35, 38, 41, only the function of the control circuit having the lowest output voltage at that time works effectively, and the other control functions do not work. .

Each reference voltage is, for example, Vref = PFref
<Iref, and each gain is c =
It is set so that b> a. Therefore, normally, the reference voltage is the lowest, and the output voltage of the constant voltage control circuit 41 having a large gain is the lowest, and the voltage converter is controlled at the constant voltage. Each parameter of the constant current control circuit 38 functions, for example, when the output current value exceeds about 1.2 times the rated output current, that is, is set so as to output the lowest voltage among the three control circuits. .

In the power factor control circuit 35, the gain (a) of the subtractor is set small, and only when an extreme current peak occurs, the output voltage of the power factor control circuit 35 is reduced by another control circuit 38, By lowering the output voltage of the device 41 and delaying the phase, the device operates to reduce the output voltage of the device and suppress the peak value of the current. When the constant current control or the power factor control function works, the constant voltage control function does not work, so that the voltage is not kept constant.

FIG. 7 is a block diagram showing the configuration of the signal generation circuit 27 and the phase shift circuit 43 of FIG. 5, and FIG. 8 is a waveform diagram showing waveforms at various parts in FIG. The oscillating circuit 90 is an oscillating circuit that generates a square wave at twice the switching frequency of the switches 5 to 8. Flip-flop 91
Is an input-side switch driving signal (B) having a 50% duty ratio by dividing the output signal (A) of the oscillation circuit 90 by half.
Is output.

Fall detection circuit 92 in phase shift circuit 43
Detects a falling edge of the output signal (A) of the oscillation circuit 90 and generates a short pulse signal (C). The sawtooth wave generating circuit 93 is composed of a circuit that charges a capacitor by the pulse signal (C) and discharges the capacitor with a predetermined time constant or constant current, for example, and outputs a signal having a waveform as shown in FIG. I do. The comparison circuit 94 compares the output signal (D) of the sawtooth wave generation circuit 93 with the phase control voltage Vcon output from the low value selection circuit 42, and the output signal (D) of the sawtooth wave generation circuit 93 is larger. In this case, "1" is output.

The exclusive OR circuit 95 takes the exclusive OR of the output signal (E) of the comparison circuit and the output signal (B) of the flip-flop 91 and outputs an output-side switch drive signal (F). . This signal F is delayed from the signal B by the output pulse E of the comparison circuit (d). As is apparent from the figure, this delay amount is equal to the control voltage Vco.
The lower the value of n, the greater the value.

FIG. 4B is a waveform diagram showing waveforms of the respective parts when the drive signal of the output side switch is delayed by about 45 degrees by the phase shift circuit 43 in the embodiment of FIG.
When the drive signals of the output side switches 7 and 8 are delayed,
The polarity of the voltage waveform Eo 'at the output terminal of the switch is not uniform, and a voltage of opposite polarity is generated by the delay amount (d). Therefore, the voltage waveform after passing through the output filter 10 is as shown in FIG.
, The output voltage Eo decreases in accordance with the delay amount. When the delay amount reaches 90 degrees, positive and negative voltages are output for an equal time, and thus the output voltage Eo after passing through the filter 10 becomes zero. When the driving phase is delayed by 180 degrees, an output voltage in which the polarity of the input voltage is inverted is obtained.

When the constant voltage control is performed, for example, at the time of rated input and rated output, the input voltage is delayed by a predetermined delay amount θ (for example, several degrees to several tens of degrees), and the input voltage is 90% of the rated value.
When the load is 120% of the rated value, the delay amount becomes 0, and
The gain c (determined by R1 and R2) and the reference voltage PFref of the subtractor 51 in FIG. 6 are adjusted so that the input voltage is 110% of the rated value and the delay amount becomes approximately 2θ when the load is 0%. Is desirable.

As described above, the gain b and the reference voltage Iref are desirably adjusted so that the constant current control functions when the output current value exceeds about 1.2 times the rated output current. Further, the gain a and the reference voltage PFref are adjusted so that the power factor control operates only when an extreme current peak occurs, and the output phase of the device is reduced by delaying the operation phase of the output side switch, It operates so as to suppress the peak value of the current. The control characteristics can be arbitrarily set according to the required specifications. With the above configuration, it is possible to realize a voltage converter that is small and lightweight and has an output constant voltage, an output constant current, and an input power factor improvement function.

Although the embodiment has been described above, the following modifications are also conceivable. In the embodiment, an example in which a transformer having a center tap is used as the transformer is disclosed. However, for example, a bridge circuit using four bidirectional semiconductor switches is provided on each of the input side and the output side, and the direction of the current is reversed. By turning on and off two at a time, a transformer without a center tap can be used.

Further, in the circuit configuration of FIG. 1, the switches 6 and 8 are deleted, and the switching without the center tap is performed, and only one switch is provided on each of the input side and the output side. The same voltage conversion function can be achieved by a simple configuration using. However, in this case, since only half of the BH curve can be used as the transformer, the transformer becomes large, and in order to prevent magnetic saturation of the transformer, a well-known reset circuit (a capacitor and a resistor) is provided on the primary side of the transformer. (A circuit in which a parallel circuit and a diode are connected in series) need to be connected in opposite directions.

In the embodiment, an example in which a commercial transformer is used as an AC voltage converter instead of a commercial transformer has been disclosed.
The voltage converter of the present invention operates exactly the same even when the input power supply is DC. Further, when the phase is delayed by 90 degrees, the output becomes 0, and when the phase is delayed by 180 degrees, an output voltage whose polarity is inverted is obtained. Therefore, in the third embodiment shown in FIG. 5, a DC power supply is input, and ON / OFF and polarity inversion can be controlled by changing a control voltage.
An AC output can also be obtained by applying an AC voltage as the control voltage.

In the embodiment, an example has been disclosed in which the phase of the secondary side switch is delayed. However, if there is a phase difference between the two switching means, the output decreases. For example, the phase of the primary side is delayed and controlled. Alternatively, control may be performed to advance the phase. Further, the primary side and the secondary side may be controlled by different control signals. For example, control may be performed such that the phase on the primary side is advanced by a power factor control signal, and control may be performed such that the phase on the secondary side is delayed by a constant voltage control signal.

[0036]

As described above, in the present invention,
By determining the winding ratio of the transformer 2 according to the voltage to be supplied to the load, it is possible to directly convert the input AC voltage or DC voltage to an arbitrary voltage. Further, there is an effect that it is smaller and lighter than a commercial transformer, has high conversion efficiency, has a simple circuit configuration, and can be manufactured at low cost. Furthermore, by providing filters at both ends, a bidirectional voltage conversion function can be realized, and by controlling the drive phases of the input side and output side switches, output constant voltage, output constant current, and input power factor improvement functions can be realized. There is an effect that a voltage conversion device having the same can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a first embodiment also serving as an explanatory diagram of the principle of the present invention.

FIG. 2 is a circuit diagram showing a circuit configuration example of switches 5 to 8;

FIG. 3 is a block diagram showing a circuit configuration of a second embodiment.

FIG. 4 is a waveform chart showing waveforms at various portions in the first or third embodiment.

FIG. 5 is a block diagram showing a circuit configuration of a third embodiment.

FIG. 6 is a circuit diagram showing a circuit configuration example of three control circuits 35, 38, 41 and a low value selection circuit.

FIG. 7 is a block diagram showing a configuration of a signal generation circuit 27 and a phase shift circuit 43 of FIG. 5;

FIG. 8 is a waveform chart showing waveforms at various parts in FIG. 7;

FIG. 9 is a waveform chart showing signal waveforms in the power factor control circuit.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Input side frequency conversion circuit, 2 ... Transformer, 3 ... Output side frequency conversion circuit, 4 ... Control circuit, 5, 6, 7, 8 ... Bidirectional semiconductor switch, 9 ... Commercial power supply, 10 ... Output filter, 11 ... Load, 15, 16 ... IGBT, 17, 18 ...
Diodes, 20 filters, 21 to 24 driver circuits, 25, 26 inverter circuits, 27 signal generation circuits

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Bunsei Anan 2-47, Shiobara, Minami-ku, Fukuoka City, Fukuoka Prefecture Inside Kyushu Electric Power Co., Inc. (72) Inventor Kiyomi Yamazaki 2, Shiobara Minami-ku, Fukuoka Prefecture 1-47, Kyushu Electric Power Co., Inc. (72) Inventor Kosuke Harada 2-4-6 Sakurazaka, Chuo-ku, Fukuoka City, Fukuoka Prefecture (72) Inventor Katsuaki Murata 9-53, Tsuboi-cho, Kumamoto City, Kumamoto Prefecture 72) Inventor Tetsuya Nakajima 1-2-8 Minoshima, Hakata-ku, Fukuoka Pref. NT Building Inside Nissim Electronics Co., Ltd. (72) Inventor Masahito Chenno 1-2-8 Minojima, Hakata-ku, Fukuoka Pref. Inside Nissim Electronics Co., Ltd. (72) Inventor Taisuke Kawata 1-2-8 Minojima, Hakata-ku, Fukuoka, Fukuoka Prefecture NT Building Nissim Electronics Co., Ltd.

Claims (6)

[Claims] A first switching means for switching an input current flowing through a primary winding of the transformer; a second switching means connected to a secondary winding of the transformer means; Voltage conversion, comprising: smoothing means connected to the output of the switching means; and control means for turning on and off the first switching means and the second switching means at a frequency higher than the frequency of the input current. apparatus. 2. The first switching means and a second switching means.
The switching means comprises two switches each having one terminal connected to each other, and the transformer means includes a center tap on each of the primary winding and the secondary winding, and an end of each winding is Connected to the other terminal of the switch, wherein the control means alternately turns on and off the two switches in each of the first and second switching means such that when one is on, the other is off. The voltage conversion device according to claim 1, wherein the voltage conversion device controls the first switching means and the second switching means in a synchronized manner. 3. The voltage conversion device according to claim 1, further comprising a second smoothing means between the input terminal and the first switching means. 4. The apparatus according to claim 1, wherein said control means includes a phase adjusting means for adjusting a phase difference between operations of said first switching means and said second switching means. The voltage converter according to any one of the preceding claims. 5. The control means includes an output voltage, an output current,
5. The voltage converter according to claim 4, further comprising a phase control unit that detects any one of the input power factors and controls the phase adjustment unit according to the detection result. 6. The control means detects an output voltage of the device, and detects a voltage control means for generating a lower control voltage as the output voltage increases, and detects an output current of the device, and controls the output current as the output current increases. Current control means for outputting a voltage, including at least two of the power factor control means for detecting the input power factor of the device and outputting a lower control voltage as the input power factor is smaller, further comprising the voltage control means, Current control means, low value selection means for inputting each output control voltage of the control means provided in the device among the power factor control means, selecting the lowest voltage value among them, and outputting to the phase adjustment means. The voltage conversion device according to claim 4, wherein the voltage conversion device includes: