KR20030093530A - Converter for converting a three-phase alternating current to a direct current - Google Patents

Abstract

PURPOSE: A converter for converting three-phase AC to DC is provided to simplify a structure of the converter by reducing the number of inductors and the number of capacitors. CONSTITUTION: A converter for converting three-phase AC to DC includes a first to a third switches(S1-S3), a first to a third capacitors(C1-C3), a transformer(30), and a rectification circuit(40). The first to the third switches(S1-S3) are connected to output terminals of each phase of a three-phase AC power source. The first to the third capacitors(C1-C3) are connected in parallel to the output terminals of each phase of the three-phase AC power source. The transformer(30) includes the primary coil and the secondary coil. The primary coil is connected to the first to the third switches(S1-S3) and the first to the third capacitors(C1-C3). The secondary coil is coupled to the primary coil. The rectification circuit(40) is used for rectifying the output voltage of the secondary coil of the transformer(30).

Description

CONVERTER FOR CONVERTING A THREE-PHASE ALTERNATING CURRENT TO A DIRECT CURRENT}

The present invention relates to a converter for converting three-phase alternating current into direct current, and more particularly, to a converter for converting three-phase alternating current into direct current using a small number of capacitors and switches.

1 is a view showing an example of a converter for converting a conventional three-phase alternating current to direct current. The conventional converter has a power factor improving circuit section 10, a converting section 20, a transformer 30, and a rectifier circuit 40.

The power factor improving circuit unit 10 includes three inductors L1, L2, L3, and each inductor L1, L2, L3 connected to the output terminals of the respective phases Vac1, Vac2, Vac3 of the three-phase AC power supply Vac. It consists of six switches (S4 to S9) connected to. Both ends of the smoothing capacitor C5 are connected to the common terminals of the switches S4 to S9 of the power factor improving circuit unit 10.

The converting unit 20 includes two switches S10 and S11 connected in parallel with the smoothing capacitor C5, and two capacitors C6 and C7 connected in parallel with the switches S10 and S11. Consists of

One end of the primary coil Lp of the transformer 30 is connected between the switches S10 and S11 in the converting section 20 and the other end is between the capacitors C6 and C7 in the converting section 20. It is connected. The rectifier circuit 40 is connected to the secondary coil Ls of the transformer 30.

The power factor improving circuit unit 10 boosts the output voltage of the three-phase AC power source Vac to generate a DC voltage having a voltage higher than the input voltage. The boosted voltage is smoothed by the smoothing capacitor C5 and converted back to alternating current by the converting unit 20. The AC voltage output by the converting unit 20 is transformed by the transformer 30 and rectified by the rectifier circuit 40. Accordingly, a DC voltage is supplied to the load R1.

As described above, the conventional three-phase AC / DC converter performs two stages of conversion, which is composed of a boost operation for improving the power factor and a DC-DC converting operation. To this end, the conventional three-phase AC / DC converter requires a large number of switches (S4 to S11) and capacitors (C5, C6, C7) and inductors (L1 to to accumulate the input current of the three-phase power supply (Vac)). L3) is required.

The present invention has been made to solve the above problems, an object of the present invention, a three-phase AC / DC converter capable of directly converting three-phase AC voltage to direct current without converting a three-phase AC voltage to a high-pressure direct current To provide.

Another object of the present invention is to provide a three-phase AC / DC converter, which eliminates the need for a large number of capacitors and inductors by using a small number of switches and capacitors, and is highly efficient.

1 is a circuit diagram of a conventional three-phase AC / DC converter,

2 is a circuit diagram of a three-phase AC / DC converter according to the present invention;

3 is a diagram showing voltage waveforms of each phase of the three-phase power supply of FIG. 2;

4 shows waveforms of voltage and current of each switch at detailed periods in section A of FIG. 3;

5A through 5D are diagrams illustrating equivalent circuits of FIG. 2 according to changes in switching states of respective switches in section A of FIG.

6A-6C illustrate various embodiments of the switch of FIG. 3, and

7 is a circuit diagram of a control circuit for outputting a signal for controlling a switch in a converter according to the present invention.

Explanation of symbols on the main parts of the drawings

S1, S2, S3: Switch C1, C2, C3: Capacitor

30: transformer 40: rectifier circuit

Three-phase AC / DC converter according to the present invention for achieving the above object, three switches each end is connected to the output terminal of each phase of the three-phase AC power supply; Three capacitors each of which has one end connected in parallel with the three switches to an output terminal of each phase of the three-phase AC power source; A transformer having a primary coil one end connected in common to the other end of the switches and the other end connected in common to the other end of the capacitors, and a secondary coil coupled to the primary coil; And a rectifier circuit for rectifying the output voltage of the secondary coil of the transformer.

By using a small number of switches and capacitors to configure the converter, the circuit structure is simplified, and the process of converting three-phase voltage into high-voltage direct current is not required.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the present invention. In the description of this embodiment, the same reference numerals are given to the same components (three-phase AC power supply, transformer, rectifier circuit) as the conventional converter shown in FIG.

2 is a circuit diagram of a three-phase AC / DC converter according to the present invention. The three-phase AC / DC converter according to the present invention is composed of three switches S1, S2, S3, three capacitors C1, C2, C3, a transformer 30, and a rectifier circuit 40.

One end of each switch (S1, S2, S3) is connected to the output terminal of each phase (Vac1, Vac2, Vac3) of the three-phase AC power supply (Vac), and one end of each capacitor (C1, C2, C3) is three-phase It is connected to the output terminal of each phase Vac1, Vac2, Vac3 of AC power supply Vac. The capacitors C1, C2, C3 and the switches S1, S2, S3 are arranged in parallel with each other.

The transformer 30 has a primary coil Lp and a secondary coil Ls coupled to each other. One end of the primary coil Lp is commonly connected to the other end of the switches S1, S2 and S3, and the other end of the primary coil Lp is commonly connected to the other end of the capacitors C1, C2 and C3. . The AC voltage applied to the primary coil Lp is transformed according to the turns ratio of the primary coil Lp and the secondary coil Ls, and the transformed AC voltage is output from the secondary coil Ls.

The rectifier circuit 40 is composed of a pair of diodes D1 and D2, an inductor L4, and a capacitor C4. AC is converted into direct current by a bridge circuit composed of a pair of diodes D1 and D2, and the converted direct current is accumulated in the inductor L4. The capacitor C4 smoothes the output voltage of the inductor L4, and the DC voltage Vout output from both ends of the capacitor C4 is applied to the load R1.

FIG. 3 is a graph showing waveforms of output voltages Vac1, Vac2, and Vac3 of each phase of the three-phase AC power supply Vac shown in FIG.

Each output voltage Vac1, Vac2, Vac3 is a sinusoidal voltage having a phase difference of 120 degrees. Vac1 is zero degrees in phase, Vac2 is lag 120 degrees behind Vac1, and Vac3 is 120 degrees behind Vac2 (or leads 120 degrees out of Vac1).

For convenience of description, in FIG. 3, one period in which the output voltages Vac1, Vac2, and Vac3 are output is divided into 12 sections (sections A to L) each having a phase width of 30 degrees. Each section is divided into several subsections as described below, and each subsection is divided into five periods.

4 shows the output of each part in the circuit by the switching operation control of each switch S1, S2, S3 in section A. FIG. Section A is divided into several subsections, and each subsection consists of five periods. 4 shows only two subsections among several subsections existing in section A. FIG. The number of such subdivisions may be many or may exist several hundred in one interval.

FIG. 5A is a view showing a part of an equivalent circuit in section A of the circuit shown in FIG. 2 and shows a power supply Vac to a part of the primary coil Lp of the transformer 30. FIGS. 5D shows the equivalent circuit of FIG. 5A according to the switching state of each switch S1, S2, S3 in section A. FIG.

As can be seen in FIG. 3, in section A, the voltage of Vac1 is positive, the voltage of Vac2 is negative, and the voltage of Vac3 is positive. Thus, the circuit of FIG. 2 can be represented as an equivalent circuit having three independent DC power supplies V1, V2, V3 arranged in polarity as shown in FIG. 5A.

In period 1, S2 is turned on, and S1 and S3 are turned off. Thus, the circuit of FIG. 5A is equivalent to the circuit shown in FIG. 5B. Therefore, a negative current flows through the primary coil Lp through V1 and V2 (hereinafter, the direction in which the current is input to the portion where the dot is stamped on the primary coil Lp in the positive direction, and The direction in which the current is output from the portion where the dot is printed is referred to as the negative direction.) And the current supplied to the primary coil Lp by the power supplies V1 and V2 is the secondary coil Ls and the rectifier circuit 40. It is supplied to the load R1 via.

In period 2, all of S1, S2, and S3 are turned off. Therefore, in period 2, the state is as shown in Fig. 5A, and the inductor L4 on the rectifier circuit 40 side supplies power to the load R1.

In period 3, S1 is turned on, and S2 and S3 are turned off. Thus, the circuit of FIG. 5A is equivalent to the circuit shown in FIG. 5C. Accordingly, the positive current flows through the primary coil Lp through V1 and V2, and the current supplied to the primary coil Lp by the power supplies V1 and V2 is rectified with the secondary coil Ls. It is supplied to the load R1 via the circuit 40.

In period 4, S3 is turned on, and S1 and S2 are turned off. Thus, the circuit of FIG. 5A is equivalent to the circuit shown in FIG. 5D. Therefore, a positive current flows in the primary coil Lp through V2 and V3, and the current supplied to the primary coil Lp by the power sources V2 and V3 is rectified with the secondary coil Ls. It is supplied to the load R1 via the circuit 40.

In period 5, all of S1, S2, and S3 are turned off. Therefore, in period 5, the state is as shown in Fig. 5A, and the inductor L4 on the rectifier circuit 40 side supplies power to the load R1.

In this manner, in period 1, voltage is applied to the primary coil Lp in a negative direction, and in periods 3 and 4, voltage is applied to the primary coil Lp in a positive direction. In cycles 2 and 5, no voltage is applied to the primary coil Lp.

As described above, the AC voltage applied to the primary coil Lp is transformed by the secondary coil Ls, and the transformed voltage is rectified by the diodes D1 and D2, smoothed by the capacitor C4, and then applied to the direct current. Is output.

The process of period 1 to period 5 is repeated by the number of sub-sections in section A. 4 shows the magnitudes of the currents and voltages flowing through the switches S1, S2, and S3 in each period within each subdivision. In Fig. 4, the voltages of the switches S1, S2 and S3 are denoted as Vs1, Vs2 and Vs3, respectively, and the currents of the switches S1, S2 and S3 are denoted as Is1, Is2 and Is3, respectively.

The control of the switching operation of the switches S1, S2, S3 in section B is somewhat different from the switching control method in section A described above. As shown in FIG. 3, in section B, the voltage of Vac2 is negative and the voltages of Vac1 and Vac3 are positive, except that the voltage of Vac1 is larger than the voltage of Vac2 in section A. Therefore, in section B, control is performed in a manner similar to the control method of switches S1, S2, and S3 in section A, but the ON / OFF states and timings of the switches S1, S2, and S3 in section B are as described above. Depending on the difference, it is changed to be slightly different from section A. That is, in section B, the pulse width of S1 and the pulse width of S2 are reversed.

According to the same principle, in other sections (section C to section L), control is performed in a similar manner to the switching control method in section A. The state and timing of S1, S2, S3) are changed and controlled. Accordingly, control of the switches S1, S2, S3 in the entire period of the converter is performed.

6A to 6C are diagrams showing specific examples of the switches S1, S, S3 used in the three-phase AC / DC converter as described above. The switches S1, S2 and S3 used in the converter according to the present invention should be bidirectional switches capable of switching regardless of the direction of the current.

6A shows an example of configuring a bidirectional switch using two MOSFETs whose sources are interconnected. The control voltage is applied to the gates of the two MOSFETs.

6B shows an example of configuring a bidirectional switch using two MOSFETs and two diodes. Each MOSFET acts as a switch that controls the current flowing from drain to source, and a control voltage is applied to the gate of each MOSFET.

6C shows an example in which a bidirectional switch is configured by using a bridge circuit using four diodes and a MOSFET connected to the center portion of the bridge circuit. The MOSFET is turned ON / OFF by the control voltage applied to the gate of the MOSFET, and thus the entire switch is turned ON / OFF.

7 is a diagram showing the configuration of a circuit for generating a control signal for controlling the switching operation of each switch S1, S2, S3 of the converter according to the present invention. The converter control circuit includes a comparator 170, three waveform generators 110a, 110b, 110c, three multipliers 120a, 120b, 120c, an oscillator 130, a flip-flop 140, and a PWM gate signal generator ( 150).

The comparator 170 receives an output voltage Vout, which is a voltage applied to the load R1 of the converter, and a predetermined reference voltage Vref. The comparator 170 amplifies the difference between the two voltages Vout and Vref and inputs them to the multipliers 120a, 120b, and 120c.

The waveform generators 110a, 110b, and 110c generate signals synchronized with the respective phases Vac1, Vac2, and Vac3 of the three-phase power source Vac. The outputs of the waveform generators 110a, 110b, 110c are input to the multipliers 120a, 120b, 120c.

The multipliers 120a, 120b, and 120c output a value obtained by multiplying the output of the waveform generators 110a, 110b, and 110c by the output of the comparator 170. The outputs of multipliers 120a, 120b, 120c are input to PWM gate signal generator 150. The output of the oscillator 130 and the output of the oscillator 130 via the flip-flop 140 are input to the PWM gate signal generator 150. The PWM gate signal generator 150 PWM modulates the outputs of the oscillator 130 and the flip-flop 140, and outputs a control signal as shown in FIG. 4 and a switching control signal slightly different for each section as described above. In order to output the switching control signal, the outputs of the multipliers 120a, 120b, and 120c are used.

According to the present invention, since the converter is configured using a small number of switches and capacitors, a large number of capacitors and inductors are unnecessary and the structure of the circuit is simplified.

In addition, since the three-phase voltage is not converted to a high-voltage direct current, the three-phase AC voltage is directly converted to direct current, and the power factor is improved.

Although the above has been illustrated and described with respect to the preferred embodiment of the present invention, the present invention is not limited to the above-described specific embodiment, and those skilled in the art, various modifications that do not depart from the gist of the present invention. Of course, such modifications will fall within the claims of the present invention.

Claims (1)

Three switches, each end of which is connected to an output terminal of each phase of a three-phase AC power source; Three capacitors each of which has one end connected in parallel with the three switches to an output terminal of each phase of the three-phase AC power source; A transformer having a primary coil one end connected in common to the other end of the switches and the other end connected in common to the other end of the capacitors, and a secondary coil coupled to the primary coil; And And a rectifier circuit for rectifying the output voltage of the secondary coil of the transformer.