JP2003244967A - Three-phase constant current power source - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that since a conventional three-phase inverter for converting DC power into a three-phase AC supplies a constant current irrespective of a load change, the current value of the load side is detected and feed-back controlled, bus this cannot be a complete constant current source. <P>SOLUTION: A high-frequency voltage V<SB>a</SB>is converted into a high-frequency current I<SB>b</SB>via an immittance converter IMT, and the current I<SB>b</SB>is distributed to three phases by using three semiconductor switches (S<SB>1</SB>, S<SB>2</SB>and S<SB>3</SB>) having conducting angles of 120° and different in the conducting angles at 120° from one another. Thus, when the voltage V<SB>a</SB>is constant, three-phase constant current outputs I<SB>2</SB>of low frequencies are obtained. As the voltage V<SB>a</SB>, a DC current of a solar battery SB is converted into a high-frequency voltage via an inverter INV, and the converted voltage can be used. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses an immittance converter to supply a constant current from a DC power supply to a three-phase load or a power system without being affected by the voltage on the load side. Regarding the circuit. The device according to the present invention can be used, for example, as a circuit that converts direct-current generated by solar power generation into a high-frequency voltage with an inverter and supplies electric power to a three-phase distribution system or a power system with a constant current. It can also be used as a circuit for stably interconnecting two independent three-phase power systems.

[0002]

2. Description of the Related Art FIG. 5 shows a first three-phase power system ↑ Va, ↑ V.
b, ↑ Vc and the second three-phase power system ↑ Vu, ↑ Vv, ↑ Vw are interconnected by three interconnected reactors Lint, and a circuit diagram of a conventional circuit for transmitting electric power (symbol “↑ Va Represents the "vector Va"). The same applies to the case where one of the three-phase power systems ↑ Va, ↑ Vb, and ↑ Vc is generated by converting solar-generated power into a three-phase voltage by a three-phase inverter. In this way, the two power systems cannot be directly connected because they are voltage sources,
The interconnection reactor Lint absorbs the voltage change and transmits the power from the system with the advanced voltage phase to the system with the delayed voltage phase.

In this circuit, assuming that the three-phase alternating current is balanced, the a-phase current ↑ Ia is

[Equation 1] Can be expressed as However, ω is the power supply angular frequency (= 2π
f), L _int is the inductance of the reactor.

[0004] Therefore, the voltage drop in the interconnection reactor L
Lower ω ・ L_int・ When Ia is sufficiently smaller than the voltages Va and Vu, see Fig. 6.
As is clear from the above, adjustment of the magnitude of the current Ia is ↑ Va, ↑ Vu
Can be realized by changing the phase difference q of
To be understood. Of ↑ Va and ↑ Vu, the phase advance is slower
Supply power to those who are

[0005] FIG. 7 shows another prior art immittance transformation.
It represents a vessel. The immittance converter is connected to the reactor L and
4 terminal circuit consisting of capacitor C, series L1 with T connection
-Parallel C-series L2 structure, L1 and L2 inductor
And the capacitance of C is

[Equation 2] Chosen to meet. However, L = L1 = L2, and ω is the angular frequency of the input voltage V1.

When the equation (2) is satisfied, the relationship between the voltage and the current in the circuit of FIG. 7 can be expressed by the following four-terminal constant matrix.

[Equation 3] The characteristic of the immittance converter is that the four-terminal constants A and D are 0. V1 and I2 are proportional, and I1 and V2 are proportional. Therefore, if the input V1 is a constant voltage source and a constant voltage, the output is a constant I2, that is, a constant current output.

[0007]

A constant current power source using such an immittance converter is disclosed by the present inventor in Japanese Patent Laid-Open No. 09-1.
As disclosed in 63757, this was a single phase power supply. An object of the present invention is to apply this to a three-phase AC constant current power supply.

Conventionally, there has been a three-phase inverter circuit for converting a DC power supply into a three-phase AC by a method different from the present invention. In such a conventional circuit, in order to supply a constant current irrespective of load fluctuation, the current value on the load side is detected and feedback control is performed. However, this has the following problems. (1) Since it is a method that controls load fluctuations,
It cannot be a perfect constant current source. (2) The strong feedback control that changes the constant voltage output to the constant current output easily causes an oscillation state and the system becomes unstable. (3) It is difficult to modify the design considering the load and surrounding conditions. (4) The voltage range in which the constant current can be maintained can be performed only between zero and the power supply voltage.

[0009]

A three-phase constant-current power supply according to the present invention, which has been made to solve the above-mentioned problems, converts a high-frequency voltage into a high-frequency current through an immittance converter, and the high-frequency current has a conduction angle of 120. It is characterized by using three semiconductor switches whose conduction phases are sequentially different by 120 degrees for each phase and distributing them to each of the three phases. Thus, when the high frequency voltage is constant, a low frequency three-phase constant current output can be obtained.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The above-mentioned high frequency voltage is obtained by obtaining a high frequency voltage having positive and negative pulse waveforms from a DC voltage by an inverter using a semiconductor switch, and changing the pulse width of the pulse waveform to obtain the amplitude of the fundamental wave. Can be made variable (PWM).

Further, the immittance converter is a four-terminal circuit consisting of a reactor L and a capacitor C, has a structure of series L-parallel C-series L in a T connection, and the resonance frequency of L · C is the above high frequency. It is configured as a circuit that outputs a high frequency current equal to the frequency of the voltage and proportional to the voltage.

The three semiconductor switches are driven so as to be repeatedly turned on and off at the sum frequency or the difference frequency of the frequency of the high frequency voltage and the frequency of the low frequency three-phase constant current output.

FIG. 1 shows an example of the above circuit configuration. Assuming that the DC voltage source DCS is a solar cell in FIG.
The direct current generated by solar power generation is converted into a high frequency voltage source by the inverter INV, and the electric power is converted into the immittance converter according to the present invention
The IMT and the three-phase switch circuit 3SW are connected to the three-phase distribution system ACS to provide a reverse supply circuit. As described above, the circuit according to the present invention makes it possible to stably connect the solar power to the three-phase power distribution system ACS. Further, by connecting the three-phase load LD instead of the three-phase distribution system ACS, it is possible to flow a constant current without being affected by the voltage on the load LD side.

Current iA and voltage V in inverter INV
1 and the waveform of the current i1 are shown in FIG. In addition, the high-frequency current i2 input to the three-phase switch circuit 3SW and each semiconductor switch S
Drive signals of a, Sb, Sc, and partial currents ia, ib, ic cut by them, and low-frequency currents Ia, Ib, Ic generated by them
Is shown in FIG.

As another mode of use of the present invention, an interconnection circuit of two three-phase power supply systems ACS1 and ACS2 as shown in FIG. 4 can be mentioned. In this case, the high frequency voltage is generated as follows. That is, three-phase power system AC
Three semiconductor switches connected to S1 and having different conduction phases of 120 degrees at a conduction angle of 120 degrees are turned on / off at the sum frequency of the high-frequency voltage frequency and the three-phase power system ACS1 frequency or the difference frequency. Drive to repeat. This makes it possible to obtain a high-frequency voltage equal to the resonance frequencies of L and C of the immittance converter.

The three-phase constant current load is the second three-phase power supply system ACS2. By setting the conduction phase of the three semiconductor switches to a predetermined value, the phase of the first three-phase constant current output with respect to the voltage of the second three-phase AC system is set to a predetermined value, and the second three-phase It becomes possible to adjust the active power / reactive power supplied to the AC system.

[0017]

INDUSTRIAL APPLICABILITY The present invention, when it is necessary to supply electric power from a DC power supply to a three-phase load or a power system including a voltage source, for example, electric power obtained by converting solar-generated DC into a high-frequency voltage source by an inverter. In the case of connecting the three-phase power supply system to the three-phase distribution system for reverse supply, by converting the high-frequency voltage source into a three-phase current source, it is possible to flow current without being affected by the voltage on the load side. Enables stable interconnection of the power supply system.

Further, when the three-phase load is an AC motor, it is driven by a three-phase constant current source, and a unique control characteristic can be obtained.

Furthermore, if both the input side and the output side of the immittance converter are divided into three phases by switches, it is possible to connect three-phase systems having different frequencies and voltages.

[0020]

EXAMPLE The present invention was applied to the solar cell (SB) -three-phase AC load circuit (3LD) shown in FIG. In this circuit,
A simulation was conducted in which the characteristic impedance Z0 of the immittance converter IMT was set to 10 Ω and a 400 V voltage source of 20 kHz square wave was connected between a and a '. At this time, as shown in FIG. 9, the output current Ia of the high frequency inverter INV is equal to the load resistance R
It was confirmed that the output current I2 to the three-phase load was kept constant, while it increased according to the magnitudes of 1, R2, and R3.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a three-phase constant current power supply which is an embodiment of the present invention and includes a DC power supply, an inverter, an immittance converter, and a three-phase switch circuit.

2 is an input / output waveform diagram in the inverter of the circuit of FIG.

3 is a waveform diagram of a switch drive signal and the like in the three-phase switch circuit of the circuit of FIG.

FIG. 4 is a circuit diagram of an interconnection circuit of a three-phase AC power source, which is another embodiment of the present invention.

FIG. 5 is a circuit diagram of a conventional three-phase AC power supply interconnection circuit.

FIG. 6 is a vector diagram showing a phase difference between both power supply voltages in a power supply interconnection circuit.

FIG. 7 is a circuit diagram of an immittance converter.

FIG. 8 is a circuit diagram of a solar cell-three-phase AC load circuit according to an embodiment of the present invention.

9 is a graph showing a simulation result of the circuit of FIG.

[Explanation of symbols]

DCS ... DC power supply INV ... Inverter IMT ... Imittance converter 3SW ... Three-phase semiconductor switch circuit ACS: Three-phase power supply (distribution) system LD ... load

Continued front page    F-term (reference) 5H007 BB06 BB07 CA01 CB02 CB04                       CB05 CC09 DA06 EA02                 5H410 CC02 CC03 DD03 DD09 DD10                       EA10 EA35 EA39 EB05 EB09                       EB38 EB39 FF11 FF22 FF26                 5H420 BB02 BB12 BB13 BB15 BB16                       CC03 CC04 DD04 DD06 EA11                       EA39 EA40 EA49 EB01 EB05                       EB09 EB22 EB38 EB39 FF11                       FF26

Claims (6)

[Claims] 1. A high-frequency voltage is converted into a high-frequency current through an immittance converter, and the high-frequency current is distributed to three-phase and three-phase by using three semiconductor switches which sequentially differ in conduction phase by 120 degrees at a conduction angle of 120 degrees. However, when the high frequency voltage is constant,
A three-phase constant current power supply characterized by obtaining a low-frequency three-phase constant current output. 2. The high-frequency voltage has a positive-negative pulse waveform obtained from an inverter using a semiconductor switch from a DC voltage, and the amplitude of the fundamental wave is made variable by changing the pulse width of the pulse waveform. The three-phase constant current power supply according to claim 1, which is a power supply. 3. The immittance converter is a reactor L.
It is a 4-terminal circuit consisting of a capacitor C and a series L-parallel C-series L structure with T connection, and the resonance frequency of LC is equal to the frequency of the high frequency voltage, and the high frequency current proportional to that voltage. The three-phase constant current power source according to claim 1 or 2, which is a circuit that outputs 4. The three semiconductor switches are driven so as to be repeatedly turned on and off at a sum frequency or a difference frequency of the frequency of the high frequency voltage and the frequency of the low frequency three-phase constant current output. The three-phase constant current power source according to any one of claims 1 to 3. 5. The high-frequency voltage is generated by a three-phase AC power source and three semiconductor switches connected to the three-phase AC power source, which sequentially differ in conduction phase by 120 degrees, and the three semiconductor switches are high-frequency. It is characterized in that a high frequency voltage equal to the resonance frequency of the immittance converter is obtained by being driven so as to be repeatedly turned on and off at a frequency of a sum of a frequency of a voltage and a frequency of a three-phase AC power source or a frequency of a difference. The three-phase constant current power source according to claim 1. 6. The load of the three-phase constant current is a second three-phase alternating current system, and the second phase of the three-phase constant current output is obtained by setting the conduction phase of the three semiconductor switches to a predetermined value. The phase for the voltage of the three-phase AC system of
The three-phase constant current power source according to any one of claims 1 to 5, wherein active power / reactive power supplied to the three-phase AC system is adjusted.