JP2004260991A - Ac power supply regenerating magnetic energy - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an AC power supply capable of improving power factor of an AC load while realizing reduction in cost and size. <P>SOLUTION: The AC power supply regenerating magnetic energy comprises a bridge circuit consisting of four reverse conduction semiconductor switches, a capacitor connected between the DC terminals of the bridge circuit and storing magnetic energy at the time of interrupting a current, an AC voltage source connected in series with an inductive load and being inserted between the AC terminals of the bridge circuit, and a control circuit for turning each reverse conduction semiconductor switch on/off by providing a control signal to the gate thereof. The control circuit turns a pair of reverse conduction semiconductor switches on a diagonal, out of four reverse conduction semiconductor switches constituting the bridge circuit, on/off simultaneously such that when one of two pairs is turned on, the other pair is turned off and the control signal is switched in synchronism with the voltage of the AC voltage source. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to an AC power supply device capable of improving the power factor of an AC load, and more specifically, a bidirectional current switch for regenerating magnetic energy in series with an AC load is inserted in place of a conventional phase advance capacitor. The present invention relates to an AC power supply device that realizes a low cost and a miniaturization to perform the role of a phase capacitor.

When an alternating current is passed through a load with inductance, it is necessary to apply a voltage larger than the DC resistance component (resistance component voltage in steady state) at startup, and the power factor decreases due to the delay in the phase of the current. In order to improve the AC power factor, the power factor was improved by inserting a phase advance capacitor in series to reduce the reactance and increasing the current.
The power factor improvement by the phase advance capacitor system inserted in series has a problem that it is not suitable for a circuit in which the power factor of the load changes depending on the operating state or in which the power supply frequency changes greatly.

On the other hand, the power factor of the load current changes at the time of starting from startup to steady operation like an induction motor. To compensate for this, an inverter / converter set of AC-DC-AC link using a semiconductor switch is used. It is used, starts at a reduced frequency and voltage, and controls the number of revolutions during operation, but it is expensive and requires harmonic disturbance due to PWM control and a large electrolytic capacitor to maintain the DC voltage. There is a disadvantage that the size is increased.
In addition, when the induction motor is started, there is a problem that the inductance component is large and the power factor of the current is low, and the effective current is small and a large torque (starting torque) cannot be obtained at the time of starting.
JP 2000-358359 A

There is a limit in the conventional power factor improvement method, and there has been a demand for an AC power supply device that has a power factor improvement circuit that replaces the phase advance capacitor method and realizes low cost and miniaturization.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an AC power supply apparatus that realizes low cost and downsizing that can improve the power factor of an AC load.

  The inventors of the present application store the magnetic energy remaining in the circuit when the load current is cut off in a capacitor, and at the next turn-on, discharge the energy to the load to rapidly increase the current, thereby increasing the power factor. We focused on what can be improved. In other words, the current flowing through the load stops when the current is cut off because the magnetic energy is stored in the capacitor and regenerated by the load at the next turn-on, so that the current rises rapidly. This is because a current can be flowed, and the power source power factor is improved in a broad sense.

  Therefore, by using a magnetic energy regenerative bidirectional switch in an AC circuit, the current is interrupted at an arbitrary timing, the magnetic energy is stored in the capacitor, and the current is passed through the load again at an arbitrary timing in the reverse direction. It came to the idea that the current phase of the current can be controlled forcibly.

  The magnetic energy regenerative bidirectional switch stores the magnetic energy remaining in the circuit when the load current is cut off in a storage capacitor provided in the switch bridge, and discharges the energy to the load at the next turn-on. This is a lossless current switch that rapidly raises the current, and has already been applied for a patent by the applicant of the present application (see Patent Document 1).

  The present invention relates to an AC power supply apparatus capable of improving the power factor of an AC load. As described above, the object of the present invention is to supply an AC current to an inductive load and regenerate magnetic energy when the current is interrupted. An AC power supply device used as a supply current to the inductive load, the AC power supply device being connected between a bridge circuit composed of four reverse conducting semiconductor switches and a DC terminal of the bridge circuit A capacitor for storing magnetic energy when the current is interrupted, an AC voltage source connected in series to the inductive load and connected between AC terminals of the bridge circuit, and each of the reverse conducting semiconductor switches. A control circuit that applies a control signal to the gate to perform on / off control of each semiconductor switch, and the control circuit includes four reverse conducting semiconductor switches that constitute the bridge circuit. The pair of reverse conducting semiconductor switches on the diagonal line are controlled to be turned on / off simultaneously, and when one of the two pairs is on, the other pair is turned on. Is turned off, and the control signal is switched in synchronization with the voltage of the AC voltage source, and is achieved by an AC power supply device for regenerating magnetic energy.

  As described above, according to the AC power supply device for regenerating magnetic energy according to the present invention, the current phase can be forcibly synchronized with the same phase as the power supply phase, so that the power factor of the current can be improved. Compared with the conventional DC link system, a low-cost and compact AC power supply can be realized.

  By using the AC power supply device according to the present invention as the power source of the induction motor, the starting torque at the time of starting can be increased. FIG. 3 shows an experimental circuit for actually measuring the starting torque, and FIG. 4 is a graph comparing the actually measured value of the starting torque and the starting torque when a conventional AC power source is used. As can be seen from this figure, when the AC power supply apparatus according to the present invention is used, a starting torque of about four times can be obtained at the same phase voltage.

  The present invention provides a pulse current generation of a magnetic energy regenerative bidirectional current switch inserted between an AC voltage source and an inductive load in order to provide an AC power supply device that is simple in structure and can be reduced in size and cost. If the function is used to turn on / off at a timing synchronized with the power source, the fact that the phase of the alternating current can be controlled is utilized. Hereinafter, it will be described in detail with reference to the drawings.

FIG. 1 is a diagram showing a basic configuration of an AC power supply apparatus 10 according to the present invention, in which a magnetic energy regenerative bidirectional current switch 30 (four elements) is connected between an AC voltage source 20 and an inductive load 50 having inductance. Each of the power MOSFETs 31 (an example of a reverse conduction type semiconductor switch) is inserted by a control means 40 with a signal synchronized with the voltage of the AC voltage source 20. The current is turned on / off by controlling the gates (G1 to G4).
Since the magnetic energy regenerative bidirectional current switch 30 has a built-in capacitor 32 for storing magnetic energy at the time of current interruption, the same current as at the time of interruption is regenerated by discharging the capacitor 32 at the next turn-on. be able to.
A pulse-like voltage is applied to the inductive load 50 when the current is turned on / off, and the magnitude of the voltage is within the allowable withstand voltage range of the power MOSFET 31 and the inductive load 50 by selecting the capacitance of the capacitor 32. In the end, it is an advantage that a DC capacitor can be used unlike a conventional series power factor correction capacitor.

The control means 40 controls the gates of the four power MOSFETs 31, but the opposite pair, that is, the forward current pair (G1 and G2) or the reverse pair (G3 and G4) is turned on according to the direction in which the current flows. However, it should be noted that the forward current pair and the reverse pair are not simultaneously turned on while the capacitor 32 has a voltage.
The gate control is performed in synchronization with the voltage of the AC voltage source 20. For example, in the case of improving the power factor of the current, the forward gates (G1, G2) are turned on while the voltage is positive, When the reverse gate (G3, G4) is turned on while the current is negative, the current flows in exactly the same direction as the voltage, but not only that, but this switch is the magnetic energy when the current is cut off. Is stored in the capacitor 32, and this energy is then discharged in the reverse direction to quickly start up the current and increase the load supply current. The relationship between the voltage of the AC voltage source 20 and the state of the gate is as shown in Table 1 below.

Hereinafter, the principle of operation of the magnetic energy regenerative bidirectional current switch in alternating current will be described with reference to FIG.
(A) While SW1 and SW2 are on, current flows from the bottom to the top (in the positive direction), and two parallel conduction states are established (the current is flat in FIG. 2).
(B) When SW1 and SW2 are turned off immediately before the voltage of the AC voltage source 20 is inverted from positive to negative (about 2 ms before in this embodiment) (at this time, SW3 and SW4 are turned on). The magnetic energy is charged to the capacitor through the path 1).
(C) When charging is completed, the current is cut off, and when the voltage is reversed (positive to negative), SW3 and SW4 are already on, so the discharge starts in the path (2) (current flows from top to bottom) Flowing.) When the discharge is finished, the two parallel conductive states are established.
(D) When SW3 and SW4 are turned off immediately before the voltage of the AC voltage source 20 is inverted from negative to positive (in this embodiment, about 2 ms) (At this time, SW1 and SW2 are turned on), (3 ) Is charged with magnetic energy.
(E) When charging is completed, the current is cut off, and when the voltage is reversed (from negative to positive), SW1 and SW2 are already on, so discharge starts in the path (4) (current flows from bottom to top) Flowing.) When the discharge is finished, the two parallel conductive states are established, and the state returns to the state (a). This is repeated below.
As described above, the magnetic energy remaining in the circuit when the load current is interrupted is stored in the capacitor, and the power is rapidly increased by discharging the energy to the load at the next turn-on to improve the power factor. Can be made.

FIG. 2 is a diagram showing an operation simulation result of the AC power supply apparatus according to the present invention. In the case where the magnetic energy regeneration bidirectional current switch 30 is provided, it can be seen that the current phase is in phase with the voltage and the current is increased. However, this is nothing but an improvement in the power factor of the load, and this device worked as a power factor improving device in a broad sense.
If the phase of the gate signal is further advanced, a current with an advanced phase flows, and if it is delayed, the current can be decreased, and if it is delayed 180 degrees, the current is stopped.

  In addition, although it demonstrated using power MOSFET as an example of the said reverse conduction type semiconductor switch, it is the same even if it uses the unit which consists of parallel connection of semiconductor switches, such as a reverse conduction type GTO thyristor or a diode, and IGBT. An effect is obtained.

The Example of the alternating current power supply device which concerns on this invention is shown. It is a figure which shows the simulation result of the current voltage waveform of the alternating current power supply device which concerns on this invention. The application example to the induction motor of the alternating current power supply device which concerns on this invention is shown. It is a figure which shows the comparison of the actual value of the starting current and starting torque of an induction motor when the AC power supply device which concerns on this invention is connected (with a switch), and when not connecting (without a switch). It is a figure for demonstrating the operation | movement principle in alternating current of a magnetic energy regeneration bidirectional | two-way current switch.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 AC power supply device 20 AC voltage source 30 Magnetic energy regeneration bidirectional current switch 31 Reverse conduction type semiconductor switch (power MOSFET)
32 Magnetic energy storage capacitor 40 Control means 50 Inductive load 60 Cage type three-phase induction motor

Claims (2)

An AC power supply apparatus that supplies an alternating current to an inductive load, regenerates magnetic energy at the time of current interruption, and uses it as a supply current to the inductive load,
The AC power supply device
A bridge circuit composed of four reverse conducting semiconductor switches;
A capacitor connected between the DC terminals of the bridge circuit and storing magnetic energy when the current is interrupted;
An AC voltage source connected in series to the inductive load and inserted between AC terminals of the bridge circuit;
A control circuit that applies a control signal to the gate of each reverse conducting semiconductor switch to perform on / off control of each reverse conducting semiconductor switch;
The control circuit controls so as to simultaneously perform on / off operations of a pair of reverse conducting semiconductor switches located on the diagonal among the four reverse conducting semiconductor switches constituting the bridge circuit, and 2 When one of the pairs is on, control is performed so that the other pair is off, and the control signal is switched in synchronization with the voltage of the AC voltage source. AC power supply that regenerates magnetic energy. The regenerative magnetic energy according to claim 1, wherein each of the reverse conducting semiconductor switches is one of a power MOS FET, a reverse conducting GTO thyristor, or a unit comprising a parallel connection of a diode and a semiconductor switch such as an IGBT. AC power supply.

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