Alternating-current power supply device recovering magnetic energy

Abstract

The present invention relates to an alternating-current power supply device which can improve a power factor of an alternating-current load, realizes low cost and miniaturization, and recovers magnetic energy. The alternating-current power supply device includes a bridge circuit composed of four reverse conducting semiconductor switches, a capacitor that is connected between direct-current terminals of the bridge circuit and absorbs the magnetic energy at the time of cutting off the current, an alternating-current voltage source that is connected to the induction load in series and is inserted between alternating-current terminals of the bridge circuit, and a control circuit that gives a control signal to gates of the respective reverse conducting semiconductor switches and controls on / off states of the respective reverse conducting semiconductor switches. The control circuit simultaneously controls the on / off operation of the paired reverse conducting semiconductor switches positioned on a diagonal line of the four reverse conducting semiconductor switches composing the bridge circuit, makes a control so that when one pair of the two pairs is ON, the other pair is OFF, and switches the control signal in synchronization with a voltage of the alternating-current voltage source.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to an alternating-current power supply device that can improve a power factor of alternating-current load. More specifically, the invention relates to the alternating-current power supply device where a bi-directional magnetic energy recovery switch is inserted in series with the alternating-current load so as to function as a phase advancing capacitor instead of a conventional phase advancing capacitor and low-cost and miniaturization are realized. [0003] 2. Description of the Related Art [0004] In the case where an alternating current is applied to an inductive load, it is necessary to apply a voltage higher than that of a direct-current resistance (resistance voltage at stationary state) at the time of start-up, and thus a power factor becomes poor due to a delay of a phase of current. However, in order to improve the power factor of the alternating current, a phase advancing capacit...

AI Technical Summary

Benefits of technology

[0009] The present invention is devised in order to solve the above problems, and its object is to provide an alternating-current power supply device which can improve a power factor of an alternating-current load and realizes low cost and miniaturization.

[0010] The inventors of this application give attention to that magnetic energy remaining in a circuit in the case where a load current is cut off is absorbed by the capacitor, the energy is recovered to the load at next ON time and the current is quickly raised so that the power factor can be improved. That is to say, the magnetic energy is absorbed by the capacitor so as to be stopped at the time of cutting off the current and the magnetic energy is recovered to the load at next ON time so that the current quickly rises. For this reason, the applied current increases, and thus the higher current can be applied to the load by a lower voltage, so that the power factor of the power source is improved in the general meaning.

[0013] The present invention relates to an alternating-current power supply device which can improve the power factor of the alternating-current load, and an object of the present invention is to provide the alternating-current power supply device which supplies the alternating current to an induction load and recovers the magnetic energy at the time of cutting off the current so as to utilizes it as an current to be supplied to the induction load. The alternating-current power supply device comprises: a bridge circuit composed of four reverse conducting semiconductor switches; a capacitor that is connected between direct-current terminals of the bridge circuit and stores the magnetic energy at the time of cutting off the current; an alternating-current voltage source that is connected to the induction load in series and is inserted between alternating-current terminals of the bridge circuit; and a control circuit that gives a control signal to gates of the respective reverse conducting semiconductor switches and controls on / off states of the respective reverse conducting semiconductor switches. The control circuit simultaneously controls the on / off operation of the paired reverse conducting semiconductor switches positioned on a diagonal line of the four reverse conducting semiconductor switches composing the bridge circuit, makes a control so that when one pair of the two pairs is ON, the other pair is OFF, and switches the control signal in synchronization with a voltage of the alternating-current voltage source.

Problems solved by technology

In the case where an alternating current is applied to an inductive load, it is necessary to apply a voltage higher than that of a direct-current resistance (resistance voltage at stationary state) at the time of start-up, and thus a power factor becomes poor due to a delay of a phase of current.

The improvement of the power factor by inserting the phase advancing capacitor in series is not suitable for the case where the power factor of the load changes according to an operating state or a circuit where a frequency of power source greatly changes.

However, since the cost is high, harmonics distortion occurs due to PWM control and a large electrolytic capacitor is necessary for maintaining a DC voltage, the entire size becomes large.

At the time of the start-up of the induction motor, an inductance component is large, the power factor of the current is poor, and an active current is low.

For this reason, a large torque (starting torque) cannot be obtained at the time of start-up.

Such a conventional method of improving the power factor has a limitation, and thus an alternating-current power supply device which has a power factor improving circuit instead of using the phase advancing capacitor and realizes low cost and miniaturization is requested.

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