Fuji Electric Co., Ltd.

Kundenko Co., Ltd.

Kazuo Kuroki

Hiroshi Yamamoto

Kazuaki Mino

Yasuhiro Okuma

Makoto Yatsu

Mikio Kato

Seiji Sadayoshi

Yasuo Taguchi

Toshiyuki Takanaga

A series circuit of two switching devices and a series circuit of two diodes are connected together in parallel to constitute a bi-directional switch circuit for one phase. N bi-directional switch circuits are provided, and the junction between the switching devices of each of the switch circuits is connected to an AC input terminal of a corresponding phase via a reactor. A cathode of the diode series circuit of each switch circuit is connected to a positive output terminal via a diode, and an anode of the diode series circuit of each switch circuit is connected to a negative output terminal via a diode. Two capacitors are connected in series between the positive and negative output terminals, and the junction between the diodes of each switch circuit is connected to the junction between the two capacitors.

Rectifying circuit and control method therefor

A voltage amplitude adjuster including semiconductor switches for power conversion, an AC chopper for converting an input AC voltage to an AC voltage of the same phase and different amplitude relative to the input AC voltage, and a smoothing AC filter for providing a clear signal to a primary winding of a transformer. Further, by providing a wattmeter, the saved power can be displayed.

Power conversion apparatus

An uninterruptible power supply apparatus includes a storage battery for providing a DC voltage, a switch for switching from an AC power source for providing an AC voltage to the storage battery, and an AC-stabilizing circuit connected to an output side of the switch. The AC-stabilizing circuit performs an AC/AC conversion or a DC/AC conversion in response to a switching operation of the switch in order to output an AC voltage therefrom. Namely, for a commercial power supply, the AC-stabilizing circuit supplies a stable AC voltage despite variations in power supply voltage. The size of the apparatus is reduced, and its service life is prolonged.

Uninterruptible power supply apparatus

An AC current source circuit converts a DC input voltage into an AC output current, and comprises a chopper circuit for converting a DC input voltage into a chopper voltage; and an inverter for converting the chopper voltage into an output AC current of a predetermined frequency. The inverter comprises at least four switch elements, and clamp-type snubber circuits corresponding to each of the switch elements are provided. The snubber circuit releases electric charges to the input terminal of the DC input voltage of the chopper circuit. The chopper circuit is connected to the inverter through a DC reactor. The DC input voltage is converted into a DC current by the chopper circuit and the DC reactor and transmitted to the inverter.

AC current source circuit for converting DC voltage into AC current

The bus line of an electric power system is connected to an inverter which can be placed in a forward operation mode or in a reverse operation mode, and batteries are connected to the inverter to store the dc energy thereof. When a commercial power source is normal, an ac switch is closed, so that the inverter is placed in the forward operation mode to perform an active filter operation for eliminating harmonic current and reactive current. When necessary, the batteries are charged, and the inverter is placed in the reverse operation mode to perform a peak cut power generation. At loss of the commercial power source or momentary drop of the supply voltage, the switch is opened so that the inverter is placed in the reverse operation mode to perform an UPS operation (emergency power generation). Hence, electric power is supplied without interruption to an important load and the emergency load.

Multi-function electric power conversion system

In the particular embodiment of the invention described in the specification, a circuit for interrupting the operation of a switching transistor includes a reactor connected in series with the transistor emitter and a plurality of diodes connected in series between the reactor and the base of the transistor so that the electromotive force induced in the reactor when the reactor current decreases is supplied to the base of the transistor. This makes it possible to maintain the reactor storage time when the transistor is switched off and to adjust the fall time so that the changing rate (di/dt) of the current flowing in a snubber circuit for controlling overvoltage may be minimized so that the structural restrictions imposed on the snubber circuit can be eased and reliability is improved. Noise is also reduced because the current drop rate (-di/dt) when the transistor is switched off can be minimized.

Control circuit for switching transistors

In the particular embodiments described in the specification, an inverter connected to a DC source and a load includes two or more inverter units operating on a phase basis, and three connecting wires, consisting of two wires connecting each inverter unit and the power source and one wire connecting each inverter unit and the load, are arranged close to one another or twisted together. With this arrangement the distributed inductance is reduced not only for the wires connecting the DC source and the inverter but also for the wires connecting the inverter units.

Inverters with reduced distributed inductance

Disclosed is an isolation circuit for a power transistor that enables a control circuit to turn the power transistor on and off, while insulating the control circuit from DC currents that may flow to or from the power transistor. The isolation circuit includes a first pulse transformer for receiving a pulse string signal corresponding to an ON command signal from the control circuit to alternatingly energize and de-energize the first pulse transformer. In addition, the isolation circuit includes a fast circuit path comprising a pair of serially connected diodes coupled between the secondary winding of the first pulse transformer and the base resistor of the power transistor for rapidly supplying base current drive to the transistor as soon as the first pulse transformer is energized. Also included in the isolation circuit is a base drive maintaining circuit coupled to the fast circuit path and to the base resistor of the power transistor. The maintaining circuit includes a capacitor that charges while the first pulse transformer is energized and discharges to supply base current drive to the power transistor when the first pulse transformer is de-energized. Furthermore, the isolation circuit includes a second pulse transformer for receiving a pulse signal corresponding to an OFF signal from the control circuit. The secondary winding of the second transformer being coupled to the base drive maintaining circuit for discharging the capacitor and terminating the base current drive to power transistor when the pulse signal corresponding to the OFF signal is received.

Circuit for driving the base of a transistor

A highly stable, tunable oscillator circuit includes a crystal oscillator providing a reference pulse signal of frequency fcry, a voltage-to-frequency converter responsive to a control voltage vc for providing a control pulse signal of frequency fv substantially lower than fcry, and a flip-flop circuit receiving the reference and control signals and providing a negative going pulse signal synchronized with the reference signal and having a frequency fv and a pulse width equal to l/fcry. The signal provided by the flip-flop circuit and the complement of the reference signal are received by a NAND gate which periodically removes a pulse from the reference signal at intervals of l/fv and provides a resulting signal having a frequency of (fcry).sup.2 /(fcry+fv). The resulting signal is received by a frequency divider network which divides the frequency of resulting signal by an integer N and provides an output signal of a desired frequency. The output frequency is tunable by varying the frequency fv of the control signal by means of the control voltage vc. By selecting the frequencies of the reference and control signals such that fcry&gt;&gt;fv, a highly stable and smoothly tunable output signal is obtained.

Variable-frequency oscillation circuit

A highly stable, tunable oscillator circuit includes a crystal oscillator providing a reference pulse signal of frequency Fco, a voltage-to-frequency converter responsive to a control voltage for providing a control pulse signal of frequency Fv substantially lower than Fco, a toggle circuit receiving the reference signal and providing a first and a second complementary signals, each having a frequency Fco/2 and the same pulse-width as the reference signal, a flip-flop circuit receiving the reference signal, the control signal and the first complementary signal and providing a pulse signal having frequency Fv and a pulse-width equal to the period of the reference signal, and synchronized with the first and second complementary signals. The signal provided by the flip-flop circuit is logically combined with the first complementary signal in and AND gate. The output of the AND gate is then logically combined with the second complementary signal in an OR gate to derive a combined signal of frequency (Fco/2)+Fv. The combined signal is received by a frequency divider network which divides the frequency of the combined signal by an integer N and provides an output signal at a desired frequency. By selecting the frequencies of the reference, control and output signal such that Fco&gt;&gt;Fv&gt;&gt;Fo, a highly stable, smoothly tunable output signal is obtained.

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Tokyo, Japan

Kazuo Kuroki