Abstract: A system for detecting a connection between two devices includes a first device and a second device. The first device includes a first connection terminal and a first reactance element connected to the first connection terminal. The second device includes a second connection terminal; a first resistance element, and a first frequency generator for allowing a signal to pass through the first resistance element and be applied to the first device via the second connection terminal. The second device further includes a first comparator having both input terminals connected to both ends of the first resistance element, and comparing and outputting a signal of both ends of the first resistance element, and a first control unit for determining whether or not the first connection terminal of the first device is connected to the second connection terminal by means of the output signal of the first comparator.

Abstract: Provided is an impedance matching device capable of promptly improving an impedance mismatch between a high-frequency power source and a load even when the impedance of the load continuously changes. An impedance matching device according to the present invention is for use in a high-frequency power system configured to supply a load with an output from a high-frequency power source via a matching circuit whose constant is mechanically changed, and the impedance matching device includes a matching condition value acquisition portion for acquiring a matching condition value indicating a matching condition between the high-frequency power source and a load, and a control portion for controlling an oscillation frequency of the high-frequency power source based on the matching condition value.

Abstract: A memory system may include: a plurality of resources; and a frequency adjuster configured to adjust operating frequencies of the plurality of resources at a predetermined adjustment timing, wherein the adjustment timing comprises at least one timing for dividing partial operation periods of at least one resource among the plurality of resources.

Abstract: A three-phase resonant cyclo-converter, the cyclo-converter comprising a feed forward control module arranged to develop a feed forward signal for controlling a switching frequency of the cyclo-converter dependent on conditions of a power supply arranged to provide power to the cyclo-converter.

Abstract: A frequency converter is provided that has high reliability, low electromagnetic noise, and a high efficiency. A frequency converter includes: a primary winding 12 in which a plurality of windings on which a polyphase alternating voltage is applied are arranged periodically along a particular direction; a secondary winding 22 which is magnetically coupled to the primary winding 12 and in which a plurality of windings are arranged along the particular direction with a repetition period different from the primary winding 12; and a frequency modulation part 3 which is arranged on a magnetic path between the primary winding 12 and the secondary winding 22 magnetically coupled to each other and in which a plurality of magnetic materials 31 are arranged periodically along the particular direction.

Abstract: A method for transferring electrical power in the sea includes generating AC power, guiding, at least partially underwater, the AC power through a cable from a first end of the cable to a second end of the cable, and changing a frequency of the AC power guided through the cable based on a value of power consumption of a load connected to the second end of the cable.

Abstract: A static energy supply unit has an energy store connected to an ac supply network by a power converter. A unit controller for the static energy supply unit includes an amplitude controller, a phase controller and a frequency controller. These measure and record characteristics of the supply network and provide output signals indicative of the voltage characteristics for an operating condition of the supply network. A signal generator for generating a simulated output voltage signal for each phase of the supply network is provided. A comparator is used to compare the simulated output voltage signal for each phase and a measured voltage for a corresponding phase of the supply network. The controller controls the operation of the power converter to vary the amount of power that is supplied to the supply network from the energy store based on the comparison of the simulated output voltage signal(s) and the measured voltage(s).

Abstract: There is provided a high frequency power supply device. The power control unit comprises an impedance adjuster that includes a variable reactance element and adjusts a load side impedance by changing a reactance value of the variable reactance element, and an impedance control unit that controls the variable reactance element of the impedance adjuster in response to a power value detected by a power detection unit so as to perform control of approximating the power value of the high frequency power, which is fed from the high frequency power generation unit to the load, to the setting value or control of maintaining the power value within the set allowable range by changing a resistance of the load side impedance in response to the power value detected by the power detection unit.

Abstract: In one embodiment, a DC converter has a frequency adjusting device with a frequency selection circuit, a frequency change-over switch (17), a frequency generator (18), a threshold signal generator (19), a state machine (20) and a unit (21) for providing a ready signal (S3). The frequency selection circuit has an output (15), at which a control signal (S5) is provided, which is set up to select a frequency of the switching frequency signal (DCLK) of the DC converter. The invention further relates to a method for selecting a frequency of the DC converter.

Abstract: A frequency converter includes a comparator, an error computation unit and a calibration unit. The comparator receives a reference voltage signal and a triangle wave signal, and outputs a switching signal. The switching signal is fed back to the error computation unit to calculate an error signal by computing the reference signal and the switching signal. The calibration unit calibrates the triangle wave signal or the reference voltage signal according to the error signal.

Abstract: A method and system for workload balancing to assist in power grid load management. The method includes receiving a request to perform a task at a site powered by connection to an AC power grid, the task comprising either data processing or manufacturing an article; measuring an AC frequency of the AC power grid to obtain a current AC frequency; and performing or not performing the task at the site based on the current AC frequency.

Abstract: A method and apparatus for generating an arbitrary current waveform for use in characterizing power supply impedance for power delivery networks are provided. The method begins by providing an arbitrary waveform as an input to a test circuit. The current and voltage at an output of a device under test in then examined A frequency is then swept through a pre-determined range; and the frequency of the arbitrary voltage waveform is changed to match a predetermined frequency and impedance point.

Abstract: Disclosed is a method for controlling an inverter, the method including, calculating the number of PWM pulses from a current frequency of the inverter, compensating the number of PWM pulses using a predetermined number of pulses when the number of PWM pulses is less than the predetermined number of pulses, and calculating a new frequency of the inverter using the compensated number of PWM pulses.

Abstract: There is provided a method for controlling a switching power unit that converts AC input voltages of an AC source into a DC voltages while improving a power-factor of the AC input voltages, the switching power unit comprising an AC/DC converter circuit that is composed of a power-factor correction unit and a current resonance converter unit wherein at least a part of switching elements of the current resonance converter unit is shared with switching elements of the power-factor correction unit, wherein around timing that polarities of the AC source are switched between a positive half cycle and a negative half cycle, ON-and-OFF control of the switching elements are performed as that high frequency voltages that are applied to a primary winding of a high frequency transformer which is a part of the current resonance converter unit are to be symmetrical in a positive and negative relation.

Abstract: A method and system for workload balancing to assist in power grid load management. The method includes receiving a request to perform a task at a site powered by connection to an AC power grid, the task comprising either data processing or manufacturing an article; measuring an AC frequency of the AC power grid to obtain a current AC frequency; and performing or not performing the task at the site based on the current AC frequency.

Abstract: A high frequency device for supplying a high frequency power to a load, the high frequency device includes: an oscillating unit that can vary an oscillation frequency; a high frequency power supplying unit that serves as a power source by amplifying an oscillation signal output from the oscillating unit for supplying the high frequency power to the load; a reflected-wave information calculating unit that calculates reflected wave information on a reflected wave power, and outputs the reflected wave information; a frequency control unit that controls the oscillation frequency of the oscillating unit so as to lower the reflected wave information; an impedance adjusting unit that is disposed at a downstream of the high frequency power supplying unit in a power supplying direction, and that has at least one variable reactance element which can be controlled; and an element control unit that controls the variable reactance element of the impedance adjusting unit so as to lower the reflected wave information.

Abstract: A power-conversion control system includes an inverter, a cycloconverter, and a sliding mode controller. The inverter is operable to receive a DC voltage input and produce a first AC voltage output having a first frequency. The cycloconverter has a plurality of bidirectional switches, and is operable to receive the first AC voltage and to synthesize a second AC voltage having a second frequency that is lower than the first frequency. The sliding mode controller is operable to provide a control signal to command the plurality of bidirectional switches to turn OFF and ON when the first AC voltage is at a zero crossing condition. The sliding mode controller is also operable to selectively adjust the frequency and amplitude of the second AC voltage.

Abstract: An apparatus for providing an AC voltage includes a synthesizer for generating at least one periodic output voltage signal, each periodic output voltage signal having an output frequency. The synthesizer is supplied by an input AC voltage having an input frequency, and is configured such that each output frequency differs from the input frequency.

Abstract: An output voltage command signal for outputting a specified three-phase ac output voltage is generated by a line voltage control command signal generating section, and a signal representing a current flow ratio is generated by a current flow ratio generating section based on a specified input current command signal. The output voltage command signal is corrected by a command signal computing section based on the output voltage command signal generated by the line voltage control command signal generating section and the signal representing the current flow ratio generated by the current flow ratio generating section. A PWM conversion signal is generated by a PWM conversion signal generating section based on the corrected output voltage command signal and a carrier signal. Based on the generated PWM conversion signal, a three-phase ac input voltage is converted into a specified three-phase ac input voltage by a conversion section.

Abstract: A control method for a PWM cyclo-converter is provided in which a voltage can be accurately generated even when a voltage command is small. In the PWM cyclo-converter, the turning on and off operations of two-way semiconductor switch are repeated at intervals of short time. As switching patterns, within the intervals of short time, a first terminal of output side terminals outputs in order a maximum potential phase P, an intermediate potential phase M and the maximum potential phase N, a second terminal of the output side terminals outputs in order the maximum potential phase P, the intermediate potential phase M, a minimum potential phase N, the intermediate potential phase M and the maximum potential phase P, and a third terminal of the output side terminals outputs in order the intermediate potential phase M, the minimum potential phase N and the intermediate potential phase M.

Abstract: A method for thermal protection of a frequency converter and a frequency converter includes means for controlling the output current of the frequency converter. The method includes the steps of determining predetermined data points which define a thermal current limit for a semiconductor component of the frequency converter at specific temperatures at plural switching frequencies, and determining predetermined data points which define a thermal current limit for the semiconductor component at specific temperatures at a zero converter output frequency. The method also includes determining the highest allowable thermal current as a function of a measured temperature, a determined switching frequency, and a determined output frequency based on the defined data points, and limiting the output current of the frequency converter to the determined highest allowable thermal current.

Abstract: An inverter type AC generator includes an inverter circuit converting a DC output into AC output of a predetermined frequency and supplying the AC output to a load via a load line in order to improve the quality of an AC output waveform at least in parallel operations. The inverter AC generator includes a zero-crossing detection circuit for detecting a timing of zero-crossings of an AC output voltage waveform on the output line. A controller generates a drive signal in synchronization with the timing of the detected zero-crossings, when a predetermined number of zero-crossings have been detected, and drives the inverter to perform a synchronized operation process.

Abstract: The parallel multiplex matrix converter couples in parallel at least two matrix converters, each of which PWM-controls bidirectional switches coupling input phases from an AC power supply to each output phases so as to output an arbitrary AC voltage or DC voltage. The output sides of the matrix converters are directly coupled in parallel to each other without any reactor. The input sides of the matrix converters use reactors inserted between the input phases from the AC power supply and the AC power supply at each of the respective matrix converters coupled in parallel.

Abstract: An apparatus and method for controlling an inverter, the apparatus including an adjustable frequency controller receiving a reference frequency value and generating a command frequency value as a function thereof, an adjustable voltage controller receiving a reference voltage value and generating a command voltage value as a function thereof and independent of the command frequency and a modulator receiving the command frequency value and the command voltage value and generating pulse width modulated (PWM) inverter control signals as a function thereof.

Abstract: It is an object of the present invention to provide a PWM cycloconverter that can compensate an error between a voltage command and a real voltage generated by a commuting operation. The PWM cycloconverter for solving the above-described problem includes: an input voltage phase detector (6) for detecting the phase of the voltage of a three-phase ac power source (1); a current direction detector (7) for detecting the direction of a current supplied to a two-way semiconductor switch (3); and a commutation compensator (11) for receiving the outputs of the input voltage phase detector and the current detector as inputs to compensate for a voltage command.

Abstract: A DC-DC converter is provided with a control circuit 6 which comprises a drive signal generator 11 for producing on-off signals to a control terminal of a MOS-FET 3 in synchronization with pulse signals VOSC from an oscillator 10; an intermittent controller 12 for producing a control signal VC1 to drive signal generator 11 in response to the level of detection signal from an output voltage detector 5 to convert MOS-FET 3 to the intermittent operation during the light load period; and a power control circuit 16 for ceasing power supply VCC to oscillator 10 in response to control signal VC1 from intermittent controller 12 to stop production of pulse signal VOSC from oscillator 10 for the cessation term of MOS-FET 3 during the intermittent operation.

Abstract: There is described a method for controlling a quenching device for a converter bridge with line regeneration, whereby the converter bridge controlled by a network-timed control circuit by ignition pulses is connected with its three inputs to the phases of a three-phase network and the two outputs of the bridge are connected to a direct-current motor which feeds, when operated as a generator, current back to the three-phase network via the bridge. The quenching device is controlled by a trigger unit which emits trigger pulses depending on the monitoring of electrical and temporary variables. The device has measuring values “direct output current” and/or “supply voltages” used to determine characteristic values which are compared with theoretical characteristic values. Depending on the result of said comparison, the quenching device is optionally activated.

Abstract: A high frequency device for supplying a high frequency power to a load, the high frequency device includes: an oscillating unit that can vary an oscillation frequency; a high frequency power supplying unit that serves as a power source by amplifying an oscillation signal output from the oscillating unit for supplying the high frequency power to the load; a reflected-wave information calculating unit that calculates reflected wave information on a reflected wave power, and outputs the reflected wave information; a frequency control unit that controls the oscillation frequency of the oscillating unit so as to lower the reflected wave information; an impedance adjusting unit that is disposed at a downstream of the high frequency power supplying unit in a power supplying direction, and that has at least one variable reactance element which can be controlled; and an element control unit that controls the variable reactance element of the impedance adjusting unit so as to lower the reflected wave information.

Abstract: A high frequency power supply device and power supplying method are disclosed, which can rapidly and accurately control power used for generation of plasmas. The device includes a first high frequency power supply, providing power at frequency f1, and a second high frequency power supply providing power at frequency f2 (f1>f2). The first power supply includes: a first high frequency oscillator, which excites the high frequency power at the first frequency and has a variable frequency; a first power amplification block, which amplifies the power of the high frequency oscillator; a heterodyne detection block, which performs heterodyne detection of a reflected wave; and a first control block, which receives a signal after detection of the heterodyne detection block and a traveling wave signal, and controls an oscillating frequency of the first high frequency oscillating block and an output of the first power amplification block.

Abstract: A motive power outputting apparatus includes motor generators, inverters, and a transformer. The motor generator includes a three-phase coil, and the motor generator includes a three-phase coil. The inverter allows an in-phase AC current to pass through an U-phase coil, a V-phase coil and a W-phase coil of the three-phase coil. The inverter allows an in-phase AC current, which has a phase being inverted relative to that of the in-phase AC current passing through the three-phase coil, to pass through an U-phase coil, a V-phase coil and a W-phase coil of the three-phase coil. The transformer converts an AC voltage generated in a primary coil and outputs a commercial-power-source AC voltage to terminals.

Abstract: The invention relates to a method for compensating for a voltage unbalance in an electrical network, which is fed by using an apparatus based on controlling a flux linkage vector or a voltage vector. Concerning the apparatus based on controlling the flux linkage vector, the method comprises the steps of determining a flux linkage reference vector comprising a positive sequence component and a negative sequence component, and controlling the feeding apparatus of the network in such a manner that the flux linkage vector thereof follows the reference vector with predetermined precision. The negative sequence component of the flux linkage reference vector is arranged to compensate for the amplitude and phase unbalance of the voltage in the electrical network to be fed.

Abstract: A power-supply voltage frequency control circuit capable of changing a clock frequency in accordance with processing and assuring an operation of a target circuit when supplying a power-supply voltage in accordance therewith, comprising a clock supply circuit capable of supplying a system clock of a plurality of clock frequencies and supplying a system clock having a clock frequency in accordance with a first control signal to a target circuit performing processing in synchronization with the system clock, a power-supply voltage supply circuit for supplying a power-supply voltage of a value in accordance with a second control signal to the target circuit, and a control circuit for outputting the first control signal to the clock supply circuit and a second control signal to the power-supply voltage supply circuit by following an instruction of a frequency change value and a change time from the target circuit.

Abstract: A power-supply voltage frequency control circuit capable of changing a clock frequency in accordance with processing and assuring an operation of a target circuit when supplying a power-supply voltage in accordance therewith, comprising a clock supply circuit capable of supplying a system clock of a plurality of clock frequencies and supplying a system clock having a clock frequency in accordance with a first control signal to a target circuit performing processing in synchronization with the system clock, a power-supply voltage supply circuit for supplying a power-supply voltage of a value in accordance with a second control signal to the target circuit, and a control circuit for outputting the first control signal to the clock supply circuit and a second control signal to the power-supply voltage supply circuit by following an instruction of a frequency change value and a change time from the target circuit.

Abstract: A method for a frequency converter, when the frequency converter controls a motor and operates torque-controlled partly or entirely in a field weakening region. The method comprises the steps of defining the direction of travel and sector of a stator flux vector ({overscore (&psgr;)}s) in the motor, predicting a torque estimate (Tpred) produced by a voltage vector of the output of the frequency converter at the end of the voltage vector when a voltage vector change occurs at the instant of prediction, comparing the predicted torque estimate (Tpred) with a reference torque (Tref) of the frequency converter, and implementing the voltage vector change when the predicted torque estimate (Tpred) is smaller than the reference torque (Tref) and the stator flux vector ({overscore (&psgr;)}s) is moving in a positive direction of travel or when the torque estimate (Tpred) is greater than the reference torque (Tref) and the stator flux vector ({overscore (&psgr;)}s) is moving in a negative direction of travel.

Abstract: An adaptive shunt system for controlling vibrations of a frequency-varying structure, the system comprising: a detector for detecting vibrations generated from a predetermined structure and generating vibration signals corresponding to the vibrations; a computer for inputting the vibrations signals from the detector; a signal processing unit for processing the vibration signals from the computer and generating a voltage command in real-time; and an adaptive shunt device for adaptively controlling the vibrations of the structure of which natural frequency varies at every moment according to the voltage command.

Abstract: A load matching circuit is disclosed for use with a frequency controlled power supply. The load matching circuit includes an input connectable to the frequency controlled power supply and an output connectable to the load, such as an induction heating coil. A load matching section is connected between the input and the output to provide enough resonance to allow the power supply to operate at or below the maximum frequency when the load is connected to the power supply and at or above the minimum frequency when the load is disconnected from the power supply. In this manner, a solid-state variable frequency power supply can continue to run even when the external load is disconnected from the power supply.

Abstract: An electronic method and apparatus are described for an isolated, universal input, power supply in the form of a single-ended resonant converter that utilizes capacitive energy storage versus magnetic energy storage, for converting an ac or DC input voltage to a variable voltage and current DC output or a variable ac output voltage, current, frequency, or phase. The preferred topology is a direct ac to ac, single-ended resonant converter using a single switch (4) and integrated magnetic element (1) with inherent near-unity power factor. Advantages of this method include a significant reduction in global energy consumption, simpler circuitry, substantially lower cost, higher efficiency, and longer operational life.

Abstract: A power supply unit provides therein a first power unit outputting a first excitation amplitude and operating from rising of a reference pulse signal outputted from a reference oscillator until rising of a first time delay signal having a time delay to the reference pulse signal, a second power unit outputting a second excitation amplitude and operating from rising of the first time delay signal until rising of a second time delay signal having a time delay to the first time delay signal, and a third power unit outputting a third excitation amplitude and operating from rising of the second time delay signal until falling of the first time delay signal, and supplies output by synthesizing output from the first power unit, second power unit and the third power unit to the exciting unit.

Abstract: An inductively coupled power distribution system for moving vehicles, in which resonating primary circuits to distribute power for resonating secondary circuits to collect and use in an optimized manner. In order to have all circuits resonating at substantially the same frequency, devices which detect and adjust resonating components are used, such as a frequency drift compensator in which the present frequency is compared to a reference voltage and causes a driver to be ON or OFF accordingly. Switches are driven CLOSED or OPEN respectively and when CLOSED, supplementary capacitors are included with a main capacitor in a primary resonant circuit. Dithering or pulsed control provides a continuous control of resonance, as the system takes some milliseconds to respond.

Abstract: An electric power generation and distribution system having a basic variable frequency distribution bus to which wide frequency variation tolerant utilization equipment is coupled and an enhanced frequency distribution bus to which wide frequency variation intolerant utilization equipment is coupled, comprises a variable speed generator driven by an external variable speed prime mover such as an aircraft engine. This generator produces output electric power having a frequency which varies with the speed at which the generator is driven. The system further comprises a converter which is electrically coupled to the generator and produces output electric power having a controlled frequency. A switching network operates to couple the generator to and decouple the converter from this enhanced bus when the frequency of the electric power produced by the generator is within a predetermined acceptable range to allow the generator to supply power thereto.

Abstract: A method for controlling the speed of an AC machine (12) is described.The AC machine (12) receives three output phases (A,B,C) supplied from a cycloconverter (10) which is connected to an input supply (R,Y,B) of frequency f.sub.1. The cycloconverter (10) is caused to operate in three modes under control of a microprocessor (25).The first mode supplies the AC machine (12) in the frequency range 0 to f.sub.0, by conventional cycloconverting to generate a near continuum of frequencies.The second mode operates the cycloconverter (10) to synthesize a number of frequency steps in the frequency range f.sub.0 to f.sub.1 from the input supply (R,Y,B) and provides speed control of the AC machine (12) by phase control of the output voltage (A,B,C) between each frequency step.The third mode operates the cyclonverter (10) to be transparent, such that the input frequency f.sub.1 is effectively directly supplied to the AC machine (12) without speed regulation being applied.

Abstract: An improvement in a control for a DC link power converter includes a phase command signal generator responsive to DC power on a DC link wherein the phase command signal generator develops a phase command signal for a control of the power converter whereby a parameter the DC power is caused to approach a certain level.

Abstract: An automatic frequency control system applicable to home automation system and electronic appliances requiring precise frequency, comprising a resonance transmitter, a carrier transmitter, a frequency detector, highest and lowest limit oscillators for generating highest and lowest limit frequencies, a comparator including first and second phase comparators, and a resistance varying unit. The system provides the precise frequency to the electronic appliances by detecting the frequency of the data transmitted to power lines, comparing by the comparator the transmission frequency with the highest and lowest limit frequencies and decreasing or increasing the resistance of the resistance varying unit depending upon the compared resultant.

Abstract: Prior variable speed constant frequency (VSCF) system controls which operate the VSCF system while it is coupled in parallel with an external AC source across a load have controlled inverter output voltage based only upon the reactive current level supplied by the inverter. This has in turn resulted in the possibility of unstable system operation under load. In order to overcome the foregoing problem, a control for controlling the supply of power to a load from an inverter coupled in parallel with an AC power source across the load senses the real and reactive components of the current supplied by the inverter and the phase displacement of the power developed by the inverter relative to the power developed by the AC power source to derive an angular displacement signal.

Abstract: The present invention achieves the above objects, among others, by providing apparatus for converting a supplied AC input signal into an AC output signal having a selected lower frequency than the frequency of the AC input signal, which apparatus translates individual half cycles of the supplied AC input signal to an intermediate output signal with selected amplitude and polarity such that during successive pairs of first and second periods, each such period corresponding to a predetermined number of half cycles of the AC input signal, the translated half cycles of the AC input signal all have the same first selected polarity during each first period and have the same second selected polarity during each second period, with the first and second polarities being opposite. The apparatus filters the intermediate output signal to develop the AC output signal having the selected lower frequency.

Abstract: A circuit for operating an electromagnet of a feeder or vibrator incorporate phase control for a triac used for oscillating the feeder at line frequency or at a selectable subharmonic frequency.

Abstract: A system for providing a regulated low voltage DC source and a regulated higher voltage AC source at a preselected frequency, such as 60 Hz. from the same windings of an alternator rotated at variable speeds including a phase WYE connected engine driven alternator providing three output posts and a neutral post and having a field circuit, a half-wave rectifier connected to each of the output posts of the alternator providing a low voltage DC source, a cycloconverter having a three phase input connected to the posts of the alternator and providing a single phase output at the preselected frequency, a resonating transformer having the primary connected to the output of the cycloconverter and having a capacitor in the secondary providing a resonant frequency at the desired AC frequency, such as 60 Hz., and a clock circuit providing an AC control voltage at a preselected frequency, such as 60 Hz.

Abstract: A power source using high-frequency phase control possessing an ability to cause the transfer of electric power between a power source side and a load side to be made through a high-frequency transformer and to effect control of the output voltage by subjecting the power source side and the load side circuits to on-off control with a certain phase difference. This power source can be used as an uninterruptible power source, a device for controlled drive of a motor, a DC constant-voltage power source, or a constant-current device, for example.

Abstract: Power sources of a parallel AC electrical power system are synchronized by producing a voltage difference signal representative of the difference in output voltages of the power sources and demodulating that signal to produce a frequency control signal and a voltage magnitude control signal. The output frequency and voltage magnitude of at least one of the power sources is varied in response to the frequency control signal and voltage magnitude control signals, respectively, to minimize the difference in output voltages between the power sources.

Abstract: A 3-phase-to-3-phase power converter is intended to control the output voltage and current so as to provide a 3-phase sinusoidal wave which is controlled in compliance with the input voltage. The main circuit has a switching period shorter than 30.degree. of the power voltage waveform and it is controlled so that switching of lines takes place in alternate fashion, whereby the input power factor is improved.