Abstract: For open loop phase pre-charge, an apparatus includes a Switching Mode Power Supply (SMPS) charging diode and a charge generator. The SMPS charging diode pre-charges an SMPS to a regulation set point from at least one phase of an Alternating Current (AC) voltage. The charge generator is powered by the pre-charged SMPS. In response to detecting the regulation set point iteratively, the charge generator detects a specified phase angle of the AC voltage. In response to the specified phase angle, the charge generator iteratively generates a charging voltage during positive voltage interval that charges a Direct Current (DC) bus capacitor to a target DC bus voltage within a charging time interval. At least a portion of the charge generator comprises one or more of hardware and executable code, the executable code stored on one or more computer readable storage media.

Abstract: A method and apparatus to detect cell voltage of each of a plurality of battery cells in a rechargeable battery pack is disclosed. The method comprises generating a wave form with a positive phase and a negative phase by a current limited square wave generator. The wave form is a square wave having a maximum peak-to-peak voltage when the square wave generator is not loaded to be current limited. Then, sending the positive phase of the wave form to a first loop from a capacitor to the positive side of a battery cell. And, sending the negative phase of the wave form to a second loop from the negative side of the battery cell toward the capacitor. Finally, detecting a change of an electrical signal from the square wave generator. The voltage detection method and apparatus of this invention can be applied to detect whether a rechargeable battery cell has voltage lower than a low voltage limit or to measure the voltage of the battery cell in order to check its status.

Abstract: Isolated Dynamic-Current (“Dyna-C”) converters are converters that convert incoming 3-phase AC or DC power to a mix of DC and AC power via an isolation link. In various embodiments, the isolation link is a high-frequency isolation transformer. Isolated Dyna-C converters may provide a high-frequency galvanic isolation and are able to convert three-phase AC power to three-phase AC power, or three-phase AC power to DC and vice versa. The topology is minimal and the costs are low. Isolated Dyna-C converters provide fast current responses and keep the losses low by using a simplified two-stage conversion and providing a magnetizing current that is dynamically controllable and tailored to the load. An isolated Dyna-C converter may synthesize currents at its input or output ports with an arbitrary phase that is relative to the grid or load voltages, thereby enabling a full independent control over the active and reactive power at its ports.

Abstract: In a cycloconverter generator equipped with an AC power generator that generates single-phase AC power to be supplied to a load by turning on positive and negative switching elements at variable timing every half-period of a desired AC power frequency based on a phase signal and a DC power generator that generates DC power by turning on the positive switching elements in accordance with a timing determined by desired DC voltage, there is installed with a selection switch that is installed to be operable by an user and produces an output indicative of a result of the user's selection between the AC power and DC power thereby enabling to the user to easily select either one of alternating current and direct current.

Abstract: A system for controlling a commutation of a load current is provided. The system comprises a AC-to-AC converter that includes a plurality of switching elements, an energy source that provides an oscillating voltage and is connected to the converter, an electrical load connected to the converter, and a controller that controls the converter, and monitors the oscillating voltage and the load current delivered to the electrical load. The controller determines a plurality of machine states of the converter, each of the plurality of machine states representing a corresponding conducting set of the plurality of switching elements, and controls switching between the plurality of machine states based on polarity commutations of the load current in the electrical load and polarity commutations of the oscillating voltage.

Abstract: A converter circuit with short-circuit current protection having a DC voltage circuit (1) is proposed, which DC voltage circuit (1) is formed by a DC voltage circuit subsystem (2.1), the DC voltage circuit subsystem (2.1) having a first energy store (3) and a second energy store (4), which is connected in series with the first energy store (3), and a fuse (5). Furthermore, the converter circuit has at least one pair of branches (6) provided for each phase (R, S, T) and connected in parallel with the DC voltage circuit (1), each pair of branches (6) having power semiconductor switches. In order to achieve a low-inductance converter circuit, the fuse (5) forms the connection between the first energy store (3) and the second energy store (4).

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: A power unit is provided which can perform stable feedback control by reducing a feedback gain, and sufficiently cope with fluctuations in the output voltage occurring according to fluctuations in the input voltage caused by fluctuations in the rotational speed of an engine. A pair of variable control bridge circuits are connected to three-phase output windings of a three-phase generator driven by the engine, and connected in an antiparallel manner to each other to form a cycloconverter for generating a single-phase alternating current to be supplied to a load. A voltage-detecting circuit detects a voltage of the three-phase alternating current. An effective voltage value-calculating circuit calculates an effective value of the voltage of the alternating current. A reference sinusoidal waveform-forming circuit generates a voltage of a reference waveform for controlling the single-phase alternating current.

Abstract: A power unit is provided which is capable of controlling electric current to be supplied to a load connected to the power unit, in a flexible manner in dependence on a load condition. Postive and negative converters of a cycloconver are connected to three-phase output windings of a three-phase generator and connected in an antiparallel manner to each other for generating a single-phase alternating current to be supplied to the load. A firing angle control device causes the positive and negative converters to be alternately switched to operate every half a repetition period of the single-phase alternating current, to thereby cause the cycloconverter to generate the single-phase alternating current. A desired wave-forming circuit forms a desired waveform of a drive signal input to the firing angle control device, for causing the firing angle control device to drive the positive and negative converters, such that the output single-phase alternating current has a desired alternating current waveform.

Abstract: A power unit is provided which is capable of controlling a rise in voltage applied to each of thyristors constituting a cycloconverter even when the output voltage of the power unit undergoes a temporary sharp rise due to characteristics of a load connected thereto. Positive and negative converters of the cycloconverter are connected to three-phase output windings of a three-phase generator and connected in an antiparallel manner to each other for generating a single-phase alternating current to be supplied via a pair of output lines to the load. A firing angle control device causes the positive and negative converters to be alternately switched to operate every half a repetition period of the single-phase alternating current, to thereby cause the cycloconverter to generate the single-phase alternating current. A bridge rectifier is connected between the pair of output lines.

Abstract: A power converting apparatus and a power converting method for driving a high voltage AC motor at a variable speed. Conventional invertor systems cannot solve technical subjects such as energy conservation, resource conservation, miniaturization, efficiency promotion and voltage and current waveform distortion suppression for improvement in environment needed by the market, and cannot solve another technical subject of improvement in redundancy such that, upon failure, operation is performed with a normal part.

Abstract: A portable power unit has a magneto generator having three-phase output windings. A synchronizing signal is formed in synchronism with an output frequency of the magneto generator. A pair of variable control bridge circuits are connected to the three-phase output windings and connected in antiparallel connection to each other to form a cycloconverter for generating a single-phase alternating current having a desired frequency to be supplied to a load. A bridge drive circuit is responsive to the synchronizing signal from the synchronizing signal-forming circuit, for causing the pair of variable control bridge circuits to be alternately switched to operate every half a repetition period of the single-phase alternating current, to thereby cause the cycloconverter to generate the single-phase alternating current. An output voltage-detecting circuit detects an output voltage of the pair of variable control bridge circuits.

Abstract: A current fed unrestricted frequency converter (UFC) for supplying power with balanced voltages to a three-phase unbalanced load generates two sets of existence functions for controlling the switching matrices of the UFC to generate positive and negative sequence current components in the load. Existence function generators generating the positive and negative sequence existence functions are phase locked, respectively, to a positive sequence reference signal generated by a clock and a negative sequence reference signal derived by circuits which monitor the negative sequence voltage in the load. Select circuits alternately gate the positive and negative sequence existence functions to the UFC switching matrices in proportion to the detected magnitude of the negative sequence voltage in a sense to drive the negative sequence voltage in the load to zero.

Abstract: A high frequency link power converter apparatus includes a power source, a circulating current type AC-AC converter having an output terminal connected to the power source, a high frequency phase-advancing capacitor connected to an input terminal of the AC-AC converter, a phase controller for controlling a firing phase of the AC-AC converter, an external oscillator for supplying phase reference signals to the phase controller, a first circuit for controlling a crest value of voltages applied to the phase-advancing capacitor, a second circuit for detecting a phase difference between the reference signals and the voltages applied to the phase-advancing capacitor, and a third circuit for controlling the phase difference, so that the magnitude of the phase difference becomes substantially zero.

Abstract: An electric motor having a rotor, a stator and a plurality of windings on the stator is provided with power, via a plurality of rectifiers, from an a.c. polyphase source. The rectifier means are coupled between individual ones of the plurality of windings and respective individual ones of the a.c. polyphase source. The rectifier means may be full-wave or half-wave rectifiers. The rectifiers may be diodes, SCR's, TRIACS or the like. The windings are wound on the stator with substantially equal angular distribution. The winding may have a concentric and/or overlapping relationship. High and low (half) speed operation may be affected, using a plurality of switches.

Abstract: An electric power converter, in which a plurality of converters convert a first electric power having a first frequency into a second electric power having a second frequency, and the second electric power is supplied to a load such as an electric motor, and in which a correction controller changes a reference voltage to generate reference voltage signals to be supplied to the converters in order to shift firing phase angles of the converters, thereby preventing a generation of higher harmonics of integer orders of the first electric power.

Abstract: The present invention provides a digital gate pulse generator which controls the output of a cycloconverter used for electrical power conversion applications by determining the timing and delivery of the firing pulses to the switching devices in the cycloconverter. Previous gate pulse generators have been built with largely analog or discrete digital circuitry which require many precision components and periodic adjustment. The gate pulse generator of the present invention utilizes digital techniques and a predetermined series of values to develop the necessary timing signals for firing the switching device. Each timing signal is compared with a reference signal to determine the exact firing time. The present invention is significantly more compact than previous gate pulse generators, responds quickly to changes in the output demand and requires only one precision component and no adjustments.

Abstract: A harmonic suppressing device provided in a power system such as, for example, a transmission and distribution system or a power generating system, to filter higher harmonic currents generated by a higher harmonic current source of the power system such as, for example, a cycloconverter. The harmonic suppressing device comprises, as the principal components thereof, a passive filter serving as a high-order higher harmonic filtering unit for filtering higher harmonic currents of comparatively high order among those generated by the higher harmonic current source, and an active filter serving as low-order higher harmonic filtering unit for filtering higher harmonic currents of comparatively low orders among those generated by the higher harmonic current source.

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: The performance of the cycloconverter when used to drive an induction motor is at present limited because of inadequate methods of modulating the thyristor conduction angles. The main problems are: low maximum frequency due to subharmonics; voltage distortion due to discontinuous current and to uncertainty of current cross-over (for non-circulating current mode); and poor power factor on the input. This specification describes a modulation method which overcomes the first two of these problems without sacrificing performance in any area and proposes a new method to greatly improve the input power factor, although at the expense of possible input current subharmonics. A non-limiting application of the method to a 3 pulse, 3 phase, non-circulating current cycloconverter is described. The technique may also be applied to static power frequency changers other than the cycloconverter.

Abstract: A current-circulating cycloconverter includes a positive converter and a negative converter connected in anti-parallel with each other through a DC reactor. A load is connected to an intermediate tap of the DC reactor. When a load current flowing to the load is smaller than a predetermined value, a circulating current flowing through the positive and negative converters is held at a minimum required value. A circulating current is caused to additively flow for canceling a voltage drop produced across the DC reactor when the load current exceeds the predetermined value.

Abstract: There is disclosed a polyphase power line adapter for providing polyphase electric power to operate a motor at a speed less than rated speed particularly useful for pump motors and the like where it is undesirable to stop the motor. A bridge of from nine to eighteen thyristors, which is also conventially used in cycloconverters, connects the input terminals to the output terminals. A delta-to-Y transformer arrangement and a wave shaping circuit produces cyclic pulse control signals synchronized with the wave-forms of the respective phases of the polyphase power line input; one such signal is transmitted to a divider circuit with a maximum division factor (always an integer) corresponding to the factor, N, by which the frequency, and hence, motor speed is to be reduced. A plurality of logical "and" circuits each has its inputs connected to receive one output from the divider circuit and cyclic pulse control signals are supplied to another of the inputs.

Abstract: A UFC is controlled with polar coordinates, a phase checked loop combining with an angular demand to establish a predetermined and tuned sequence of switch combinations between the converters of the UFC, to generate between the output phase-loads the desired voltage vector.

Abstract: A control system for a cycloconverter of the circulating current type produces an ac current of a variable frequency. The cycloconverter is configured to connect a power factor compensating capacitor at its receiving-end, thus to control a lagging reactive power due to a circulating current flowing in the cycloconverter so as to cancel a leading reactive power due to the power factor compensating capacitor. Such a control is carried out under the condition of an operation below the rated load. In contrast, under the condition of an operation above the rated load, a control is effected so that the circulating current flowing in the cycloconverter is substantially kept constant.

Abstract: A frequency converter apparatus is provided with a frequency converter coupled to an AC power supply and to a load. The frequency converter converts an AC input with a given input frequency into an AC output with a given output frequency. The frequency converter apparatus is further provided with a frequency reference circuit and a harmonic cancel circuit. The frequency reference circuit supplies a reference signal to the frequency converter so that the output frequency of the AC output follows the reference signal. The harmonic cancel circuit supplies a harmonic cancelling signal to the frequency reference circuit so that the prescribed order of the higher harmonic of the AC output is substantially cancelled according to the frequency, magnitude and phase of the harmonic cancelling signal.

Abstract: A three-pulse UFC system uses three groups of three bilateral switches controlled according to a switch polarity pattern to generate AC currents to a load, and a deadband hysteresis having upper and lower limits is used to maintain the load current so as to match a reference current.

Abstract: The invention resides in providing bilateral switches between the respective phase lines of an AC input source and a common phase line of an AC output to form a phase line group of said bilateral switches on each AC output line; in fact, controlling the bilateral switches of each group so as to generate with AC input lines a DC link voltage with respect to the associated AC output line, and secondly in controlling the bilateral switches in such group to modulate such DC link voltage in relation to a desired AC voltage for such associated AC output line, each of said groups being operated with a corresponding phase shift to provide a corresponding phase shift between the respective output phase lines.

Abstract: Fault-protection is added to static AC-to-AC converter to protect the GTO devices bilaterally by adding at least two line bridges of diodes having an inductor thereacross. Fault-protection is extended to a UFC system by incorporating such inductor in the diode bridges of the GTO devices forming the bilateral switches of the UFC system. The dissipating energy is minimized by combining such fault-protection bridges. The inductors may be coupled controlled demagnetization of the inductors is provided.

Abstract: A direct a.c. supply converter for converting an N (.gtoreq.2) phase input voltage system into an a.c. output voltage system of different frequency, amplitude, and/or phase using width-modulated contributions from the phases of the input voltage system to produce the output voltage system suffers from the disadvantage that the maximum output voltage amplitude can be limited to the minimum instantaneous voltage of the input voltage system because of the arbitrary timing relationship between the two voltage systems. This limitation is relieved by the addition of a component at the N.sup.th harmonic of the input system frequency to the width-modulation so that the effective minimum instantaneous voltage of the input system is increased. An increase in the maximum output voltage amplitude can also be obtained by adding to the width-modulation a component at the P.sup.th harmonic of the output system frequency; this can be used along or in conjunction with the component at the N.sup.

Abstract: In a pulse-width modulated unrestricted frequency changer (UFC) the harmonic contents of the input current are minimized by splitting the active time intervals within the fundamental time frame into at least two pulses which are located within such time frame and controlled in width as if individual PWM single-pulse UFC's were controlled having a phase shift between each other so as to eliminate or reduce undesired frequency components. Such elimination or minimization of selected frequency components is used to reduce the size of the lowpass filter at the input of the UFC, namely by allowing a higher cut-off resonance limit.

Abstract: In a static frequency changer controlled by adjusting the time of conduction of the bilateral switching units forming static converters, the time of conduction is split into n time intervals of respective subdurations adding up to be equivalent to the effective time of conduction of the controlled switching unit, and such subdurations are spread and distributed throughout the time period of control of the switching unit both within the original switching pattern of each converter and between the effective times of conduction of the respective converters, thereby to minimize harmonic distortion of the input supply current of the frequency changer.

Abstract: In an unrestricted frequency changer (UFC) the control pulses are generated by the intersection of a reference ramp of controllable slope and frequency with a succession of timing ramps characterizing the succession of phase voltages at the input of the UFC, whereby by increasing the slope and exceeding the peaks of the timing waves the sinusoidal shape of the output becomes trapezoidal and by increased slope increasingly close to a square-shaped wave, thus maximizing the output voltage at high frequency of operation.

Abstract: A power control apparatus which includes a cycloconverter having thyristors in which a circulating current flows, for supplying a compensating current to AC power lines; capacitors for supplying a reactive current component of the compensating current to the thyristors; a trigger control circuit for controlling the triggering of the thyristors; a detector coupled to the cycloconverter, for detecting from switching currents flowing through the thyristors a circulating signal corresponding to the circulating current. The compensating current serves to improve the power factor of the AC lines as well as to reduce higher harmonic currents on the AC lines. The circulating signal is fed back to the trigger control circuit so that the amount of the circulating current is kept substantially constant according to a negative feedback operation.

Abstract: An optically-triggered converter directly changes the frequency of an incoming voltage waveform to half frequency thereby causing an induction motor, driving a ventilation fan or the like, to operate at half speed. At this lower speed, the induction motor consumes significantly less power. A center-tapped power transformer is used to lower the magnitude of the incoming voltage waveform and a number of optically-triggered thyristor switches are connected between the transformer secondary and the induction motor. The novel trigger circuit includes a synchronous motor connected to receive the input voltage waveforms so that a cylinder attached thereto is rotated in synchronism with the input voltage waveforms. The optically-triggered thyristors are circumferentially positioned about the rotating cylinder and are triggered by a light pulse emerging through an aperture in the cylinder sidewall.

Abstract: An improvement of a thyristor converter drive wherein a thyristor converter drives a load, such as an electric machine, with which a series resonance circuit (1) has been connected in parallel. The components (2,3) of the series resonance circuit (1) are so selected that the charging phase and discharging phase of the circuit have equal length.

Abstract: a multiphase AC current of one frequency is converted to a multiphase current of another frequency by a frequency changer having its output terminals terminated by a load having the impedance characteristics of a voltage source. In this arrangement the multiple phases of a practical AC current source such as a synchronous generator are connected directly to each load phase, even where the bidirectional switches of the UFC are arranged in pulse groups or a bridge configuration.

Abstract: A circulating current of a cycloconverter in each phase is distributed and controlled in such a way that a circulating current in a phase having a large absolute value of a load current is small, and the circulating current of a phase having a small absolute value of the load current is large. Therefore, the reactive power is so compensated that the sum of lagged reactive powers of the phases and advanced reactive power of a phase advancing capacitor cancel out each other.

Abstract: A solid state control circuit is connected to the output of an engine or motor driven alternator to provide a direct current output primarily for welding purposes. The control circuit includes gate controlled thyristors (SCRs) which are gated on at precise times within each cycle in order to provide an output having desired characteristics, such as constant current or constant voltage. Synchronizing windings associated with the alternator provide signals used to control the time of gating for the SCRs. Circuit means are included to insure that the control signals will be unaffected by any disturbances generated within the synchronizing signals due to the operation of the SCRs, and one such means includes an amplifier having a feedback circuit providing a hysteresis greater than any voltage change in the synchronizing signal caused by the operation of the SCRs.

Abstract: Firing signals for the power switches in static power frequency changers are generated by comparing the integral of the output waveform ripple voltage to a repetitively generated stabilizing signal phase locked to, but having a time dependent magnitude independent of, the component waveforms of the output voltage. The stabilizing signal which changes in magnitude in one direction with time is reset to an initial level each time a firing signal is generated.

Abstract: The firing pulses to the nonload carrying bank only of the naturally commutated thyristor power circuit of a static power converter are retarded to reduce or eliminate the interbank circulating current. In one form of the invention, half wave rectified load current signals are summed with the output waveform reference signal applied to the positive and negative bank firing pulse generators in a sense to retard the pulses in the nonload carrying bank. In another form of the invention, the inversion end stops are used to generate the retarded firing pulses in the nonload carrying bank.

Abstract: An inverter-cycloconverter power supply providing for the selective augmentation of the battery source (17) output voltage as needed to compensate for reductions in the effective voltage output of the latter source. The output tap points (for example, 48, 50) of the coupling transformer secondary winding (43) of the cycloconverter section (30) are selected to produce a pseudo-sine wave voltage (FIG. 2, 81) composed of alternating square wave voltages of a first and a second, higher level. A regulator section (60) including a second transformer secondary winding (63) controlled by a pair of thyristors (61, 62) adds a rectified voltage to the battery source (17) voltage as required as determined by regulator control circuitry. The latter comprises monitoring circuit means (83, 84, 85, 86, 87, 92, 95) for detecting the output voltage levels of the cycloconverter and for generating control signals (FIG. 2, 86) of a duration corresponding to the effective voltage drop of the battery source (17).

Abstract: An apparatus and method for reducing the overvoltage transients present on the alternating current power signals provided by the cycloconverters of a variable speed constant frequency (VSCF) system during the first several cycles of the alternating current after a load reduction or no-load condition occurs. An overvoltage transient reduction circuit is connected to each of the plurality of D.C. control signals provided by the phase voltage regulators to the waveform generator of a conventional VSCF system. The overvoltage transient circuit and method of the present invention senses the current amplitude level in each of the alternating current power signals in the VSCF system, and automatically reduces the voltage amplitude levels of the D.C. control signals provided by the phase voltage regulators to a preselected lower level within one-half cycle of the alternating current after a load reduction occurs. This reduction in the amplitude level of the D.C.

Abstract: A dual converter for use in a static direct current motor drive is operated with circulating current and the circulating current is adjusted by firing angle control to automatically maintain reactive power compensation during varying torque and speed conditions of the load.

Abstract: A low frequency, high output alternating current generating device comprising a high frequency generator having an output winding capable of generating a continuous wave high frequency output with an almost constant amplitude, a rectifying means for rectifying the high frequency output of the output winding, a plurality of condition control means for connecting the output of the rectifying means to a load by time-selectively and alternately reversing the polarity of the output, and a reference signal generating means for applying low frequency control signals to each of the conduction control means regardless of the phase of the high frequency output.

Abstract: The invention includes a number of high frequency inverter circuits which develop high frequency signals, preferably in the 20 KHz to 50 KHz range, for use in a work coil, which exhibits inductance and generates a magnetic flux in response to a supplied current, or in a transformer primary winding to effect a magnetic flux output in the form of a transformer action. The magnetic flux output from a work coil may be used, for example, to effect heating of a cooking utensil or the like, and the signal transmitted through a transformer may be used, for example, in electrical welding or the like. Both current fed and voltage fed inverters, which use one or more high frequency switches, such as SCR's, as well as multiplexed and stacked inverters for efficient time sharing of components, are disclosed.

Abstract: A control unit for a six-pulse reversing (two-quadrant) thyristor converter is disclosed. More particularly, a first integrator is provided for generating a sawtooth voltage for controlling the thyristors associated with all negative half-waves of the applied phase voltage, and a second integrator is provided for generating a sawtooth voltage for controlling the thyristors associated with all positive half-waves of the phase voltages. Additionally, an evaluation circuit is provided which is responsive to the zero crossings and polarities of the phase voltages and which controls the integrations of the integrators so that they start and end above and below respective first and second predetermined limits.

Abstract: A control unit for the thyristors of a cycloconverter is disclosed. The thyristors are supplied by a three phase network and the control unit is also responsive to such network. In particular, in the control unit a measuring voltage is derived from a phase voltage, and phase-shift means and smoothing means are provided to shift the phase of the measuring voltage so that its zero crossing is in the vicinity of the zero crossing of a phase voltage. The phase-shifted measuring voltage is then fed to a sawtooth integrator which generates a sawtooth voltage in dependence on the zero crossing of the applied phase-shifted measuring voltage. The sawtooth voltage is then used to generate firing commands for the thyristors.

Abstract: A voltage and frequency control circuit converts an alternating current input signal with inconstant frequency and voltage amplitude to an alternating current output signal with constant voltage amplitude and a constant nominal frequency which is lower than the lowest occurring frequency of the input signal. An amplitude control circuit converts the input signal to an ac signal having constant voltage amplitude. A rectifier circuit is regulated by an ac voltage source to provide positive half-cycles of the output signal from the amplitude control circuit during the positive half of the ac voltage source cycle and to provide negative half-cycles of the output signal during the negative half of the ac voltage source cycle. A filter circuit smooths and shapes the output of the rectifier circuit to provide a sinusoidal output signal having constant voltage amplitude and constant frequency.