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: A demodulator circuit utilizes a switching demodulation technique to detect the real and reactive components of load current unbalance in a parallel source alternating current power system. A signal representing load current unbalance is selectively switched to a pair of output terminals in response to a series of pulse wave control signals which bear a phase relationship with the Thevenin equivalent voltage of one of the power sources such that the signal appearing at one of the output terminals represents the real load current component while the signal at the other output terminal represents the reactive load current component. The signals at these terminals are fed back to control the frequency and voltage magnitude of one of the power system sources to eliminate load current unbalance.

Abstract: A system for forming address signals which address respective converter switches in a frequency converter. The frequency converter is of the type wherein a DC voltage is provided for supplying electrical energy to phase outputs thereof in response to the states of the converter switches. In accordance with the invention, the phase output voltages, phase output currents, and predetermined desired phase currents are treated as space vectors from which are generated control difference space vectors. In one embodiment, a trigger pulse is generated externally and may be suppressed when the control difference vector has a value which is below a preselected tolerance limit. In a further embodiment, the trigger pulse is generated internally and is suppressed if the tolerance limit is exceeded. Upon the occurrence of each trigger pulse, a voltage space vector is addressed having a direction which is opposite to the control difference space vector.

Abstract: A system for forming addressing signals for addressing respective converter switches of a frequency converter; the frequency converter being of the type which is provided with DC input terminals for receiving electrical energy which is conducted to phase output terminals when the converter switches are operated in response to the addressing signals. Each of the combinations of converter switches is associated with a discrete space vector, and a load voltage vector is determined. In operation, two of the discrete space vectors which are adjacent to the voltage space vector are addressed for respective dwell times which correspond to the components of the voltage space vector as impressed upon the adjacent discrete space vectors. Either prior to or after the addressing of the adjacent discrete space vectors within a switching cycle, a short circuit state is addressed. In one embodiment, the order in which the adjacent discrete space vectors are addressed is reversed for each subsequent switching cycle.

Abstract: When the input frequency is below a preselected value, an unrestricted frequency changer (UFC) is operated in the conventional manner by sequentially switching to more positive input phases while the fundamental component of the output waveform is positive going and to more negative input phases while it is negative going. Above the preselected input frequency, the UFC is operated in a complementary manner; that is, by switching to more negative input phases while the output waveform fundamental component is positive going and to more positive input phases when it is negative going. The switching instants occur in UFC operation when the reference waveform is equal in amplitude but opposite in slope to each waveform in a set of timing waveforms phase locked to the input waveforms. During complementary UFC operation, switching occurs when the reference waveform is not only equal in amplitude to the timing waveforms but also has a slope of the same sense.

Abstract: In an induction heating cooking apparatus, the frequency of electromagnetic energy is varied in response to a desired power setting level within an allowable range and the duty cycle of the energy is varied in response to the setting level while the frequency is set at the lower limit of the allowable range. The combined effects of frequency and duty cycle controls permit the power to vary from as low as 50 watts to as high as 2 kilowatts.

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.