Importance

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Abstract

An apparatus and method for compensating a polyphase electrical power supply for reactive power loads on an AC supply line is disclosed. The static VAR compensator disclosed herein can provide a selectable, constant amount of VARs to compensate for reactive loads on the line, or alternately provide a fixed phase angle. The static VAR compensator may be controlled to compensate for fluctuating reactive loads. The static VAR compensator includes a transistorized inverter, connected between the AC supply and a constant voltage, that has switches to control the instantaneous current on each phase line of the AC power supply. By modulating the inverter switches at a high frequency, the instantaneous currents flowing through each of the phase lines can be modulated for precise control of the real and the reactive power. A voltage waveform is obtained from each phase of the utility grid, and used as a reference waveform. The control system applies the reference waveform to create two waveforms: a real waveform and an imaginary waveform for each phase. The imaginary waveform is multiplied by a VAR multiplier M.sub.1 to supply the desired number of VARs, the real waveform is multiplied by a real multiplier M.sub.2 that is derived to control the constant voltage source, and resultant waveforms are added together to provide a current control waveform for each phase that is applied to the inverter through a current regulator and drive circuits.

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First Claim