Abstract: An active power quality conditioner for compensating reactive power and harmonic distortion in power systems. A pulse width modulated (PWM) inverter (70) for each phase is controlled to produce a harmonic distortion compensation signal that is coupled to an inductor. The inductor is connected in series between a stepped-wave inverter (84) and one phase of the power line. A current produced by the stepped-wave inverter compensates for the reactance of a load coupled to the power line. The PWM inverter operates at a frequency that is substantially greater than the fundamental frequency of the power line and is not exposed to the full power line voltage; it can be constructed using components of relatively low power and voltage rating. In contrast, the stepped-wave inverter, which is decoupled from the PWM inverter, operates at the fundamental frequency and is subjected to most of the stress. Both shunt coupled and series coupled compensators are described.

Abstract: A system and method for determining and providing reactive power compensation for an inductive load. A reactive power compensator (50,50') monitors the voltage and current flowing through each of three distribution lines (52a, 52b, 52c), which are supplying three-phase power to one or more inductive loads. Using signals indicative of the current on each of these lines when the voltage waveform on the line crosses zero, the reactive power compensator determines a reactive power compensator capacitance that must be connected to the lines to maintain a desired VAR level, power factor, or line voltage. Alternatively, an operator can manually select a specific capacitance for connection to each line, or the capacitance can be selected based on a time schedule. The reactive power compensator produces control signals, which are coupled through optical fibers (102/106) to a switch driver (110, 110') to select specific compensation capacitors (112) for connections to each line.

Abstract: The reactive power of an induction machine is compensated by providing fixed capacitors on each phase line for the minimum compensation required, sensing the current on one line at the time its voltage crosses zero to determine the actual compensation required for each phase, and selecting switched capacitors on each line to provide the balance of the compensation required.