Microcontroller-based strategy for reactive power control and distortion compensation

Abstract

Compensation of the fundamental displacement and harmonic distortion currents drawn by nonlinear loads can be achieved by using a three-phase voltage-source inverter to generate an appropriate correction voltage. The real time feedback control scheme of the inverter presented in the paper is a full three-phase switching strategy based on a ‘periodic integral’ version of the error sawtooth pulse-width modulation technique. The switching commands for the transistors within the inverter are generated by a 16-bit single-chip microcontroller. This device has sufficient computational power to implement all aspects of the controller tasks as well as handling the man/machine interface. The output waveform of the compensator is precisely determined by theoretically perfect tracking of the periodic reference signal to cancel the harmonic components up to the synthetised switching frequency (2.7 kHZ). The value of the proposed algorithm is experimentally verified on a 5.5 kVA inverter circuit and is found to give very fast and precise compensation characteristics. Details are given for operation of the experimental system as well as the control algorithm implementation. Harmonic analysis of the voltage on the test system demonstrates the effectiveness of the developed control strategy for the compensator.