Harmonic current cancellation techniques

The reduction of supply current distortion by harmonic cancellation is examined. The technique to be described involves the use of four-quadrant controlled-current sources/sinks as parallel-connected current-waveform correctors. The add-on units are arranged to inject harmonic currents into the supply as demanded by the distorting loads so that the supply current may be near-sinusoidal and in-phase with the supply voltage. If current injection is correctly carried out and in close proximity to the distorting load, EMC problems associated with common impedances and radiation from wiring will be minimised and wiring and plant requirements may be reduced