ABSTRACT
Converters operate by switching the alternating current (AC) supply to produce a direct current (DC) voltage at their output. The resulting deviation of the current drawn from the AC system from the ideal sinusoidal waveform results in the introduction of harmonic currents and voltages into both the AC and DC systems. In many power systems, the distribution of the phase angles of the individual harmonic sources is essentially random which, when taken together with the variation of system harmonic impedance with changes in load, means that the precise computation of harmonic effects is not practical. The output voltage waveform of a fully-controlled converter will contain harmonic components at frequencies which are multiples of the ripple frequency. In addition they provide low impedance over a wide range of harmonics without the need for parallel branches and associated switching. At lower power levels the use of an active filter can be considered as a means of controlling harmonic content.
