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Harmonic control techniques for inverters and adaptive active power filters

This thesis is concerned with the general issue of power quality. The specific areas of interest include harmonic distortion and its minimisation. In particular the thesis considers a P W M switching strategy which yields near optimal performance in terms of harmonic distortion as well as on-line harmonic detection mechanisms and adaptive active power filtering solutions. For the purpose of load side harmonic reduction, a novel equal area based PWM ( E A P W M ) switching strategy is developed which is suitable for voltage source full bridge inverter applications. The objective of this strategy is to minimise both the harmonic distortion and the switching losses in the inverter. Switching losses in the inverter are minimised by developing a hybrid switching sequence. The harmonic distortion is minimised by adopting a technique which ensures that the P W M pulses are placed at appropriate positions of choice based on an equal area criterion so that their areas are better matched with the areas under the reference waveform. The EAPWM technique is evaluated and its performance is compared with existing P W M techniques including natural and regular P W M switching strategies. The performance evaluation and comparison is based on the total harmonic distortion and maximum inverter fundamental output voltage. For a case where the ideal output waveform is sinusoidal it is shown through simulation that the proposed technique provides a P W M output with minimum harmonic distortion and maximum fundamental voltage. The second issue addressed by the thesis is adaptive active power filtering. The objective is to develop an economical solution where a partial and flexible harmonic reduction technique is provided such that the established harmonic standards are satisfied. Partial and selective compensation of those individual harmonics which exceed the