An electric supply system should invariably show ideal sinusoidal voltage and current signals at every consumer end. But in fact electric utilities hardly find such desirable conditions due to several factors. Use of wide variety of domestic and industrial equipments is one of the reasons. In order to improve the performance to cope up with technological advancements, modern semiconductor based converters are often used. These equipments are often referred to as Power Electronics loads. Solid state control of ac power using thyristors and other semiconductor switches is widely employed to feed controlled electric power to electric loads, such as adjustable speed drives, furnaces, computer power supplies, electrical transportation systems, electro domestic appliances etc. The objective of the paper is to study, simulate and design a shunt active power filter capable of compensating current harmonics generated at the supply side due to presence of such non-linear loads. The basic topology of the shunt active filter is a PWM controlled three-phase voltage source inverter bridge. A SCR or diode based rectifier is connected to the utility and the PWM controlled inverter generates specific current harmonics. These generated harmonics are injected into the source in phase opposition to the harmonics generated by the load. Thus harmonic cancellation takes place, so that these harmonics are not drawn from the source. In this paper, harmonic waveforms are generated in MATLAB software based on Fourier series of the ideal wave shapes created at the supply lines due to non-linear loads. A selection criterion for different components of the active filter has been made.
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