HARMONIC REDUCTION IN HYBRID FILTERS FOR POWER QUALITY IMPROVEMENT IN DISTRIBUTION SYSTEMS

A flexible and versatile solution to voltage qualit y problems is offered by active power filters. Curr ently they are based on PWM converters and used to connect to low and medium voltage distribution system in shunt or in series. Active power filters can perfor m one or more of the functions required to compensa te power systems in improving power quality. Hybrid Filter, which is a combination ofan active series fil ter and passive shunt filter is quite popular because t he solid-state devices used in the active series pa rt can be of reduced size and cost (about 5% of the load size ) and the major part of the hybrid filter is made o f the passive shunt L-C filter used to eliminate lower order harmonics. It has the capability of reducing voltage and current harmonics at a reasonable cost. To prov ide high power quality at the Point of Common Coupling (PCC) of power distribution systems, elimi nation of the harmonics is indispensably necessary. The power quality and allowable Harmonic levels in power system are defined by International standards (like IEEE-519-1992, IEC-61000). Hence, it is invar iably necessary to design filters meeting the said International standards. Harmonics in hybrid filter s can be reduced by using multilevel inverter. A se ven level cascaded multilevel is used in the present wo rk to mitigate the harmonics in Hybrid filter. The simulation results of the same are presented in thi s paper for a distribution system of voltage 11KV.