Harmonic Reduction in Hybrid Filters for Power Quality Improvement in Distribution Systems

A flexible and versatile solution to voltage quality problems is offered by active power filters. Currently 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 perform one or more of the functions required to compensate power systems in improving power quality. Hybrid Filter, which is a combination ofan active series filter and passive shunt filter is quite popular because the solid-state devices used in the active series part can be of reduced size and cost (about 5% of the load size) and the major part of the hybrid filter is made of 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 provide high power quality at the Point of Common Coupling (PCC) of power distribution systems, elimination 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 invariably necessary to design filters meeting the said International standards. Harmonics in hybrid filters can be reduced by using multilevel inverter. A seven level cascaded multilevel is used in the present work to mitigate the harmonics in Hybrid filter. The simulation results of the same are presented in this paper for a distribution system of voltage 11KV.