MITIGATION OF HARMONICS OF RENEWABLE ENERGY SYSTEMS BY USING ACTIVE POWER FILTER TECHNIQUES

Abstract

Semiconductor switches are widely used to deliver controlled electrical power to loads such as furnaces, adjustable speed drives, and uninterruptible power supplies. Non-linear loads and solid-state converters are sources of harmonics, and draw reactive power from the AC system. In three-phase unbalanced power systems, non-linear loads may cause unbalanced excessive harmonic currents (including the triplen) to flow in the neutral wire. Harmonic currents, reactive power demand, and excessive neutral currents cause adverse effects on the power system such as low efficiency of distribution systems, abnormal operation of protection systems, poor power factor, overloading of capacitor banks, nuisance tripping, de-rating of distribution and user equipment, noise and vibration in electrical machines, etc. Traditionally, passive filters have been used to reduce definite harmonic orders but have some disadvantages such as large size, possibility of resonance and fixed compensation. The significant increase of non-linear loads in electrical power systems makes engineers to design many solutions to solve power quality problems. Active power filters (also called active power line conditioners or active power quality conditioners) are one of the most effective solutions for power quality problems. Active power filter can be classified into several categories. These are; shunt active power filters (SHAPF), series active power filters (SEAPF), and unified power quality conditioners (UPQC). Several algorithms are available to control the operation of active power filters. Among these methods are the instantaneous active and reactive power theory (p-q theory) and the Synchronous reference frame control theory (the d-q theory).