Power quality improvement in distribution systems using fuzzy logic based shunt hybrid active power filter

Abstract

The past several years have seen a rapid increase of power electronics-based loads connected to low and medium voltage power distribution systems. These loads draw non-sinusoidal current from the mains, degrading the power quality by causing harmonic distortion. This thesis proposes a three phase Shunt Hybrid Active Filter (SHAF) topology for harmonic reduction and power factor improvement in low and medium voltage power distribution systems. The proposed SHAF topology interconnects a three phase shunt active filter and tuned passive filters in parallel with the load. For low voltage system 3-arm universal bridge voltage source inverter is used as active filter and in medium voltage system asymmetric cascaded seven level inverter (ACSLI) is used as voltage source inverter. The uniqueness of the proposed topology is the fact that it improves the harmonic filtering performance of a basic shunt active power filter, as well as simultaneously improves the power factor by injecting reactive power at the point of common coupling (PCC). The compensation current reference for the proposed SHAF topology is obtained by using synchronous reference frame theorem. This theorem simplifies the equations for the current reference estimation in d-q co-ordinates thus leading to a more efficient and fast computation. To generate the compensation current that follows the current reference, the hysteresis current control method is adopted for 2-level VSI in low voltage system and constant switching frequency subharmonic pulse width modulation (CSFSHPWM) is used for asymmetric cascaded seven level inverter (ACSLI) in medium voltage power distribution system. Fuzzy logic controller is adopted to maintain constant dc bus voltage at the dc buses of two level inverter and ACSLI. This work describes the design of the proposed SHAF circuit topology which includes shunt active filter (SAF), control strategy of shunt active filter and tuned passive filter (TPF). The system is verified by developing simulation model using MATLAB/Simulink sim