Power Quality Enhancement Employing A Novel Variable Frequency Drive Regulated Harmonic Mitigation Technique

This paper presents a novel approach to replace the dedicated grid resource i.e. active power filters (APF) with variable frequency drives (VFD) for power quality enhancement in AC power networks. Non-linear loads, based on power electronic (PE) devices, generate harmonics in source current resulting in overheating of transmission wires, degradation of electrical equipment, and energy losses. Active power filters being a dedicated resource for harmonic compensation, mitigate harmonics by injecting compensating currents which are equal in magnitude and opposite in phase to the harmonic currents caused by non-linear loads. However, a VFD being an existing resource of motor driven systems can be utilized for harmonic compensation, instead of APF, as an ancillary service provider in AC distribution network. By modifying the control of front-end rectifier section of VFD can enable it for harmonic and reactive power compensation. The control scheme of VFD is based on vector controlled method in synchronous reference frame (SRF). In order to extract desired current components from source current for shunt active filtering, instantaneous reactive power (IRP) p-q theory has been employed. Simulations of system before and after the integration of VFD as APF demonstrate that VFD with modified control can compensate harmonics from source current along with effectively controlling the motor dynamics. The use of existing VFDs can therefore, eliminate the need for a dedicated harmonic compensator, resulting in a cost effective, intelligent and autonomous solution for power quality enhancement.