Power Quality Improvement using Unified Power Quality Conditioner

Abstract

Power quality can be defined as any power problem faced in the frequency, current or voltage deviation which leads to mal operation of the customer’s equipment. Mainly the use of power electronics devices that acts as the nonlinear load is responsible for the degradation in the poor power quality. Poor power quality results in various problems in the distribution systems like higher power losses, harmonics, sag and swells in the voltage, poor distortion. The recent developments in communications, digital electronics, and control system have rapidly increased the number of sensitive loads that require ideal sinusoidal supply voltage for their proper operation. So, it became necessary to include some sort of compensation in order to meet limits proposed by standards. Here Unified power quality Conditioner (UPQC) has been used to overcome the power quality problem. UPQC which is a combination of back to back connected series and shunt APFs through a common DC link voltage, the two APFs function differently. The shunt active filter is mainly advantageous in removing the current related problems and the improvement of power factor and regulation of DC link voltage. Whereas the series APF helps in correction of voltage related problems by acting as a controlled voltage source. The voltage that is injected in series with the load by series Active Power filter is made to follow a control law which results in a sinusoidal load voltage that is the sum of the voltage injected by the series inverter and the input voltage. Whereas the shunt APF acts as a current source that injects a compensating harmonic current in order to have sinusoidal, in-phase input current. Several control strategies have been reported in literature that determines the reference values of the voltage and the current. One of them the synchronous reference frame, d-q technique. this method synchronous reference frame method is used for the control of Series APF and is used for the control of shunt APF. UPQC has the capability of compensating the harmonic current, reactive power, voltage imbalance and voltage sag and swell. It also helps in reducing the energy losses that happens in the power systems.