ANALYSIS, DESIGN AND CONTROL OF DSTATCOM AND ITS APPLICATIONS

Abstract

The widespread use of power electronics based equipment is increasing these days. Poor power quality at power distribution level is attributed to a number of reasons and the increase in power electronics based loads is one of the major causes. These loads are nonlinear in nature and generate harmonic currents which propagate to other connected loads at the point of common coupling (PCC). Some other power quality problems viz. high reactive power demand, voltage regulation, load unbalancing and poor power factor cause concern to the electric utility and consumers of electric power supply. The current related power quality problems include harmonic currents, high reactive power burden, poor voltage regulation and unbalanced loads. A number of power converter based solutions have been developed in the recent past due to the progress in speed and capacity of power semiconductor technology. The group of devices used for power quality improvement in distribution systems is referred to as custom power devices. A specific shunt connected custom power device used for the mitigation of current related power quality problems is widely known as a distribution static compensator (DSTATCOM). An implementation and control of DSTATCOM have become possible due to advancement in digital signal processing (DSP) and self-commutating semiconductor devices. The major components used for design of DSTATCOM include voltage source converter (VSC), interfacing inductors, ripple filters and DSP (Digital Signal Processor). Performance of DSTATCOM mainly depends on the control algorithm used for the estimation of fundamental active and reactive components of reference currents. These reference currents are used for the generation of switching pulses for control of VSC used in DSTATCOM. The control algorithms for DSTATCOM have been divided into four categories in this proposed work. These v include the conventional control algorithms, adaptive theory based control algorithms, recursive theory based control algorithms and artificial intelligence based control algorithms. The conventional control algorithms considered are based on power balance theory (PBT), instantaneous reactive power theory (IRPT), conductance based and instantaneous symmetrical component theory (ISCT). These control algorithms for the control of three-phase DSTATCOM, are used for harmonic currents reduction, reactive power compensation and load balancing in power factor correction (PFC) and voltage regulation modes. These algorithms are extended for voltage regulation operation, which are also required in various isolated power generation systems such as an isolated diesel generator, isolated micro hydro, biogas and biomass based generation systems. The control algorithms developed under adaptive theory are based on Wiener filter, fixed step size least mean square (FSSLMS) along with its variants and variable step size least mean square (VSSLMS). The control algorithms developed under the category of recursive theory are based on variable forgetting factor recursive least square (VFFRLS), recursive inverse (RI) and immune feedback principle. The category of artificial intelligence based algorithms includes adaptive neuro fuzzy inference system (ANFIS), real time recurrent learning (RTRL) and immune feedback based control algorithms. All these control algorithms are developed in MATLAB using SIMULINK and Sim-power system (SPS) tool boxes. Real time performance of these control algorithms for power quality improvement has been extensively tested using simulation studies and experimentally on the prototype of DSTATCOM developed in the laboratory. vi Additionally, the three phase DSTATCOM system is utilized for grid integration of solar photovoltaic (SPV) array. The VSC used in this system serves the purpose of power converter, which is used to transfer power generated from SPV array to the grid along with functions of power quality improvement such as harmonic currents elimination, reactive power compensation and load balancing in PFC and voltage regulation modes under linear and nonlinear loads. The performance of this system is studied with three control algorithms viz. synchronous reference frame theory (SRFT), Wiener filter and recursive inverse based control algorithms.