In the modern electrical distribution system, there has been a sudden increase of nonlinear loads, such as power supplies, recti er equipment used in telecommunication networks, domestic appliances, adjustable speed drives, power electronic devices etc. These loads are responsible up to a great extent for deteriorating the efficiency and quality of the power. In this paper a number of different methods, controllers and logics are discussed which are already implemented like hybrid fuzzy logic proportional plus conventional integral derivative (fuzzy P +ID) controller, TakagiSugeno (TS)-type fuzzy logic controller, asymmetrical nine-level active power filter (APF), a novel modular multilevel series/parallel converter, a modulation strategy for n-phase neutral-pointclamped (NPC) converters, a Y-D multifunction balance transformer (YD-MFBT) based power quality control system (MBT-PQCS) and a variable forgetting factor recursive least square (VFFRLS)-based control algorithm. In general it was seen that total harmonic distortion (THD) was appreciably reduced and efficiency of the system was improved. Multilevel-THSeAF eliminates source harmonic currents and improves power quality of the grid without the usual bulky and costly series transformer. APLC/FPIC Spectrum analysis measurements showed that the line voltage typically had a THD of approximately 3%. A comparison between the THD in output of Proportional (P), Proportional plus Integral (PI) and Proportional plus Integral plus Derivative (PID) controllers for different linear as well as non linear loads is further going to be discussed in upcoming work.
