www.tjprc.org editor@tjprc.org International Journal of Electrical and Electronics Engineering Research (IJEEER) ISSN(P): 2250-155X; ISSN(E): 2278-943X Vol. 4, Issue 2, Apr 2014, 211-222 © TJPRC Pvt. Ltd. POWER QUALITY IMPROVEMENT USING FUZZY LOGIC CONTROLLER BASED CMLI AND FACT DEVICES FOR MODERN POWER SYSTEMS M. KAVITHA 1 , A. SREEKANTH REDDY 2 & D. MOHAN REDDY 3 1 M. Tech Student, Department of Computational Engineering, RGUKT, RK Valley, Kadapa, Andhra Pradesh, India 2 Lecturer, Department of EEE, RGUKT, RK Valley, Kadapa, Andhra Pradesh, India 3 HOD & Associate Professor, Department of EEE, SVIET, Pedana, Krishna, Andhra Pradesh, India ABSTRACT Modern power systems are highly complex and are designed as such to fulfil the growing demands of power with better power quality. And electrical power quality had obtained more attention in power engineering in recent years. But due to faults in power systems many power quality problems including voltage sags and swells, harmonics and reactive power burden etc,. are taking place which are effecting the power quality and stability of power supply etc,. The fuzzy logic controller can easily demonstrate a better dynamic behaviour of the system. The CMLI and FACT devices have the capability to reduce the power quality problems. Therefore, the fuzzy logic controller based CMLI and FACT devices improve the power quality by considerably reducing THD as prescribed by IEEE-519 standard. This paper presents MATLAB/SIMULINK circuits of fuzzy logic controller based CMLI and FACT devices which can improves the power quality for modern power systems. KEYWORDS: Power Quality, Power Quality Problems, Fuzzy Logic Controller, CMLI, FACT Device and PWM Technique INTRODUCTION The power quality problems include high reactive power burden, harmonics currents, load unbalance, excessive neutral current etc. Electrical Power Quality had obtained more attention in power engineering in recent years. Traditionally, current harmonics caused by non-linear loads have been dealt with using passive filters. They provide simple solutions but, very often, have large size and weight, they cannot provide flexible compensation. Moreover, the passive filters are known to cause resonance, thus affecting the stability of the power distribution systems [1]. The increased severity of harmonic pollution in power networks has attracted the attention of power electronics and power system engineers to develop dynamic and adjustable solutions to the power quality problems. Now-a-days due to usage of many non-linear loads and other faults like L-G, L-L and etc,. The power quality is affecting more. This paper deals with many technologies which are collectively improving the power quality. Due to occurring of faults in power systems the stability of the voltage get distorted which is commonly called voltage instability. Voltage instability is the inability of the power system to meet the demand for reactive power in the heavily loaded system. One of the most important causes of voltage instability in a system is the occurrence of reactive power imbalance in the system. Reactive power imbalance occurs when system is faulted, heavily loaded and voltage fluctuation is there. This problem can be effectively tackled by the introduction of high power electronic controllers which can inject or absorb reactive power as per system requirement. One of the most important reactive power sources is FACTS (Flexible A. C