978-1-4244-2800-7/09/$25.00 ©2009 IEEE ICIEA 2009 Voltage Flicker Compensation using STATCOM Mahmood Joorabian 1 1. Shahid Chamran University of Ahvaz, Ahvaz, Iran mjoorabian@scu.ac.ir Davar Mirabbasi 2 Alireza Sina 3 2. Shahid Chamran University of Ahvaz, Ahvaz, Iran 3. Academic center for education, culture & research Abstract— Voltage flicker is considered as one of the most severe power quality problems (especially in loads like electrical arc furnaces) and much attention has been paid to it lately. Due to the latest achievements in the semiconductors industry and consequently the emergence of the compensators based on voltage source converters, FACTS devices have been gradually noticed to be used for voltage flicker compensation. This paper covers the contrasting approaches; dealing with the voltage flicker mitigation in three stages and assessing the related results in details. Initially, the voltage flicker mitigation, using FCTCR (Fixed Capacitor Thyristor Controlled Reactor), was simulated. Secondly, the compensation for the Static Synchronous Compensator (STATCOM) has been performed. In this case, injection of harmonics into the system caused some problems which were later overcome by using 12-pulse assignment of SATCOM and RLC filters. The obtained results show that STATCOM is very efficient and effective for the flicker compensation. All the simulations have been performed on the MATLAB Software. Index Terms Power Quality, Voltage Flicker, Static Synchronous Compensator (STATCOM) I. INTRODUCTION The relationship between power quality and distribution system has been a subject of interest for several years. The concept of power quality describes the quality of the supplier voltage in relation to the transient breaks, falling voltage, harmonics and voltage flicker [1]. Voltage Flicker is the disturbance of lightning induced by voltage fluctuations. Very small variations are enough to induce lightning disturbance for human eye for a standard 230V, 60W coiled-coil filament lamp. The disturbance becomes perceptible for voltage variation frequency of 10 Hz and relative magnitude of 0.26% [1-2]. Huge non-linear industrial loads such as the electrical arc furnaces [3-4], pumps, welding machines, rolling mills and others are known as flicker generators. In this respect, the quality of supplied voltage is significantly reduced in an electrical power system and the oscillation of supplied voltage appears to be a major problem. Electric arc furnace, the main generator of voltage flicker, behaves in the form of a constant reactance and a variable resistance. The transformer-reactance system is modeled as a lumped reactance, a furnace reactance (included connection cables and busses) and a variable resistance [5] which models the arc. Connecting this type of load to the network produces voltage variation at the common point of supply to other consumers. The relative voltage drop is expressed by equation (1): 2 n n U Q X P R U U Δ + Δ = Δ (1) where ΔP and ΔQ are the variation in active and reactive power; U n is the nominal voltage and R and X are short circuit resistance and reactance. Since R is usually very small in comparison to X, ΔU is proportional to Q (reactive power). Therefore, voltage flicker mitigation depends on reactive power control [5]. Two types of structures can be used for the compensation of the reactive power fluctuations that cause the voltage drop: A: shunt structure [1, 5-14]: in this type of compensation, the reactive power consumed by the compensator is kept constant at a sufficient value. B: series structure [15-16]: in this type, all the efforts are done to decrease the voltage drop mentioned above, and finally the reactive power is kept constant despite the load fluctuations by controlling the line reactance. In addition to the aforesaid procedures for the compensators, the active filters are used for the voltage flickers mitigation as well [17]. Furthermore, the mitigating devices based on Static VAR Compensator (SVC) such as Thyristor Switched Capacitor TSC [18], Thyristor Controlled Reactor (TCR) [19], and FCTCR [20], are the most frequently used devices for reduction in the voltage flicking. SVC devices achieved an acceptable level of mitigation, but because of their complicated control algorithms, they have problems such as injecting a large amount of current harmonics to the system and causing spikes in voltage waveforms. Advent of FACTS devices make them ideal for use in a power system and especially in the voltage flicker mitigation. In this respect, the FACTS devices based on voltage-source converters have been able to improve the problems related to SVC [5]. A new technique based on a novel control algorithm, which extracts the voltage disturbance to suppress the voltage flicker, is presented in this paper. The technique is to use 2273