A New Method for Power Factor Correction and Harmonic Elimination in Power Systems
6
81 0 - A New Method for Power Factor Correction and Harmonic Elimination in Power Systems I. Kasikci, MIEEE, V D E University of Applied Sciences of Mannheim, Germany TeVFax: +49-620 1 I 82301, E-mail: Imail. ~~si~ciiu!rh~iniii~in.~~.inil Abstract : The influence of power electronics-based technology, which is increasingly used, has disadvantageous effect on the qua lity o f electric power supply. Pure sinusoida l voltage supply does not exist anymore. Low and medium voltage power systems are polluted to an increasing extent by harmonic currents and voltages, voltage fluctuation, voltage unbalance, voltage sags, volta ge sw ells and flicker T his paper present s an ne w configura tion for power factor correction and harmonic current elimination in electrical power systems. A single-phase control conce pt is discussed for simplicity. It also presents a brief discussion of the main problems in the distribution power systems. Keywords: Reactive power comp ensation, Harmonics , Active Filters, Control , EM1 I. INTRODUCTION The increased use of non-linear devices cause voltage distortion in the network. This leads to malfunctions of the electric facilities and to costly interruptions of production. The filter circuit parameters are analysed and described. This filter configuration provides an alternative approach to the existing one. According to the test results, the proposed approach can achieve a complete elimination of harmonics. The switched-capacitor active filter was first presented in 1982 by C.C. Marouch os [ I ] an d i s fundamentally different fiom the inverter configuration. The switched- capacitor configuration removes the requirement for a large current or voltage source, which leads, not only to a reduction in cost but also in physical size [2,3]. Another configuration of shunt active filter was developed in [4]. The major drawback of these circuit is that the control algorithm is very complicated, time consuming and produces itself resonances. As described in [5] a sampling contro l is used and a load is applied to the inverter which requires only the control of the fundamental current for power factor correction. In this paper, it i s shown that the circuit is capable of correcting not only the power factor of the fundamentals but also of eliminating the harmonics and ver easy to control. In recent years the proliferation of non-linear loads has lead to the development of active filters designed to eliminate current harmonics from the power supply network. 0- 78C3- 49!?-6:00:$18. O C 20901 E E E This paper examines shunt active filter inverter and passive filter, highlighting th e com plexity of the control. Two different approaches are investigated, with the aim of reducing the computational requirements associated with the control technique and hence increase the applicability of the proposed system. A significant simplification is presented which eases the somewhat laborious, but never the less unavoidable computational requirements. A new control unit is also developed providing an alternative to the dominated computer controlled very complicated techniques. The main characteristics of a non-linear supply are the voltage interruptions, harmonic pre-distortions and unbalance in the three phase systems. On the other side, the main characteristics of a non-linear loads are the harmonics, hndamental reactive current, unsymmetrical parts and the stochastic fluctuations called flicker. There is a strong coupling between reactive power balance and of a power system and the voltages. Today, many techniques are used to compensate the reactive power. Shunt and series compensation is widely used in the industry. Two possible loads can be discussed in this point of view. The non-linear supply voltage which influences the loads behaviour and non-linear loads which cause voltage distortions in other supply feedings. Fig.1 represents the proposed active power filter configuration. The proposed new control block diagram shows nine main sections constituting the power active filter structure. The harmonic current generated by non- linear load is detected and fed back to the reference current estimator, in conjunction with the other system variables. The resulting reference signal drives the overall system controller, which, in turn, generates the control effort necessary fo r the switching pattern. The resulting filter current is also detected and fed back to the controller. The power and filter circuit is then connected to the PCC. Shunt active filter is connected to the main power circuit as shown in the single-line diagram of Fig.2. I t is mainly aimed towards cancelling the load current harmonic as it has the ability of controlling the amount of current flowing in the circuit. It can also contribute to reactive power compensation and balancing of three-phase currents, transients and flicker.
