Implementation of a Novel Control Strategy for Shunt Active Filter M. GHANDCHI 1 , A. AJAMI 2 Electrical & Computer Engineering Faculty Islamic Azad University_ Ahar Branch I.R. IRAN Abstract: - Use of nonlinear loads, such as thyristor controlled inductors for FACTs devices, converters for HVDC transmission and large adjustable speed motor drives, is expected to grow rapidly. All of these loads inject harmonic currents and reactive power into the power system. This paper presents a new control scheme for a 3 phase parallel active filter. The presented control system is able to compensating current harmonics, reactive power and current unbalance of non linear loads. The conventional controllers based on pq theory need more calculations, since they need the use of Clark transformation (abc to αβ transformation). The proposed control system is very simple and therefore practical implementation of active filters is available. The presented simulation and experimental results show the validity of control strategy. In this paper the PSCAD/EMTDC program and LAB VIEW software are used for simulation and hardware implementation, respectively. Key-Words: - Shunt Active Filter, Harmonic Compensation, Power Factor Correction, Lab View Soft ware. 1 Introduction In power systems, thyristor controlled inductors for static VAR compensators, converters for high voltage DC transmission line, large adjustable speed motor drivers and a variety of nonlinear loads are used widely in industrial plants. These devices are major sources of current harmonics and low power factor in power system. Conventionally, passive filters were the choice for the elimination of harmonics and to improve power factor. These passive filters have the disadvantages such as large size, resonance and fixed compensation. Active filters avoid the disadvantages of passive filters by utilizing a switch mode power electronic converter to supply harmonic currents equal to those in the load currents [1-3]. Almost, all controllers developed by other authors, for active filters use the pq theory [4, 5]. The major disadvantages of active filter controllers based on pq theory are: 1. These need to low pass filters to separate the average and oscillating parts of instantaneous powers. This factor introduces time delays and therefore, the dynamic performance of active filter is not guaranteed. 2. These demand more calculation, since they need the use of Clark transformation, and are not suitable for hard ware implementation. This paper presents a simple control scheme for shunt active filter. In active filter the main object is to maintain sinusoidal and unity power factor supply currents. The simulation and experimental results, carried out by PSCAD/EMTDC [6] and LAB VIEW [7] soft wares respectively, show effective and validity of presented control system. The steady state and transient performance of the proposed control scheme is found quite satisfactory to eliminate the harmonics, unbalances and reactive power components from source currents. 2 Basic Configuration of Active Filter The basic configuration of shunt active filter is shown in Fig.1. The AF is composed of a standard 3-phase voltage source inverter bridge with a DC link capacitor to provide a effective current control. The shunt active filter generates the compensating currents ica, icb, icc to compensate the load currents ia, ib, ic in order to guarantee sinusoidal, balanced, compensated currents isa, isb, isc drawn from the AC system. For the 3- phase ungrounded system only two current sensors could be used, since ic=-ia- ib. The non linear load is combination of RL load supplied by 3-phase controlled rectifier and a 3- phase unbalanced RL load. 3 Proposed Control System The presented control system of shunt active filter is concise and requires less computational efforts than 7th WSEAS Int. Conf. on MATHEMATICAL METHODS and COMPUTATIONAL TECHNIQUES IN ELECTRICAL ENGINEERING, Sofia, 27-29/10/05 (pp249-254)