International Journal of Engineering Research and Development eISSN : 2278-067X, pISSN : 2278-800X, www.ijerd.com Volume 2, Issue 4 (July 2012), PP. 01-10 1 Comparison between Two Types of Current Control Techniques Applied to Shunt Active Power Filters and Development of a Novel Fuzzy Logic Controller to Improve SAPF Performance Ipsita Sahu 1 , D.A.Gadanayak 2 1 M.Tech Student, Electrical Department, The Techno School, BPUT, Bhubaneswar, Orissa, India 2 Asst.Professor, EEE Department,Institute of Technical Education & Research, SOA University, Bhubaneswar, Orissa, India Abstract— In this paper two types of current control techniques, namely, direct and indirect current control techniques are employed to a three phase shunt active power filter for the compensation of the harmonics in the current caused by the non-linear loads. The difference between these two types of current control technique is in the number of current sensors used. In direct current control technique both load and filter currents are sensed whereas indirect current control technique is based up on sensing source side current only. For both the schemes a simple PI-controller is used to obtain reference current templates. Also, a novel fuzzy logic based controller is developed to replace the conventional PI- controller. The advantages of fuzzy controllers over conventional controllers are that they do not require an accurate mathematical model, they can work with imprecise inputs, can handle non-linearity and they are more robust. Various simulations are presented for direct and indirect current control techniques along with PI-controller and Fuzzy Logic Controller under both steady state and transient conditions. Keywords— shunt active power filter, harmonics, direct current control technique, indirect current control technique, fuzzy logic controller, dc-link voltage List of Symbols   ∗ ,   ∗ ,   ∗ Three phase reference source currents   ,   ,   () Instantaneous value of source, load and filter current   ,   () Instantaneous and peak value of source voltage   ,   Source resistance and inductance   ,   Filter resistance and inductance   ,   Peak value of reference current and loss current   ,   Actual and reference value of DC capacitor voltage   () Instantaneous load power   ,   ,  ℎ () Instantaneous fundamental(real), reactive and harmonic power cos  1 Displacement factor I. INTRODUCTION Power electronics based non-linear loads are increasing in a never before rapid rate both in industry and domestic application. Power electronics based converters are increasingly used in industrial applications such as adjustable speed drives, furnaces etc. HVDC transmission systems and renewable electric power generation systems also use power electronics based instruments. Use of power electronics based home appliance like TV set, personal computers are also growing rapidly. These loads are known as generators of current harmonics and tend to distort the supply current. They are also responsible for low system efficiency, poor power factor, disturbance to other consumers and interference in nearby communication networks. Conventionally shunt passive filters consisting of LC filter have been used for suppression of harmonics. But, passive filters have many disadvantages such as resonance with source impedance, larger size and weight. The concept of using active power filters in order to compensate harmonic currents and reactive power of the locally connected non-linear loads has been so far investigated and shown to be viable solution for power quality improvement [1,2]. APFs, may be classified into pure active filters and hybrid active filters [4,5]. Hybrid APFs are primarily used for harmonic mitigation. Fast switching, low power loss power electronic devices and fast digital signal processing devices available at an affordable cost, it is feasible to embed a variety of functions into a pure APF to make it a power quality conditioner [9]. APF eliminates system harmonics by injecting a current to the system that is equal to the load harmonic current. Since the load harmonics to be compensated may be very complex and changing rapidly and randomly. APF has to respond quickly and work with very high control accuracy in current tracking [3]. Two types of current control techniques, namely, direct and indirect current control have been discussed in [6,7]. The difference between these two types of current control technique is in the number of current sensors used. In direct current control technique both load and filter currents are sensed whereas indirect current control technique is based up on sensing source side current only. For both the schemes a simple PI- controller is used to obtain reference current templates. However, the design of PI controller requires precise linear mathematical model of the system which is difficult to obtain and may not give satisfactory performance under parameter