ETEP zy DSP-Based Implementation of zy an Impmvd Control AlgorithmofaThreePhase ActiveFilter for Compensation of Unbalanced Non-Linear Loadds B. Singh, B. N. Singh, A. Chandra, K. Al-Haddad Abstract zyxwvutsrqp This paper deals with an implementation of a new control algorithmfor a three-phase activefilter (AF)to elimina- te harmonics, compensate reactive power and to balance unbalanced non-linear loads. An insulated-gate-bipolar transistor (1GBT)-based current-controlled pulse-width modulated (P WM) voltage-source inverter (VSI) with a DC-bus capacitor zyxwvuts is used as an AE The reference supply currents are derived in phase with supply voltages using a sliding mode controller (SMC) over DC-bus voltage zyxwvuts of the AE zyxwv A digital signal processor (DSP) is used to imple- ment the control algorithm zyxwvutsrq of the AE An indirect PWM current control over the reference and sensed supply cur- rents is implementedf o r generating the gate signalsf o r IGBT of the AE Test results of the proposed AF are given to demonstrate the harmonic elimination, reactive power compensation and load-balancing capabilities of the AE 1 Introduction Solid state power converting equipment are widely used in a number of applications such as adjustable speed drives (ASD), power supplies, asynchronous AC-DC- AC links in power transmission and power conversion in appliances. These power converters behave as non-line- ar loads on AC mains, which inject harmonics and result in reactive power burden to AC network, Moreover,there is also an unbalancing in some typical loads such as fur- naces, traction etc., which further deteriorate the quality of power supply. Traditionally passive filters are consid- ered as the obvious choice for elimination of harmonics and improving the power factor at AC mains. However, these passive filters have the demerits of fixed compen- sation, large size and resonance. To overcome these drawbacks of passive filters, a device namely active fil- ter (AF) is introduced and number of attempts zyxwvut [ l - 101 have been made on configurations, topologies, and im- proving the performance and design of zyxwvut AF. Many control approaches for AF are reported namely instantaneous reactive power theory [2], notch filters [4], flux-based controller [5], power-balance theory [7 - zyxw 81 and compensa- tion is carried out both in frequency domain and time domain. Most of these control algo- rithms require various transformationsand are difficult to implement. This paper presents a simple control algorithm of the AF, which is capable of harmonic elimination, reactive power compensation and load balancing. The main objective is to maintain unity power-fac- tor supply currents (by shunt AF) to feed only active power to the system. The remaining re- quirements of harmonics, reactive power and balancing of the non-linear load have to be met by the AF locally resulting in it as a linear re- sistive load. The proposed control method of a three-phase AF is implemented on a DSP. An IGBT- based current-controlled PWM-VSI with a DC-bus ca- pacitor is used as an AF. The reference supply currents proportional to supply voltages are derived using a slid- ing mode controller (SMC) on DC-bus voltage resulting in self supporting DC bus of the AF. An indirect current control [9] over the computed and sensed supply currents is implemented to generate gating pulses of the JQBT of the AF. Test results on the developedprototype of the AF are presented and discussed in detail demonstrating its capabilities of harmonic elimination, reactive power compensation and load balancing. 2 System Configuration and Control Scheme Fig. 1 shows a schematic diagram of the shunt AF system. The AF is composed of a standard three-phase IGBT-based VSI bridge with a DC-bus capacitor to ' loads Active filter DC bus Fig. 1. Fundamental building block of the active filter ETEP Vol. 10, No. 1, JanuarylFebruary Zoo0 29