Harmonics Suppression in Distribution Networks composed of Uninterruptible Power Supply Systems

In recent years, utilization of power electronic converters has been drastically increased. These converters act like non-linear loads for utility grid. Such non-linear loads distort the supply current through injection of harmonics. One such example is the uninterruptible power supply (UPS) system, which is a major source of current harmonics. These harmonics affect the performance of distribution transformers in terms of losses, heating of core, stress on insulation and tripping of the protection relays. In this paper, the increase of total harmonic distortion (THD) of the supply current, caused by uncontrolled rectifiers used in UPS systems, has been minimized. Two methods including passive filters (PF) and active filters (AF) have been applied to minimize the THD. The simulations have been performed in MATLAB/Simulink environment where the results of both schemes have been compared under various load conditions (RL and unbalanced load). It has been found that AF provides a better solution as compared to PF for such load conditions.