Active power filter for the cancellation of harmonic line current distortion

Graduation date: 2001With the increased attention on high efficiency and energy savings, power electronic\ud energy conversion equipment is increasingly incorporated in all levels of the power system.\ud The drawback of such equipment is the generation of nonsinusoidal currents in the power\ud distribution network due to the nonlinear operation. Harmonic currents may distort\ud the line voltages and lead to several unwanted effects including equipment overheating,\ud system failure, interference with communication systems, etc.\ud In response to these concerns, this research presents an active filter for the cancellation\ud of harmonic line current distortion. The active filter used in this research is\ud connected in parallel with the nonlinear load and is designed for a three-phase three-wire\ud industrial power system. The filter consists of a voltage source inverter connected\ud through a coupling inductor to the terminals of the ac-source. The inverter is controlled\ud via a space vector-pulse width modulation (SVPWM) algorithm that is generated using\ud a digital signal processor (DSP). In order to reduce the distortion resulting from the\ud switching nature of the active filter inverter, a switching ripple filter is connected in\ud parallel.\ud The control algorithm of the active filter is based on the rotating reference frame\ud theory. For each harmonic which is to be cancelled, a corresponding synchronous reference\ud frame is generated to extract the harmonic phase and magnitude. With this\ud information, each harmonic current component can be separately controlled and the\ud proposed algorithm can therefore compensate for hardware effects such as measuring delays and component transfer functions. For the extraction of the harmonic components,\ud a finite impulse response filter is used in order to quickly react to changing load currents.\ud An adapting algorithm is implemented to compensate for slowly varying system\ud parameters.\ud Simulations under varying load and transient conditions are performed. The results\ud show nearly perfect cancellation performance for the proposed active filter control\ud algorithm