Series active filter based resonance damping of high power three-phase, LCL filtered, grid connected voltage source inverters

Abstract

A series active filter (SAF) based method for the damping of resonant harmonics created by the LCL-filter of the grid connected PWM-VSI is proposed. Oscillations in multi-megawatt rated high power inverters with LCL-filters are damped with resistors which create undesired power losses typically up to 1% of the rated power of the system. The method stated in this paper overcomes the stability/oscillation problem while providing a solution to the resistive power loss. The proposed SAF compensated system performs satisfactorily under rated load conditions and the transition from passive damping to SAF is flawless. Adaptability of the proposed method to dynamic loads is also advantageous as opposed to passive damping methods. Simplified circuit diagrams and schematics are provided through the paper. Mathematical model of the passively damped filter is compared and contrasted with the SAF compensated system. The validity of the proposed method is proven via simulations.