Improved Selective Frequency Active Damping for Voltage Source Inverter With Output LC Filter

Stand-alone applications employ voltage source inverter with output LC filter to provide a high-quality ac supply at load terminals. These typically use filter inductor current as feedback to actively damp the LC resonance. But it also magnifies the output impedance of the inverter and, thus, deteriorates the output voltage quality under nonlinear load conditions. Existing literature also reports a selective frequency active damping (SFAD) scheme, using the filter inductor current feedback, to overcome the drawback of the conventional active damping scheme. It effectively localizes the effect of the damping loop around resonance frequency only, hence the output impedance for rest of the frequency region remains unaffected. This article comprehensively examines the performance of the existing SFAD algorithm. It is analytically shown that the damping performance of digitally realized SFAD is adversely affected by digital delays. Then, an improved design is proposed for SFAD, which results in extra phase-lead around the resonance frequency to compensate for the digital delays. Finally, the proposed improvement is experimentally demonstrated to provide a better transient and steady-state performance.