Control Strategies, Robustness Analysis, Digital Simulation and Practical Implementation for a Hybrid APF with a Resonant Ac-link

This paper proposes a novel hybrid active power filter (HAPF) topology based on the cascaded connection of the AC-side capacitor and the third-order LCL-filter, which has the advantage of the conventional hybrid filter and the LCL-filter in terms of reduced dclink voltage and better switching ripple attenuation. The robust deadbeat control law is derived for the current loop, with special emphasis on robustness analysis. The stability and robustness analysis under parameter variations are presented for the converter-side current tracking scheme and the grid-side current tracking scheme. It is found that the stability margins obtained from the converter-side current tracking control scheme are generally higher than those obtained from the grid-side current tracking scheme. However, the converter-side current tracking scheme is sensitive to the variation of the damping resistance, and it would impose additional parameter uncertainty on the control system and complicate the problem. Hence the grid-side current tracking scheme is implemented. The simulation results obtained from Matlab/Simulink are presented for verification, where the inductance variation and grid disturbance scenarios are also taken into consideration. The effectiveness of the proposed hybrid APF is substantially confirmed by the simulation and experimental results.