This paper presents the benchmark study of ac and dc active power decoupling (APD) circuits for the second-order harmonic mitigation in kilowatt-scale single-phase inverters. First, a brief comparison of recently reported APD circuits is given, the best solution that can achieve high efficiency and high-power density is identified and comprehensively studied, and the commercially available film capacitors, the circuit topologies, and the control strategies adopted for APD are all considered. Then, an adaptive decoupling voltage control method is proposed to further improve the performance of dc decoupling in terms of efficiency and reliability. The feasibility and superiority of the identified solution for APD together with the proposed adaptive decoupling voltage control method are finally verified by both the simulation and experimental results obtained on a 2-kW single-phase inverter.@en