DC-Bus Design with Hybrid Capacitor Bank in Single-Phase PV Inverters

The active or passive decoupling method has to be utilized to deal with the second-order harmonic existing in the DC-bus of the grid-tied single-phase inverters. Compared with the active decoupling method, the passive decoupling method is simpler, cheaper and more reliable. The electrolytic capacitors are usually used in the DC-bus as typical passive decoupling components. The film capacitors can be added in parallel with the electrolytic capacitor to help filtering out the high frequency harmonics to extend the electrolytic capacitors' life. In addition, the LC resonant filter can be utilized for the decoupling purpose to achieve better performance. However due to the relatively low resonant frequency, it results in large inductance which will significantly increase the size and cost of the system. A current sharing method is proposed in this paper. With this method, an inductor with reasonable size can be utilized in the LC resonant filter to further extend the electrolytic capacitors' life. In this paper, the design procedure of the hybrid capacitor bank for the single-phase inverter with unipolar modulation will be discussed. The simulation and experimental results will be provided to verify the design of the hybrid capacitor bank for a 3kW single-phase PV inverter.