Hybrid cascaded multilevel inverter with supercapacitor energy storage for grid integration of renewable energy systems

Short-term power exchange using supercapacitors is actively pursued in the renewable energy sector. The most common approach taken in integrating supercapacitors into the power conversion system is the connection to the dc-link of the grid connecting inverter through an interfacing dc-dc converter which introduces additional power losses. Therefore, this paper proposes to use the grid-side inverter itself as the interface for supercapacitors and thereby eliminate the need of an additional converter. The inverter used in this study is the well-known hybrid cascaded multilevel inverter which consists of a two-level inverter and three series-connected H-bridge modules. In the proposed system three supercapacitor banks are directly connected to dc-links of H-bridge modules. The supercapacitor charging/discharging method used in the proposed system, corresponding control strategies and the supercapacitor sizing method used to estimate the required capacity are presented in this paper. Simulation results and a power loss analysis are also presented to show the efficacy of the proposed system.