With the growing demand for distributed generation from renewable energy sources, many utility grid management problems have emerged (RES). It makes sense to solve these problems with a microgrid. A dedicated energy storage system could facilitate the integration of RES into the microgrid by reducing the unpredictable behaviour of the resource, improving the quality of the power, and performing other functions such as voltage and frequency regulation. Due to technological limitations, hybrid energy storage systems are often needed (HESS). The second-order sliding-mode controller presented in this paper uses a 4-Leg 3L NPC inverter as the only interface between RES /HESS and the microgrid to control the power flow of a HESS. A 3D space vector modulation and sequence decomposition based ac control allows the inverter to operate with unbalanced loads while maintaining a balanced ac voltage at the point of common coupling. This study focuses on the DC current harmonics and discusses unbalanced loads, sliding NPC mean voltage, and power sharing limits. The proposed HESS power flow control method is shown to outperform a conventional PI control scheme by using an experimental 4-Leg 3L NPC prototype on a test bench.
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