Control strategy of double-stage cascaded multilevel converters energy storage system

Abstract

Energy storage technology is the key technology to building a new power system with new energy as the main body and an important guarantee to maintain the reliable and stable operation of microgrids. Existing theoretical research and projects at home and abroad are mainly concentrated on single-level cascaded energy storage systems. The power module and battery system are connected with passive devices. The structure is simple without enough control degrees of freedom. In the meantime, aiming at an unbalanced state of charge (SOC) of the battery in cascaded energy storage, the existing intra-phase SOC balance control strategy has disadvantages such as poor adaptability to different load ratesand possible over-modulation in case of extreme imbalance. Based on the double-stage cascaded energy storage system, its overall control strategy and the inter-phase and intra-phase SOC balance strategies are illustrated in this paper. An adaptive intra-phase state of charge balance strategy is proposed and its design principle of the balanced control parameters is explained in detail. The adaptability and balance effect of the cascaded energy storage system under different working conditions such as light loads and heavy loads are improved effectively. Finally, the feasibility and effectiveness of the proposed control strategy are verified by simulation, thus providing theoretical reserves and technical support for project implementation.

Keywords

• cascaded multilevel converters
• cascaded energy storage
• state of charge (soc)
• load rates
• balance control
• double-stage cascaded energy storage system