A New Energy Storage System Based On Cascaded Multilevel Converter

To develop wind and solar and other renewable energy sources, reducing greenhouse gas emissions, the construction of environment-friendly country has a very important strategic significance for our national energy security, environmental improvement, economic sustainable development. Meanwhile, the energy storage system has been widespread concern and research because of its flexibility to quickly adjust active/reactive power handling, load fluctuations stabilize and its ability to improve power quality and other advantages. Especially, energy storage systems based on cascade multilevel converters was becoming the research focus of large-capacity storage systems because of its significant advantages of simple structure and easy reconfiguration, high equivalent output voltage, high equivalent switching frequency and output power of a good quality and so on. However, due to the structural characteristics of the energy storage system based on cascade multilevel converters, DC voltage/SOC equalization control of the energy storage system was becoming increasingly important since this important issue related to the running quality of the whole energy storage system.The cascade multilevel converter(CMC) topology is recognized as the most suitable one for battery, supercapacitors and other energy storage systems. Firstly, a comprehensive analysis of the basis for a variety of multi-level modulation strategy has been studied. Then this paper proposes a novel single-phase CMC based battery storage system which includes a LC branch(which defined as auxiliary power loop) and dual-frequency phase-shifted carrier PWM (DF-PSC PWM). Based on the auxiliary power loop and dual-frequency phase-shifted carrier PWM method, this paper introduced an effective regulatory mechanism which could realize active power exchange between different cells. In addition, the paper also discusses design methods of auxiliary power loop and output filter of the system.Both MATLAB/SIMULINK simulation and experiment platform of lkW single-phase battery energy storage system which consist of three H-bridge module with battery energy storage unit were established. The simulation and experimental results verify the DF-PSC PWM and operation principle of the power exchange.