DESIGN AND IMPLEMENTATION OF A SINGLE-PHASE 3-WIRE TRANSFORMERLESS BATTERY ENERGY-STORAGE SYSTEM

This paper, presents a single-phase three-wire (1phi3w) transformerles s battery energy storage system (BESS). Its power circuit is simple, s ince it consists of only one converter. It has three legs to provide 1 phi3w 220/110 V output without use of a transformer. For switching con trol, the BESS is decoupled into differential-mode and common-mode sub systems. Each subsystem has its own inner-loop current-forced switchin g control mechanism; their current commands at various operating modes are generated by outer-loop controllers. The controllers of the diffe rential mode are designed to control the main voltage (220 V) source, while achieving the desired functions of BESS. As to the common-mode s ubsystem, its controllers are used to maintain the voltage balance of two subcircuits (110 V circuits) when the utility grid fails, and to k eep the current in neutral line of utility grid at zero when the utili ty grid is in normal condition. The operation principle of the propose d BESS and the design of controllers in various operating modes are de scribed in detail. Some experimental results are provided to show the performance of the proposed BESS.