Modular Voltage Equalizer Circuit With AC-Bus Inter-Modules Connection

A modular multilayer voltage equalizer with a distributed controller is proposed to equalize the voltage of series-connected energy storage cells. In the cell-level equalizer, every two cells are connected in series through a module, and in the module-level equalizer, all modules are connected through the ac bus established with the transformer’s secondary side windings. As the module-level equalizer topology is an ac fully coupled structure, based on the proposed controller method, all cells can transfer or receive energy in a switching cycle simultaneously. The implemented distributed controller requires only one voltage sensor per two cells, and each module benefits from using only one switch without the need for current feedback. Therefore, this method has fewer components than the existing methods with similar features and prevents increasing component rates, as the number of battery cells increases. The proposed circuit is comprehensively analyzed, and its feasibility is verified by experimental results.