Research On Active Equalization Circuit Of Series Connected Energy Storage System Based On Voltage Multiplier

For large-scale series connected energy storage systems,two of the representative voltage equalization technologies and architectures are cell to cell and module to cell balancing.The cell to cell balancing architecture usually uses a bidirectional converter(buck-boost converter)or switching capacitors.The circuit is complicated and the energy effiency is relatively low since the power transmission is only conducted between adjacent cells.In the module to cell architecture the energy of the entire module is transferred directly to the smallest charging cell with the lowest voltage,but the number of switches required is proportional to the number of cells and a complex control system is needed.While the use of multi-winding transformers will result in design and manufacturing difficulties due to strict parameter matching of the secondary windings.This thesis mainly studies the active equalization circuit based on voltage multiplier.Because of its own characteristics of the voltage multiplier,the AC voltage input is equivalently converted to independent DC voltage outputs of each branch,only at least one switch is needed to achieve module to cell active balancing.So its circuit is simple and easy to control.And when combined with bidirectional converter circuit(such as the synchronous rectifier),we do not even need to add additional switches,making the circuit complexity,control difficulty and hardwere cost are further reduced.The key to active equalization with a voltage multiplier is to control the generation of an AC input voltage source.First of all,for the application of smaller convertion ratio,we use a non-isolated SEPIC circuit.Because only one switch and no transformer is used,the circuit is simple,low cost and easy to control.Secondly,for large convertion ratio and multi-module applications,we used an isolated half-bridge inverter.In addition,in order to share the switch with the synchronous rectifier converter,we use a series resonant inverter to form the so-called integrated equalization circuit.Finally,using the integrated equalization circuit and its DC equivalent circuit,we discuss the multi-module battery management strategy of largescale battery system.The the superiority of the integrated equalization circuit is proved through simulation analysis,that is,with module voltage control the cell voltage balancing can be achieved automatically.