A Study On Energy Storage System Based On Cascade Multilevel Converter

In the field of electric vehicles and renewable energy,in order to accommodate the large load-side power fluctuations,inverters are often required to have a storage function.H-bridge cascaded multilevel inverters have been widely used for the advantages of good output waveform,easy to modularize and easy to achieve higher power output.However,for the H-bridge cascade multilevel inverter traditional control methods are built on the H-bridge DC voltage equal to the premise.In this paper,a multilevel cascaded converter fed with a single dc source has been presented and been used to build an energy storage system.For a single-phase multilevel cascade H-bridge converter,a improved feed-forward space vector modulation method converter can achieve any dc voltage ratio(inside the stable operation area of the converter)between the H-bridge cells.Moreover,it also achieves power flow control of energy storage system.The energy storage system can work in three different operation modes-Normal operation mode,High power output mode and Reverse power absorption mode.In addition,combined with motor control algorithm,the energy storage system(ESS)is applied to motor drives of electric vehicle.Simulink simulation results show that cascaded multilevel converter plays the role of a power buffer between energy storage system and energy sources.With the proposed control strategy,the ESS can work in three different operation modes.Experimental results from a three-cell cascaded converter show that the proposed feed-forward space vector modulation method is feasible and effective to achieve power flow control.