Research On Hybrid Energy Storage System Based On Cascaded Multilevel Converters

Asymmetrical cascaded multilevel converter,because of its simple structure,high power quality and enhanced output voltage,is a promising topology for hybrid energy storage system.However,in the existing modulation method based on the hybrid energy storage system,it is challenging to control the power distribution between different cascaded H-bridges with use different energy storage components as dc sources.In this paper,two novel control methods,odd-harmonic-hybrid modulation techniques and feed-forward-space-vector modulation technique are proposed for hybrid energy storage systems based on asymmetrical cascaded multilevel converters.For the odd-harmonic-hybrid modulation technology,on the basis of the traditional asymmetric cascaded multilevel hybrid energy storage system topology,an LC branch is incorporated at the end of the cascaded H-bridge as a tuned filter.Control of harmonic frequency components through the LC branch through odd harmonic mixing modulation enables power exchange between different energy storage elements.The principle of the odd-harmonic-hybrid modulation technique and the design of the LC branch are analyzed.Based on the proposed topology and modulation method,the energy recovery and SOC equalization control system are introduced.Feed-forward-space-vector modulation technique is used to distribute active power between a battery and a super capacitor.Through the proposed voltage feedforward mechanism,the hybrid energy storage system can operate flexibly under normal operation mode,high power output mode and reverse absorption power mode,and analyzes the principle and effectiveness of one-dimensional feedforward space vector modulation technology.At the same time,the SOC equilibrium control mechanism was introduced.Both modulation techniques are verified by MATLAB/ Simulink simulation,and a hybrid energy storage system experimental platform based on asymmetric cascaded multilevel converters is also built.Simulation and experimental results verify the effectiveness of the proposed modulation technology.