Research On Distributed Voltage Equalization Control Strategy For DC Side Of Cascaded H-Bridge Rectifier

Cascaded H-bridge multilevel rectifiers can use low capacity devices to achieve high capacity output without transformers and are easy to modularize.They are widely used in energy storage systems,high-speed railway traction systems,and power electronic transformers.However,due to the inherent losses of each H-bridge module and system stray parameters,the phenomenon of unbalanced DC side voltage may occur.Moreover,as the number of cascaded modules increases in traditional centralized control schemes at this stage,their control algorithms will also become more complex,and the hardware requirements for the central processing unit will become increasingly strict.A distributed voltage balancing control scheme was proposed in this article for cascaded H-bridge multi-level rectifiers to address this phenomenon,which can better compensate for this deficiency.Firstly,the working mode,modulation method,and mathematical model of cascaded H-bridge multilevel rectifier are studied,and the causes of DC side voltage imbalance are analyzed.Based on extensive reading of relevant literature,a new distributed voltage balancing strategy was proposed.In this scheme,the unit modules of the cascaded Hbridge multilevel rectifier are divided into voltage control modules and current control modules,and are controlled separately.The proposed control does not require information interconnection between modules,and the control algorithm is simple,facilitating the development of the system towards high-power and modularization.Finally,the new distributed voltage balance control and the traditional centralized voltage balance control were used to simulate in the cascaded H-bridge multi-level rectifier,achieving DC side voltage balance control and unit power factor operation.The proposed control was also used to simulate in the cascaded H-bridge SVG,achieved the function of system power factor correction.Based on the above analysis,an experimental platform of three module cascaded Hbridge multilevel rectifier is established and experimental research is carried out.Experimental results demonstrate the effectiveness of the proposed control scheme.