Research On Voltage Balance Control Of Dc Side Of Three-phase Cascade Multilevel H-bridge Rectifier

Power electronic transformers have important application prospects in the process of high-speed trains becoming intelligent,efficient,energy-saving and lightweight.At the same time,they are developing rapidly in smart grids as electrical energy conversion devices.As the input stage of power electronic transformer,the three-phase cascade H-bridge multi-electric flatrunner circuit is the basis for the safe operation of the whole system,but there is a problem of voltage imbalance on the DC side in practice.Traditional voltage balancing schemes mostly use centralized control.The complexity of the balancing control algorithm increases rapidly with the increase of modules.At the same time,the limited port of the processor limits the number of cascaded modules.It is difficult for the system to expand in a modular,high-power direction.In view of this problem,a new type of equilibrium control strategy of quasi-distributed is proposed.The new equilibrium control strategy combines the traditional closed-loop control and modulation ratio correction method,and on the basis of the traditional closed-loop control,the equilibrium control module is added to achieve the equilibrium output of DC side voltage.The equalization control module is simple to control and consists only of a given voltage and the DC voltage of the module.The new voltage balancing strategy adopts quasi-distributed control,the distance between the processor and the main circuit is shortened,the loss of driving and sampling signals is low,and the control is accurate and flexible.At the same time,the complexity of the balancing control algorithm is independent of the number of modules,and the control system is easy to modularize.It is conducive to the expansion of the system to high voltage and high power.In this paper,firstly,the working process and modulation mode of three-phase cascaded H-bridge multilevel rectifier are analyzed,and then its mathematical model is established,and its equalization control principle is analyzed.Then,under the control of the new equalization strategy,the closed-loop simulation of the three-phase cascade H-bridge multilevel rectifier circuit is carried out.The simulation results verify the effectiveness and feasibility of the strategy.Finally,this paper takes DSPTMS320F28335 and FPGA as the digital control system,under the control of the new balanced control strategy,the closed-loop experiment is carried out on the three-phase cascade H-bridge multilevel rectifier circuit.The experimental results show that this strategy can achieve the DC side voltage balanced output and the AC side high power factor operation.