A Start-up Optimization Control Strategy For Electronic Power Transformer

In recent years,as one of the key technologies of smart grid,the topology structure,control strategy and operation mode of electronic power transformer has been widely studied by a large number of domestic and foreign scholars.The electronic power transformer is composed of a large number of power electronic converters,so hard-start directly will produce large inrush current at the start moment,not only damage the precision power electronic devices such as IGBT,the worst case affect the operation of the power system.In this thesis,the basic principle and topology structure of the electronic power transformer will be introduced first,then select a cascade multilevel AC/DC/AC electronic power transformer as the research object and the control strategy of all the links is introduced.And the two power electronic transform links of AC/DC rectifier and DC/DC isolation stage are studied,combined with the basic principle and control strategy of each link,the mechanism of starting inrush current is given.Therefore,a new starting control optimization strategy is proposed for each link.In view of the overall start of the electronic power transformer,based on the new starting control optimization strategy of the each link,the scheme of step by step start up of the transformation units at all levels is proposed.the simulation results verify the correctness and feasibility of all the starting control optimization strategy.In order to make the electronic power transformer has a certain ability of self reset when the power grid transient fault condition,optimization of the existing protection system,a restarting strategy for transient faults on the power grid side is proposed.This strategy can not jump gate in the circuit breaker under the condition of complete restart and return to normal steady state operation the state,according to the different grid side fault conditions(short-time power down,various symmetric and asymmetric short-circuit)verified the restart strategy,the simulation results prove the feasibility of the program.