Reaserch On Voltage Balance And Circulating Current Elimination Of Interleaving Paralleled Three-level Converters With Reverse Blocking IGBTs

Over the recent decades,new opportunities have emerged due to the boom of the rapid development renewable energy.Moreover,converters as the key part of the power transfer system,are necessary of the system's stability and safety,and have gained academic and industrial attention.On the one hand,Three-Level Converters with RB-IGBTs are considered as having low THD,low switching loss high power factor,high level of withstand voltage and easy modular integration.On the other hand,interleaving parrelled system has strong flexibility and expansibility,so that it has become the research focus.Based on the background above,the paper conducted the study on multi-device interleaving(Common DC Bus and AC Bus)parrelled converters system with RB-IGBTs.Firstly,the paper has studied on the topology structure of Three-Level Converters with RB-IGBTs,and then analyzed its ciucuit.Eight working states and output voltage within one fundamental frequency period have been described in detail.Then,the paper has founded the model of the circuit of Three-Level Converters with RB-IGBTs under three different coordinate system:abc-coordinate,??-coordinate and dq0-coordinate.Aimed at the model under dq-coordinate,the paper has studied on the grid-connect strategy of the converters,and analyzed the three-phase-locked loop and the current loop control.Secondly,the paper has introduced the SVPWM modulation strategy,explained the reason of unbanlanced votage on DC side.Then the paper proposed a control strategy of neutral point voltage balance control method,which is based on modulation of redundant small vectors action time by using SVPWM.This method can be expanded to multi-device interleaving paralleled converters system with RB-IGBTs.Moreover,the control methods of the non-common neutral line and common neutral line structure have been analyzed.Compared with each other,the common neutral line structure is more suitable for the interleaving parrelled converters system.Thirdly,the paper has analyzed 9 paralleled circuits of multi-device interleaving parrelled converters system with RB-IGBTs.Then the generation,mathematic model establishment and classification of ciuculating current has been described in detail.According to the analysis,for Three-Level Converters with LCL filter and current loop grid-connected controller,the high-frequency zero-sequence circulating current could be efficiently reduced,so that the low-frequency zero-sequence would become the main component of the circulating current.The paper has proposed an elimination method of low-frequency zero-sequence circulating current based on PR controller.At the end of this chapter,an overall control strategy of the neutral point voltage balance control and zero-sequence current elimination is proposed.Every Three-Level Converter is controlled seperataly for more accuracy.At last,the paper has established simulation model in MATLAB/SIMULINK software.The grid-connected control strategy,the SVPWM modulation,the neutral point voltage balance control strategy and elimination method of zero-sequence circulating current of Interleaving Paralleled have been analyzed through the simulation.Three-Level Converters with RB-IGBTs have been verified the viability of the proposed strategy.