Control Schemes For Bidirectional Power Converter And Its Application In Hybrid AC/DC Microgrid

With the increasing of distributed energy utilization ratio,microgrid,as an effective method integrating distributed energy and load,has received much attention.Meanwhile,Bidirectional power converter has also been widely studied and applied as core of AC/DC hybrid microgrid.Control strategy of bidirectional power converter usually transplanted from the traditional power electronic converter,such as double closed loop,constant power,V/F,etc.Ignoring the characteristics of hybrid ac/dc microgrid,this paper proposed a autonomous operation control schemes for bidirectional power converter in hybrid ac/dc microgrid Which can achieve part of the regional autonomy and modular parallel of bidirectional power converters.Have the advantages of both free of communication and plug-and-play.This paper intensively studies and discusses the autonomous operation strategy based on the low voltage microgrid droop characteristics,zero sequence circulation suppression and key technology of engineering.The main contents are as follows:First,model of bidirectional power converter and double closed-loop control method have been studied.Mathematical model of the bidirectional power converter in different coordinate systems is established.Concerning the features of hybrid AC/DC microgrid,the voltage and current double closed-loop control strategy is designed,and the basis for selection parameters is also given.This control strategy can achieve stability of DC bus voltage,reversal of power flow,and unity power factor.Finally,the proposed control method is verified in Matlab/Simulink.Second,this paper proposed an autonomous operation control schemes for bidirectional power converter.Solve the problems of regional autonomy in low voltage hybrid ac/dc microgrid.By analyzing the power transmission characteristics of low voltage microgrid,Relationship between power balance and bus voltage or frequency has been established,And the connection between the power outer ring and the inner loop is established based on the theoretical derivation analysis,the design of the single module autonomous operation control system is completed,retaining configuration flexibility of the hybrid ac/dc microgrid while improving the operational reliability,which provides the prerequisites for modual design.The simulated results validate the control performances of this strategy.Third,method of zero sequence current suppression and scheme of modular autonomous operation have been studied.This paper establish equivalent model of zero sequence circulation for the multi-bidirectional power converter modules connected in parallel,a zero sequence current suppression method is put forward which solves the problem that current harmonic distortion when bidirectional power converters connect in parallel.Based on the average equivalent model,relationship between zero sequence current and power control bas been analyzed.Combining autonomous operation method the modular autonomous operation control scheme is presented.The hybrid AC/DC microgrid model for multi-bidirectional power converter modules connected in parallel is established in Matlab/Simulink.The circulation inhibition effect is verified by simulations.The autonomous operation control scheme improve the performance of zero sequence circulating current restraint,Reduce the current waveform distortion,Implements modular extensions of bidirectional power converters.Fourth,the prototype of autonomous operation strategy based bidirectional power converter is implemented.This paper studies the key techniques for the prototype: hardware parameter,control circuit and software control system.Finally,a low-voltage AC/DC hybrid microgrid experimental platform is built on the basis of the prototype,and the control strategy proposed in this paper is verified.