Decentralized Coordinated Control Method For AC/DC Power Interface In AC/DC Microgrid

The AC/DC microgrid combines advantages of AC microgrid and DC microgrid,providing a new and effective way high-density distributed renewable energy gains access to the distribution network.The AC/DC power interface of the AC/DC microgrid,which is composed of multiple parallel AC/DC bidirectional converters,plays a key role in maintaining the power dynamic balance of the AC and DC area,as well as the stability of AC-area frequency and DC-area voltage.Due to the complex characteristics of the AC/DC microgrid such as various supply and consumption modes of AC/DC power,and the strong randomness of the intermittent power supply(such as wind power and photovoltaic)and interference load,the frequency and amplitude of internal power fluctuation of the AC/DC microgrid are greatly increased,and the power interaction between AC and DC area is more frequent.Therefore,it is urgent to study the method of decentralized coordinated control of the AC/DC power interface.In this paper,four typical operation modes are analyzed based on a typical AC/DC microgrid topology.In particular,the droop control principle of AC/DC bidirectional converters in islanding mode is studied,and the mathematical model of the converter with droop control is established.For flexible control of a single AC/DC bidirectional converter,the stability margin evaluation method based on singular value of the return difference matrix is studied.In order to co ordinate the contradiction between frequency response speed and oscillation amplitude,a fuzzy-adaptive inverse control method is proposed.The fuzzy control limits the adjustment speed and range of the adaptive inverse control on the droop coefficient,so as to achieve the coordination between the dynamic response speed and the steady-state performance of the bidirectional converter while ensuring precise power adjustment.For parallel operation of multiple AC/DC bidirectional converters,a method for decentralized coordinated control is proposed based on the theory of adaptive inverse control with variable step size.This method combines advantages of the droop control and adaptive inverse control and takes into account the steady-state power distribution and dynamic response of AC/DC power interface.Finally,combined with the demonstration project of the first commercial AC/DC hybrid microgrid in China,the correctness and feasibility of the proposed control method are verified by the simulation experiment.