Research On Key Technologies Of Micro-grid Inverter's Wireless Networked Control Systems

Micro-grid can realize the local absorption of great amount distributed energy,and it is an effective means to make the rapidly increasing penetration of renewable energy and power grid connection friendly.With the rapid development and integration of automatic control theory,computer information technology and network communication technology,a new distributed,intelligent,network real-time feedback power electronic device control system has emerged,which has better adaptability,scalability and performance.However,because of wireless communication network is introduced into the micro-grid,many new issues arise,such as system transmission delay,sampling rate,electromagnetic interference and other factors will bring adverse effects on the micro-grid control.First,In view of the problem that the transmission delay caused by the introduction of communication network will increase the output THD of the micro-grid inverter,a composite control method is proposed to effectively reduce the total harmonics distortion(THD)rate of the inverter output.Firstly,the mechanism of increasing inverter output current THD due to delay in communication network is analyzed.Time delay modeling of Zigbee wireless communication network of AC micro-grid is carried out.A compound control method(internal mode control and quasi-PR control)is proposed to suppress the increase of THD,which can effectively overcome the problem of the increase of THD caused by the delay of communication network.This method improves the accuracy of the output current and reduces the circulation of the inverter in the AC micro-grid.In this method,internal mode control is used to minimize the negative effect of communication network delay,and quasi-pr control with resonance compensation is used to suppress the low harmonics caused by inverter power supply circuit.By comparing with PQ droop control method,simulation and experimentalThen,for the research of micro-grid inverter control sampling rate,this paper proposes a multiplier based on Alternating Direction Method of Multipliers(ADMM)sampling rate optimization algorithm,which is realized under the premise of without changing switching frequency inverters optimal design of sampling rate.Considering the constraints of system control delay,transmission delay and network load rate,a mathematical optimization model for sampling rate of micro-grid inverter is established with the objective of minimizing the output THD of the inverter.First,by augmented Lagrangian dual function,it transforms the original optimization problem to the parallel optimization sub-problem.Second,this paper proposes a sampling rate optimization algorithm based on ADMM,and the algorithm through the distributed parallel iterative way calculates the approximate optimal sampling coefficient.The simulation results show that the proposed algorithm can obtain the calculation results similar to those of CVX toolbox,and the calculation time is only 3%of that of CVX toolbox.The experimental results of inverter verify the effectiveness of the algorithm,and have practical engineering value.Next,aiming at the interference problem of wireless communication network caused by complex electromagnetic environment of micro grid,a communication topology optimization algorithm based on minimum spanning tree is proposed to minimize interference of communication network and improve the reliability of micro-grid.Fully considering the time-varying characteristics of the degree of interference of the communication network,it constructs the dynamic optimization model of minimum spanning tree.A spanning tree is build through a distributed algorithm.The simulation results show that the minimum spanning tree constructed by this algorithm has a smaller average weight than the Bottom Up Algorithm(BUA),that is,the communication topology of micro-grid has stronger anti-interference ability.Last,in view of the deficiency of traditional centralized and distributed control of micro-grid,a control architecture based on edge computing is designed,which improves the reliability of micro grid control.Based on the idea of edge computing technology,the control information of micro grid is classified according to the time-delay sensitivity and computing power demand,and then processed in different control layers.In the Zigbee wireless network communication layer,an information flow scheduling strategy is proposed to dynamically select edge control nodes based on the holistic health degree of nodes,which reduces the dependence of traditional centralized control and distributed control on micro-grid control center and master controller,and improves the reliability of micro grid control.Finally,the effectiveness and correctness of these methods are verified by joint simulation.