Research On The Distributed Optimal Dispatch With Communication Constraints And Coordinated Control In Microgrid

With the increasing serious global problems such as environmental pollution and the shortage of resources,the development and utilization of the new energy such as light energy and wind energy,etc,attracts the attentions of all countries in the word.Distributed generation technology,as an important means of new energy geration,has been greatly developed in recent years.In order to mitigate the impact of distributed generation on the main grid and make full use of the advantages of distributed generation technology,microgrid system is proposed.Hierarchical control structure is widely used in microgrid,which consists of three control layers,primary control layer,secondary voltage/frequency control layer and tertiary optimal dispatch control layer.Since the conventional centralized control relies heavily on the communication network of the system to obtain the global information of system,it is no longer suitable for the control of microgrid with flexible structure.Therefore,distributed control methods based on the multi-agent coordination control theory have been extensively studied.In this paper,the optimal dispatch problem of microgrid with considering the communication constraints such as time delay,low communication traffic and packet loss has been studied.Meanwhile,in order to eliminate the frequency deviation caused by conventional droop control,we investigate the distributed coordinated control problem of microgrid.The main work and the innovations of this thesis are as follows:(1)Research on the distributed optimal dispatch problem of microgrid with communication delays.Three distributed optimal dispatch algorithms are proposed to deal with the optimal dispatch problem of microgrid with different forms of time delays,respectively.Meanwhile,the impacts of time delay on the algorithms have been studied with the strict theoretical analysis.For the uniform time delays,firstly,we prove that the algorithm can converge to the optima solution the optimal diapach problem of microgrid via the analytic method and matrix perturbation method.And then,we obtain the strict allowable bound of time delays.For the ununiform time delays,two distributed optimal dispatch algorithms are peoposed and analyzed by applying the generalized Nyquist criterion and Gerschgorin disc theorem.The sufficient condition for the stability of each algorithm and the corresponding maximum allowable delay bounds are derived.(2)Research on the distributed optimal dispatch problem of microgrid with low communication traffic.In order to reduce the communication traffic during the operation process of optimal dispatch algorithm,a series of distributed event-triggered optimal dispatch algorithms are proposed.Based on the mechanism of event-triggered control that the controller is updated only when the system state satisfies some preset condition,we propose three distributed event-triggered optimal dispatch algorithms.Firstly,based on the conventional continuous distributed optimal algorithm,we propose its distributed event-triggered form.Two different event-triggered conditions are designed via Lyapunov function method.Moreover,Zeno behavior is avoided which is proved by the strict mathematical analysis.The algorithm significant reduce the communication burden of system.Then,in order to avoid continuous detection of event-triggered condition by controller,a sample-based distributed event-triggered optimal algorithm is proposed.By combining sample control and event-triggered control,the controllers of distributed generators only detect the event-triggered conditions periodically at sampling instants.Zeno behavior can be easily avoided by sampling control.The sufficient condition for stable convergence of algorithm is derived by Lyapunov function method.Finally,we consider the optimal dispatch problem with uniform time delay and solve it via a sample-based distributed event-triggered optimal algorithm.The corresponding theorem results are derived.(3)Research on distributed optimal dispatch problem of microgrid with communication packet loss.While there exist peaked loss in the communication networks of microgrid,the conventional optimal dispatch algorithms cannot normally work.In order to solve distributed optimal dispatch problem of microgrid with communication packet loss,we transformed the optimal dispatch problem of microgrid into a distributed average consensus problem by Newton-Raphson method.Then,we use distributed average consensus algorithm with considering packet loss to solve it.The method to deal with the inequlity constraints of generation units is proposed.Finally,the distributed optimal dispatch algorithm with considering the communication packet loss and its detailed implementation steps are given.(4)Research on distributed coordination control problem of microgrid.In order to eliminate the frequency deviation caused by conventional droop control of inverters and realize that the active power outputs of the generating units are equal to the optimal power values obtained by the dispatching layer of the microgrid,two different distributed optimized coordination control methods for microgrid are proposed.Firstly,a hierarchical structure optimized coordination contrl method which considers disfferent control laters with different time scales is given.By using the distributed secondary control and adjusting the parameters of the droop controllers,it can achieve the above control objectives.Moreover,a real-time distributed optimized coordination control method is poroposed.The control objectives can be achieved only by the primary control and the tertiary optimal dispatch control.