Optimization And Coordination Control Strategies For Multiple Distributed Generators

Recently,serious environmental condition has led to increasing focus on global environmental issues.In order to protect the environment and solve the energy crisis caused by severe shortage of natural resources,renewable energy sources such as solar energy and wind energy have been widely concerned.More and more renewable energy sources are connected to the power grid in the form of distributed generators.High penetration of distribution generation is considered as an important trend in the development of future smart grid.However,as the penetration of distributed generation in the power grid continues to increase,the intermittency of the renewable energy sources’ power generation output may increase the difficulty of planning and power dispatch scheduling of the power grid and have a great impact on the power system’s stable operation.This thesis mainly focuses on solving the control and power dispatch problems of distribution network and microgrid which contain a large number of distributed generators.The development concept of smart grid is creating an economical,environmental and safe power ecosystem.This thesis proposes a series of active control methods to control the distributed generators so as to make the distributed generators to be "friendly" to the power grid and improve the economy of the operation of the power system.The main research work in this thesis can be summarized as the following three parts:(1)Economic Dispatch Algorithm for Multiple Distributed Generator UnitsIn order to reduce the total generation cost of the power grid,this thesis proposes an economic dispatch algorithm which based on the distributed consensus theory.The algorithm only needs the neighboring nodes in the power grid exchange their virtual incremental costs during com-munication.Different from the previous algorithms which driven by the mismatch of supply and demand power,the proposed algorithm will not break the constraint of power supply and demand balance even in the transient process.It can be used online.In addition,the algorithm also can be used in the case that the communication topology is switching.When the commu-nication topology satisfies the jointly connected condition,the algorithm can converge to the global optimal solution.(2)Coordination Control Strategy for Distributed Generators in a Distribution Network In order to meet the challenges in distribution network’s safe and stable operation which brought by the connection of large number of distributed generators,this thesis proposes a coordination control strategy for distributed generators in the distribution network.The strate-gy is based on hierarchical control.It mainly includes the following four control objectives:1.Control the injection power at the common coupling point of the distribution network so as to regulate the power references given by the main grid control center.2.Share the active power among distributed generators(excluding battery energy storage systems).3.Realize voltage balance among distributed generators(including battery energy storage systems).4.Recover the state of charge of battery energy storage systems.The main feature of the control strategy is that it can make the distribution network’s common coupling point injection power regulate both the active and reacti’ve power references by the coordination control of the distributed generators,such that,the entire distribution network can be treated as a controllable PQ node.The strategy can facilitate the optimization and scheduling problems of the power system.In addition,the strategy balances the interests of three groups including the operators of power system,independent investors of distributed generators and the users in the distribution net-work.(3)Dispatchable Droop Control Method for Distributed Generators The traditional droop control method cannot achieve active power regulation,which makes the distributed generators operating in the traditional droop control mode unable to perform precise power regulation control.Based on the hierarchical control structure,this thesis proposes an dispatchable droop control method.It retains the characteristics of the traditional droop control method,and help the distributed generators realize precise power regulation by modifying their power reference values in the improved droop control scheme.In addition,the proposed droop control method can also achieve frequency recovery in the microgrid.The effectiveness of the proposed control strategies in this thesis are verified by theoretical analysis and Matlab/Simulink simulation test.