Research On Distributed Operation Control Strategy For Microgrid

Microgrid is a small power generation and distribution electricity system,including distributed generations,load,distribution facilities,monitoring and protection devices,if necessary,also contains energy storage equipment.In order to ensure stable operation of the system,distributed generations' output power,voltage and frequency need to be coordinated controlled to realize system stability and optimize system performance.Based on hierarchical control architecture,the operation control for islanded microgrid is studied from three aspects:distributed generation,microgrid and microgrid clusters.In order to overcome the deficiency of the existing centralized control and decentralized control method,distributed operation control method for islanded microgrid is mainly studied in this thesis.The main contents of this thesis are as follows:(1)The hierarchical control structure of microgrid is studied and three kinds of microgrid optimization methods of centralized control,decentralized control and distributed control are compared and analyzed.Then,three control methods of distributed generations are studied:PQ control,V/f control and droop control.The principle of droop control and the existence problem of droop control including low power allocation precision,voltage and frequency deviation are analyzed emphatically.(2)In order to compensate for the shortcoming of primary control,the principle of secondary voltage and frequency regulation is studied.The discrete consensus algorithm and the information interaction and implementation method of distributed controllers are analyzed,so as to establish the distributed optimization operation control architecture for islanded microgrid:Through the information interaction between neighbors,distributed controllers can obtain the information which reflects the global state using the consensus algorithm and sends it to the local secondary controller,and secondary control produces the adjustment amount to optimize the voltage and frequency parameters of droop control,so as to achieve the system optimization control target.(3)The distributed strategies for microgrid are studied from two perspectives of power allocation:1)Aiming at the problem of low power allocation precision of droop control,the distributed proportional power sharing control strategy is studied,to realize the control target of the accurate proportional power sharing.2)In view of the shortcoming of droop control in the aspect of economy,considering the generation cost of distributed generations,an improved droop control based on increment cost and distributed secondary economic optimization strategy are put forward.The power is allocated according to the equal increment cost,so the system generation cost can be reduced.In addition,the voltage control and frequency control are used to reduce the voltage and frequency deviation by adjusting the global average voltage and average frequency.The corresponding control objectives can be realized by the proposed distributed strategies without the system line impedances and load parameters.(4)Aiming at islanded microgrid clusters,considering the effect of transmission losses,a distributed economic operation control strategy is studied.The transmission loss correction factor is used to correct the increment cost to loss-increment cost,the economy of the system is improved by implementing equal loss-incremental costs of distributed generations.In addition,the voltage control including global voltage control and single node voltage control can realize that the global average voltage adjusted to the rated value while each node voltage controlled within the normal range used the virtual incremental cost method.And the frequency control which can sWitch between single microgrid and microgrid cluster operation modes is realized to ensure the proportional reactive power.