Research On Distributed Photovoltaic Cluster Based Multi-level Coordinated Voltage Control In Distribution Network

As global economic develops,energy shortage and environmental pollution problems become increasingly severe.With prominent advantages of abundant resources,wide distribution and non-pollution,photovoltaic(PV)power generation has aroused worldwide attention and got rapid development.As the output power of distributed PV has characteristics of intermittence,fluctuation and uncertainty because of environmental impact,its large-scale and decentralized integration into distribution network brings significant changes to grid structure and load flow distribution.Power quality problems regarding voltage fluctuations and voltage beyond limits become major concerns of distribution network voltage control,which poses great challenge to high-efficiency voltage management strategy.Therefore,for solution to overvoltage of distribution network integrating large scale distributed PV,research around voltage control strategy based on distributed PV cluster is carried out as follows:(1)Firstly,the concept and realization of distributed PV cluster are introduced briefly.Then,considering observability and controllability,the selection method of pilot node is studied.Also,a dynamic index system of distributed PV cluster partition is established to adapt to the change of control requirements of the distribution network.On the basis of this,the distributed PV cluster partitioning method based on community structure is proposed by using the community modularity index and its discovery algorithm.Finally,the controllable capacity of the cluster is evaluated from the point of view of the demand of distribution network voltage regulation.(2)For the prominent problem of voltage beyond limits,a multi-level coordinated control strategy of distribution network voltage based on distributed PV cluster is proposed to achieve balance between the real-time performance and the complexity of the distribution network.Firstly,considering the reactive power regulating characteristics of distributed PV,a dual-time-scale global optimization model including day-ahead plan and intraday short-term scheduling is presented.Then,according to the voltage operation area of pilot node,the latest control requirement of the distribution network is determined,and a cluster optimal control model based on power delamination is established,which includes inter-cluster coordination and intra-group power allocation.Finally,in order to suppress voltage overshoot during closed-loop control process and considering the delay of inverter power tracking,a control model of local consumption focusing on the voltage fluctuation at grid-connected point of distributed PV is put forward,including voltage pre-compensation and dynamic correction modules.(3)Considering the improvement of regulation efficiency and control effect,the assessment index system of distribution network voltage control with participation of distributed PV is established.For comparing voltage control effects of distributed PV in different ways,a comprehensive assessment method of voltage control result based on TOPSIS is put forward,which provides instructive reference for selection of optimal way for distributed PV to participate in voltage control of distribution network.(4)A typical topology of distribution network with scale distributed PVs is designed systematically.And simulations are carried out under the extreme scene of 'high PV output and low system load' where voltage beyond limit is most likely to appear.The simulation results show that the cluster partition method proposed in this paper has great adaptability with variable control requirements of distribution network.Also,it is proved that the proposed multi-level coordinated control stategy can effectively solve the problem of voltage off-limits and improve the voltage profile.And it is indicated that cluster control has a significant advantage over voltage control of distribution network with large-scale distributed PVs.