Cluster Partition Based Voltage Control And Optimal Scheduling For Active Distribution Networks

With the shortage of the traditional energy and the increasing electricity demand,the structure of energy development tends to be pluralistic.As a clean and renewable energy,solar energy has become one of the main energy.The proportion of photovoltaic(PV)in the distribution network is constantly increasing with the accessing of large-scale distributed PVs.The high-proportion distributed PVs change the unidirectional power flow of traditional distribution network,which results overvoltage,and challenge the safety,stability and economic operation of distribution network.In addition,because of large scale,scattered location,large number,uncertain output and other characteristics in high-proportion distributed PVs,the voltage control in distribution networks will be more complex,as well as the economic scheduling.In this paper,aiming at solving the above problems,the research works on voltage control and optimal scheduling carried out for the active distribution network with high-proportion distributed PVs.Specific work is as follows:(1)Combined with reactive / active power balance index and the coupling index of area nodes,an improved modularity partition algorithm is proposed,which can automatically divide a distribution network with high proportion distributed PVs into the optimal clusters of reactive and active power layer.Based on the cluster partition,the voltage control strategy of priority using reactive power and subsequent using active power,which controlled the key PV nodes to regulate the voltage of key load nodes within a cluster,and it can effectively narrow the search range of controlled PVs and greatly reduce the number of controlled nodes to accelerate the computing time of control.(2)A two-level voltage control method combined day-ahead scheduling and real-time control is presented.In the day-ahead level,based on the PV-output and load-demand forecast,a community detection algorithm using an improved modularity index is introduced to divide the distribution network into clusters;a day-ahead optimal scheduling is drawn up on the basis of the network partition,and the objective is to minimize the operation costs of the distribution networks.In the real-time level,under the day-ahead optimal scheduling and cluster partition of the upper level,a real-time optimal voltage control algorithm is proposed based on the real-time operation data of the distribution networks,and the objective is to correct the day-ahead optimal scheduling through modifications.Thus,the algorithm realizes the combination of day-ahead scheduling and real-time control,and achieves coordination of schedulings in different time scales for future distribution networks with high-proportion of PVs.(3)A two-layer optimal scheduling strategy to handle the overvoltage problem in distribution networks with high-proportion of PVs is proposed.The voltage regulators can be classified as the power utility and PV owners,which are referred to as stakeholders in this work.To relieve the scheduling burden due to the large number of PV owners,an improved modularity index is proposed to divide active distribution network into several clusters,and PV owners in each cluster are defined as PV reactive/ active power stakeholder.The proposed two-layer optimal scheduling strategy includes in the parallel optimization layer and coordination optimization layer.In the In the parallel optimization layer,a min–max robust game model and a second-order cone programming-based scheduling model are respectively proposed to minimize the operating costs of PV reactive/ active power stakeholder and the power company stakeholder.A parallel optimization is employed to solve the two models in the in the parallel optimization layer.In the game optimization layer,a non-cooperative game based model is presented to coordinate scheduling solutions of each stakeholder by information exchange among stakeholders,so that global optimization can be realized.(4)In view of the problems caused by multiple uncertainties in the economic scheduling of distribution network,a three-layer optimal scheduling strategy for distribution network considering source-load and cluster partition uncertainties is proposed.In the cluster dynamic adjustment layer,the stakeholders in the distribution network is updated by the dynamic adjustment of clusters,and the results of stakeholders division are transmitted to the parallel optimization layer.In the parallel optimization layer,a two-stage robust model for the dispatching of PV inverters is proposed to deal with the uncertainly of PV outputs and load demands for the PV reactive/ active power stakeholders,and an optimal reconfiguration based linear optimal scheduling model for distribution network is established for the power utility stakeholder.The model of stakeholder is optimized in a parallel way,which can quickly obtain the optimization results.After the optimization,the results in parallel optimization layer are transmitted to the game optimization layer.In the game optimization layer,the optimization results of each stakeholder are exchanged and returned to the d cluster dynamic adjustment layer and parallel optimization layer for the calculation of next generation.When the cluster partition and the operating costs of each stakeholder no longer change,the optimal scheduling scheme under this strategy is finally obtained.The proposed strategy can simplify the optimization contains multiple uncertainty in distribution network,and realizes the coordination of various voltage regulating devices and network topology,which can quickly get the economic scheduling scheme for active distribution networks with high-proportion distributed PVs.The proposed strategy can overcome the limitation of robust game model which can only model one single uncertainty,deal with the cluster partition uncertainty that caused by source-load uncertainty and network topology changing,realize the coordination of various voltage regulating devices and network topology changes in the distribution network,and quickly get the economic schelding of the distribution network.The cluster partition based voltage control and optimal scheduling strategy proposed in this paper can provide theoretical reference for solving the overvoltage problem caused by high-proportion distributed PVs,and it can help to realize the friendly connection of high-proportion distributed PVs,the long-term coordinated development with power grid and PVs,as well as the innovative operation and management mode for future power system.