| With the deepening of electric power system reform in China,the retail market will gradually open in the future.In the future,distribution network,distributed generation,energy storage and microgrid may belong to different independent owners.As the number of owners increases,the centralized dispatch manner will face with the challenge of high-capacity massive information storage and information exchange.Besides,the centralized manner will damage the data privacy of each independent owner.The decentralized optimization method provides a feasible way to solve these problems above and become an effective method to reduce the burden of communication and protect the data privacy.Therefore,it is of great significance to study the decentralized optimization of medium and low voltage power grids with multiple owner participation.This paper focuses on the decentralized optimization methods under various scenarios,such as a coordination between distribution network and microgrid,a coordination for the internal components of distribution network and a coordination among different microgrids.The main research contents and achievements of this paper are summarized as follows:Firstly,a high precision linearized alternating current(AC)power flow model was introduced,which was suitable for the medium and low voltage networks.Several improvements have been exerted to make the linearized power flow model suitable for a variety of decentralized optimal operation scenarios.The Ward equivalent method for the linearized power flow model,the linearized power flow model with node granularity for a radial distribution network and the linearized optimal power flow model for the isolated microgrid are presented.The accuracy of the linearized AC power flow model was verified in the IEEE 33 bus system and the IEEE 69 bus system respectively.At the same time,simulation tests were carried out in a real 35 bus distribution system and a real 13 bus microgrid to verify the feasibility and accuracy of the improved method for the introduced linearized AC power flow model.Secondly,a decentralized optimal power flow(OPF)model for active distribution network with multiple microgrids was proposed.The Ward equivalent models for the linearized AC power flow equation of distribution network and microgrid were constructed.Thus,the original coupling network equation of distribution network and microgrid was decoupled.A quadratic programming model for the proposed decentralized optimal power flow is further constructed.The decentralized saddle-point dynamics(DSPD)method was used to transform the optimization process into an asymptotically stable process of a dynamic feedback control system.The proposed model is simulated in two groups of real distribution systems with multiple microgrids.The effectiveness and accuracy of the proposed DSPD method were verified.The simulation results also showed that the proposed model had the plug-and-play characteristic.Then,in order to cope with the huge real-time information capacity and the difficulty of centralized dispatching caused by the large-scale integration of the photovoltaics(PVs)and electric vehicles(EVs)in the distribution network,a decentralized OPF model for the active distribution network was built.Based on the per-node granularity linearized power flow model,a point-to-point communication structure was constructed.Then,a decentralized quadratically constrained quadratic programming model based on the alternating direction method of multipliers(ADMM)was built to solve the optimal power flow problem.a closed-form iterative solution method for the decentralized optimization was developed to improve the calculation speed for each iteration.Finally,case studies for a real 35-bus distribution system and a real 110-bus distribution system in China were used to verify the effectiveness,the accuracy and the plug-and-play characteristic of the proposed method.Finally,a single-leader and multi-follower Stackelberg game model was established.A look-ahead dispatch model for the plug-in electric bus(PEB)operator was regarded as the upper optimization problem,while a look-ahead dispatch model for the microgrid operators as the lower optimization problem.For the upper-level optimization problem,a time-space trip model for a fleet of PEBs was established based on the travel laws of buses.a mixed integer linear programming(MILP)problem was constructed considering the maximization of profits for the PEB operator.For the lower-level optimization problem,a quadratic programming problem considering the maximization of the profit for the microgrid operators was constructed.Based on the Karush-Kuhn-Tucker(KKT)condition and the big-M method,the lower-level optimization problem could be transformed into a set of linearized constraints with discrete variables,and the solution of the original Stackleberg game model was transformed into a MILP problem,which could be solved by mature commercial solvers.The proposed game model was tested on three practical microgrid and BYD series-K9 electric bus.Simulation verification have been carried out to analyze the effect of PEBs as mobile load or mobile storage on the profits of the PEB operator and the microgrid operators.The simulation results provided suggestions for the reasonable configuration and operation strategy of PEBs. |
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