Optimal Operation Of The Power Router In Active Distribution Networks

Under the background of the energy Internet,a large scale of renewable energy and electric vehicles intensifies issues such as voltage violation and bidirectional power flow in the radial distribution network.As a core energy management device of the energy Internet,the power router is a multi-port intelligent device based on advanced power electronic technology and communication technology,which is committed to achieving flexible energy routing.The power router can be organically utilized to promote the optimization of power flow,power quality and the consumption of renewable energy in the active distribution network,and thus the energy routing at the network level can be achieved.Presently,the power router is mainly defined as the interface between distributed generation and distribution network,focusing on integrating different types of equipment.The vital application on realizing network-level energy routing is less considered and needs further research.This paper preliminarily explores the form of active distribution network under the background of energy Internet.The peer-to-peer energy sharing between distribution networks through power routers will be focused to analyze the optimal operation of power router in the active distribution network.Such an application has a significant impact on the operation of the distribution network,and some new requirements on the structure and energy management of power router should be reconsidered.The existing relevant research is not fully applicable to the focus of this paper.Thus,there should have an essential bottom-up scheme involving the structure of the power router,internal energy management,equipment configuration method and peer-to-peer energy sharing strategy among distribution networks.The main contributions are as follows:(1)A novel structure of power router is proposed for peer-to-peer energy sharing.In order to promote peer-to-peer energy sharing between distribution networks,a multi-layer structure of power router is proposed,including the distribution-network layer,routing layer,forwarding layer,the buffer layer and multi-energy layer.Such a structure considers factors of the typical structure of a power router,the energy routing among distribution networks,and the design of the information router.Based on the proposed structure,a detailed topology and its systematic control strategy are proposed,in which the routing layer and forwarding layer can be backup for each other.Thus,the redundancy and flexibility of the device are increased;Finally,the electromagnetic transient simulation model of the proposed power router is constructed on Matlab/Simulink.(2)A double-layer energy optimization strategy for a power router is proposed.Considering a limited capacity of the energy buffer and the fluctuation of the intraday power fluctuation of the microgrid,the upper level(15min level)based on an improved model predictive control tracks the peer-to-peer energy sharing dispatching commands of day-ahead.The instruction of the energy storage energy is corrected when the instruction is at its limit(upper/lower limit)for the first time to avoid the standby operation.Such a change does not damage the buffer capacity of other periods.To eliminate the gap between the energy state in real-time scale(1 min)and its energy instructions in a short-time scale(15 min)in the energy storage device,the gap is only expected to be eliminated before the expected period as far as possible in the lower-layer strategy.The fuzzy control strategy is designed to modify values of sharing power,and the power fluctuation within 15 min in the entire system is absorbed distributedly.(3)The planning method of the power router for energy routing is proposed.First,the power flow calculation model of the power router proposed above is established,considering the influence of multi-layer structure and new lines.Then,the configuration method of a single power router is proposed to obtain its location,quantity of ports,capacities of ports,and the construction of interconnection lines.The main strategy traverses the candidate location and provides the parameters of new electric lines.The sub-strategy establishes an optimal configuration model of the power router considering the distribution network.The configuration results can be obtained by solving the optimization model based on the parameters from the main strategy.The installation location with minimum cost will be selected as the final scheme.Second,considering the peer-to-peer energy sharing between distribution networks,an optimal configuration model of multiple power routers is established.Such a model involves the power flow optimization of the AC and DC system combined with the joint operation of multiple power routers.The capacity and number of ports at each layer,interconnected AC and DC lines will be configured.Additionally,both planning models are transformed into a mixed-integer second-order cone programming model,and the ability to derive the optimal solution is improved.Finally,two configuration models are constructed in GAMS.The simulation results show that the proposed model can effectively configure the power router.The derived configuration scheme significantly optimizes the network loss and power quality in the distribution network.(4)Considering that the source and load have equal rights in the electric market,a two-layer distributed peer-to-peer energy sharing strategy is proposed to facilitate the consumption of renewable energy.The upper-layer strategy determines the initiator to solve the congestion problem of multi-source and multi-load.The bottom-layer strategy puts forward the corresponding distributed routing strategy for the source-type and load-type power routers,respectively.A feedback strategy is designed to judge the convergence in a distributed way.The source-load pair and optimized path can be carried out according to the type of the power router(source/load type)in the current round.Additionally,a novel loss allocation method is proposed,making the current routing strategy suitable for the application where forwarding and reverse power flows exist in the network,and the loss allocation is fairer than the present one.