Research On Integrated Power Architecture And Coordinated Control In Active Distribution Network

With the ever-increasing serious social and environmental issues like energy crisis,environmental pollution,and climate change,the green,lowcarbon,and sustainable concept guilds the development of power systems.Especially for the distributed power system,a large number of distributed energy resources and new-type loads like electric vehicles(EVs)change the conventional unidirectional generation-transmission-distribution power usage scheme.The coexistence of varied energy sources/loads,flexible power flow,and coupling characteristics of multi-sources bring new challenges for the effective management and stable operation of power distribution networks,the traditional passive management scheme needs to be changed.The active distribution network is a kind of distribution system that can manage distributed resources and controllable load effectively.Classified by the system scale,the active distribution network contains a series of multilevel distribution subgrids,namely,the small-scale nanogrid,medium-sized microgrid,and large-scale cluster.The concept of the distributed subgrid architecture covers the power network architecture and energy management architecture.The conventional AC-coupled architecture is of a simple topology and is compatible with existing utility grid naturally,yet does not support high efficient connection and management of varied resources and loads,as well as flexible power flow dispatching and varied control functionalities.The conventional hierarchical energy management architecture ignores a series of critical factors in specific application scenario like system scale,control complexity,cost economy,etc,leading to the unmatched issue with application scenarios.Based on the novel power network architecture and energy management architecture,the coordinated strategy that features flexible control functions and adaptive ability is critical to realize the stable,efficient,and economical system operation.Initially,a review for varied power network archiectures with EVs widespread integration is conducted.The vehicle-to-grid(V2G)operation between EVs and utility grid is helpful for reducing the charging cost of EVs,and improve the operation performance of the utility grid.From the perspective of vehicle-grid coordination,the power network architectures applied in nanogrid,microgrid,and cluster are comprehensively reviewed and evaluated,which provides valuable technological references for widespread integration of EVs and V2 G application.First,according to the roles of EVs,viz.,as power resources,storage,and loads in smart grid,the relevant standards of vehiclegrid coordination are summarized.Then,referred to significant indexes in standards,a comprehensive evaluation for various power network architectures is conducted considering six aspects,viz.,charging demand compatibility,power quality risk,V2 G availability,architecture scalability,local control complexity,and technology maturity.The evaluation results show that the hybrid AC/DC coupling architecture based on the multi-stage,multi-port integrated converter could promote the V2 G application furtherly,but there still remains room for improvement in terms of cost,efficiency,and standardization.For the active distribution networks,this paper carries out a systematic research regarding power network architecture,energy management architecture,and coordinated control strategy.The completed innovative works are as follows:(1)In order to realize mutual power support between AC and DC subgrid,mitigate power fluctuation at point of coupling(PCC),and achieve highefficient utilization of renewable energy resources,this paper proposed a novel multi-stage,multi-port integrated hybrid AC/DC microgrid architecture.The core component of this architecture is a novel interlinking converter named smart interlinking unit,which has multiple plug-and-play interfaces to facilitate the connection of AC,DC loads,and the utility grid.In addition,the architecture has dedicated interfaces to access AC and DC charging piles and facilitate the centralized power management for EVs’ charging and discharging behavior.Based on the proposed architecture,the corresponding hierarchical control strategy is introduced,which considers the power balance conditions in subgrids and operation conditions of battery storages.Case studies show that the proposed architecture and control strategy could guarantee the stable operation of systems in grid-connected and islanded scenarios.Meanwhile,the executed power exchange between AC and DC subgrid could smooth the power fluctuation at PCC,and significantly enhance the utilization and local consumption of renewable energy resources.(2)In order to realize the power coordination within the hybrid microgrid and between multiple individual microgrids,simultaneously,as well as construct the unified interconnected systems,this paper proposes an integrated and reconfigurable hybrid AC/DC microgrid clustering architecture and autonomous coordinated control strategy.The core interlinking unit of the clustering architecture features scalability,reconfigurability,and modularity,and can realize flexible AC or DC interconnection between individual microgrids by switching topology and multiplexing power conversion modules.Based on the proposed architecture,a decentralilzed control strategy is developed,realizing the autonomous power interaction among subgrids in the individual microgrid.Additionally,the introduced architecture and strategy could make full use of the power capacity of clusters,thus realizing the adaptive and autonomous power coordination between neighboring microgrids.The power support capability of the cluster is to be enhanced significantly with guaranteeing the realible operation of systems.(3)Regarding unmatched issues induced by the conventional hierarchical energy management architecture applied in nanogrid,the pseudo hierarchical energy management architecture based on intelligent charging piles is proposed.The pseudo notion aims to distinguish the traditional hierarchical architecture with multiple control layers and control agents.The proposed architecture combines the upper-level central controller with the local smart charging piles creatively,decreases the number of control layers and control agents,features integrated structure,low system complexity,and high cost economy.(4)Considering the low real-time performance of the traditional EV-grid coordination in responding short-timescale varied operation conditons,a multimode operation strategy with supporting autonomous EV-grid coordination is introduced.The introduced strategy considers different control time intervals.In the short time-scale local control layer,a state-triggered droop control strategy based on the decentralized control mechanism is proposed to achieve autonomous power coordination without extensive communication links,which provides real-time power support capability for the nanogrid,thus mitigating the short time-scale power fluatuation at the PCC.In the power dispatching level,the paper introduced a multi-mode power dispatching strategy.This strategy features low computational complexity and could realize peak-shaving and valley-filling of load curves,improve the nanogrid operation economy.A detailed simulation model and hardware-in-loop(HIL)experiment platform verify the effectiveness of the proposed energy management architecture and control strategy.