Performance Oriented Interconnection Modeling And Regulation Optimization Methods For Microgrid

Microgrid is an effective technological means to mitigate the impact of new energy connection with a large proportion into the grid.It also strongly supports large-scale power grid.It features flexible conversion of electrical energy and a variety of regulation models to effectively connect large-scale distributed generation to large-scale power grid,achieving mutual support.Although microgrid is able to operate with grid-connected or islanded mode,it faces challenges for stable operation and coordinated control of devices and systems posed by its highly power-electronized underlying devices and the complex networking pattern and bi-directional energy flow.These challenges include easy interaction of power quality between the equipment and the grid connected due to low inertia,inadequate voltage support of networking power supply affected by external disturbances,system steady-state error caused by model parameter mismatching,and system power balance affected by the intermittent properties of renewable energy.Facing the reality of high-power quality demand,these issues restrict the promotion of "reliable,friendly,and economical" microgrid connection.Therefore,in this paper,following the line of thinking of system modeling-core device control-system regulation-system optimization,it is explored how to ensure the safety and reliability of microgrid by optimizing microgrid regulation and enhancing power output in four different dimensions,namely modeling of interconnection,control of the underlying inverter,coordinated regulation of interconnection state and power,and optimization.The main innovative work herein is summarized as follows:(1)Addressing such problems with the microgrid interconnection model under complex dynamic coupling as high degree of coupling,many control parameters,and high order,a modeling method based on regional division and facing different regulation problems was proposed.First of all,considering the coupling characteristics of interconnected power systems,the coupling relationship of voltage stability at each node was established,and different microgrid regions were marked off based on voltage and loss sensitivity calculations and Euclidean distance.Secondly,since microgrid had many control parameters,the uncertain disturbances and control models of microgrid were combined by different regulation requirements to construct the overall description architecture of different regulation problems and thereby characterize in multiple dimensions the regulation problems under microgrid interconnection.In the end,the dynamic modeling of the complex coupling status of microgrid interconnection was realized by characterizing the mechanism and state of different operating conditions of microgrid by class and by level,reducing the dimensions of different microgrid regulation problems,and building the mechanism models of different regulation problems in each subsystem.(2)Addressing such problems with the existing microgrid controllers mostly customized for specific devices as poor compatibility and scalability,limited functions,and absence of plug-and-play(PnP)modular and universal components to improve the controller performance,an observer-based PnP robust residual performance enhancement controller design facing underlying devices was proposed on top of robust control and optimization algorithm.First of all,by mining microgrid power quality data under uncertain disturbances,a generalized performance enhancement algorithm was designed for underlying devices based on the residual generator.Then,an observer-based stabilizing controller was generated by Youla parameterization,and an active power quality controller was designed with the PnP flexible structure,thus improving power quality without changing the structure and parameters of the original controller.In the end,by adopting a gradient descent optimization algorithm,the tuning/control parameters were estimated online and optimized to improve the performance of the power quality controller,thus extending the control performance of the power electronics devices,overcoming many power quality problems,and realizing dynamic compensation control of system power quality.(3)Addressing the difficulties in stability control between multi-inverter interconnectors and in achieving both highly stable operation and flexible,interactive,cooperative system regulation under disturbances and uncertainties,a robust control strategy for comprehensive performance optimization was formulated taking into account system dynamics and steady-state performance.First of all,based on the physical interconnection structure of voltage source converters(VSCs),VSCs were physically decoupled using the Droop multi-loop control structure,thereby realizing the decentralized operation of VSCs in terms of physical interconnection.Secondly,addressing the impact of uncertain disturbances on system dynamic performance,a distributed robust controller was designed;on top of the communication-free Droop multi-loop control structure,the influence of disturbance and compensation signals on the output in the dimensionally-reduced single VSC model was converted into the problem of model matching;the controller for dynamic performance enhancement was solved by LMI to improve the dynamic performance of VSC output under external load disturbances.After that,in view of the output steady-state error of VSCs due to line uncertainties,based on the VSCs communication network and "Ⅵ+improved Droop" control strategy for better steady-state performance,the optimal steady-state performance controller was designed on top of the steady-state error-driven distributed consistency optimization to optimize the steady-state performance of VSCs.In the end,to solve the problems of dynamic performance affected by load disturbances in the physical interconnection layer and the steady-state performance affected by line uncertainties,a control strategy was proposed for better comprehensive performance under physical connection,following which the overall microgrid system performance was enhanced under varied load disturbances and interconnection state.(4)Addressing the high degree of association between the stable coordination of microgrid underlying devices and upper-level economic optimization at multiple levels under the interconnecting structure,and the diverse way of matching of optimization algorithms,a hierarchical optimization strategy was formulated for multi-device coordination in microgrid by matching the optimization algorithms of synergistic elements of different levels,which took into account economic efficiency and voltage stability.First of all,considering the effect of upper-level dispatch optimization on the regulation of microgrid underlying devices,a three-level distributed structure of coordinated optimization was designed,emphasizing both economic efficiency and voltage stability.Secondly,based on Droop optimization and consistency iterative optimization through cost control and local estimation of nodal supply-demand imbalance,the power allocation precision of Droop control was enhanced while effectively lowering system operating cost,improving microgrid economic efficiency.In the end,through closed-loop feedback and optimization of microgrid node voltage and detection of the remaining capacity of adjustable devices,the particle swarm optimization(PSO)embedded with power flow calculation was adopted to regulate the output reactive power of adjustable devices and solve the problem of microgrid steady-state voltage out-of-limit.The above research results were verified on multiple hardware-in-the-loop(HWIL)experimental platforms and compared with traditional methods to further demonstrate the effectiveness and practicality of the proposed method.