Research On Coordinated Control And Distributed Optimal Scheduling Of Multi-microgrid System

Microgrid(MG)provides an efficient solution for local consumption of renewable energy.With the development of distributed generation(DG)control,energy management and other technologies,multi-microgrid(MMG)system is composed of multiple microgrids to realize power mutual assistance between different microgrids,which can further improve the reliability and economy of power supply.Similar to single microgrid,the MMG system also needs to coordinate control the energy storage devices and DGs in system to ensure their safe and reliable operation.On this basis,the optimal scheduling of MMG system not only needs to optimize the running cost of system,but also needs to coordinate the conflict of interest in power trading among different microgrids.In response to the above problems,a hierarchical structure of operation control and energy management of the off-grid MMG system is established,and then the research on its operation control method and optimal scheduling strategy are conducted.The main contents and innovations of this thesis are as follows:Firstly,a micro-source control strategy is proposed to realize the state of charge(So C)balance of energy storage system.According to the regulation plan of the energy management layer,different control modes of micro-source are proposed to control the operation of distributed generation and energy storage system.Then,aiming at the problem of So C imbalance in the operation of energy storage system in microgrid,the So C-based improved droop control is proposed to reasonably distribute the charging and discharging power of battery energy storage system(BESS),which realizes adjusting the So C of different BESS units to change towards in the direction of consistency through a unified control equation.The state space model of BESS based on the So C-based improved droop control is constructed,and the root locus analysis method is used to select appropriate control parameters to ensure the stability of the improved droop control.The comparison results of the examples verify that the proposed strategy can achieve So C balance quickly,which effectively avoids overcharge and discharge of energy storage system.In addition,compared with the conventional two quadrant control strategy to achieve So C balance,the proposed strategy does not need to change the control equation under the charging and discharging state of energy storage system,which reduces the control complexity and improves the applicability of the strategy.Secondly,a coordinated control strategy for voltage source type micro-source to realize frequency/voltage non-deviation adjustment is proposed.In order to suppress the output frequency/voltage deviations of distributed generation and energy storage system in each microgrid,state space models including frequency and voltage secondary adjustment items are constructed for distributed generation inverter based on the traditional droop control and energy storage converter based on the So C-based improved droop control respectively,which are used as the prediction model of model predictive control.The predictive model is discretized,and the secondary adjustment items to compensate the converter output frequency and voltage offset are quickly generated by feedback correction and rolling optimization for suppressing the output frequency and voltage offset of distributed generation and energy storage system.Combining the control strategy of realizing So C balance of energy storage and frequency/voltage non-deviation adjustment,a microgrid coordination control that takes into account both power control and frequency/voltage offset suppression is formed.Example results show that the proposed strategy reduces the sensitivity to line parameters,which improves the robustness of the system.In addition,the strategy makes full use of the prediction characteristics of model predictive control for future information,which improves the dynamic response of suppressing frequency and voltage offset.Thirdly,a distributed optimal scheduling strategy is proposed to minimize the total running cost of MMG system.According to the feature that the power trading costs among microgrids can be offset,the the MMG system total running cost is equivalently transformed,and the power trading value among microgrids is taken as the coupling variable.Then a distributed optimal scheduling strategy that minimizes the MMG system total running cost is proposed and its distributed optimization solution steps are given meanwhile.According to the characteristic that the prediction error of the optimization results decreases with the shortening of time scale of the prediction data,the scheduling results of minimizing the total running cost of the MMG system is adjusted based on the short-time scale prediction data,and the adjusted optimization scheme is given.Compared with the centralized optimal scheduling strategy,the proposed distributed optimal scheduling strategy reduces the dependence on the central autonomous energy management controller of MMG system,improves the reliability,and protects the privacy of each microgrid to a certain extent.In addition,the proposed distributed optimal scheduling strategy simplifies the traditional double-layer energy management model of MMG system to a single-layer energy management model only including the independent scheduling layer of microgrid,which improves the scalability of the system.Fourthly,a distributed optimal scheduling strategy of the MMG system that takes into account the overall interests of system and the individual interests of microgrid is proposed.Aiming at the aforementioned optimal scheduling strategy of minimizing the total running cost of system does not solve the conflict of interests in power trading among microgrids,the multi-microgrid peer-to-peer cooperative game strategy based on benefit compromise algorithm is proposed.The solution method of the benefit compromise algorithm is proposed to obtain the equilibrium solution of the power trading scheme,which solves the problem of conflict of interest in power trading among microgrids.Combining the peer-to-peer cooperative game strategy based on the benefit compromise algorithm with the scheduling strategy that minimizes the total running cost of the MMG system,a distributed optimal scheduling strategy for the MMG system that takes into account the overall benefits of system and the individual benefits of each microgrid is formed.