Research And Application Of Energy Management For AC/DC Hybrid Microgrid

With the widespread application of distributed power generation and the growth of load types,microgrid has achieved rapid development.The AC/DC hybrid microgrid has the advantages of both AC microgrid and DC microgrid.It can not only supply power for a variety of AC and DC loads,but also serve as an excellent carrier for a variety of distributed generators to connect to the grid in large scale.Energy management strategies can realize the coordinated management of microgrid,the maintenance of power balance,the improvement of renewable energy consumption and the reduction of operation costs.However,compared with the traditional microgrid,AC/DC hybrid microgrid has the characteristics of AC/DC regional operation,energy interaction coupling,variety of sources and loads,and diversified operation modes.This makes the energy management of AC/DC hybrid microgrid face more complex challenges than that of traditional microgrid.Therefore,AC/DC hybrid microgrid energy management is the key research content and direction of smart grid in the future.Accurate and efficient energy management strategy of AC/DC hybrid microgrid is the basis of ensuring the safe,stable and economic operation of AC/DC hybrid microgrid,and plays a crucial role in improving the added value of microgrid.According to the structure and operation characteristics of AC/DC hybrid microgrid,the energy management model and strategy of AC/DC hybrid microgrid are intensively studied in this paper.The main researches are as follows:In view of the poor accuracy of the current conversion efficiency model of bidirectional AC/DC power converter,which affects the operation economy.According to the operation and loss characteristics of bidirectional AC/DC power converter,the quantitative relationship between conversion efficiency and transmission power of bidirectional AC/DC power converter is studied,and a dynamic conversion efficiency model of bidirectional AC/DC power converter is presented.On this basis,an AC/DC hybrid microgrid energy management strategy integrating dynamic conversion efficiency of bidirectional AC/DC power converter is proposed.Simulation results show that the proposed model can accurately reflect the operation state of the converter.The proposed energy management strategy has excellent economic performance.Aiming at the multiple uncertainties of AC/DC hybrid microgrid,a multi-time scale stochastic energy management strategy based on multiscenario analysis is proposed.In the day-ahead energy management stage,the two stage day-ahead stochastic optimal dispatch model is developed to minimize the daily operation cost.The multi-scenario analysis technology is used to simulate the uncertainties of wind power,photovoltaic and loads.The day-ahead schedule takes account of robustness on the basis of economy.In the intraday rolling energy management stage,according to the intraday ultra-short-term forecast data,an intraday optimization model based on model predictive control is developed to minimize the control variables and the difference between the output vector and the target vector.Combining the rolling optimization with feedback compensation,the closed-loop optimization is carried out.Depending on that,the model makes rolling revisions to the day-ahead schedules of distributed generations and energy storages,and takes the tracking of the day-ahead tie-line schedules as the primary objective,so as to ensure the effectiveness of the day-ahead schedules and avoid affecting the stable operation of the upper power grid.The simulation results show that the proposed strategy can effectively reduce the intraday operation cost caused by the day-ahead forecast errors and improve the operation economy,robustness and grid-friendliness of the AC/DC hybrid microgrid.Due to the limited adjustable capacity of islanded AC/DC hybrid microgrid,it is difficult to meet the operation economy and stability at the same time.In view of the issues,a dual mode coupling energy management strategy for islanded AC/DC hybrid microgrid is proposed.This strategy sets two operation modes: economic mode and emergency mode.The two operation modes are switched by the state of charge(SOC)of the voltage/frequency control unit.Owing to the coupling and close coordination of the two operation modes,this strategy ensures long-term economic operation of the AC/DC hybrid microgrid and short-term risk management.Simulation results show the effectiveness of the proposed energy management strategy.The AC/DC hybrid microgrid energy management system is developed.The overall function,system architecture and communication system of AC/DC hybrid microgrid energy management system are designed.The measurement and control principle of the energy management system is introduced.The software development of energy management system is described in detail,including development environment,software architecture and interface design.Based on the AC/DC hybrid microgrid experimental platform,the proposed grid-connected energy management strategy and islanded energy management strategy are verified in the developed AC/DC hybrid microgrid energy management system.The results show the effectiveness and feasibility of the proposed energy management strategies.The developed AC/DC hybrid microgrid energy management system shows excellent working performance.