Research On Coordination Control Strategy In AC/DC Hybrid Microgrid EMS

Distributed generation provides an effective way to vigorously develop renewable energy.AC/DC hybrid microgrid can integrate distributed generation,energy storage system and load into microgrid more efficiently.The coordinated control strategy of its energy management system is the basis of making full use of renewable energy and ensuring the safe and stable operation of hybrid microgrid.This paper takes AC/DC hybrid microgrid as the research object,analyses the design of its topology structure,studies the coordinated control strategies of converters in grid-connected mode and island mode,and proposes a power fluctuation suppression strategy for grid-connected mode.Firstly,the design principle of AC/DC hybrid micro-grid topology is studied,and a complementary ring-shaped AC/DC hybrid micro-grid topology is proposed based on the advantages of both end power supply network and ring network.According to the capacity,distribution mode,power supply capability and economy of distributed generation and load,the suitable bus voltage level sequence is selected for hybrid microgrid,and the flexibility and reliability of the topology are analyzed.According to the control strategy of energy management system,the hierarchical control architecture of AC/DC hybrid microgrid is designed,which combines local control with system-level control automatically.To ensure the stability of voltage and frequency of AC/DC hybrid microgrid and the power balance of the whole network,the working modes of converters at each end are adjusted.Secondly,the key problems of coordinated control of AC/DC hybrid microgrid under grid-connected operation and islanding operation are analyzed.According to DC bus voltage and AC side frequency,islanding operation is divided into four operation modes,and grid-connected operation is divided into two operation modes.Considering DC bus voltage,AC side frequency,charging state of energy storage system,charging and discharging power of energy storage system and energy transmission constraints of converter,a coordinated operation control strategy based on hybrid microgrid energy management system is proposed.A hybrid AC/DC microgrid simulation system is built in PSCAD/EMTDC,and simulation analysis is carried out under different operating conditions to coordinate control.The strategy can automatically coordinate the control modes of each converter according to different operating conditions to maintain the stable operation of AC/DC hybrid microgrid.Finally,in view of the power fluctuation caused by uncertainties such as wind and light in AC/DC hybrid microgrid,a power fluctuation mitigation strategy based on coordinated control of micro-gas turbine and hybrid energy storage system is proposed.The power fluctuation in AC/DC hybrid microgrid is divided into high frequency component and medium-low frequency component according to frequency range,and the power distribution among supercapacitors,micro-gas engines and batteries is coordinated by fuzzy control strategy.The effectiveness of the proposed power stabilization strategy is verified by simulation analysis in PSCAD/EMTDC simulation software by calling MATLAB fuzzy control toolbox.