Control Strategy Of Inter-Connected Converter For AC/DC Hybrid Microgrid

In recent years,with the rapid increase of DC loads such as EVs and LED lighting,combined with development of DC sources such as photovoltaic cells and fuel cells,the AC/DC hybrid micro grid has become a hot spot in microgrid technology research due to distributed energy access and high efficiency of power supply.In AC/DC hybrid microgrid,inter-connected converters are the key devices to connect AC microgrid and DC microgrid,which plays the role of maintaining the power balance of microgrid and supporting the stable operation of the system.It is of great practical significance and application value for the research of inter-connected converter.Under such circumstances,this paper takes the three-phase two-level inter-connected converter as an example to study the operation characteristics and control technology of inter-connected converter under off-grid working operation.First,the hardware and control system parameters of inter-connected converter are studied,the basic topology and working principle of the inter-connected converter are described,a mathematical model of the inter-connected converter is established under off-grid mode,then,according to the operation demand of the AC/DC hybrid microgrid,combined with the actual situation of the control system,the hardware parameters of the inter-connected converter is designed;based on the above,the controller parameters of the control system are designed by using the open-loop transfer function of the system,the rationality of designed parameters is verified through simulation.Secondly,the control strategy inter-connected converters is studied on balance condition of AC microgrid,the objective of autonomous operation control for AC/DC hybrid microgrid is proposed,then,the power-voltage(P-V)characteristics of DC microgrid and power-frequency(P-f)of AC microgrid based on droop characteristics are analyzed.On this basis,the operation control rules,droop characteristics and control strategies of inter-connected converter are studied,and the strategy is theoretically analyzed and verified by simulation.Thirdly,the control strategy inter-connected converters is studied on imbalance condition of AC microgrid.The influence of AC microgrid with three-phase asymmetric load and the compensation principle based on virtual admittance are analyzed,and the negative sequence component of the AC bus voltage is extracted by band-pass filter,The feedback of the product of virtual admittance and negative sequence voltage is introduced to realize the compensation function of inter-connected converter to negative sequence current.The control strategy of inter-connected converter can be used to achieve transmission power features and improved power quality of AC microgrid.The feasibility of control strategy of inter-connected converter is verified by simulation in unbalanced operation.Fourthly,on the basis of theoretical research,a semi-physical experiment platform based on dSPACE is established to form an AC/DC hybrid microgrid.The effectiveness of the proposed control strategy is verified through experiments.The experimental results show that the AC/DC hybrid microgrid can run autonomously under the balanced condition,and the voltage stability and power balance of the system can be guaranteed under the regulation of the inter-connected converter.Under unbalanced condition,the inter-connected converter can improve the performance of the AC microgrid voltage quality.