Multi-paralleled Bidirectional Interlinking Converters Control Strategy In Hybrid AC/DC Microgrids

With the continuous development of new energy generation technologies such as wind energy and solar energy and power electronics technology,microgrid has been widely used in the field of distributed power generation due to its advantages of effectively utilizing and integrating distributed electricity.Hybrid AC/DC microgrid integrates the advantages of AC microgrid and DC microgrid,which can effectively reduce frequent power conversion,reduce energy consumption and operate in a flexible mode.Therefore,Hybrid AC/DC microgrid will be the mainstream structure and main development trend in future microgrid.In order to increase the capacity of BIC(bidirectional interlinking converter)in hybrid AC/DC microgrids,a paralleled BIC is often used.However,the inconsistency of parameters in the paralleled BIC leads to the excessive zero-sequence circulation in the system,which leads to the increase of system loss and even the failure of the BIC in serious cases.In addition,due to the complex structure of AC/DC hybrid microgrid,which integrates various power transformations,the design of power coordination control strategy is also of great significance in order to maintain the power balance of the system.At first,this paper determines the topology of hybrid AC/DC microgrid,respectively studied AC sub-grid,DC sub-grid topology and control strategy,analyzes BIC working principle,mathematical model and control strategy of power balance,and built in the MATLAB/Simulink simulation model has been verified,DC sub-grid and AC sub-grid control strategy,BIC power balance control strategy is effective and feasible.In this paper,the zero sequence circulation of two paralleled BIC is analyzed in detail when the inductance parameters are not consistent.The zero vector circulation is suppressed based on space vector pulse width modulation technology,and the traditional PI controller is used to adjust the zero vector to achieve the purpose of circulation suppression.The effectiveness of the control strategy is verified by simulation experiments.In order to further improve the parallel capacity,a circulation suppression strategy was designed for multi-parallel BIC systems.A virtual BIC was proposed to apply the circulation suppression strategy to multiple parallel systems,and feedforward control was introduced to improve the zero-vector circulation suppression effect.A hardware-in-loop experimental platform was built.Experimental results show that the proposed control strategy can effectively suppress multiple BIC parallel zerosequence circulations,and can still achieve the circulation suppression even when the inductance parameters and flow power of each BIC are not consistent.Finally,the multi-parallel BIC system was applied to the hybrid AC/DC microgrid.Based on the power balance control of the AC/DC sub-grid,a local distributed controller was designed for each BIC.The controller could distribute the power proportionally according to the rated capacity of each BIC,effectively balance the load of the BIC,and realize the plug-and-play function.The system simulation was built in MATLAB/Simulink to verify that the proposed control strategy can realize BIC power bidirectional flow,plug and play and circulation suppression functions,and the effectiveness and feasibility of the proposed control strategy are verified by RT-Lab hardware in-loop experiment.