Virtual Synchronous Machine Control Strategy For Interfacing Converter In Hybrid AC/DC Micro-grid

The increasing penetration of distributed generators(DGs)has brought new challenges to the safe operation and control of the power system.Hybrid AC/DC micro-grid,which integrates traditional AC power system,both AC and DC renewable energy generations,energy storage systems and loads,operates as a self-running and self-managing unit and avoids bad impact from uncertainty and randomness of DGs and loads on power system effectively,will be the most important and essential part of the smart grid in the future.The interfacing converter(IFC)between AC bus and DC bus in hybrid micro-grid,which is the key component to control the power balance of the whole system,have been widely concerned and studied.To solve the problems of small inertia for IFC between AC bus and DC bus with traditional droop control in hybrid AC/DC micro-grid,a virtual synchronous machine(VSM)control strategy for IFC is proposed.With this control,inertia can be provided by taking advantage power absorbing-releasing characteristics of various generators and loads,resulting in the extension of inertia sources.The dynamic characteristic of frequency,which is similar to the synchronous generator,is combined with the steady-state characteristic of droop control for IFC.Anti-disturbance characteristics of AC frequency and DC voltage are improved effectively.The main contents are as follows:Firstly,the instantaneous power balance features of hybrid AC/DC micro-grid and power transmission principle for IFC are studied.Based on above,the VSM control strategy for IFC is designed,including AC frequency and DC voltage control to regulate active power and improve frequency dynamic response,virtual excitation control to adjust reactive power and voltage-current closed-loop control to improve the output power quality.Secondly,the small signal model of the proposed VSM control strategy for IFC is established.The stability of the closed-loop system is analyzed through root locus analysis and the Routh Criterion.Then,the control parameters of the system are designed according to the stability analysis results.Thirdly,the effectiveness of VSM control strategy for IFC in AC/DC hybrid micro-grid,which operates in inverter mode,rectifier mode and mode switching process,respectively,is verified through simulation based on MATLAB/Simulink software.The superiority of VSM control strategy compared with traditional droop control is proved according to compare the corresponding simulation results.Finally,the hardware experiment platform of an IFC based on d SPACE is built.The effectiveness and superiority of the proposed VSM control strategy for IFC is verified again by hardware experiments.