Study On The Coordinated Control Strategy Of The Series Compensation Link And The AC-DC Bus Interface Converter In The Hybrid Microgrid

In order to effectively deal with the increasingly serious energy crisis and environmental pressure,the proportion of clean renewable energy power generation is increasing rapidly,and the distributed utilization technology of new energy power generation is getting more and more attention The hybrid microgrid(HMG)is one of the important development directions of smart grid in the future,which can improve the utilization rate of the new energy,accept the AC and DC loads and AC and DC sources,give full play to the potential of distributed power and reduce the negative impact of intermittency and volatility of the photovoltaic and wind power generation on the utility grid.The HMG is connected to the utility grid from the low-voltage distribution network at the end of the power system.On the one hand,it is easy to be affected by unbalanced,harmonic and impact loads.On the other hand,the short-term faults such as voltage sag and swell in the utility grid will also seriously affect the normal operation of the HMG.Therefore,it is necessary to consider the problems of fault ride through(FRT)capability,safety protection capability and power quality of the HMG when the utitlity grid is not ideal.This paper proposes that the AC bus of the traditional HMG be connected to the utility grid after the series compensation link,and control the series compensation link to coordinate with the bidirectional power converter,which is between the AC and DC bus in the HMG,to improve the power supply quality and FRT capability.The main contents are as follows:(1)This paper introduced the research status of HMG and its bus interface converter and the main direction for the operation of HMG under the non ideal utility grid environment.Based on this,the paper proposes an improved AC-DC HMG,compared with the traditional HMG,a compensation link is connected between the low-voltage feeder side of the utility grid and the HMG,the whole model of the HMG with the series compensation link was constructed,and its state space average model in abc-frame and dq0-frame and small signal model were deduced.(2)The overall operation mode of the improved HMG,which includes the series compensation link and the AC-DC bus interface converter,was designed,and it included the operation switching conditions of the series compensation link and the AC-DC bus interface converter and the preset functions under different modes.Besides,the basic control strategies of the series compensation link and AC-DC bus interface converter were designed.(3)Considering the mutual influence of series compensation link and AC-DC bus interface converter through the external circuit,the principle of coupling problem was analyzed,and the coupling law between different control variables when they realize preset function was clarified.Based on this,the corresponding decoupling methods were designed and embedded in the basic control strategies of converters.(4)Based on simulation software of MATLAB / Simulink,a simulation model of the improved AC-DC HMG with the series compensation link was built,and the decoupling and coordination control strategy of the entire system was compared and analysed.The preset functions of series compensation link and AC-DC bus interface converter were verified preliminarily,and the FRT capability and power quality of the improved HMG were improved.(5)Based on dSPACE,a HMG physical platform including the series compensation link and AC-DC bus interface converter is built for experimental research.The experimental results further verified the the effectiveness of the decoupling coordinated control strategy and the effect of series compensation.