| As the penetration rate of new energy in the power grid continues to increase,the particularity of new energy also brings challenges to the smooth operation of the power grid.The energy produced by new energy distributed power generation equipment is rationally distributed through power electronic converters.Providing high-quality and stable electrical energy to the grid and local loads has always been the control goal of the microgrid.In the AC/DC hybrid microgrid,the use of multiple energy storage units with different characteristics and suitable inverter control strategies can smooth the fluctuation of the microgrid and ensure the stable operation of the distributed power generation equipment and loads in the grid.First,the converter in the AC/DC hybrid microgrid is introduced.The DC/DC converter and the DC/AC converter are respectively modeled and analyzed.The voltage and current double closed loop controller used in the DC/DC converter is designed.And the SVPWM algorithm used by the inverter is introduced to ensure that the control structure has better dynamic performance.Based on these,the main research work of this paper is as follows:(1)Aiming at solving limitation of power distribution of the droop control method which used in energy storage system control,this paper proposes an adaptive virtual parallel impedance control algorithm.Most current control algorithms are unable to distribute the unbalanced power in the system according to frequency.Especially when there are multiple energy storage units with different characteristics in the system,the irrationality of the power distribution is particularly prominent.The virtual parallel impedance control method adopted in this paper connects the virtual resistance in parallel with the virtual impedance.The method can determine the range of unbalanced power distribution rate of energy storage unit response.At the same time,considering the impact of the state of charge on the output,the charge coefficient adjustment item is added to the system.Finally,the parameter design method of parallel impedance control is given.(2)Traditional energy storage unit control methods often neglect the energy recovery of energy storage equipment.When the energy storage equipment is insufficient,the system’s ability to withstand fluctuations decreases.In this paper,a virtual parallel impedance control with a stateof-charge compensator is used to ensure rapid energy recovery of the energy storage unit.The energy storage unit can recover more quickly when the coefficient of state-of-charge is low,ensuring that the grid has sufficient flexibility.(3)In the inverter control strategy,the previous control strategy imagined the DC side of the inverter as an ideal state.However,in practice,the inverter output is often limited by the DC side energy storage situation and the renewable energy resource.Taking into account the fluctuation and change speed of photovoltaic and wind power generation,this paper adds a fuzzy control module with DC bus voltage as input to the droop control module based on the improved virtual synchronous generator.The inverter output using this control method can respond to the unbalanced power on the DC side of extremely low frequency,so that the microgrid can operate more stably.(4)According to the hybrid microgrid model,the operation model of the hybrid energy storage system and the grid-connected operation model of the inverter were built in Matlab/Simulink simulation software.The simulation results show that the control method is effective and feasible,and the steady and dynamic performance of the micro grid is improved effectively. |
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