Research On Collaborative Control Of SOC Of Multi-energy Storage In Island Low Voltage Microgrid

Since microgrids are often used in remote areas with isolated environment and the renewable energy is fluctuating and uncontrollable,different types of energy storage devices should be used in island microgrid to meet the demand for power quality for the load.This kind of microgrid can be called multi-energy storage microgrid.Due to the differences in energy storage equipment,transmission line impedances and initial states of charge and energy storage capacities for the different energy storages the system will have problems such as uneven output of active and reactive power and unbalanced SOC.These problems can cause power quality problem like circulation in the system and reduces the power utilization and service life of energy storage equipment.Therefore,this paper studies the output power distribution control and SOC balance of the distributed multi-energy storage system under the island low voltage microgrid environment.Firstly,introducing and analyzing the characteristics of low-voltage island microgrid.Comparing the influence of the difference of transmission line impedance between the low-voltage island microgrid and the traditional large power grid to decide the control method of droop control.A method of droop control which suitable low-voltage island microgrid is chosed.And the control method of each part in the inverter is analyzed.The range of value of the parameters also be discussed.The correctness of this droop control can be verified through MATLAB/Simulink simulation.Secondly,considering the different energy storage and power generation equipment in the island low-voltage micro-grid system and their transmission line impedance,the distributed generations cannot divide their output active and reactive power by their capacity,which can cause power quality problem,especially the circulation problem in the system.An adaptive virtual impedance scheme for improving PV droop control is proposed to ensure that the active and reactive power evenly divided according to their capacity.This scheme can monitor the active power output of the distributed power generation unit in the system in real time to adjust the virtual impedance value,and ensure that the power generation unit distributes the output power according to capacity without causing voltage and frequency shift.This method reduces the influence of circulation in system.Effectiveness of the scheme is verified through simulation.The hardware-in-the-loop experimental system based on RTDS was used to verify the scheme.The experimental results proved the feasibility of the scheme.Finally,the SOC balance of multi-energy storage devices with different capacities,transmission line impedances and initial SOC is studied.A multi-agent based SOC balancing scheme for multi-energy storage in low-voltage island microgrid is proposed.The proposed scheme improves the distributed energy storage unit into a distributed agent,and a consensus algorithm is used through communication between adjacent multi-agents to obtain average SOC information and returns to the agents.The SOC balance factor is introduced based on the consensus algorithm to the P-V droop control to achieve the SOC balance of multiple energy storage devices with different initial SOCs.This scheme cooperates with the proposed adaptive virtual impedance scheme to eliminate the effects of different capacities and impedance of transmission lines without causing frequency and voltage offsets.Under the circumstance of cooperative control,the SOC balance of multiple energy storage devices with different capacities,transmission line impedances and initial SOC is achieved.The simulation verifies the effectiveness of the scheme.