Research On Energy Management Strategy Of AC-DC Hybrid Microgrid

AC-DC hybrid microgrid is a power supply and distribution system integrating distributed generation,local load and energy storage devices,with both grid-connected and islanded operation modes,providing a good platform for efficient and large-scale utilization of distributed generation.Distributed generation as the basic unit that makes up the microgrid,its unstable output power poses a great challenge to the stable operation of AC-DC hybrid microgrid.The hybrid energy storage unit composed of energy storage device battery and power storage device supercapacitor can give full play to the advantages of both,and with corresponding energy management strategy,the operational stability of AC-DC hybrid microgrid can be effectively improved.Based on this,several key technologies such as power allocation strategy of hybrid energy storage unit and energy management strategy of hybrid AC-DC microgrid are investigated around the problem of stable and coordinated operation of AC-DC microgrid.First,a power allocation strategy considering the State-of-Charge of supercapacitor and battery is studied to cope with the power fluctuations caused by load changes and to optimize the operation of hybrid energy storage units.Based on the measured SOC of the supercapacitor,a low-pass filtering algorithm with time constant T varying with it is used to initially allocate the fluctuating power between the two types of energy storage units,with the supercapacitor taking up the high-frequency part of the fluctuating power and the battery taking up the low-frequency part.When multiple batteries share the allocated power,a power allocation strategy based on adaptive droop control is studied in order to balance the SOC of each battery group,where the droop coefficient is set to be proportional to SOC~nduring charging and inversely proportional to SOC~n during discharging,so as to control the charging/discharging rate of each battery.A simulation model is built in Matlab/Simulink to simulate and verify the effectiveness of the power allocation strategy of the studied hybrid energy storage unit.Then,the control strategies of PV power generation unit and bidirectional DC/DC converter are studied to realize the maximum power tracking and power-limited operation by changing the operating point of PV modules,and the charge/discharge control of hybrid energy storage unit is realized by using the double closed-loop control of voltage outer loop and current inner loop;the PQ control,V-f control and droop control strategies of DC/AC inverter are studied to realize the AC/DC hybrid micro The PQ control,V-f control and droop control strategies of DC/AC inverters are studied to achieve AC-DC hybrid microgrid bus voltage and frequency stability.In order to realize the stable operation and power balance of the hybrid AC/DC microgrid,an energy management strategy is studied to realize the power supply of the hybrid AC/DC microgrid to the load and external grid under various operating conditions by coordinating the control of the PV generation units and each energy storage device.The simulation results verify the effectiveness of the proposed energy management strategy and ensure the safe and stable operation of the system.Finally,using the semi-physical simulation experiment platform,the main circuit is run on the FPGA board,and the controller adopts the TMS320F28335 of TI C2000 series,and the two realize the signal interaction through the interface board to form a closed-loop system to experimentally verify the effectiveness of the above control strategy.