| The rational configuration and control of energy storage systems can serve to absorb new energy excess power generation,stabilize the fluctuations of new energy generation,improve power quality,and reduce peak loads.It can also provide an emergency power support for a certain period of time when unplanned power failure in densely-accessed areas of new energy generation..Therefore,a properly configured and operated energy storage device can be an effective supplement and guarantee for stable operation of the microgrid.This paper divides the problem of the capacity allocation and control strategy of the energy storage system that can independently supply power for a certain length of time to the specific loads into three sub-problems:Establishment and fitting of mathematical model of battery life cycle and capacity attenuation,optimal configuration of the energy storage systems that can independently supply power for a certain length of time to the specific loads,and the battery energy storage system operation mode switching that can independently supply power for a certain length of time to the specific loads.For the problem that establishment and fitting of mathematical model of battery life cycle and capacity attenuation:Firstly,the charge-discharge depth and charge-discharge current are introduced as the key influence factors of the battery cycle life to establish the mathematical model of battery cycle life;Secondly,the mathematical model of battery capacity attenuation was established by using the cycle number and charge-discharge depth as the key influence factors of battery capacity attenuation;Finally,the experimental data of the cycle life and capacity attenuation of the battery were fitted to the model to verify the feasibility of the two models.For the problem that optimal configuration of the energy storage systems that can independently supply power for a certain length of time to the specific loads:Firstly,the battery economic efficiency index and cost model are analyzed,and under the premise of guaranteeing the independent power supply for for a certain length of time to the specific loads,taking the maximum annual investment return rate of the battery energy storage system within its life cycle as the objective,the economic benefit model of configuring the battery energy storage system is established which including income of arbitrage in the whole life cycle of BESS and the other three income indicators and the life cycle cost under the premise of ensuring a certain length of time independent power supply for the specific loads;Secondly,a method that can gradually simplify the optimization model by extracting key influence factors and the charge/discharge mode of the battery energy storage system that ensures independently supply power for a certain length of time to the specific loads in a grid-connected mode are proposed;Finally,the configurations and annual investment return rate of Pb-C battery(PCB),Lithium iron phosphate(LFP)battery and second-use battery are compared through case studies,ensuring a certain length of time independent power supply for the specific loads,to validate the feasibility of the established model and the proposed algorithm.For the problem that the battery energy storage system operation mode switching that can independently supply power for a certain length of time to the specific loads:Firstly,a method for achieving smooth switching between constant power control and virtual synchronous generator control for energy storage system DC/AC converters by adding mode switch in PI control link is presented;Secondly,the conditions of seamless switching from isoland mode to grid-connected mode are analyzed,and a pre-synchronization control method based on virtual synchronous generator control is given. |
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