Research On Lithium-ion Battery Energy Storage System And Wind Farm Energy Storage Capacity Allocation

The application of energy storage is very important in wind power field. It has become the common understanding that improve the output of wind power generation system by adjusting inherent volatility problem of wind power using energy storage equipment. The lithium-ion battery has become the most potential energy storage battery due to its unique advantages. However, the differences of voltage, resistance and capacity among lithium-ion battery monomers lead to battery voltage fluctuation in the process of charge and discharge, which affects the normal operation of energy storage system. On the other hand, wind farm energy storage capacity allocation is also a problem that cannot be ignored. Too little energy storage will not improve the output effect obviously, but too large energy storage will result in unnecessary investment.Take lithium-ion battery energy storage system as the research object, this paper mainly focused on the voltage fluctuation of lithium-ion battery group and corresponding solutions were proposed. In the end, combined with the wind farm energy storage system, this paper also made a study on the energy storage capacity allocation.First, this paper gave simulation analysis of lithium-ion battery characteristic and discussed the lithium-ion battery equivalent model. And then, we proposed that the optimization problem of the lithium-ion battery group can be solved by bi-directional DC/DC converter. We set up a small lithium ion battery energy storage system model. In the two modes of charging and discharging, it gave the mathematics model and designed the control system for bi-directional DC/DC converter working in buck and boost modes. Based on the design, it made simulation analysis in the two modes of charging and discharging. The result proved that the bi-directional DC/DC converter can meet the requirements of the regulated output voltage of energy storage system..Secondly, this paper introduced the typical structure of wind farm energy storage system. Based on the probability distribution function of wind speed and the function of wind farm output power, a method of energy storage capacity allocation was proposed. The data from actual wind farm verified the feasibility of the proposed method. It took the cost of energy storage capacity and the degree of stability of wind power output into account and obtained the reasonable value of wind farm energy storage capacity.