The Application And Evaluation Of Supercapacitors In Renewable Energy System

Supercapacitors are adopted in this paper for leveling the renewable energyoutput power fluctuation. The principle and characteristics of supercapacitorsare introduced firstly, then the charging and discharging models areestablished and the control strategies of the supercapacitor energy storagesystem(SCESS) in two different applications are designed in this paper.SCESS compensate the power deviation out of the leveling target of power systemto leveling the renewable energy as a scheduled power. In order to reduce thefluctuation of renewable energy output power, the moving average algorithmis used to determine the leveling target, then the power of SCESS is regulatedaccording to its state of charge(SOC). In addition, the feasibility and effect ofSCESS and lithium battery energy storage system in leveling the fluctuationof renewable energy power based on the same cost have been compared, andtheir best applications have been analyzed according to their current energy,power and cost parameters.Due to the mutual complementarity of supercapacitors and batteries, forimproving the power performance of energy storage system and prolongingbatteries’ life, the hybrid energy storage system(HESS) comprised ofsupercapacitors and batteries is studied. For reducing the fluctuation ofrenewable energy output power in maximum degree and optimizing theoperation of HESS, the time constant of the low-pass filter is controlled toregulate the leveling target, according to the SOC of HESS, and the fuzzycontrol theory is used to allocate the power out of the leveling target betweenthe two storage mediums, according to the SOCs of batteries and supercapacitors.In order to reduce the charging and discharging number of times of batteries,supercapacitors compensate the power deviation out of the leveling targetindependently when its energy is sufficient. When the remaining capacity ofsupercapacitors is insufficient, the batteries and supercapacitors should share thepower variation.Finally, in order to improve the cost performance of energy storagesystems(ESS) and reduce the cost of ESS, the relationship between the leveling effect of ESS and its installation capacity is studied. Theoptimization models of ESS in independent system and grid connectedoperation system of renewable energy have been established respectively.This paper adopts the enumeration method to calculate the optimal installedcapacity of ESS, discretizes the installation energy and power according to acertain rule and works out their collections firstly, then compares the levelingeffects of all energy-power combinations so as to determine the optimalenergy-power combination. In addition, for optimizing the installation andcontrol methods to improve the performance of ESS maximumly, thedistributed control and central control methods of ESS’s capacity are studied,and the leveling effects of the two methods are compared.