Research Of Capacity Optimization And Control Strategy About Hybrid Energy Storage System In Microgrid

In a operational independence microgrid, sometimes users or load wouldnot get a continuous and reliable power because of the randomness andvolatility of wind and photovoltaic power generation. In order to enhance thestability of microgrid and ensure the power quality, it is necessary to takeenergy storage system into account. To inprove the economical efficiency andstability of microgrid, this paper has studied some research on capacityoptimization and control strategy of hybrid energy srorage system in microgrid.Due to the low power output capacity of the battery, the greater capacity ofthe battery is need to meet the short-term and high power load when thesysterm power fluctuates heavily. To avoid waste of energy storageconfiguration, battery-ultracapacitor hybrid energy system is presented in thepaper to improve the power output capacity of energy storage system andreduce the battery capacity allocation by the advantage of high power densityand fast response speed.Moreover, The optimization model of composite storage battery-supercapacitor energy storage capacity is established in the paper, which theobjective function is one-time investment minimum of the composite energystorage system, and finally the composite energy storage capacity of the systemis determined in consideration of the energy and power supply ability of theenergy storage system. By using the improved particle swarm algorithm tosolve and analyse the given example, the model of composite energy storagepresented in this paper can surely improve the efficiency of the use ofrenewableenergy and save significant economic costs in final.To realize reasonable distribution of the comprehensive load in the hybridenergy storage unit, the power allocation strategy is put forward in the paper,which the time constant based on fuzzy control is variable. Depend on thesituation of the storage unit state of charge and system power need, the timeconstant of the low pass filter need to be adjusted properly, so is the poweroutput of the battery and super capacitor. And the state of charge needs to avoidthe specified upper and lower bound. To realize the system stabilize operation, the control circuit of the storageunit needs to be designed reasonably. The small signal model of buck/boostconverter which is controlled by PWM is established in the paper, and thespecial control circuit is designed for the battery and supercapacitor. Thebattery apply the current control to suppress low frequency component of loadpower, and the supercapacitor uses the voltage-current double loop control tosuppress the shortfall between the load power and the battery power. Due to thedisadvantage of the voltage-current double loop control on suppressing the dcbus voltage fluctuation, power feed-forward is presented in the paper toeliminate the bus voltage fluctuation caused by the change of the input voltageand load current. In the final, the control strategy is proved correctly in thepaper by the given example, and through the simulation result of the example,we know that the control strategy can maintain the system stabilization, and thebus voltage can work in the reasonable range. Moreover, the charging anddischarging curve of the battery is optimized by the control strategy, and thebattery can lengthen the work time.