Super-capacitor Voltage Management System Based On Active Equilibrium Technology

As a new energy storage device,a supercapacitor has the features of high power density,excellent reversibility,very long cycle life(>500 000 cycles),suitability for quick charge and discharge,and wide temperature range,perfect characteristic in low temperature.Therefore,they have been widely used in consumer electronics,new energy electric vehicle,Uninterruptible Power Supply,smart grid and other fields.The rated voltage of supercapacitor cell is very low,for example,1-3V,so generally several supercapacitors are series connected to be used in applications to meet high voltage demands.For the reason of manufacturing deviations,errors will unavoidably exist in the parameters of different supercapacitor cells,such as internal resistance,capacity and leakage current,thus the voltage change rate of each cell is not in step during charging and discharging in series,even some of the supercapacitor will be overcharged or overdischarged.Finally,their life will be reduced gravely and the supercapacitor’s energy can not be used efficiently.Voltage management,often referred to as voltage balancing or voltage equalization,is a technology that can prevent voltage deviations effectively and ensure energy utilization efficiency and service life of series connect supercapacitor group.Therefore,voltage balancing is very necessary and critical module for series connect supercapacitor group in the practical application.In this paper,through analyze charge storage mechanisms,charge and discharge characteristics and equivalent module of supercapacitor,combining with the features of existing voltage balancing solution,a new supercapacitor voltage equalization precept is proposed.Finally,a equalization system is designed to test the actual effect.As core data processing unit of the balancing system,the main controller is designed with FPGA.The main sub-modules of this system include voltage sampling module,AD conversion module,driver module of power MOSFET,switch network(voltage equalization)module and LCD display module.The working principle of this system is: voltage sampling module monitor the voltage of each supercapacitor and then transmit those data to the main controller-FPGA.After analysis and handle,main controller selected the maximum & minimum voltage of supercapacitor monomer at this moment.Meanwhile,the switch network module was controlled to make corresponding shut off or conduction.As a result,the voltage of the maximum and minimum supercapacitor monomer was connected directly,then the energy flow from the highest voltage to lowest voltage directly.During this period,if the mian controller detect there has a change of voltage sequence(namely,there has a new momomer which have the maximum or minimum voltage),the switch network makes some act again to ensure the highest voltage monomer and the lowest voltage monomer is connected and energy transfer from high to low.Repeat those above process,each individual supercapacitor was balance eventually.The simulation by PSIM prove the fessibility of this system.Experiment results demonstrating the effectiveness of the proposed equalizer.Compared with other equilibrium system,it has a higher balance speed,simpler structure and easy to modular.There is no insffective energy consumption in theory because this system did’t need other energy storage device in the process of balancing.