| Super-capacitor is a new kind of energy storage devices that performance between the battery and conventional capacitors. With the merits of high power density, long cycle life, no pollution, etc, super-capacitor has been widely used in the field of energy storage, such as electric vehicles, uninterruptible power supply, power system, etc. As a result of the limitation of capacitance monomer working voltage is too low, it is necessary to connect them in series or parallel. But the interior parameters of the super-capacitors has certain deviation, this parameter deviation will lead to different speed of charging and discharging between super-capacitors. So, when used in series, there are voltage imbalance phenomena, resulting in voltage over-charging or voltage over-discharging of some super-capacitors, affect the lives of the super-capacitors and the stability of the energy storage system. In addition, super-capacitors have the same discharge characteristics with traditional capacitors, namely the voltage drop too fast in the process of dis-charging, causing the voltage of the energy storage system can’t satisfy the requirement of load on voltage level for a long time. So, take the appropriate voltage balancing solutions and reasonable designs of voltage stabilizing circuit have the vital significance.Firstly, this paper gives the basic structure, working principle and characteristics of super-capacitor, and analyzes the three kinds of equivalent circuit models of super-capacitor: series RC model, the classical model and transmission line model, discusses the structural characteristics and scope of application of the equivalent circuit model, and to determine the RC equivalent circuit model is used in this paper. At the same time, introduces the super-capacitor charging ways, and the charging and discharging characteristics of super-capacitor is analyzed.Secondly, the article gives the working principle analysis, simulation verification, advantages and disadvantages of several common voltage balancing circuits which belong to the type of energy consumption or energy transfer. Then, in view of the characteristics of super-capacitor that low internal resistance, good linear, and low energy density, the equalizing circuit based on super-capacitor series parallel switching which uses super-capacitors self as equalizers is proposed. The equalizing circuit consists only of super-capacitors and switch tubes, by controlling the two groups switch tubes on and off to achieve voltage balancing. And the equalizing circuit has characteristics of simple structure, fast speed to balance the advantages. The feasibility of the equalizing circuit is verified through the simulation experiment.The simulation results show that the speed and effect of equalizing circuit is good, and the energy storage of system is maximum.Finally, aim at the problem that the voltage drop too fast in the discharging process of super-capacitor, there proposes a voltage stabilizing circuit in this paper allows the super-capacitor output voltage which has fallen booster to the load required voltage range through the PID control of the boost converter, solved the output voltage of the super-capacitor drop too fast in the process of discharging, to achieve the best in energy storage utilization. |
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