Abstract
This paper deals with an ultracapacitor (UC) model and its identification procedure. To take UC’s fractional characteristic into account, two constant phase elements (CPEs) are used to construct a model structure according to impedance spectrum analysis. The different behaviors of UC such as capacitance, resistance, and charge distribution dynamics are simulated by the corresponding part in the model. The resistance under different voltages is calculated through the voltage rebound method to explore its non-linear characteristics and create a look-up table. A nonlinear fractional model around an operation voltage is then deduced by applying the resistance table. This time identification is carried by a proposed hybrid optimization algorithm: Nelder-Mead seeker algorithm (NMSA), which embeds the Nelder–Mead Simplex (NMS) method into the seeker optimization algorithm (SOA). Its time behavior has been compared with the linear fractional model for charging and discharging current profiles at different levels.
Highlights
Ultracapacitors (UCs) are currently gaining attention rapidly as a new type of energy-storage component with a higher density than ordinary capacitance and longer cycle life than batteries [1,2].its energy storage principle determines its capacity cannot temporarily surpass the battery [3].Thence, it is always associated with batteries in the energy storage unit when it supplies energy to electric vehicles (EV) or hybrid electric vehicles (HEV)
The model structure is connected to UC dynamic characteristics; The using of fractional order reduces the number of parameters; The resistance voltage dependence has been taken into account; The hybrid optimization algorithm improves recognition accuracy
Because of that energy storage principle and the use of carbon electrodes, UC performance is affected by distributed surface reactivity, inhomogeneity, and roughness, which can be better characterized by constant phase elements (CPEs) according to the electrochemical impedance spectroscopy (EIS)
Summary
Ultracapacitors (UCs) are currently gaining attention rapidly as a new type of energy-storage component with a higher density than ordinary capacitance and longer cycle life than batteries [1,2]. To take into account the fast dynamics, a model consisting of three RC branches is proposed that reflected the internal charge distribution process within a specific voltage range [10]. Compared to the local search algorithm, they have a global performance nature and a greater possibility to converge to the global optimal point. Seekers determine their direction and step size, update their location, and, find the optimal point Since it is proposed, it has been used by researchers in different engineering applications like system modeling and optimal control [22,23]. The model structure is connected to UC dynamic characteristics; The using of fractional order reduces the number of parameters; The resistance voltage dependence has been taken into account; The hybrid optimization algorithm improves recognition accuracy
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