Modelling of Supercapacitor Banks for Power System Dynamics Studies

Abstract : The paper presents accurate and simple dynamic model of a supercapacitor bank system for power system dynamics studies. The proposed model is derived from a detailed RC circuit representation. Furthermore, a complete control system of the supercapacitor bank is also presented. The proposed model is easy to integrate in any power system simulation software and consists of only up to four standard datasheet parameters. The performance of the proposed model in grid frequency control and low-voltage ride through is illustrated on IEEE 14-bus test system in DIgSILENT PowerFactory. It is shown that in case of transient stability simulations the ideal (simplified) model of the supercapacitor can be used while in case of frequency control the ideal representation may not always be appropriate.
 ? This paper is unique because it focusses on the electrical applications and end use models rather than the models that focus on predicting chemical characteristics of the DLCs. Considering these factors, the timeliness and uniqueness of this review cannot be overemphasized. ? The goal of this paper is to review the many available electrical models of DLCs for power electronics applications in order to bring to light both their limitations and advantages, as well as the opportunities for further research into the subject of electrical modeling of DLCs.Additionally, this paper also seeks to raise awareness regarding the need for more research into the existing electrical models in order to address the limitations of these models, which are highlighted in this paper
 ? The difference from the other control schemes however, is that the voltage measurement is directly used as a measure of energy (State-of-Voltage, SoV) rather than State-of-Charge (SoC) through current integration since the energy of a capacitor is directly proportional to the voltage. ? Furthermore, capacitors are much more sensitive to applied voltage, which varies significantly more than in batteries. ? Therefore, a special care must be taken not to overcharge the SC since even the voltage which is only 5% above the rated voltage can damage the cell. Similarly the SC should not overly discharge because of current limitation for constant power.
 • This might have been due to the number of rungs on the ladder circuit, since the authors proposed more resistor-capacitor (RC) branches on the ladder circuit to enhance the ability of the ladder circuit model to better predict the characteristics of the DLCs. • Their research is particularly interesting because their method could be used in selecting the best alternative when comparing DLCs of the same capacitance across different manufacturers. • The RC circuit looks quite similar to the ladder circuit model; the circuit parameter identification was also done using AC impedance measurements. It was concluded that the temperature dependency of the equivalent series resistance of the DLC can be expressed using a quadratic function of temperature.
 ? The performance of the ideal model is compared to the performance of the nonlinear model. There are several parameters which may affect the performance of both models: initial capacitor voltage, ideal capacitor capacitance and how much the SC capacitance varies with voltage (i.e. ratio of capacitance at 0 V to capacitance at rated voltage). ? However, the used disturbances were smaller than the size of a fully charged supercapacitor and the time scale was not long enough to observe the differences in time-to-discharge (i.e. when the stored energy is depleted). ? As will be shown in this paper, both initial SoC and the size of a disturbance impact the performance of different supercapacitor models.

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