This paper focuses on the parameter identification issue of electrochemical double layer capacitors (EDLCs). The superiority of the fractional-order equivalent impedance model is revealed mathematically and electrochemically by analyzing the variation trends of different models and the general electrochemical impedance spectroscopy (EIS) of EDLCs. Since the fractional-order models can be used to describe the long-tailed variation trend of the EIS of EDLCs in the low-frequency band and can reflect the self-charging phenomenon of EDLCs, the accuracy of parameter identification can be ensured. In addition, the idea of Levy flight is introduced and combined with the intelligent algorithms in the parameter identification process, thus accelerating the convergence rate of the parameter identification process. At the same time, the problem of nonconvex fitness function falling into local optimum can be solved. To confirm the effectiveness and superiority of this work, we provided diverse test scenarios. We used three different types of EDLCs, while a series of scenarios with or without Levy flight strategy were included in the tests. In our work, we compared not only the accuracy of the parameter identification but also the convergence rate of the identification process. The test results show that, by applying the proposed scheme, the sum of square error (SSE) between experiments and parameter identification results is less than 1.9%. Moreover, the convergence rate of the parameter identification process was improved. In extreme conditions, the convergence rate is 1287% faster than the schemes without Levy flight strategy.
In this paper, a family of a novel single-phase three-level PFC based on a switch-capacitor cell is proposed. The proposed PFC topologies have the characteristics of high power factor, low voltage stresses, and low power losses. Firstly, the derivation process of the novel PFC topologies is introduced in detail. Based on a representative circuit of the proposed novel PFC topologies, its operation principle is analyzed from the aspects of working current paths, key waveforms, and pulse distribution. Meanwhile, its equivalent circuit model is deduced. Secondly, the performance of the proposed PFC topologies is analyzed. Then the modulation technology based on capacitor voltage balancing is designed for the proposed topologies. Finally, an experimental prototype with a rated power of 800 W and a DC output voltage of 400 V is built. The experimental analysis is carried out from both the steady state and dynamic state. The experimental results verify the feasibility of the proposed novel three-level PFC topologies and the effectiveness of the modulation technology.
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