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The complex derivative D α±jβ , with α, β ∈ R+ is a generalization of the concept of integer derivative, where α = 1, β = 0. Fractional-order electric elements and circuits are becoming more and more attractive. In this paper, the complexorder electric elements concept is proposed for the first time, and the complex-order elements are modeled and analyzed. Some interesting phenomena are found that the real part of the order affects the phase of output signal, and the imaginary part affects the amplitude for both the complex-order capacitor and complex-order memristor. More interesting is that the complex-order capacitor can do well at the time of fitting electrochemistry impedance spectra. The complex-order memristor is also analyzed. The area inside the hysteresis loops increases with the increasing of the imaginary part of the order and decreases with the increasing of the real part. Some complex case of complex-order memristors hysteresis loops are analyzed at last, whose loop has touching points beyond the origin of the coordinate system.

Summary An enhanced level‐increased nearest level modulation (eNLM) method is proposed to improve the performance of modular multilevel converter (MMC) with relatively small number of submodules. The eNLM method can almost double the level number of ac output voltage, compared with conventional NLM. Consequently, the ac output voltage quality of the MMC using eNLM is significantly enhanced. The proposed method inherits the advantages of the conventional NLM such as simple implication and low switching loss and avoids the disadvantages of the existing improved NLM method such as increasing in submodule capacitor voltage ripple amplitude and voltage offset, arm inductor voltage peak, complexity in topology, etc. PSCAD/EMTDC simulation results confirmed the effectiveness of the proposed method.

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Generally, the thermal conductivity of gas insulation medium is generally worse than that of liquid insulation medium. The heat dissipation problem is the key to developing large-capacity gas-insulated transformers. The traditional SF6 gas-insulated transformers are facing the challenge of upgrading and updating due to the strong greenhouse effect of SF6. As an ideal substitute gas for SF6, i-C4F7N/CO2 gas mixture is used as a new insulation medium to develop eco-friendly gas-insulated transformers. In this work, we described the structure and parameters of 10 kV GIT and measured the temperature and pressure by mounting sensors in different parts of 10 kV GIT. Further, we analyzed the heat dissipation performance of the Transformer based on the pressure and temperature data. The results show that the GNAN cooling mode may not be applicable to eco-friendly GITs with large capacities and high loads.