Dual Fundamental Frequency HSS-Based Reduced Order Impedance Modeling of AC/AC Modular Multilevel Converter for Tundish Heating

Due to the specificity of continuous casting production, the application of ac/ac MMC structure in induction heating power supply requires the realization of frequency conversion from grid AC to low and medium single-phase AC, which makes the conventional modeling methods inappropriate. In this article, an HSS-based reduced order impedance model is proposed. Firstly, due to the complexity of the internal harmonics, the harmonic attenuation of the internal signals is calculated quantitatively by analyzing the three-dimensional signal-flow graph and then the harmonic frequencies are truncated, which provide a basis for model simplification. Furthermore, to precisely describe the amplitude-phase characteristics of the ac/ac MMC under different output frequencies, the harmonic state space modeling method is improved by combining the double Fourier integral transform. Finally, the correctness of the frequency analysis and the accuracy of the reduced order model are verified.