A novel AC loss measurement method for HTS coils based on parameter identification

Abstract

In the presence of AC current or AC magnetic field, superconductors will suffer AC loss. The measurement of AC loss is of great significance for applied superconductivity field. There are three main different methods for AC loss measurement. Among them, electrical measurement methods are widely researched by different laboratories. The existing electrical measurement method mainly has two shortcomings: it is difficult to be used in High temperature superconductivity (HTS) coils with high inductance and only available for periodic current conditions (only obtains average value of AC loss for one or several current periods and cannot obtain AC loss at any instant). In this paper, a novel AC loss measurement method based on parameter identification is proposed to solve the second shortcoming (only available for periodic current conditions). This novel method measures AC loss by identifying HTS coils’ resistance and inductance at any moment, which is completely different from previous measurement methods. The theoretical basis of this novel method mainly contains three parts: equivalent circuit of HTS coils, instantaneous power identification from Poynting theorem and parameter identification based on recursive least squares with fixed forgetting factor. Compared with AC loss measurement results of previous electrical method (integral method), the validity of this novel measurement method is demonstrated. In theory, this novel method can measure AC loss for any current waveform (periodic and aperiodic current), which greatly widens measurement range of previous electrical method. The principle of this novel method and detailed experimental results are discussed and analyzed in this paper.