Studying the magnetic properties of the Grain-Oriented(GO) electrical steel under different stresses in a wide frequency range is of great significance for improving the energy conversion efficiency of the motors or transformers. Residual bending stress can cause deterioration of the magnetic properties of the motor and lead to an increase in core losses1. However, only the effect of bending stress on the magnetic properties of GO electrical steel sheets at 50 Hz has been studied so far, and the magnetic properties at higher frequencies magnetization under bending stress is still unclear2. Aiming at this problem, the magnetic properties of GO electrical steel sheet under different bending stress up to 1kHz is investigated by developing a measuring system under different curvature loading mechanisms.
II Method and Discussion
For investigating the magnetic properties of the GO steel sheet under different bending stress, the single sheet specimen to be measured were bended into different radius of curvatures as shown in Fig.1. Because of the deterioration of the magnetic characteristics caused by the bend of the sample, it is very difficult to maintain the sinusoidal waveform for standardized testing in the measurement process. A robust digital control algorithm in the frequency domain with a normalized dual-loop control loops is proposed. Fig.2 shows the some measuring results of GO steel B27R090. It can be found that with the increase of bending stress, the loss increases significantly and the higher the frequency, the greater the influence of bending stress is found.
III Conclusion
The magnetic properties of electrical steel under different bending stress over a wide frequency range are measured by the proposed measuring system with a normalized frequency domain dual-loop feedback control algorithm in this paper. Obtained results show that the bending stress of electrical steel sheet has a great influence on the iron loss, and the influence becomes more obvious with the increase of frequency.
References:
1 T. Wang et al . Fabrication and Experimental Analysis of an Axially Laminated Flux-Switching Permanent-Magnet Machine J. IEEE Transactions on Industrial Electronics, vol. 64, no. 2, pp. 1081-1091, Feb. 2017.
2 H. Hagihara, Y. Takahashi, K. Fujiwara, Y. Ishihara and T. Masuda. Magnetic Properties Evaluation of Grain-Oriented Electrical Steel Sheets Under Bending Stress J. IEEE Transactions on Magnetics, vol. 50, no. 4, pp. 1-4, April 2014, Art no. 2002104.

Fig.1. Magnetic properties measurement system for electrical steel under bending stress and dual-loop control algorithm used.

Fig.2. Measurement results of electrical steel at different bending stresses.