1. College of Electromechanical Engineering, Qingdao University of Science & Technology, 99 Songlin Rd., Laoshan District, Qingdao 266061, People’s Republic of China (Corresponding author), e-mail: mbj2018@sina.com, https://orcid.org/0000-0002-4247-5616
2. College of Electromechanical Engineering, Qingdao University of Science & Technology, 99 Songlin Rd., Laoshan District, Qingdao 266061, People’s Republic of China