1. College of Electrical Engineering and Automation, Shandong University of Science and Technology, Qingdao 266590, P. R. China
2. Department of Electrical Engineering, Tshwane University of Technology, Pretoria 0001, South Africa
3. Faculty of Engineering and Built Environment, Tshwane University of Technology, Pretoria 0001, South Africa
4. Department of Mechanical Engineering, Mechatronics, and Industrial Design, Tshwane University of Technology, Pretoria 0001, South Africa
5. Department of Electrical and Electronic Engineering Science, University of Johannesburg, Johannesburg 2006, South Africa