1. Kwame Nkrumah University of Sci. and Technology,Electrical and Electronic Eng. Dept.,Kumasi,Ghana
2. Kumasi Technical University,Electrical and Electronic Eng. Dept.,Kumasi,Ghana
3. Wuhan University of Technology,School of Automation,Wuhan,China
4. Lanzhou Jiaotong University,School of Elect. Power & Automation,Lanzhou,China