1. Department of Electrical Engineering, Faculty of Engineering, Khon Kaen University, Khon Kaen 40002, Thailand
2. Business Development Engineer, Sermsang Power Corporation Public Company Limited, Bangkok 10300, Thailand
3. Department of Electrical Engineering, KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden
4. Center for Alternative Energy Research and Development, Khon Kaen University, Khon Kaen 40002, Thailand