1. Department of Electrical EngineeringAmirkabir University of TechnologyTehran15916‐34311Iran
2. Department of Electrical EngineeringShanghai Jiao Tong UniversityShanghaiPeople's Republic of China
3. Key Laboratory of Control of Power Transmission and ConversionMinistry of EducationShanghai Jiao Tong UniversityShanghaiPeople's Republic of China