1. Department
of Electrical Engineering, Yale University, New Haven, Connecticut 06511, United States
2. National Renewable Energy Laboratory, Golden, Colorado 80401, United States
3. Department
of Electrical and Computer Engineering, University of Illinois Urbana−Champaign, Urbana, Illinois 61801, United States
4. Área
de Tecnología Electrónica, Universidad Rey Juan Carlos, Móstoles, Madrid 28933, Spain
5. School
of Electrical, Computer and Energy Engineering, Arizona State University, Tempe, Arizona 85287, United States