1. Bradley Department of Electrical and Computer Engineering Virginia Polytechnic Institute and State University Blacksburg Virginia USA
2. School of Electrical Engineering, Beijing Jiaotong University Beijing P. R. China
3. Pacific Northwest National Laboratory, Battelle Seattle Research Center Seattle Washington USA
4. School of Electrical Engineering and Computer Science, Washington State University Pullman Washington USA
5. U.S. Department of Energy Office of Electricity Delivery and Energy Reliability Washington DC District of Columbia USA