[1] Chungnam Natl Univ, Dept Elect Engn, Daejeon 34134, South Korea
[2] Magnetar, Dept Res & Dev, Daejeon 34103, South Korea
[3] Korea Inst Machinery & Mat, Dept Syst Dynam, Daejeon 34103, South Korea
[4] Korea Inst Machinery & Mat, Dept Energy Convers Syst, Daejeon 34103, South Korea