?????????? Chengdu University of Information Science and Technology ????? Southwest Jiaotong University ? National Key Laboratory of Traction Power ????????? ?????????? ???????????????????? ?????????????? ???????????????????????? ???????????????? ???????? ????????????? ???????????????? ?????????????? ??????????? ?????????????????????????????????? ??????????? ?????????? ?????????????????? ??????????????????? ?????????? ??????????????????????? ??????????? ?????????? ?????????????????????????? ?????????????????? ??????????? ?????????????????????? ??????????????? ???????? ??????????????????? ???????????????????????????? ?????????? ???????????????????