短語詞組短語current of commutation 換向電流zero electric current commutation 零電流換向the current commutation principle 電流轉移原理zero -current commutation 零電流換流current commutation principle 電流轉移原理current commutation in line 電流換流four step current commutation 四步換流zero current commutation 零電流換流forced current commutation 強迫換流 返回 current commutation