| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide an alternating-current motor drive system wherein it is possible to detect only a direct current without detecting phase currents to start an inverter in free run and a current detector is simplified for cost reduction. <P>SOLUTION: The alternating-current motor drive system is constructed of: an n-phase inverter 40 having a direct-current voltage portion and n arms formed by connecting both ends of a series connection circuit of at least two switching elements in parallel with the direct-current voltage portion; and a motor 30 with n-phase fields. A current is passed only through a switching element S<SB>3N</SB>in one phase in at least either of the upper arm and the lower arm of the inverter 40. In the other arm, a current is passed through switching elements S<SB>1P</SB>, S<SB>1P</SB>in phases different from the one phase. In this state, a direct current flowing between the direct-current voltage portion and the switching element group is detected by the current detector 42, and the rotor position of the motor 30 is estimated based on the detected value. <P>COPYRIGHT: (C)2006,JPO&NCIPI |
