Abstract: When finding a current on an AC side of an inverter by observing that on a DC side, a current that is not affected by pulsating components contained in the AC current must be detected. Timing of change of a gate signal for driving a switch element of a phase having an intermediate magnitude among three-phase voltage command signals to ON/OFF is used as a reference time point for DC bus current detection. DC bus currents sampled T1 before and T2 after the reference time point are designated as IDC1 and IDC2, respectively. A detected current value of a maximum voltage phase is computed by using IDC2 and IDC1 respectively in an increase period and a decrease period of a carrier signal alternately. A detected current value of a minimum voltage phase is computed by using IDC1 and IDC2 respectively in an increase period and a decrease period alternately.

Abstract: A voltage detector is connected to a connection terminal connected to one phase of an AC output of an inverter through a diode. A removable charge power supply is connected to said connection terminal and another connection terminal. A charge-power-supply connection judging circuit judges whether the charge power supply is or isn't connected, based on a charge power supply voltage detected by a voltage detector. A mode change control circuit outputs switch signal by the result of said judgment. By receiving this switch signal, the inverter controller switches the operation of the inverter between the Motor Drive mode or the Battery Charge mode. Thereby, a motor drive device detects a connecting status of an external charge power supply and steadily switches the operation of the inverter between the Motor Drive mode or the Battery Charge mode.

Abstract: A vector control system for a permanent magnet synchronous motor, using a current control equivalent output value, a frequency instruction value, a current detection value, an inference phase error value, and a motor constant, identifies a motor resistance equivalent or a resistance setting error equivalent. Next, the vector control unit, using the identified value, corrects a set value R* equivalent of a voltage instruction calculation unit and a n inference phase error calculation unit. Thereby, a vector control system for a permanent magnet synchronous motor can realize a robust control characteristic for changing of a resistance constant of a motor in a low rotation speed area under position sensor-less control. Further, a vector control system for a permanent magnet synchronous motor can be applied in common in a system performing inexpensive current detection.