Abstract: In a speed detector having a fixed frequency oscillator for producing two-phase sine waves to excite two-phase exciting windings of a resolver, first and second multipliers for multiplying the output of the detecting winding of the resolver by the two-phase sine waves respectively, and a position conversion circuit and speed conversion circuit, the speed conversion circuit comprises: a third multiplier for multiplying a signal of the first multiplier by a signal of a VFO; and a fourth multiplier for multiplying a signal of the second multiplier by a signal of the VFO, the outputs of the third and fourth multipliers being applied through a comparator to a proportional integration amplifier, the output of which is used as the rotation speed signal and applied to the VFO, thereby to eliminate the necessity for provision of a countermeasure against harmonics and harmonic noise involved in the use of an integration circuit required when a resolver is used as a detector.

Abstract: There is disclosed a current type inverter excellent in transient response which comprises a two-phase sine wave generator for receiving signals corresponding to a motor speed signal and a speed deviation signal, to provide sine waves shifted 90.degree. in phase, and a vector calculating circuit for calculating stator current instruction vectors from exciting current components and torque current components, the outputs of the vector calculating circuit being applied as frequency instruction signals of a conventional current type inverter.

Abstract: In a control device of an AC motor wherein a torque equivalent to that of a DC motor is created by controlling the instantaneous values of its stator current, or in a vector control device, signals from a position detector such as a resolver coupled to the AC motor are utilized to form stator current instruction signals and to provide rotation position feed-back signals and rotation speed feed-back signals for the AC motor, thereby to perform precise servo-control.

Abstract: In a control device of an AC motor wherein a torque equivalent to that of a DC motor is created by controlling the instantaneous values of its stator current, or in a vector control device, signals from a position detector such as a resolver coupled to the AC motor are utilized to form stator current instruction signals and to provide rotation position feed-back signals and rotation speed feed-back signals for the AC motor, thereby to perform precise servo-control.