The first coordinate converter 130 may perform reference coordinate transformation to the sum of the fundamental wave voltage command (v_dqsf^{{circumflex over (r)}}*) and the high frequency voltage command (v_dqsh^{{circumflex over (r)}}*) on the basis of the estimated angle ({circumflex over (θ)}_r) from an estimated synchronous coordinate system (d{circumflex over (r)}, q{circumflex over (r)}) to a stationary coordinate system. The second coordinate converter 150 may perform reference coordinate transformation to the current (i_dqs^{{circumflex over (r)}}) of the motor 101 on the basis of the estimated angle ({circumflex over (θ)}_r) from a stationary coordinate system to an estimated synchronous coordinate system.

The inverter 140 may apply a voltage (v_abcs) to the stator of the motor 101 on the basis of the voltage command (v_dqs^{{circumflex over (r)}}*). The stator of the motor 101 rotates the rotor since the stator voltage forms a rotating magnetic field by the applied voltage (v_abcs). The inverter 140 may be a single-phase inverter or a multi-phase inverter.

The angle estimator 180 may estimate the position of the rotor of the motor 101 on the estimated coordinate system on the basis of the current signal (i_sig) of the motor 101. Namely, the angle estimator 180 may output an estimated angle ({circumflex over (θ)}_r). The current signal (i_sig) may be a signal obtained by demodulating the high frequency current component (i_dqsh^{{circumflex over (r)}}) extracted from the motor current (i_dqs^{{circumflex over (r)}}) of the motor 101.