Rotary machine controller, refrigerant compressor, refrigeration cycle system, and air conditioner

A rotary machine controller comprising:

• a connection switch including a switcher to switch a connection state of a winding of a rotary machine by performing a switching operation of the switcher during a rotating operation of the rotary machine;
• a current detector to detect a rotary machine current flowing in the rotary machine;
• a position/speed estimator to estimate a magnetic pole position and speed of a rotor of the rotary machine on the basis of the rotary machine current;
• a voltage applicator to apply a voltage to the rotary machine;
• and
• a control circuitry to generate a voltage command that is given to the voltage applicator on the basis of the magnetic pole position and the speed estimated by the position/speed estimator, and output a switching operation command for switching the connection state to the connection switch, wherein
• the control circuitry generates the voltage command to bring the rotary machine current close to zero before the connection state of the winding of the rotary machine is switched and, after the connection state of the winding of the rotary machine is switched, outputs an initial restoration speed determined on the basis of the estimated speed of the rotary machine before switching to the position/speed estimator, and
• the position/speed estimator receives the initial restoration speed and replaces the estimated speed with the initial restoration speed.