Rotary-machine control device, refrigerant compression apparatus, and air conditioner

A rotary-machine control device comprising:

• a connection switching device to switch a connection state of stator windings of a rotary machine;
• a current detector to detect a rotary machine current flowing in the rotary machine;
• voltage application circuitry to apply voltage to the rotary machine;
• control circuitry to generate a voltage command provided to the voltage application circuitry and output a switching command to switch the connection state to the connection switching device;
• and
• open-phase determination circuitry to determine presence or absence of disconnection in the rotary machine or presence or absence of disconnection of a power distribution line to the rotary machine, wherein
• during rotation of the rotary machine, the control circuitry outputs the switching command and the open-phase determination circuitry determines presence or absence of disconnection, and
• when a test voltage for the determination is applied to the rotary machine from the voltage application circuitry, the open-phase determination circuitry determines presence or absence of disconnection by comparing a value of the rotary machine current detected by the current detector with a reference value.