Synchronous motor drive device, air-sending device and air-conditioning device

A synchronous motor drive device that drives a plurality of synchronous motors connected in parallel to one another, comprising:

• a power converter that converts power from a power source to supply the power to the plurality of synchronous motors,
• a first switch device that electrically connects or disconnects the power converter and each of the plurality of synchronous motors, and
• a controller, based on a higher order command containing a work amount, configured to:
• perform stability judgment processing of the plurality of synchronous motors based on relationship in phase current flowing through each of the plurality of synchronous motors for the work amount,
• determine a number of synchronous motors to be driven and a total drive speed from among the plurality of synchronous motors to generate the work amount,
• select a synchronous motor corresponding to the number of the synchronous motors to be driven from among the plurality of synchronous motors to generate the work amount,
• control the first switch device corresponding to the selected synchronous motor to electrically connect the power converter to the synchronous motor and to supply the power, and
• output a signal containing the total drive speed of the synchronous motor to be driven, wherein
• the controller is further configured to determine that a single motor is to be driven in response to the work amount being below a predetermined work amount and determine that multiple motors are to be driven in response to the work amount being above a predetermined work amount, and
• the controller is further configured to allocate a portion of the total drive speed to each of the multiple motors to be driven in response to determining that multiple motors are to be driven and allocate the total drive speed to the single motor in response to determining that only the single motor is to be driven.