Patent ID: 8242724

Claim:
A driving device for synchronous motors which rotates a rotor by a rotating magnetic field produced by a star-connected stator coil, the driving device comprising: an inverter circuit which has a plurality of pairs of switching elements connected in series and in which the plurality of pairs of switching elements are connected in parallel between a positive pole bus and a negative pole bus; a capacitor; a normal operation controlling means configured to cause the plurality of switching elements of the inverter circuit to perform switching operation and thereby output alternating current to the stator coil based on an output voltage of a power supply device and an output voltage of the capacitor to produce the rotating magnetic field by the stator coil; and an initial state controlling means configured to cause the switching elements to perform switching operation prior to execution of control by the normal operation controlling means and thereby control state of charge of the capacitor, wherein a positive electrode of the power supply device is connected to a neutral point of the stator coil, and a negative electrode of the power supply device is connected to the negative pole bus.