Patent ID: 8704467

Claim:
An inverter device provided on a washing machine configured to execute a wash operation by rotational drive force exerted by a permanent magnet motor, the inverter device configured to control the permanent magnet motor, the permanent magnet motor comprising a stator including stator windings and a rotor magnet disposed on a rotor side of the permanent magnet motor, the rotor magnet comprising a first permanent magnet and a second permanent magnet having a level of coercivity smaller than the first permanent magnet, the level of coercivity of the second permanent magnet being small enough to allow variation in an amount of magnetism, the inverter device comprising: an inverter circuit configured to energize the stator windings; and a control circuit configured to control the energizing of the stator windings by the inverter circuit; a position detecting element configured to detect a rotational position of the rotor; wherein the control circuit causes the inverter circuit to produce an excitation current in the stator windings to vary the amount of magnetism of the second permanent magnet to execute a dehydrate operation with a magnetic flux of the rotor magnet reduced and to execute an operation at a lower maximum rotation count compared to the dehydrate operation with the magnetic flux of the rotor magnet increased; and wherein when the amount of magnetism of the second permanent magnet is varied while rotation of the permanent magnet motor is stopped, the control circuit switches a phase of the excitation current for varying the amount of magnetism depending on a rotation stop position indicated by a position signal outputted by the position detecting element of the rotor so that an amount of movement of the rotor is reduced.