Motor and method of controlling motor, washing machine having motor
A motor has a two rotors which are independently operated using a single inverter and without being supplied with a complex current. Further the motor is capable of shifting a rotation direction of each of two rotors by performing a magnetizing operation one time and reversing polarities of the shifting magnets when a mode of the motor is shifted from a synchronous mode in which the first rotor and the second rotor rotate in the same direction to a counter mode in which the first rotor and the second rotor rotate in opposite directions, and shifting the mode of the motor to the counter mode while the magnetizing operation is performed one time times and relative positions of the first rotor and the second rotor are changed when the first rotor and the second rotor inertially rotate in the synchronous mode.
1. A method of controlling a motor, the method comprising:
performing, at the motor including a stator, a first rotor and a second rotor disposed around the stator and independently rotatable, a plurality of shifting magnets disposed in at least one of the first rotor and the second rotor and whose magnetic poles are reversed by a magnetizing current, and a number-of-magnetic-poles shifter configured to receive the magnetizing current, reverse the magnetic poles of the plurality of shifting magnets, and shift the a number of magnetic poles of at least one of the first rotor and the second rotor, a magnetizing operation one time and reversing polarities of the plurality of shifting magnets when a mode of the motor is shifted from a synchronous mode in which the first rotor and the second rotor rotate in the same direction to a counter mode in which the first rotor and the second rotor rotate in opposite directions; and
shifting the mode of the motor to the counter mode while the magnetizing operation is performed one or more times and relative positions of the first rotor and the second rotor are changed when the first rotor and the second rotor inertially rotate in the synchronous mode.
2. The method of claim 1 , wherein the magnetizing operation performed one time includes repeating a partial magnetization process, in which the magnetizing current is supplied to a portion of the plurality of shifting magnets.
3. The method of claim 2 , wherein the partial magnetization process begins from an end at any one side in a circumferential direction of the plurality of shifting magnets.
4. The method of claim 2 , wherein:
the partial magnetization process includes a long magnetization process in which a length of time during which the magnetizing current is supplied is long and a short magnetization process in which a length of time during which the magnetizing current is supplied is short; and
in the plurality of shifting magnets, the long magnetization process is performed at a position closer to a central portion in a circumferential direction of the plurality of shifting magnets in comparison to the short magnetization process.
5. The method of claim 4 , wherein the long magnetization process is performed when a number of simultaneous rotations of a rotor corresponding to magnetization, which is subject to the magnetizing operation, of the first rotor and the second rotor exceeds a predetermined number of rotations.
6. The method of claim 5 , wherein the short magnetization process is repeatedly performed when the number of simultaneous rotations of the rotor corresponding to magnetization, which is subject to the magnetizing operation, of the first rotor and the second rotor is equal to or less than the predetermined number of rotations.
7. The method of claim 2 , wherein:
the partial magnetization process includes a strong magnetization process in which the magnetizing current is relatively large and a weak magnetization process in which the magnetizing current is relatively small; and
in the plurality of shifting magnets, the weak magnetization process is performed at a position closer to an end in a circumferential direction of the plurality of shifting magnets in comparison to the strong magnetization process.
8. The method of claim 1 , wherein, by an initial phase of a rotor corresponding to magnetization, which is subject to the magnetizing operation, of the first rotor and the second rotor being set as an initial value and a movement amount of the plurality of shifting magnets being calculated, the magnetizing operation is performed while a current-carrying phase of the magnetizing current is shifted in accordance with movement of the rotor corresponding to magnetization.
9. The method of claim 1 , wherein:
a rotor corresponding to magnetization, which is subject to the magnetizing operation, of the first rotor and the second rotor includes a plurality of fixing magnets whose magnetic poles are not reversed when the magnetizing current is supplied; and
the plurality of shifting magnets and the plurality of fixing magnets are differentiated by reduction in magnetic force of the plurality of shifting magnets being detected when the plurality of shifting magnets are magnetized so that a magnetic force thereof is temporarily reduced.