JP2885460B2 - Two stator induction motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention has a single rotor and two stators, generates a phase difference between rotating magnetic fields generated around a rotor conductor facing the two stators, and is capable of shifting. The present invention relates to a two-stator induction motor capable of generating a high torque from a low speed to a high speed with smooth startup.

[Prior art]

Torque control and speed control of an induction motor having a plurality of stators include a method of changing a phase difference between stators in a known technique, for example, Japanese Patent Application No. 61-128314, which is an invention of the present applicant. is there. The method of changing the phase difference is to provide a phase difference by rotating the stator as mechanical, or to provide some kind of phase difference by changing the connection of the stator winding as electrical. There are a wide variety such as those combining star delta switching with them. The above method uses various methods depending on the load or application, such as when the torque and speed of the induction motor are freely changed to respond to the load, when the speed is increased smoothly at the start, and when the load or application is used. Become.

[Problems to be solved by the invention]

The present invention responds to a load by providing a phase difference, and can be said to be an electrical method when distinguished by the conventional technology. By the way, the electrical transfer method in the prior art is performed by switching the connection of the stator winding, and the phase difference is 0 °, 60 °, electrical angle.
Although 120 ° and 180 ° can be implemented, the number of switches required for the switching is over ten and expensive. Further, some general induction motors are provided with a star-delta switching device for the purpose of improving startability. This is because the wiring is complicated despite the single stator, and the torque fluctuation occurs due to the temporary switching of the load current at the time of the star-delta switching, and further, the sudden change of the load current after the switching. Shock due to changes and sudden fluctuations in the generated torque was inevitable. The present invention has the same torque characteristics as those in which the connection is switched to each phase difference as described above, and is capable of continuously changing the speed, and is inexpensive with a small increase in the load current and a small change in the load torque. It is intended to provide a two-stator induction motor.

[Means for Solving the Problems]

In order to solve the above-mentioned problems, the present invention provides two rotor cores at an arbitrary interval on the same rotation axis, and a plurality of conductors connected to the two rotor cores, and both ends of the conductors are provided. And a first stator core and a second stator core circumferentially opposed to the respective rotor cores and wound around the first stator core. A stator winding and a second stator winding wound on a second stator core are arranged so that a predetermined rotation between the phase of the rotating magnetic field of the first stator winding and the phase of the second stator winding is performed. A first stator and a second stator connected to a power supply in series delta connection so as to produce a first phase difference, and connection of arbitrary phases of respective stator windings of the first stator and the second stator; A switch provided between a point and another two-phase connection point, wherein the switch is closed during energization of each stator winding. The first stator winding and the second stator winding are switched from a series delta connection to a parallel star connection, and the phase of the rotating magnetic field of the first stator winding and the phase of the second stator winding are changed. A first phase difference that produces a predetermined second phase difference between
A phase switching device; and a switch provided between a connection point of an arbitrary phase of each of the stator windings of the first stator and the second stator and a power supply of another phase. The first stator winding and the second stator winding are switched from a series delta connection to a parallel delta connection by closing the switch during energization of
A second phase switching device that produces a predetermined third phase difference between a phase of the rotating magnetic field of the first stator winding and a phase of the second stator winding; and a first phase switching device and a second phase switching device. A two-stator induction motor was constituted by a control device for controlling the opening and closing of the switches of the phase switching device. In another means, a first stator core and a second stator core are provided around each of the rotor cores, and a first stator winding wound around the first stator core and a second stator core are provided. The second stator winding wound around the two stator cores generates a predetermined first phase difference between the phase of the rotating magnetic field of the first stator winding and the phase of the second stator winding. Stator and second stator connected in series delta connection to a power supply as described above, and a connection point of an arbitrary phase of each stator winding of the first stator and the second stator and a power supply of another phase The first stator winding and the second stator winding are connected in parallel from a series delta connection by controlling the energization of the switch while energizing each of the stator windings. The phase of the rotating magnetic field of the first stator winding and the phase of the rotating magnetic field of the second stator winding are gradually switched to a delta connection. A two-stator induction motor is constituted by a phase switching device that gradually changes the phase difference between the first phase difference and the second phase difference from the first phase difference to a predetermined second phase difference, and a control device that controls opening and closing of a switch of the phase switching device. . By the way, in the cage rotor, a plurality of conductors at arbitrary intervals are short-circuited to each other by a resistance material, so that the two-stator induction motor of the present invention works effectively. Further, the switch of the phase switching device is a semiconductor element,
Alternatively, a variable resistor is an effective means.

[Action]

First, according to claim (1), the stator winding of the present invention is:
As a series delta connection. The phase difference between the stators at this time is
One of 180 °, 120 °, 60 °, and 0 ° can be considered. First,
A first operation is a circuit in which the first and second stator windings are connected to a power supply as a series delta connection so that a phase difference of, for example, 120 ° is generated between the rotating magnetic fields of the first and second stators. When a switch for short-circuiting between the connection point of the first and second stator windings and the connection point of the other two phases is provided and closed, a parallel star connection is established and the phase difference of the rotating magnetic field is reduced by 60 °. Can be switched to Therefore, at the time of start-up, a serial delta connection having an arbitrary phase difference is established, and when a short circuit occurs, switching is made to a parallel star connection and to a different phase difference. In other words, when switching from serial delta connection to parallel star as it is, the respective phase differences are, for example, 180 ° to 120 °, 120 ° to 60 °, 60 °
From 0 ° to 0 ° respectively. As a second operation, a circuit in which the first and second stator windings are connected to a power supply as a series delta connection so that a phase difference of, for example, 120 ° is generated between the rotating magnetic fields of the two stators is provided. When a switch for short-circuiting between a connection point of an arbitrary phase between the first and second stator windings and a power supply of another phase is provided and closed, a parallel delta connection is established and the phase difference of the rotating magnetic field is reduced by 0 °.
It is possible to switch to Therefore, the phase difference between the rotating magnetic fields can be switched from 120 ° of the serial delta to 60 ° of the parallel star and from 60 ° of the parallel star to 0 ° of the parallel delta by the above two actions. The above is summarized as follows. First, when the power is turned on, the phase difference between the stators is activated by the serial delta connection of the arbitrary phase difference. The load is activated by the torque characteristic curve with an arbitrary phase difference. Next, when the first operation reaches an arbitrary rotation speed and the connection point between the first and second stator windings is short-circuited by closing the switch of the first phase switching device to form a parallel star connection, the phase difference becomes 60 ° less. The torque characteristics and the current characteristics change. Further, the switch of the first phase switching device is opened by reaching the arbitrary rotation speed by the second action, and the second phase switch provided between the arbitrary connection point of the first and second stator windings and the power supply of the other phase. If the switches of the phase switching device are short-circuited to make a parallel delta connection, the phase difference between the rotating magnetic fields will be further reduced by 60 ° compared to the parallel star connection, and the torque characteristics and current characteristics will further change to the characteristics of rated operation. Will be anything. According to claim (2), in order to obtain an intermediate characteristic of the three torque characteristics in a stepless manner, a connection point between an arbitrary phase of the first and second stator windings and a power source of another phase is provided. The connection between them is made via a triac, thyristor or variable resistor, so when starting up, high torque and low current can be used, and the motor can be operated at any torque and current without any steps up to the operation after startup, and shifting is possible. It is. In this case, by changing the firing angle of the triac or thyristor or the resistance value of the variable resistor, the serial delta connection is gradually switched to the parallel delta connection, and the phase difference between the rotating magnetic fields is also reduced from, for example, 120 ° to 0 °. ° gradually changes. Regarding the change in the torque characteristic and the current characteristic due to the change in the phase difference between the rotating magnetic fields, the present applicant has filed Japanese Patent Application No. 61-2283.
No. 14 details this. The phase difference in the description of the operation is based on the electrical angle.

【Example】

Although the present invention will be described in detail as a two-stator induction motor having a cage rotor, it can also be applied as a linear motor. The configuration between the rotor cores may use a space, a non-magnetic material, a magnetic material, or the like. The present applicant has already described in detail the structure and operation of an induction motor comprising a plurality of stators, which is a part of the structure of the present invention, as Japanese Patent Application No. 61-128314. Referring to FIG. 1, one embodiment of an electric motor which forms a part of the configuration of the present invention will be described. Reference numeral 1 denotes a two-stator induction motor according to the present invention, and the induction motor 1 has the following configuration. The rotor cores 2 and 3 made of a magnetic material are mounted on the rotor shaft 4 at arbitrary intervals. A non-magnetic core 5 is provided between the rotor cores 2 and 3, or a space is provided between the rotor cores 2 and 3. Rotor core
Each of the plurality of conductors 6 provided in each of the plurality of conductors 6 is connected to and connected to the rotor cores 2 and 3 to form an integral rotor 7. Both ends are short-circuit rings 8,
Shorted by 8. In this embodiment, each of the conductors 6 provided on the rotor 7 is a resistive material for flowing a current having an arbitrary vector difference in the nonmagnetic core 5 between the rotor cores 2 and 3. 9. The torque characteristics differ depending on the presence or absence of this resistance material.
Unnecessary is selected by the load torque. A first stator 12 and a second stator 13 having first and second stator windings 10 and 11 provided on an outer portion facing the rotor cores 2 and 3 are arranged side by side on a machine casing 14. The stator 12 and the second stator 13 are fixed to the machine casing 14. The connection between the first and second stator windings 10 and 11 of the first and second stators 12 and 13 is, for example, a series delta connection having an electrical phase difference of 120 °. Next, according to the embodiment of the present invention, the electrical phase difference is from 120 ° to 60 °.
The change from 0 °, 60 ° to 0 ° is shown as an example, and the respective phase differences will be described as starting, accelerating, and operating with reference to FIG. FIG. 2 is a connection diagram of the first embodiment. Hereinafter, a case where the first and second stator windings 10 and 11 are three-phase will be described. U ₂ −X ₂ , V ₂
−Y ₂ , W ₂ −Z _2, and the winding of each phase of the stator winding 11 is U ₁ −X ₁ ,
Let V ₁ −Y ₁ and W ₁ −Z ₁ . Respective phases of the stator windings 10 and 11 are mechanically arranged at the same position, that is, U ₁ -X ₁ and U ₂ -X ₂ are arranged at the same position. As shown in the figure,
Let E ₁ , E ₂ , E ₃ , E ₁ ′, E ₂ ′, E ₃ ′. Next, the connection will be described. First, the terminals U ₁ , V ₁ , and W ₁ of the stator winding 11 are connected to three-phase AC power supplies A, B, and C, respectively.
Connect the terminals X ₁ and W _{2 of the} stator windings 10 and 11 to W ₂ , Y ₁ and U ₂ , Z ₁ and V ₂ , and further connect the terminals X ₂ of the stator winding 10 to C and Y ₂ Connect Z ₂ to B. In this state, the first and second stator windings are connected in series delta connection to the power supply. Further a switch S ₁ 20 to short-circuit the terminals X _1, Y _1, Z ₁ of the stator winding 11 and the first phase switching device, a terminal X ₁
Between W ₂ and power supply C, between terminals Y ₁ and U ₂ and power supply A, terminal Z ₁
And a switch S ₂ 21 for connecting the between V ₂ and the power of B is the second phase switching device. After connecting Thus, the switch S ₁ 20 and the switch S ₂ 21 and the powering in the released answering the divided voltage of the stator winding _{10,11 E 1, E 2, E} 3,
E ₁ ′, E ₂ ′ and E ₃ ′ are as shown in FIG. 1/2 of the magnitude the line voltage of the power supply of each of the divided voltage of the stator winding 10, 11 in this case, E ₁ is generated a phase difference between the phase lead clogging 120 ° 120 ° from E ₁ ' I do. Also, E ₂ and E ₂ ′, E ₃ and E
₃ ′ also has a phase difference of 120 °. Therefore, the rotor starts up with this characteristic. That is, the voltage applied to the stator winding is small, and thus the starting current is small. In addition, since the phase difference angle θ is 120 °, the power factor becomes high due to the characteristics of the two-stator induction motor according to the present invention, and the motor starts with a large torque for the current. Switch when the rotation speed of the rotor increases to an arbitrary speed
Shared voltage E ₁ of S ₁ 20 to be turned with the stator windings 10,11, E _2, E
₃ , E ₁ ′, E ₂ ′ and E ₃ ′ are as shown in FIG. In this case, the magnitude of the shared voltage of the stator winding is equal to the line voltage of the power supply. And E ₁ generates a phase difference of 60 ° from E ₁ ′, that is, a phase difference of 60 °. E ₂ and E ₂ ′ and E ₃ and E ₃ ′ also have a phase difference of 60 °. Therefore, the rotor is accelerated by this torque characteristic. Rotational speed of the rotor opens the switch S ₁ 20 when further increases and then turning on the switch S ₂ 21, the shared voltage of the stator winding _{E 1, E 2, E 3} , E 1 ', E 2' , E ₃ ′ are as shown in FIG. The magnitude of the divided voltage of the stator winding 10, 11 of the case is equal to the line voltage of the power supply, E ₁ generates an in-phase, i.e. the phase difference 0 ° and E ₁ '. E ₂ and E ₂ ′ and E ₃ and E ₃ ′ also have the same phase. Therefore, the rotor enters the operating state with this torque. FIG. 6 shows an example of each torque characteristic described above. As shown in the figure, the torque characteristics are changed in each stage of starting, accelerating, and driving, and the operation state is shifted to the operating state with the optimum characteristics according to the respective speeds. That is, assuming that the line voltage of the power supply is E, the shared voltage of the stator winding is E / 2, The starting current is controlled by increasing stepwise to E and the phase difference θ
Is gradually reduced to θ = 120 °, 60 °, and 0 °, and the operation state is shifted to an operation state with characteristics such that a high power factor and a high torque can always be obtained. Operation of the switch S ₁ 20 and the switch S ₂ 21 in FIG. 6 was charged with S ₁ in S = m, S ₂ after release of the S ₁ with S = n
Input. Incidentally, the rated voltage of the stator winding is a line voltage of a power supply. Next, a second embodiment will be described with reference to FIG. This is obtained by replacing the switch S ₂ 21 of the first embodiment to the semiconductor device 22. This connects the terminals U ₁ , V ₁ , and W ₁ of the stator winding 11 to three-phase power supplies A, B, and C, respectively, and connects X _{1 of the} stator windings 10 and 11 to
W ₂ , Y ₁ and U ₂ , Z ₁ and V ₂ are connected, and X ₂ of the stator winding 10 is connected to a power source C, Y ₂ is connected to a power source A, and Z ₂ is connected to B. In this state, the stator windings 10, 11 are connected in series delta connection to the power supply. Furthermore between the terminals X ₁ and W ₂ of the stator windings 10, 11 a thyristor 22 connected in parallel with opposite polarity and a power source C, between Y ₁ and U ₂ and the power supply A, and between Z ₁ and V ₂ Connected between each of power supplies B. When the power is turned on by connecting in this way and the firing angle of the thyristor 22 is controlled to 180 °, no current flows through the thyristor 22, so the shared voltages E ₁ , E ₂ , E of the stator windings 10, 11 ₃ , E
_{1 ', E 2', E} 3 ' is as Figure 3 described above. Therefore, in this case, the magnitude of the shared voltage of the stator winding is 1/2 of the line voltage of the power supply. E ₁ and E ₁ ′, E ₂ and E ₂ ′, E ₃ and E ₃ ′
Is 120 °. The torque characteristics at this time correspond to the starting torque characteristics shown in FIG. As the speed of the rotor increases, the firing angle of thyristor 22
As the angle is gradually reduced from 0 °, the shared voltages E ₁ , E ₂ , E ₃ , E ₁ ′, E ₂ ′, and E ₃ ′ of the stator windings 10 and 11 are effectively reduced as shown in FIG. Change to a state. Therefore, the magnitude of the shared voltage of the stator winding is The phase difference angle θ between E ₁ and E ₁ ′, E ₂ and E ₂ ′, and E ₃ and E ₃ ′ becomes θ = 60 °, and the phase difference angle is accelerated by the acceleration torque characteristic shown in FIG. Will be. As the rotation speed of the rotor increases, the firing angle of the thyristor is further reduced to finally control the firing angle to 0 °.
When this firing angle is 0 °, the shared voltage of the stator windings 10 and 11
_{E 1, E 2, E 3} , E 1 ', E 2', E 3 ' is in FIG. 5. Therefore, the magnitude of the shared voltage of the stator winding becomes equal to the line voltage of the power supply, and the phase difference angle θ between E ₁ and E ₁ ′, E ₂ and E ₂ ′, and E ₃ and E ₃ becomes θ.
= 0 °, ie, in phase. The torque characteristics in this state are the operating torque characteristics shown in FIG. 6 and are the same as those of the conventional induction motor. Next, a third embodiment is shown in FIG. This constitutes a switch S ₂ 21 of FIG. 2 with a variable resistor 23. This means that the terminals U ₁ , V ₁ , W ₁ of the stator winding 11 are connected to the three-phase power sources A, B,
C, and terminals X ₁ and W ₂ , Y _{1 of} stator windings 10 and 11
U ₂ , Z ₁ and V ₂ are connected, and terminal X ₂ of the stator winding 10 is connected to the power supply.
Connect C and Y ₂ to the power supply A and Z ₂ to the power supply B. In this state, the two sets of stator windings 10 and 11 are connected in series delta connection to the power supply. Moreover variable terminal of the resistor 23 stator windings X ₁ and between W ₂ and the power source C, between Y ₁ and U ₂ and the power supply of the A,
Connected between each of the Z ₁ and between V ₂ and the power of B. The connection is made in this manner, the power is turned on, and the variable resistor 23 is set to infinity and started. Incidentally, in this case, the variable resistor 23 will be described in four stages of resistance value = 0, R ₂ , R ₁ , が, but it is needless to say that the present invention is not limited to this. Now stator winding at start-up
The shared voltages E ₁ , E ₂ , E ₃ , E ₁ ′, E ₂ ′, and E ₃ ′ of the 10 and 11 are as shown in FIG. Therefore 1/2 of magnitude the line voltage of the power supply of the divided voltage of the stator winding in this case, the E ₁
The phase difference angle θ between E ₁ ′, E ₂ and E ₂ ′, and E ₃ and E ₃ ′ becomes θ = 120 °, and the motor starts with the starting torque characteristic shown in FIG. 9 as an example. When the value of the variable resistor 23 is reduced as the rotation of the rotor increases, the current flowing through this resistor changes due to the slip S, and the voltage drop of this resistor changes accordingly. That magnitude of the divided voltage of the stator winding is larger than the divided voltage at the time of starting as in the fourth diagram example, position of E ₁ and E ₁ ', E ₂ and E _2', E ₃ and E ₃ ' The phase difference angle θ is smaller than the phase difference angle θ at the time of starting. Therefore, as shown in FIG. 9, when starting, that is, when the slip S = 1, the starting torque characteristic is close to the infinite variable resistance value, and as the rotational speed increases, that is, when the slip S decreases, the conventional induction motor Approaching driving characteristics. As described above, the value of the variable resistor 23 is finally set to zero as the rotation speed of the rotor increases. Shared voltage E ₁ at this time the stator _{winding, E 2, E 3, E} 1 ', E 2', E 3 ' is equal to the line voltage of the power supply is as FIG. 5, and E ₁ E ₁ ′, E ₂
And E ₂ ′, and the phase difference angle θ between E ₃ and E ₃ ′ is θ = 0, that is, in phase. The torque characteristic in this state is the operating torque characteristic of the variable resistance value 0 shown in FIG. 9, which is the same as that of the conventional induction motor. In the above-described second and third embodiments, unlike the opening and closing of the switch, there is no interruption of the load current, so that there is no abrupt change in the characteristics of the torque and the current, and the start and the smooth operation can be performed. Also, if a phase shift device consisting of the above-mentioned switch, thyristor, triac or variable resistor is provided on the motor side, the wiring to the motor may be three in the case of three phases, and complicated wiring such as seen in star-delta starting is required. do not do. Further, a phase shift device and a sensor for detecting a rotation speed or a load current are connected via a control device to open / close a switch of the phase shift device according to a change in the rotation speed or the load current, and to fire a thyristor or a triac. It is also conceivable to control the angle and the resistance value of the variable resistor. It should be noted that the present invention can be implemented even when starting with parallel star connection and shifting to series delta connection. If another phase difference is desired, the other stator may be mechanically rotated and fixed with respect to one of the stators. For example, a phase difference of 20 ° occurs in electrical angle.

【effect】

As described above, the torque setting of the two-stator induction motor is
With a simple phase device, it can be set in a stepless manner.These torque characteristics have a small starting current at startup and a large starting torque, and have achieved low torque characteristics, improved startability with squared torque reduction characteristics, and reduced startup time. It becomes a variable motor and does not require expensive control devices such as inverters. In addition, when a three-phase power source is used by integrating a phase device formed simply with the motor and wiring to the motor, three wires are sufficient for the motor and anyone can wire it. Therefore, we will diversify the torque, expand the applications of the two-stator induction motor that can generate high torque from low speed to the rated speed range, and contribute even more to any field that requires a high-torque motor. became.

[Brief description of the drawings]

FIG. 1 is a side sectional view of a two-stator induction motor, FIG. 2 is a connection diagram showing a first embodiment of a phase shifter, and FIG.
4 is a parallel star connection diagram with a phase difference of 60 °, FIG. 5 is a parallel delta connection diagram with a phase difference of 0 °, and FIG. 6 is an example of a torque characteristic curve by opening / closing an on / off switch. FIG. 7 is a connection diagram of a phase shift device using a thyristor according to the second embodiment, FIG. 8 is a connection diagram of a phase shift device using a variable resistor according to the third embodiment, and FIG. The figure shows an example of a torque characteristic curve due to a variable resistance. DESCRIPTION OF SYMBOLS 1 ... Plural stator induction motor, 2, 3 ... Rotor core, 4 ... Rotor shaft, 5 ... Non-magnetic core, 6 ... Rotor conductor, 7 ... Rotor, 8 ... Short-circuit ring, 9 ... Resistance material, 10,11… stator winding, 12
... first stator, 13 ... second stator, 14 ... machine frame, 20 ... opening and closing switches S _1, 21 ... opening and closing switch S _2, 22 ... polar thyristor,
23… Variable resistance.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H02K 17/00-17/44 H02K 16/00-16/04 H02K 11/00 H02P 1/00-1/58 H02P 5 / 28-5/405 H02P 5/415-5/44 H02P 7/36-7/625 H02P 7/635-7/66

Claims (5)

(57) [Claims] 1. Two rotor cores are provided at an arbitrary interval on the same rotating shaft, a plurality of conductors connected to the two rotor cores are provided, and both ends of the conductors are connected by a short-circuit ring. A squirrel-cage rotor, a first stator core and a second stator core circumferentially opposed to the respective rotor cores, and a first stator winding wound around the first stator core; The second stator winding wound around the two stator cores generates a predetermined first phase difference between the phase of the rotating magnetic field of the first stator winding and the phase of the second stator winding. Stator and second stator connected in series delta connection to a power source as described above, and connection points of arbitrary phases of the stator windings of the first and second stators and other two phases A switch provided between the first stator winding and the first stator winding by closing the switch while energizing the respective stator windings. The second stator winding is switched from a series delta connection to a parallel star connection, and a predetermined second phase difference is provided between the phase of the rotating magnetic field of the first stator winding and the phase of the second stator winding. The first that produces
A phase switching device; and a switch provided between a connection point of an arbitrary phase of each of the stator windings of the first stator and the second stator and a power supply of another phase. The first stator winding and the second stator winding are switched from a series delta connection to a parallel delta connection by closing the switch during the energization of the motor, and the phase of the rotating magnetic field of the first stator winding is changed. Phase switching device that produces a predetermined third phase difference between the first phase switching device and the second stator winding, and a control device that controls opening and closing of switches of the first phase switching device and the second phase switching device. A two-stator induction motor, comprising: 2. Two rotor cores are provided on the same rotation axis at an approved interval, a plurality of conductors are provided in communication with the two rotor cores, and both ends of the conductors are connected by a short-circuit ring. A squirrel-cage rotor, a first stator core and a second stator core circumferentially opposed to the respective rotor cores, and a first stator winding wound around the first stator core; The second stator winding wound around the two stator cores generates a predetermined first phase difference between the phase of the rotating magnetic field of the first stator winding and the phase of the second stator winding. Stator and second stator connected in series delta connection to a power supply as described above, and a connection point of an arbitrary phase of each stator winding of the first stator and the second stator and a power supply of another phase And a switch provided between the first stator winding and the first stator winding. The second stator winding is gradually switched from a series delta connection to a parallel delta connection, and the phase difference between the phase of the rotating magnetic field of the first stator winding and the phase of the rotating magnetic field of the second stator winding is changed. A two-stator induction motor, comprising: a phase switching device that gradually changes the first phase difference to a predetermined second phase difference; and a control device that controls opening and closing of a switch of the phase switching device. 3. The two stator according to claim 1, wherein the cage rotor has a plurality of conductors at arbitrary intervals shorted to each other by a resistance material. Induction motor. 4. A two-stator induction motor according to claim 2, wherein the switch of the phase switching device is a semiconductor element. 5. The two-stator induction motor according to claim 2, wherein the switch of the phase switching device is a variable resistor.