Electricity: motive power systems – Induction motor systems – Primary circuit control
Patent
1995-12-14
1998-06-02
Masih, Karen
Electricity: motive power systems
Induction motor systems
Primary circuit control
318771, 318778, 318772, 318727, 310184, 310198, H02P 138
Patent
active
057605670
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a drive system for AC motors, and more particularly to a control system for reducing induced voltage to be generated in a winding for low-speed revolution of the induction motor.
BACKGROUND ART
The induction motor can produce a large torque at low-speed revolutions by switching the primary windings with the same primary current. In this case, the induction motor has windings forming a Y-Y' connection, with first terminals supplying electric current to the entire part of the primary windings of U-, V- and W-phases and second terminals provided at an intermediate portion of each winding so as to supply electric current to only a part of each winding. Changeover of the primary windings is carried out in such a manner that electric power is exclusively supplied from the first terminals to supply electric current to the whole of each winding when the motor is to be operated in the low-speed region, while electric power is exclusively supplied from the second terminals to supply electric power to the limited part of each winding when the motor is to be operated in the high-speed region. Such a changeover of the primary windings causes the change of excitation.
In the low-speed rotations, the secondary current of the rotor and the output torque can be enlarged by increasing the number of turns of the primary winding under the same current. The above-described conventional induction motor has a problem such that driving the winding for high-speed revolutions of the induction motor cause the winding for low-speed revolutions to induce voltage, which may cause its dielectric breakdown.
FIG. 12 is a diagram illustrating an induced voltage in a conventional Y-connection type induction motor. In FIG. 12, the windings of U-, V- and W-phases are respectively constituted of a winding for high-speed revolution of motor C1 and a winding for low-speed revolution of motor C2 and serially connected to forms a Y connection. The winding for high-speed revolution of motor C1 has intermediate terminals U2, V2 and W2, while the winding for low-speed revolution of motor C2 has end terminals U1, V1 and W1.
Here, the induced voltage will be explained taking the case of the U-phase winding. While the winding for high-speed revolution of motor is in operation, the intermediate terminal U2 is used to exclusively supply electric current to the winding for high-speed revolution of motor C1, and no electric current is supplied to the winding for low-speed revolution of motor C2. However, the winding for low-speed revolution of motor C2 is made to induce voltage due to the voltage applied to the winding for high-speed revolution of motor C1. This induced voltage is proportional to the number of turns of the winding for high-speed revolution of motor C1 and that of the winding for low-speed revolution of motor C2. In general, in order to increase the output torque in the low-speed rotations, the number of turns of the low-seed winding C2 is set larger than that of the winding for high-speed revolution of motor C1. Therefore, the voltage induced in the winding for low-speed revolution of motor C2 is higher than the voltage applied to the winding for high-speed revolution of motor C1.
For example, if 200 V is applied to the winding for high-speed revolution of motor C1 under the condition that the number of turns ratio of the winding for high-speed revolution of motor C1 to the winding for low-speed revolution of motor C2 is 1:4, the winding for low-speed revolution of motor C2 will induce voltage of 200 (V).times.4=800 (V). This induced voltage may cause dielectric breakdown of the winding.
In the conventional induction motor, no special countermeasure is employed for preventing the voltage from being induced in the winding for low-speed revolution of motor when the induction motor is operated at high-speed revolutions, except for adjusting number of turns ratio by taking into account the induced voltage.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an induced voltag
REFERENCES:
patent: 4477760 (1984-10-01), Kuznetsov
patent: 4947072 (1990-08-01), Watkins et al.
patent: 5065305 (1991-11-01), Rich
patent: 5068559 (1991-11-01), Satake et al.
patent: 5068587 (1991-11-01), Nakamura
patent: 5352964 (1994-10-01), Nakamura et al.
Hayashi Yoshiyuki
Maeda Hisashi
Nakamura Kosei
Fanuc Ltd.
Masih Karen
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