Electricity: motive power systems – Induction motor systems – Primary circuit control
Patent
1984-11-01
1987-04-28
Smith, Jr., David
Electricity: motive power systems
Induction motor systems
Primary circuit control
318806, 318803, 318812, 187119, 307 64, H02P 540, B66B 124
Patent
active
046617574
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
This invention relates to an AC elevator using an induction motor, and is particularly concerned with an apparatus suitable for providing low-speed running of an AC elevator in which an induction motor is controlled by a frequency converter.
2. Background Art
It is generally required that an elevator has the ability to run slowly when an abnormality occurs in its controller, or during maintenance. For example, if a motor-controlling thyristor is damaged, the elevator car is immediately stopped to ensure passengers' safety, but the car could stop between floors in this case. To rescue the passengers by moving a car which has stopped between floors to the nearest floor, a slow-running function is necessary. Because of this requirement, the low-speed running must be realizable even when a thyristor has failed, etc.
U.S. Pat. No. 4,319,665 is known, as an example of a controller for an AC elevator. In this system, a three-phase induction motor which has a high-speed winding and a low-speed winding is used, a primary voltage impressed on the high-speed winding during operation is controlled, and a DC current supplied to the low-speed winding during damping is also controlled to provide normal operation. In such a system, it is known that slow-running can be obtained by supplying AC power to the low-speed winding when, for example, a thyristor or the like controlling the primary voltage is damaged.
However, the conventional system requires low-speed and high-speed windings for the motor which increases the size of the structure and also its cost, and recent requirements for power saving and increased performance have made it necessary to change this system.
A method of using a frequency converter has been known for a long time as a system for controlling an induction motor at a reduced power consumption and increased performance is disclosed in, for example, U.S. Pat. No. 3,940,669.
It has been proposed recently that the above requirement is realized by controlling the elevator-driving induction motor by means of a frequency converter, as disclosed in British Patent Laid-Open No. 2,081,534. The frequency converter in this case is used in a system in which a frequency is converted directly between alternating currents, or a system in which an alternating current is first converted into a direct current (by a converter) and is then inverted to form an alternating current of a variable frequency (by an inverter), or a system in which only the inverter is provided, when the supply is a direct current. Any of these systems has the potential to satisfy the requirements for power saving, increased performance, and a single winding for the motor, compared with the conventional system described above.
However, such an AC elevator using a frequency converter will still have to be run slowly after the elevator car is stopped because, for example, the frequency converter has been damaged. In addition, the ability to run slowly without using the frequency converter is necessary during maintenance.
Consequently, even an AC elevator using a frequency converter must either be provided with an apparatus for low-speed running or, for example, a low-speed winding or a small motor for low-speed running. This means that a large structure and increased cost cannot be avoided with the slow-running apparatus.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a controller for an AC elevator using a frequency converter, which is capable of running slowly but which has a simple, inexpensive construction.
The invention is characterized in that the output frequency of the frequency of the frequency converter at the rated speed of the elevator is set to be at least the frequency of the AC power, the AC power is then impressed on the induction motor directly as a power frequency during slow running, so that slow running determined by the AC power frequency is provided.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 to FIG. 7 are drawings of one preferred embodiment of the present inventio
REFERENCES:
patent: 3753069 (1973-08-01), Newton
patent: 3793573 (1974-02-01), Tsuboi
patent: 4376471 (1983-03-01), Uchino et al.
patent: 4454930 (1984-06-01), Nomura et al.
Andreas, J. C., Energy-Efficient Electric Motors, Dekker Inc., 1982, pp. 141-148.
Fisher et al., "Efficiency Spurs Adjustable Frequency Drive Use" Oct. 1975, p. 41+.
Arahori Noboru
Hatakeyama Takanobu
Hokari Sadao
Hori Takamasa
Katayama Yasunori
Hitachi , Ltd.
Smith Jr. David
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