Alternating current motor control apparatus

• US 4,902,954 A
• Filed: 06/06/1988
• Issued: 02/20/1990
• Est. Priority Date: 08/22/1986
• Status: Expired due to Fees

• Current Assignee: Otis Elevator Company (Otis Worldwide Corp.)
• Original Assignee: Otis Elevator Company (Otis Worldwide Corp.)
• Inventors: Oshima, Kenji, Kito, Yasutami
• Primary Examiner(s): Smith, Jr., David
• Application Number:
  US07/196,199
• Time in Patent Office: 624 Days
• Field of Search: 157/119, 318/798, 318/806, 318/778, 318/759, 318/762
• US Class Current: 318/762
• CPC Class Codes: B66B 1/285 with the use of a speed pattern generator
• CPC Class Codes: B66B 1/302 for energy saving
• CPC Class Codes: B66B 1/308 with AC powered elevator drive
• CPC Class Codes: B66B 5/02 responsive to abnormal operating conditions
• CPC Class Codes: H02P 23/06 Controlling the motor in four quadrants

Abstract

An apparatus for controlling an adjustable-speed alternating current motor coupled to drive an elevator cage. The apparatus includes a converter connected to a source of AC power for converting the AC power into DC power, an inverter connected through relatively positive and negative conductors to the converter for inverting the DC power into DC output power having adjustable frequency, voltage magnitude, and current magnitude to drive the motor, and a control circuit for controlling an inverter to drive the motor at an adjustable speed. When a power failure occurs, the control circuit prevents flow of power through the converter to the power source and reduces the current magnitude of the inverter output power to a predetermined minimum limit enough to maintain a synchronous relationship between the inverter and the motor. When the power failure continues for a predetermined time, an electric resistor is connected between the relatively positive and negative conductors to provide a dynamic braking of the motor.

Claims

1. An apparatus connected to a source of fixed frequency alternating current (AC) for providing a motor control signal for controlling the speed of an AC motor coupled to drive an elevator cage, comprising:

a converter connected to the source of AC having rectifier means for converting the AC into direct current (DC);

an inverter connected through relatively positive and negative conductors to the converter, responsive to the motor control signal, for inverting said DC into AC having adjustable frequency to drive the motor and for providing regenerative power from the motor during regenerative conditions;

AC power failure detector means, responsive to the fixed frequency AC power source for detecting a power failure and for providing a power failure signal;

overvoltage detector means, responsive to the voltage between said positive and negative conductors, for providing an overvoltage signal upon detecting said voltage exceeding a selected magnitude;

said converter further comprising regenerative power switching means responsive to a regenerative power control signal for controlling the flow of said regenerative power from said inverter to the fixed frequency AC source during said regenerative conditions;

an electric resistor responsive to said regenerative power for dissipation thereof; and

a control circuit for providing the motor control signal for controlling said inverter for driving the motor at a selected speed, said control circuit responsive to said power failure signal for providing said regenerative power control signal for controlling said regeneration means to prevent flow of regenerative power to the power source, said control circuit for providing said motor control signal for reducing the current magnitude of said inverter output power to a predetermined minimum limit enough to maintain a synchronous relationship between said inverter and the motor, said control circuit further comprising means responsive to said power failure signal and said overvoltage signal for connecting said electric resistor between said relatively positive and negative conductors to provide a dynamic braking of the motor in the simultaneous presence of said overvoltage signal and said power failure signal after said power failure signal has persisted for a predetermined time.

2. The apparatus as claimed in claim 1, wherein said control circuit includes means for discontinuing said providing of said motor control signal to reduce the current magnitude of said inverter output power to a predetermined minimum limit after said power failure continues for said predetermined time.

3. The apparatus as claimed in claim 1, wherein said control circuit further comprises means responsive to said failure signal for controlling the inverter to drive the electric motor at a decreasing speed after said power failure signal continues for said predetermined time.

4. The apparatus as claimed in claim 1, wherein said power failure detector further comprises a undervoltage detector connected between the relatively positive and negative conductors for providing a second power failure signal when the voltage between the relatively positive and negative conductors drops below a predetermined value, said control circuit responsive to said second power failure indication signal for providing said regenerative control signal for turning off said regenerative power switching means and for providing said motor control signal for reducing the current magnitude of said inverter output power to said predetermined minimum limit.