Electricity: motive power systems – Induction motor systems – Primary circuit control
Patent
1981-10-01
1989-08-15
Smith, Jr., David
Electricity: motive power systems
Induction motor systems
Primary circuit control
H02P 130
Patent
active
048578193
ABSTRACT:
The present invention is directed to a method and apparatus for connecting a static inverter to a free-running motor, wherein the inverter is supplied with D.C. power by a regulator-controlled rectifier. An oscillator connected to both the rectifier regulator and the inverter governs the frequency of the three-phase inverter output, while voltage feedback from the inverter output to the rectifier regulator is employed to establish a proper volts/hertz output characteristic in the inverter output waveform. During the connection process, a synchronizing circuit causes the oscillator to generate a high pulse rate signal which raises the inverter output frequency to a level above that associated with the rotational speed of the free-running motor. Simultaneously, the D.C. output of the rectifier is clamped by the current regulator to current-limit the inverter output. The inverter is subsequently connected to the free-running motor and the inverter output frequency is allowed to decrease gradually. When the frequency of the inverter output equal the rotational speed of the motor, the motor impedance increases substantially to create a voltage rise in the inverter output, followed by phase equalization between the inverter output and the back e.m.f. of the motor. In this manner, smooth, synchronous connection of the inverter to the rotating motor is achieved.
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Mueller et al., "Static Variable Frequency Starting and Drive System for Large Synchronous Motors", Conference: Industry Industry Applications Society, IEEE JAS Annual Meeting, Cleveland, OH, USA (30 Sep.-4 Oct. 1979).
Collins David J.
Hall Michael O.
Maurice James
McLoughlin Peter D.
Emerson Electric Co.
Moose Richard M.
Smith Jr. David
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