Teledyne Inet

Teledyne Industries, Inc.

Robert H Lee

Alexander Levran

Gerald L Smith

Jacek J Marcinkowski

Suresh C Gupta

Chi Mak

A method is described for controlling synchronous motor torque, utilizing a three-phase switch connected in a circuit to the input of a polyphase synchronous motor, and a switch control circuit. The switch control circuit senses the AC voltages input to the synchronous motor and produces signals that open and close the three-phase switch in phase with the input motor voltage, producing positive motor torque during normal operation. If input AC power is lost, the switch control circuit acts to prevent a reverse flow of high current from the motor from entering the power source bus. When input power, after a short time, returns, the switch control circuit acts to close the three-phase switch in such a manner as to permit only real power applied to the synchronous motor and thus positive torque that accelerates the motor speed and quickly restores the motor to synchronism with the input power source.

Synchronous motor torque control device

A polyphase AC current limiting circuit, which incorporates improvements in control methods and circuitry that operate to avoid high rates of current change which occur upon initiation of a branch load fault and when the branch load fault is suddenly cleared. This 'soft' start and 'soft' load-off characteristic, reduces the voltage transients imposed on the AC power source and bus to relative insignificance compared with the voltage transients imposed by prior art current limiting circuits. The invention AC current limiting circuit comprises a high impedance circuit connected in parallel with a low impedance circuit, a load-off circuit connected in shunt with the device output power lines, and a control means for controlling the switching devices. When a branch load fault is sensed, the control means turns off the switches in the low impedance circuit through which normal current flows, and turns on the switches in the high impedance circuit, starting phased back, so that the initial current step is typically 100 percent of rated load current. Within a few cycles, the switches are phased to full on and the maximum current is limited by an inductor in series with the switches in the high impedance circuit. When the load fault is suddenly cleared and current drops to zero, the load-off circuit is energized and current continues to flow at graduated lower levels until the circuit is switched off. In the event that the load fault does not clear, the switches in the high impedance circuit are turned off, stopping current flow and a trip signal is transmitted to trip open an external input circuit breaker.

Low voltage transient current limiting circuit

An output frequency control circuit is mounted on the rotating shaft connecting a motor and generator. The motor-generator system includes exciter circuits, an input power factor control and an output voltage regulator. The input power factor control ensures that the motor input power factor is unity, which is desirable for motor control. The frequency control circuit responds to variations in the AC power source frequency by generating low frequency excitation to boost or buck the operational speed of the machine, causing the generator output frequency to remain constant at a selected frequency output irrespective of input power source frequency variation. The output frequency may be selected over a given range from a control panel adjustment pot. The major innovation is that the entire frequency control circuit is shaft-mounted and requires no slip-rings or magnetic transformers for signal transfer, thus reducing the possibilities of mechanical failure. A second innovation is that the motor input power factor is held at unity. A third innovation is that the system is enabled to ride through `brownouts` or short term input power failure.

Constant speed and frequency generating system

Methods and apparatus are disclosed for synchronizing multiple AC motor driven synchronous generators to the voltage on a common output bus. In one method, the rotating motor is disconnected from its AC power source, the generator voltage is phase synchronized to the output bus voltage, and then the generator rotor is caused to slip one generator pole at a time until the motor generated voltage is phase synchronized to the AC power source voltage. At that point, the motor is reconnected to the AC power source. Other methods are disclosed in which magnetic position sensors are employed to provide an indication of when the rotors on multiple motor driven generators are mechanically phase synchronized.

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Fullerton, CA, United States of America

Robert H Lee