Constant speed and frequency generating system

• US 4,806,841 A
• Filed: 02/29/1988
• Issued: 02/21/1989
• Est. Priority Date: 02/29/1988
• Status: Expired due to Fees

• Current Assignee: Power Paragon, Inc. (L3Harris Technologies, Inc.)
• Original Assignee: Teledyne Inet (Teledyne Technologies Incorporated)
• Inventors: Lee, Robert H., Levran, Alexander
• Primary Examiner(s): Hickey, R. J.
• Application Number:
  US07/162,025
• Time in Patent Office: 358 Days
• Field of Search: 322/29, 322/32, 322/39, 322/10, 310/68 D
• US Class Current: 322/29
• CPC Class Codes: H02P 9/42 to obtain desired frequency without varying speed of the generator

Abstract

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.

Claims

1. In a motor generator system for generating output power controlled to a desired frequency and having a variable AC input power and frequency, the system including a generator and motor, both with rotors connected by a shaft, the system also including a power factor control, a shaft-mounted frequency control circuit, an output voltage regulator, generator and motor exciter DC fields;

the power factor control sensing the input power that is supplied to the motor stator and outputting a DC control signal to the motor exciter DC field;

said motor having an exciter rotor developing an AC output voltage that is related to the speed of said shaft and outputting this AC output voltage signal to said shaft-mounted frequency control circuit;

said frequency control circuit producing a difference (Δ

f) low frequency signal that is applied to the motor rotating AC field, to add or subtract from the speed of said motor rotating AC field, causing the motor speed to remain constant and the generator output frequency to remain constant within ±

0.1 Hz;

said frequency control circuit comprising;

a crystal clock oscillator and counting circuit that delivers a precise square wave voltage signal;

a feedback loop connected to said generator output and transmitting a signal corresponding to said

a frequency and phase discriminator to which said feedback frequency signal and a reference setting frequency signal and said crystal clock signal is connected, and producing a DC error signal;

a voltage controlled oscillator and frequency dependent circuit that processes said DC error signal, producing a high frequency pulse train that is proportional to said input DC error signal;

a converter means coupled to the output of said voltage controlled oscillator and frequency dependent circuit, that converts the pulse train signal to a difference low frequency signal for application to the motor, controlling the speed of the rotating magnetic flux and thereby also the generator speed and AC frequency output, producing a constant frequency output irrespective of variations in the input AC power frequency to the motor.

2. The frequency control circuit of claim 1, wherein said converter means includes a cycloconverter control circuit and a cycloconverter drive circuit;

said cycloconverter control circuit producing pulse trains which are related to the input DC error signal and which are connected to the input of said cycloconverter drive circuit;

said cycloconverter drive circuit producing a low frequency voltage output in the range of zero to plus or minus 4.8 Hz at a low magnitude AC voltage for application to the motor AC field, thus controlling said motor speed.

3. The system of claim 1, wherein said power factor control circuit operates to deliver input AC power to the motor at unity power factor.

4. The frequency control circuit of claim 1, wherein said converter means includes a rotating electrical frequency converter of 50 to 60 Hz, or 60 to 50 Hz, said frequency converter producing a low frequency voltage output in the range of zero to plus or minus 4.8 Hz at a low magnitude AC voltage for application to the motor AC field.