SYSTEM FOR CONTROLLING THE FREQUENCY OF AN ALTERNATING CURRENT CONVERTER IN RESPONSE TO LOAD CHANGES

• US 3,829,757 A
• Filed: 01/31/1973
• Issued: 08/13/1974
• Est. Priority Date: 07/18/1970
• Status: Expired due to Term

• Current Assignee: Hermann Frank, Rudolf Huber
• Original Assignee: Hermann Frank, Rudolf Huber
• Inventors: Frank, Hermann, Huber, Rudolf
• Primary Examiner(s): Shoop, Jr., William M.
• Application Number:
  US05/326,557
• Time in Patent Office: 559 Days
• Field of Search: 321/16,18,45R 318/171,231,341,445 307/87
• US Class Current: 318/722
• CPC Class Codes: H02P 25/024 controlled by supply frequency

Abstract

Alternating current having a selected frequency is produced by a converter to operate a synchronous motor at a desired speed. The frequency of the alternating current is determined by an accumulating circuit that supplies synchronizing impulses to the converter at a rate determined by the setting of the accumulating circuit and in response to a pilot signal. During failure of power to run the converter, a trigger generator responsive to voltage from the decelerating motor changes the control setting of the circuit so that, upon restoration of power, synchronizing pulses will be produced at a lower repetition rate, causing the frequency of alternating current from the converter to be commensurate with the reduced speed of the motor.

Claims

1. A system for producing alternating current of a controlled frequency, said system coMprising:

a converter connected to a source of power and comprising a generator synchronized by a synchronizing signal to generate the alternating current at said frequency;

a load for said generator;

accumulating means to receive a pilot signal and to produce said synchronizing signal in response to accumulation of said pilot signal to a limiting value;

control means to control said accumulating means to determine the length of time between successive ones of said synchronizing signals;

generating means controlled by said load to generate a second synchronizing signal for said generator at least during intervals of failure of power from said source; and

means connecting said accumulating means to said control means to adjust the limiting value of said accumulating means during power failure, whereby said accumulating means will accumulate said pilot signal to the new limiting value and upon restoration of power hereby will synchronize the frequency of the alternating current from said generator to a value commensurate with the adjusted limiting value.

2. The system of claim 1 in which said accumulating means is a counter and said pilot signal is an oscillatory signal and said counter counts the oscillations of said pilot signal to said limiting value.

3. The system of claim 2 in which said third means comprises storage means to store a count value.

4. The system of claim 3 in which said second synchronizing signal is a series of pulses and said means connecting said second synchronizing signal to adjust the limiting value of said accumulating means comprises a gate circuit connecting said counter to said storage means.

5. The system of claim 4 in which said means connecting said accumulating means to said storage means only allows the count of the accumulating means to the storage means to pass at the second and subsequent of said second synchronizing signal pulses.

6. The system of claim 1 comprising, in addition, a failure detector connected to detect the failure of power applied to said generator, and comprising:

first switching means connected to said accumulating means to disconnect said accumulating means from said means to receive a synchronizing signal during the intervals of failure of power; and

second switching means disconnecting said converter from said load during power failure.

7. The system of claim 5 comprising additional switching means connecting said third means to said accumulating means, said additional switching means being connected to said failure detector to be controlled thereby to open-circuit said additional switching means during the intervals of power failure.

8. The system of claim 1 in which said load is a synchronous motor.