Solid state controller

• US 4,112,342 A
• Filed: 09/27/1976
• Issued: 09/05/1978
• Est. Priority Date: 08/06/1974
• Status: Expired due to Term

• Current Assignee: Varco LP (NOV, Inc.)
• Original Assignee: Varco LP (NOV, Inc.)
• Inventors: Elliott, Harry Samuel
• Primary Examiner(s): Schaefer, Robert K.
• Assistant Examiner(s): Indyk, Eugene S.
• Application Number:
  US05/727,001
• Time in Patent Office: 708 Days
• Field of Search: 318/599, 318/624, 323/21 R
• US Class Current: 318/599
• CPC Class Codes: G05B 11/28 using pulse-height modulation; using pulse-width modulation

Abstract

An improved alternating current prime mover control system and method for, for example, the control of a valve position or other physical variable whose state can be sensed or calculated wherein the state of the physical variable is compared with a reference variable to generate, in conjunction with a waveform generator, a fixed amplitude signal that has variable time duration which feeds a part of the control system that drives the alternating current prime mover source in more than one direction.

Claims

1. A control system using a power supply for positioning a device associated with a physical variable wherein the position of the device is controlled by an alternating current electric prime mover driven by an alternating current source and the position of the device is represented by a state signal whose variable amplitude is a function of the position, comprising:

means responsive to the physical variable for generating a reference input signal of settable magnitude representing a desired position of the device;

a first wave form generating means for generating an electrical generated signal;

difference means responsive to the state signal, said reference signal and said electrical generated signal for simultaneously generating at least one variable error signal having a magnitude and polarity only proportional to a difference relationship between the magnitudes of the state signal and said refernce signal over time and at least one generated error signal having a magnitude and polarity proportional to the relationship between said variable error signal and said electrical generated signal;

said error signals having waveforms differing from said electrical waveform, and said electrical generated signal and said error signals being coordinated in time;

comparator means responsive to said difference means and said first waveform generating means for producing first variable duration output pulses at a plurality of outputs;

said variation of duration being a function in time of the magnitude of said electrical generated signal and said variable error signal, said difference means being electrically connected between the state signal and said reference signal and said comparator means, and said first waveform generating means being electrically connected between said comparator means and the power supply; and

a solid state switching means responsive to said outputs of said comparator means for switching power to the alternating current electric prime mover to vary the position of the device, said solid state switching means being electrically connected between said comparator means and the alternating current electric prime mover and the alternating current source.

2. A control system according to claim 1 wherein said difference means includes:

differencing means responsive to the state signal and said reference signal for generating said variable error signal having a magnitude and polarity propotional to the difference between the magnitudes of the state signal and said reference signal over time; and

average means responsive to said variable error signal and said electrical generated signal for generating said generated error signal whose magnitude is the average of the magnitudes of said variable error signal and electrical generated signal.

3. A control system according to claim 1 wherein said comparator means produces variable duration output pulses for at most one of said plurality of outputs in any instant of time, said one output being determined by the polarity of said variable error signal.

4. A control system according to claim 2 wherein said differencing means is an operational amplifier;

said first waveform generating means is a sawtooth wave generator;

said averaging means is a resistence network;

said comparator means is a dual comparator; and

said solid state switching means is a plurality of solid state relays.

5. A control system according to claim 4 wherein said first waveform generator uses positive feedback.

6. A control system according tO claim 1 including additional variable means for varying the amplitude and offset of said electrical generated signal, said additional variable means being electrically connected to said first waveform generating means.

7. A control system according to claim 6 wherein said first waveform generator is a sawtooth wave generator.

8. A control system according to claim 4 wherein one comparator of said dual comparator provides a first output signal only when the magnitude of said variable error signal is less than the magnitude of said electrical generated signal and the other comparator of said dual comparator provides a second output signal only when the average of said variable error signal and said electric generated signal is positive with respect to a ground potential and wherein there is further included discriminator means for preventing simultaneous output of said first output signal and said second output signal.

9. A control system according to claim 4 and including manual means for the manual operation of said plurality of solid state relays overriding said plurality of outputs of said comparator means.

10. A control system according to claim 4 in which said plurality of solid state relays comprise a plurality of:

switching means responsive to said dual comprarator for controlling a power control means with an electric pulse; and

power control means responsive to said switching means for controlling the alternating current source to the alternating current electric prime mover, said switching means being electrically connected between said dual comparator and said power control means and said power control means being electrically connected between the alternating current electric prime mover and said switching means and the alternating current source.

11. A control system according to claim 10 wherein said switching means is also responsive to manual means for the manual overriding of said plurality of outputs of said comparator means.

12. A control system according to claim 10 in which said switching means is a zero crossing triac controller;

and

said power control means is a triac connected in series with the alternating current electric prime mover.

13. A control system according to claim 12 including isolation means responsive to said dual comparator to electrically isolate and control said switching means from said comparator means, said isolation means being electrically connected between said comparator means and said switching means.

14. A control system according to claim 13 wherein said isolation means is an optoelectric isolator between each output of said dual comparator and the respective input of said zero crossing triac controller.

15. A control system according to claim 12 wherein said zero crossing triac controller includes a second comparator means for controlling the output of said switching means.

16. A control system according to claim 15 wherein said switching means includes a second waveform generating means for producing a second generated signal, said second generated signal being an input to said comparator means for actuating said zero crossing triac controller.

17. A control system according to claim 16 wherein said second comparator means is adapted to turn on said triac only when the amplitude difference between said first variable duration output pulse and said second generated signal is positive.

18. A control system according to claim 16 wherein said second comparator means is adopted to turn on said triac only when the amplitude difference between said first variable duration output pulse and said second generated signal is negative.

19. A control system according to claim 16 wherein the operation of said second waveform generating means is controlled by an output of said dual comparator.

20. A control system according to claim 4 wherein the operation of either of the comparators in said dual comparator supresses the operation of the other comparator.

21. A control system according to claim 16 wherein the amplitude of said second generated signal is variable.

22. A control system according to claim 1 wherein said difference means includes reference fail safe means responsive to the absence of said reference signal for inhibiting said outputs of said comparator means when said reference signal is absert.

23. A control system according to claim 22 wherein said reference fail safe means includes reference remote reset means responsive to an external signal for permitting output of said comparator upon receipt of said external signal when said reference signal is longer absent.

24. A control system according to claim 1 wherein said difference means includes state fail safe means responsive to the absence of the state signal for inhibiting said outputs of said comparator means when the state signal is absent.

25. A control system according to claim 24 wherein said state fail safe means includes state remote reset means responsive to an external signal for permitting output of said comparator upon receipt of said external signal when the state signal is no longer absent.

26. The control system of claim 2 wherein said first waveform generating means includes means for varying the amplitude and bias of said electrical generated signal.

27. The control system of claim 1 wherein said solid state switching means is physically isolated from the rest of said system.

28. A method of controlling the state of a physical variable, comprising the steps of:

generating a reference signal representing the desired state of a device controlling the state of the physical variable proportional in magnitude and polarity to a relationship between the desired state of the physical variable and the current state of the physical variable;

generating an error signal proportional in magnitude and polarity to a relationship between the state of the device and the reference signal;

generating a first time proportional signal responsive to said error signal and a first time variable signal such that the duration of the first time proportional signal is a function of a relationship between the state of the device and the reference signal;

time proportionating said first time proportional signal to produce a second time proportional signal whose presence is a function of said first time proportional signal and whose degree of time proportionation is a function of a second time variable signal for varying the rate of change of the state of the device, and

controlling the device capable of altering the state of the physical variable with the second time proportional signal.