Triplex control system with sensor failure compensation

• US 5,757,641 A
• Filed: 07/03/1995
• Issued: 05/26/1998
• Est. Priority Date: 07/03/1995
• Status: Expired due to Fees

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Minto, Karl Dean
• Primary Examiner(s): Elmore, Reba I.
• Assistant Examiner(s): Marc, McDieunel, Marc, McDieunel
• Application Number:
  US08/498,273
• Time in Patent Office: 1,058 Days
• Field of Search: 364/133, 364/551.01, 395/20, 395/25, 395/182.08, 303/122.05, 303/122.08, 303/122.07, 235/440, 235/441, 235/446
• US Class Current: 700/4
• CPC Class Codes: G05B 19/0428 Safety, monitoring G05B19/0423 takes precedence
• CPC Class Codes: G05B 2219/14017 Triple plc's, processors and triple I-O
• CPC Class Codes: G05B 2219/14126 Redundant I-O points, two sensors, actuators for same point
• CPC Class Codes: G05B 2219/24184 Redundant I-O, software comparison of both channels
• CPC Class Codes: G05B 2219/24187 Redundant processors run identical programs
• CPC Class Codes: G05B 9/03 with multiple-channel loop, i.e. redundant control systems

Abstract

A triplex control system provides automatic compensation for a sensor bias failure in one channel while continuing to process all sensor readout signals. The triplex control system includes first through third non-linear feedback channel processors, each being coupled to a respective sensor to receive a readout signal therefrom. Each channel processor comprises a control algorithm module and feedback loop correction circuit coupled together so as to generate a channel output signal in correspondence with a channel control algorithm and a feedback loop correction signal. The respective channel feedback loop correction signal is generated by the feedback loop correction circuit to provide sensor failure compensation; the feedback signal has a bias sense and magnitude that serves to correct the channel output signal so as to drive it towards the average of the channel control signals from each of the channel processors. Each feedback loop correction circuit comprises a residual signal generator that receives the sensor readout signal from each respective sensor and is adapted to generate a signal to provide the bias sense to the feedback loop correction circuit. The control system additionally has an controller output selection module for providing an control system output signal in correspondence with a selected function, such as an average or median value of the respective channel output signals.

Claims

1. A triplex control system providing automatic compensation of sensor bias failures with continued processing of all sensor inputs, the control system comprising:

respective first, second, and third non-linear feedback channel processors, each of said channel processors being coupled to a respective channel sensor to receive a sensor readout signal therefrom and comprising a control algorithm module and a feedback loop correction circuit coupled together so as to generate a channel output signal in correspondence with a channel control algorithm;

each of said channel processors further comprising a respective residual signal generator coupled to said feedback loop correction circuit and adapted to generate a residual signal to control the bias sense of a feedback loop correction signal; and

a controller output selection module for providing a control system output signal in correspondence with a selected function of the combination said respective channel output signals, said triplex control system processing each of said respective channel readout signals while generating said control system output signal.

2. The control system of claim 1 wherein the selected function of the combination of respective channel output signals in said controller output selection module comprises arithmetic averaging and median value determination.

3. The control system of claim 1 wherein each respective residual signal generator is coupled to receive each of said respective sensor readout signals and comprises a local channel residual error signal and a plurality of external channel residual error signal circuits responsive to respective channel sensor readout signals and an averaged sensor readout signal, said residual signal generator further comprising a comparison module adapted to determine the bias sense of the largest of the respective channel residual error signals.

4. The control system of claim 3 wherein said residual signal generator comprises a sensor input signal averaging element, said averaging element being coupled to a respective combining element in each of said local and external residual error signal circuits to provide said averaged sensor readout signal thereto, each of said local and external residual error signal circuit combining elements further being respectively coupled to the respective channel sensor so as to provide in each of said residual error signal circuits a respective residual error signal corresponding to the difference between the respective channel sensor readout signal and said averaged sensor readout signal.

5. The control system of claim 4 wherein each of said residual error signal circuits further comprises a filter coupled to the respective residual signal circuit combining element to receive the respective difference signal therefrom and further coupled to said comparison module to provide a respective channel residual error signal thereto.

6. The control system of claim 5 wherein each of said residual signal generators further comprises a signum function module coupled to said local channel residual error signal circuit combining element, said residual signal generator further comprising a multiplication module coupled to said signum function module and to said comparison module so as to receive respective signals therefrom and to generate a residual signal, said residual signal being the product of the respective signals from said signum function module and said comparison module.

7. The control system of claim 6 wherein each of said residual signal generators is adapted such that said residual signal generated therein comprises a signal having a value selected from the group consisting of "+1+, "-1", and zero, so as to provide a bias sense to said feedback loop correction circuit.

8. The control system of claim 1 wherein each of said channel processors comprises a respective channel control algorithm module adapted to transform an input signal in correspondence with a selected transfer function algorithm.

9. The control system of claim 8 wherein said control algorithm module is coupled to a channel second combining element and said feedback loop correction circuit is further coupled to said channel second combining element such that a channel output signal corresponding to the combination of the signal from said feedback loop correction and the signal from said control algorithm module is passed to said control system output selection module.

10. The control system of claim 9 wherein each of said respective loop correction circuits comprises a delay block module for generating a feedback signal having a bias sense corresponding to the respective channel residual signal and having a magnitude corresponding to a channel-system difference signal.

11. The control system of claim 10 wherein each of said non-linear feedback loop correction circuits further comprises a feedback loop combining element, and a multiplication module;

said feedback loop combining element being coupled to said channel second combining element to receive the channel output signal therefrom and being coupled to said controller output selection module to receive said control system output signal therefrom, said channel first combining element being adapted to generate said channel-system difference signal corresponding to the combination of said channel output signal and said control system output signal;

said multiplication module being coupled to said feedback loop combining element to receive said channel-system difference signal and further being coupled to said residual signal generator to receive said respective channel residual signal, said multiplication module being adapted to generate a loop adjustment signal corresponding to the product of the signals received by said multiplication module;

said multiplication module being coupled to said channel delay block to provide said loop adjustment signal thereto.

12. The control system of claim 1 wherein said sensors are selected from the group consisting of speed sensors, temperature sensors, flow sensors, and tension sensors.

13. The control system of claim 12 wherein said sensors are disposed in a turbine disposed in a power generation plant.

14. The control system of claim 1 wherein said sensors are disposed in a turbine engine assembly.