Adjustable gain controller for valve position control loop and method for reducing jitter

• US 4,556,956 A
• Filed: 09/16/1983
• Issued: 12/03/1985
• Est. Priority Date: 09/16/1983
• Status: Expired due to Fees

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Jaswa, Vijay C., Dickenson, Royston J.
• Primary Examiner(s): Smith, Jerry
• Assistant Examiner(s): Lastova, John R.
• Application Number:
  US06/533,644
• Time in Patent Office: 809 Days
• Field of Search: 364/157, 364/162, 364/176, 364/183, 364/825, 415/17, 60/662
• US Class Current: 700/42
• CPC Class Codes: F01D 17/24 electrical
• CPC Class Codes: F05D 2200/11 Sum
• CPC Class Codes: G05B 11/42 for obtaining a characteristic which is both proportional and time-dependent, e.g. P. I., P. I. D.
• CPC Class Codes: G05D 7/0635 by action on throttling means G05D7/0688, G05D7/0694 take precedence

Abstract

An adjustable gain controller for a steam turbine valve position control loop includes an electronic operator, a proportional controller, a derivative controller and an integral controller. A steam flow condition error signal is amplified by the reciprocal of the valve'"'"'s regulation value. The amplified error signal is supplied to the electronic operator and to the integral controller. The electronic operator includes means for initially selecting a value of A and n and generating a gain factor from a nonlinear gain characteristic function utilizing those values in combination with the valve'"'"'s regulation value and the normalized error signal. The electronic operator multiplies the amplified error signal by the gain factor and applies the resultant signal to the proportional controller and the derivative controller. The output signals from the proportional, derivative and integral controllers are summed together and that sum is input into an electrohydraulic valve actuator system. The electrohydraulic valve actuator directly positions the steam valve. Hydraulic and mechanical jitter is reduced by adjusting the values of A and n to reduce the jitter in the electrohydraulic valve actuator system.

Claims

1. In combination with a steam turbine, wherein steam flow through a valve is controlled by a valve position control loop, the regulation of said valve being set relatively low thereby establishing a relatively high overall gain for said control loop, said control loop responding quickly to error signals and including an electrohydraulic valve actuator which directly effects the positioning of said valve, an adjustable gain controller as part of the digitized portion of said control loop which receives said error signals amplified by the reciprocal of the valve'"'"'s regulation value, wherein the adjustable gain controller comprises:

an integral controller receiving the amplified error signals and integrating said amplified error signals over a preselected time period;

an electronic operator which includes means for initially selecting a value of A between -1.0 and +1.0 and means for initially selecting a value of n from the group consisting of 0, 1 and 2, said electronic operator generating a gain factor G, which is limited to positive values from the relationship expressed by

space="preserve" listing-type="equation">G=A+(1-A)(E/REG).sup.n

wherein E is the normalized value of said error signal and the value of REG is the valve'"'"'s regulation value, and said electronic operator multiplying said amplified error signals by said gain factor;

a proportional controller in parallel with a derivative controller, both receiving the electronic operator'"'"'s output signal;

means for summing the outputs of said integral controller, said derivative controller and said proportional controller together; and

means for adjusting both said value of A and said value of n to reduce the mechanical and hydraulic jitter in said electrohydraulic valve actuator which is caused by said digitized portion of said valve position control loop and yet maintain the relatively quick response of said control loop to said error signals.

2. A combination as recited in claim 1 above further including means for monitoring said mechanical and hydraulic jitter in said electrohydraulic valve actuator.

3. A combination as recited in claim 2 above wherein said error signal is the difference signal between a signal representative of the actual steam flow condition and a signal representative of the desired steam flow condition.

4. A combination as recited in claim 3 above wherein said integral controller is adjustable, said derivative controller is adjustable and said proportional controller is adjustable and said electronic operator utilizes a microprocessor to generate said gain factor from said values of A, n, E and REG.

5. A combination as recited in claim 4 above wherein the desired steam flow condition signal is digitally formated and the actual steam flow condition signal is digitally formated, said electrohydraulic valve actuator is supplied with pressurized hydraulic fluid through an associated hydraulic system and said electrohydraulic valve actuator responds to an analog electrical signal input thereto, and said valve position control loop includes:

a digital to analog converter which receives the summed output of said summing means and converts said summed output into an analog electrical signal;

means for applying said analog electrical signal to the electrical input of said electrohydraulic valve actuator; and

wherein

said monitoring means includes means for sensing the mechanical jitter on the mechanical connection between said electrohydraulic valve actuator and said valve stem, means for sensing the mechanical jitter within and on said electrohydraulic valve actuator, means for sensing the hydraulic jitter within said electrohydraulic valve actuator and in its associated hydraulic system, and said monitoring means includes means for displaying the respective output signals from said sensors.

6. A method of reducing mechanical and hydraulic jitter in an electrohydraulic valve actuator which is part of a valve position control loop in combination with a steam turbine, said valve actuator controlling the flow of steam through said valve, the valve'"'"'s regulation being set relatively low and said control loop responding quickly to steam flow condition error signals, said error signals being amplified by the reciprocal of the valve'"'"'s regulation value thereby establishing a relatively high gain for said control loop, the method of reducing the jitter caused by a digitized portion of said control loop comprising the steps of:

(a) initially selecting a value of A between -1.0 and +1.0;

(b) initially selecting a value of n from the group consisting of 0,1 and 2;

(c) calculating a gain factor G from the relationship expressed by

space="preserve" listing-type="equation">G=A+(1-A)(E/REG).sup.n

wherein G is limited to positive values, E is the normalized value of said error signal and the value of REG is said valve'"'"'s regulation value;

(d) integrating the amplified error signals over a preselected time period;

(e) multiplying said amplified error signals by said gain factor to produce resultant signals;

(f) obtaining the derivative of said resultant signals with a preselected gain multiplier;

(g) multiplying said resultant signals by a preselected constant;

(h) summing the integrated, amplified error signal, the derivative of said resultant signal and the proportional output resultant signal together;

(i) applying the summed signal to said electrohydraulic valve actuator;

(j) monitoring the mechanical and hydraulic jitter of said electrohydraulic valve actuator; and

(k) repeating all the above steps with different values of A and different values of n until the jitter is reduced to an acceptable level and said valve responds to an error signal by establishing the desired steam flow condition within an acceptable period of time.

7. A method as recited in claim 6 above wherein said error signal is a digitized difference signal;

each step of said method is performed digitally except steps i, j and k; and

said electrohydraulic valve actuator responds to an analog electrical signal input thereto, said method further comprising the step of;

converting the digitized summed signal into an analog electrical signal before step i.

8. In combination with a computer-based control system for a steam turbine, wherein a steam valve is controlled directly by a valve positioning subloop which responds to analog electrical signals input thereto, and said computer-based control system generates digital error signals which are the difference between the actual steam flow condition through said valve and the desired steam flow condition through said valve, an adjustable gain controller as part of the digitized portion of a valve position control loop tied to said positioning subloop and said control system, said controller comprising:

an integral controller receiving said error signals and integrating said error signals over a preselected time period;

an electronic operator which includes means for initially selecting a value of A between -1.0 and +1.0 and means for initially selecting a value of n from the group consisting of 0, 1 and 2, said electronic operator generating a gain factor G from the relatioship expressed by

space="preserve" listing-type="equation">G=A+(1-A)(E/REG).sup.n

wherein G is limited to positive values, E is the normalized value of said error signal and the value of REG is the valve'"'"'s regulation value, and said electronic operator multiplying said amplified error signals by said gain factor;

a proportional controller in parallel with a derivative controller, both receiving the electronic operator'"'"'s output signals;

means for summing the outputs of said integral controller, said derivative controller and said proportional controller together;

means for converting said summed output into an analog electrical signal and inputing said analog signal into said positioning subloop; and

means for adjusting both said value of A and said value of n to reduce the mechanical and hydraulic jitter in said positioning subloop which is caused by said digitized portion of said control loop and yet maintaing the relatively quick response of said control loop to said error signals.