Turbine Valve Positioning with Redundant Hydraulic PI Control
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Solution Overview
Problem
Existing valve control systems in steam turbines face challenges in accurately controlling the position of valves, particularly in redundant configurations, leading to inefficiencies and potential hardware redundancy, as well as difficulties in stabilizing and balancing cascaded control processes.
Innovation Solution
The implementation of Solid State Relays (SSRs) for inter-module communication and driver isolation, allowing redundant field devices to connect concurrently to both valve positioners with a single termination unit, and a cascaded PI control loop that balances the control of pilot and main hydraulic valve sections within a single processor, eliminating the need for separate hardware and reducing time lag.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If redundant valve positioners are used for failover capability, then reliability is improved, but hardware complexity and cost increase
Solution Approach 1:
The patent merges the functionality of two redundant valve positioners into a single shared hardware platform. Both the primary and backup valve positioners share common field devices including the servo amplifier, position transducer, and termination unit. This sharing arrangement maintains failover capability while eliminating the need for duplicate hardware, thus improving reliability without proportionally increasing hardware complexity
Solution Approach 2:
The single termination unit and field devices are designed to serve dual purposes - supporting both the primary and backup valve positioners. The servo amplifier and position transducer can be controlled by either positioner depending on operational status, making these components universal rather than dedicated to a single positioner. This multi-functionality reduces overall hardware requirements while maintaining redundant control capability
2Reliability
If separate hardware is used for primary and backup valve positioners, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent combines the hardware resources of primary and backup valve positioners into a shared infrastructure. Both positioners utilize the same servo amplifier, position transducer, and termination unit, eliminating the need for separate hardware chains. This merging approach maintains the ability to switch between primary and backup control while reducing overall system complexity and hardware count
3Measurement precision
If cascaded control loops are implemented in separate processors, then control precision is improved, but time lag increases
Solution Approach 1:
The patent merges the cascaded control loops into a single processor architecture. Both the outer loop (controlling main hydraulic valve section) and inner loop (controlling pilot hydraulic valve section) execute within the same processor, eliminating inter-processor communication delays. This single-processing approach maintains control precision through proper loop nesting while significantly reducing time lag compared to distributed processor implementations
Data Source
AI summary
A system for controlling a turbine valve is provided. The system includes a hydraulic pilot valve section being moveable in a first direction and a second direction; a main hydraulic valve section being moveable in a first direction to close the turbine valve and a second direction to open the turbine valve; a position demand indicating a desired position of the turbine valve; a first feedback indicating an actual position of the hydraulic pilot valve section; and aa second feedback indicating an actual position of the main hydraulic valve section. The system also includes a pilot valve error; a main valve error; a turbine valve error; and a pilot valve adjustment moving the hydraulic pilot valve section in response to the turbine valve error. The turbine valve error is repeatedly determined and the pilot valve adjustment repeatedly moves the hydraulic pilot valve section to minimize the turbine valve error.