Wireless Process Control Stabilization via Adaptive Estimation
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Solution Overview
Problem
Existing process control systems in industrial automation face instability due to unreliable wireless communication, where measurements may be received non-periodically and with varying delays, leading to potential connection breaks and lost packets, which can cause the closed-loop system to become unstable.
Innovation Solution
A method is introduced where estimated process measurement values are generated based on the last received value and a setpoint signal, gradually adjusting towards the setpoint until the next measurement is received, using a lowpass filter and providing a failure indication during long communication breaks, allowing standard controllers to maintain stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If wireless communication is used to connect measurement devices to controllers, then flexibility and ease of reconfiguration are improved, but communication reliability deteriorates due to non-periodic measurements, varying delays, and connection breaks
Solution Approach 1:
An intermediary module is introduced between the wireless communication interface and the standard controller. This intermediary receives irregular measurements from the wireless device, applies interpolation to generate regular measurement values, and forwards these to the controller. This mediator shields the controller from communication irregularities while preserving wireless flexibility.
Solution Approach 2:
The system performs preliminary interpolation of measurement values before they reach the controller. By pre-processing the irregular wireless measurements into regular values in advance, the controller receives data in the expected format without needing to handle communication variability, thus maintaining both wireless flexibility and controller stability.
2Device complexity
If standard PID controllers are used with wireless measurements, then device complexity is reduced, but system stability deteriorates due to non-periodic measurements and communication breaks
Solution Approach 1:
The intermediary module acts as a buffer that transforms irregular wireless measurements into regular values suitable for standard PID controllers. This allows the use of simple, well-understood PID controllers without modifying their internal logic, while the intermediary handles the complexity of wireless communication variability.
Solution Approach 2:
The system creates a copy or representation of the measurement data in regular form through interpolation. Instead of modifying the controller to handle irregular data, a regularized copy of the measurements is generated that matches the expected input format of standard controllers, preserving their simplicity while ensuring stability.
3Stability of the object's composition
If PID PLUS controllers are used to handle non-periodic measurements, then system stability is improved, but device complexity increases due to specialized controller requirements
Solution Approach 1:
Rather than upgrading to complex PID PLUS controllers, the patent introduces a simpler intermediary module that performs interpolation. This intermediary handles the non-periodic nature of wireless measurements, allowing the use of standard, simpler controllers while maintaining stability.
Solution Approach 2:
The patent replaces the need for complex specialized controllers (PID PLUS) with a different approach: a preprocessing intermediary that transforms data before it reaches the controller. This substitutes the complexity from the controller into a separate data preparation stage, allowing standard controllers to be used.
4Ease of manufacture
If wireless transmitters are used to eliminate cabling, then installation cost and complexity are reduced, but measurement reliability deteriorates due to packet loss and connection breaks
Solution Approach 1:
An intermediary module is positioned between the wireless transmitter and the controller to handle measurement data. This intermediary uses interpolation to reconstruct missing or lost measurement values, compensating for packet loss and connection breaks while preserving the installation simplicity of wireless transmitters.
Solution Approach 2:
The system prepares for potential measurement losses by implementing interpolation in advance. When packets are lost or connections break, the intermediary has pre-established methods to generate reasonable estimates of missing values, cushioning against the impact of unreliable wireless transmission while maintaining installation ease.
Data Source
AI summary
A control loop includes a process controller for controlling a field device in a process. A remote measurement transmitter measures a desired process variable and transmits the measured variable as a wireless measurement signal to a wireless interface unit on the controller side. The interface unit passes the received measurement signal, and a trigger signal indicating a reception of a new measurement, to an adaptive estimator. When triggered by a trigger signal from the wireless interface, i.e. when a new measurement value is received, the adaptive estimator outputs the new value measurement value to the process controller. Otherwise, between consecutive trigger signals, the adaptive estimator generates an estimated measurement value that gradually moves towards a setpoint according to a predetermined estimation algorithm or process.