Wireless Networked Control with Error-Based Packet Scheduling
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Solution Overview
Problem
Networked Control Systems (NCS) face challenges with packet loss and time delays in wireless communication, leading to unstable control loops and performance losses, as existing solutions do not effectively merge wireless communication and control system technologies to optimize performance.
Innovation Solution
A networked control system that determines the rate of packet transmission based on control error and link quality, using a state observer to adjust transmission frequency and a scheduler to prioritize packets by control error, thereby improving wireless transmission performance and reducing network congestion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If control commands are transmitted over wireless network, then system flexibility and ease of installation are improved, but packet loss and time delays occur leading to unstable control loops
Solution Approach 1:
The system dynamically adjusts the transmission rate based on the control error magnitude. When control error is large, transmission rate increases to ensure timely delivery of critical control commands. When control error is small, transmission rate decreases to reduce network congestion. This dynamic adaptation resolves the contradiction by making the system reliable when needed while maintaining ease of wireless installation.
Solution Approach 2:
The patent changes the transmission parameter (transmission rate) based on the control error. By mapping control error to transmission rate through a predefined relationship, the system adapts its communication behavior to control needs, ensuring stability during critical periods while reducing unnecessary transmissions during stable operation.
2Reliability
If transmission rate is increased to prevent packet loss, then control reliability is improved, but network congestion increases
Solution Approach 1:
The transmission rate is dynamically adjusted based on control error magnitude rather than maintaining a constant high rate. This dynamic approach ensures reliable delivery when control errors are large while reducing transmissions when control errors are small, thus preventing network congestion while maintaining necessary reliability.
Solution Approach 2:
The system applies partial action by transmitting at high rate only when control error exceeds certain thresholds. When control error is within acceptable ranges, transmission rate is reduced, avoiding excessive transmissions that would cause network congestion while still maintaining control reliability when needed.
3Stability of the object's composition
If remote controller runs slower to ensure stable control loops, then control stability is maintained, but transient response performance is lost
Solution Approach 1:
The remote controller operates at variable speeds dynamically adjusted to control needs. During transient periods with large control errors, the controller runs faster to improve transient response. During steady-state operation with small control errors, the controller runs slower to maintain stability. This dynamic speed adjustment resolves the contradiction between stability and transient performance.
Solution Approach 2:
The system periodically evaluates control error magnitude and adjusts transmission rate accordingly. This periodic adaptation allows the controller to switch between fast operation during transients and slow operation during steady-state, achieving both good transient response and stability.
4Reliability
If acknowledgment receipts are used to ensure reliable delivery, then packet delivery reliability is improved, but communication overhead and system complexity increase
Solution Approach 1:
The patent extracts the acknowledgment mechanism from the communication protocol and replaces it with a control-error-based transmission rate adjustment mechanism. Instead of using complex acknowledgment receipts to ensure reliable delivery, the system proactively adjusts transmission rate based on control error, achieving reliability without the overhead and complexity of acknowledgment protocols.
Solution Approach 2:
The control system itself determines the appropriate transmission rate based on its control error, making the transmission reliability self-regulating. This self-service approach eliminates the need for external acknowledgment mechanisms, reducing communication overhead and system complexity while maintaining delivery reliability.
Data Source
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AI summary
A networked control system for controlling at least one plant includes a receiver configured to receive a feedback signal indicative of a current state of a controlled variable of a plant over a wireless link and a controller configured to determine a control command based on a control error between a reference state of the controlled variable and the current state of the control variable. The system also includes a processor configured to determine, based on a function of the control error, a number of transmission times a packet with the control command needs to be transmitted over the wireless link, and a transmitter configured to transmit the packet over the wireless link the number of transmission times.