Network Control System Packet Loss Compensation
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Solution Overview
Problem
In network control systems, packet loss leads to discrepancies between calculated and actual manipulated variables (MV) and processed variables (PV), causing internal state deterioration and response delays, resulting in increased overshoot and disturbances.
Innovation Solution
A network control system with MV and PV complementing units that provide complementary values based on trend data, and buffering units that correct calculations and compensate for packet losses by utilizing virtual set values and holding trend data, ensuring stable plant control by synchronizing MV and PV values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If packet transmission is used for MV from controller to actuator, then networked control flexibility is improved, but packet loss causes discrepancy between calculated and actual MV leading to control instability
Solution Approach 1:
The actuator transmits feedback information about the actual MV to the controller, and the controller uses this feedback to correct its internal state and recalculate MV. This feedback mechanism resolves the contradiction by allowing the system to maintain networked control flexibility while compensating for packet loss through continuous correction based on actual received values.
Solution Approach 2:
The controller changes its internal parameter (integrated value) based on feedback from the actuator. When packet loss occurs, the controller adjusts its integrated value by the difference between calculated and actual MV, thereby adapting to the actual system state and maintaining control stability despite network uncertainties.
2Duration of action of stationary object
If MV complementary value is provided by actuator when packet loss occurs, then control continuity is maintained, but internal state of controller deteriorates causing response delay
Solution Approach 1:
The actuator provides feedback about the actual MV received to the controller. This feedback enables the controller to understand the true system state and adjust its calculations accordingly, maintaining control continuity while preventing internal state deterioration that would cause response delays.
Solution Approach 2:
The controller prepares correction actions in advance by calculating the difference between expected and actual MV values. When packet loss is detected, the controller has already prepared the necessary correction to its integrated value, reducing response delay while maintaining control continuity.
3Power
If controller increases integrated value during response delay, then control effort is increased, but overshoot is increased and disturbance is generated
Solution Approach 1:
The feedback mechanism allows the controller to monitor the actual system state and adjust its control effort accordingly. By using feedback to correct the integrated value based on the difference between calculated and actual MV, the controller applies only the necessary control effort without excessive increase, thereby preventing overshoot and disturbance while maintaining adequate control power.
Data Source
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AI summary
It is an object of the present invention to implement a network control system capable of realizing stable plant control by compensating a controller in view of an occurrence of a packet loss. In a network control system for packet-transmitting a manipulated variable of a controller, which is calculated based on a deviation between a processed variable from a sensor that measures a physical quantity of a controlled object plant and a set value at a predetermined sampling period, to an actuator provided on the controlled object plant side via a network, and causing the actuator to provide the manipulated variable to the controlled object plant, the network control system includes: an MV complementing unit that provides a complementary value of the manipulated variable to the actuator when an error occurs in a packet transmission; an MV buffering unit that answers back trend data of the manipulated variable being provided to the controlled object plant from the actuator or the complementary value being complemented by the MV compensating unit for the actuator, to the controller via the network; and an MV compensating unit that corrects a calculation of the manipulated variable of the controller based on the trend data or the complementary value being answered back.