Fluid PID Autotuning Using Relay and Step Process Identification
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Solution Overview
Problem
Existing PID autotuning methods struggle to accurately tune PID controllers for fluid systems without prior knowledge, especially in industrial settings with load disturbances and noise, leading to instability and difficulty in validating settings.
Innovation Solution
A method for estimating a process transfer function using a first-order approximation with delay, involving a periodic relay process, relay with integration, and step injection to identify critical points, allowing for precise calculation of PID parameters without a-priori knowledge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If relay based autotuning is used to achieve PID tuning, then critical point frequency can be identified, but the method leads to asymmetrical oscillation under load disturbance and requires complex relay bias adjustment
Solution Approach 1:
The patent extracts and compensates for the load disturbance effect separately from the main tuning process. By measuring the asymmetry caused by load disturbance and calculating a compensation value, the method removes the harmful effect of load disturbance on the oscillation symmetry, eliminating the need for complex relay bias adjustment while maintaining accurate critical point identification
Solution Approach 2:
The patent changes the approach from adjusting relay bias to adjusting the compensation parameter. By measuring the actual oscillation asymmetry and using this information to compensate for load disturbance effects, the method transforms the complex bias adjustment problem into a parameter compensation calculation, simplifying the tuning process
2Extent of automation
If step based autotuning is used for online PID tuning, then process identification can be performed, but the method requires the system to be stabilized and may not handle load disturbances effectively
Solution Approach 1:
The patent uses feedback from the actual system response to detect and compensate for load disturbances. By continuously monitoring the oscillation asymmetry and using this feedback to adjust the compensation parameter, the method maintains reliable PID tuning even under varying load conditions, enabling robust online tuning without requiring system stabilization
Solution Approach 2:
The patent performs preliminary compensation for load disturbance effects before finalizing the PID parameters. By pre-calculating the compensation based on observed asymmetry and applying it to the process identification results, the method ensures accurate tuning even when load disturbances are present during the tuning process
3Productivity
If Ziegler-Nichols settings are applied for PID tuning, then PID parameters can be calculated, but the settings are not correlated to typical process characteristics making validation difficult
Solution Approach 1:
The patent transitions from static Ziegler-Nichols formulas to a dynamic approach that adapts to actual process characteristics. By using measured oscillation data and asymmetry compensation to identify process parameters, the method generates PID settings that are dynamically correlated to the specific process being controlled, enabling both fast calculation and accurate validation
Solution Approach 2:
The patent performs preliminary process characterization through oscillation measurement and asymmetry analysis before calculating PID parameters. This preliminary identification of process characteristics enables the generation of tailored PID settings that are correlated to the specific process, while maintaining rapid calculation through automated parameter extraction
Data Source
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AI summary
Method for calculating PID parameters of a fluid system comprising a motor driving a pump, a compressor or a fan, comprising further a feedback sensor providing a feedback signal on the system and a PID regulation controlling the motor speed, wherein the method comprises: - after an initial approximation of the fluid system by a first order transfer function with delay where three parameters of the transfer function of the process to be identified are: K Static gain, θ Delay, τ Time constant, - one or more sequences of: a - bypassing the PID regulation and implementing the following processes: - a periodic relay process providing a first point (ω-180; G-180) at -180° of phase named critical point, - a periodic relay with integration process providing a second point (ω-90; G-90) at - 90° of phase and, - a step injection providing a third point G0 at ω = 0° of phase and at null frequency, b - resolving the relevant equations in equation systems according to the points obtained through said processes to calculate the transfer function parameters available among:K = G0, τ=1ω−180KG−1802−1,θ=tan−1ω−180⋅τ+π⋅1ω−180 c -applying the transfer function parameters obtained to calculate PID parameters for the system regulation: {Kp=τK⋅λ+θTi=τTd=θ