Valve Control Gain Automation to Avoid Division by Zero at Low Flow
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Solution Overview
Problem
The tuning of proportional, integral, and derivative (PID) controller parameters for HVAC systems is a laborious task, and existing self-adapting control algorithms face challenges in determining valve positions accurately, especially when actual flow rates approach zero, leading to division by zero errors.
Innovation Solution
A self-adapting controller for HVAC systems that uses a characteristic function to determine valve stroke and employs a microprocessor with an analog-to-digital converter for processing flow rate signals, including delta-sigma modulation, to calculate valve positions based on set-point values and default flow rates, avoiding division by zero errors by using a nominal flow rate when actual flow is zero.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If self-adapting control algorithms are used to automatically determine PID parameters, then the ease of operation is improved, but reliability deteriorates due to division by zero errors when flow rates approach zero
Solution Approach 1:
The patent applies preliminary anti-action by detecting when the calculated gain would cause division by zero errors (when flow rate approaches zero) and preemptively setting the gain to a predetermined safe value before the error can occur. This prevents the reliability issue while maintaining automatic parameter determination.
Solution Approach 2:
The patent changes the gain parameter dynamically based on flow rate conditions. When flow rate is above a threshold, the gain is calculated automatically; when flow rate approaches zero, the gain is switched to a predetermined value, thus adapting parameters to avoid division by zero errors while maintaining control reliability.
2Measurement precision
If PID control parameters are manually tuned to achieve precise control, then measurement precision is improved, but loss of time increases due to the arduous tuning task
Solution Approach 1:
The patent implements self-service by enabling the control system to automatically determine its own PID parameters (particularly the gain) based on real-time flow rate measurements and characteristic curves, eliminating the need for manual tuning while maintaining precise control performance.
Solution Approach 2:
The patent applies preliminary action by pre-storing characteristic curves that relate flow rate to optimal gain values. During operation, the system quickly determines the appropriate gain by referencing these pre-calculated curves based on current flow conditions, avoiding time-consuming manual tuning while achieving precise control.
3Adaptability or versatility
If a generic control algorithm is used to improve adaptability, then adaptability is improved, but device complexity increases due to the need for characteristic functions and flow rate processing
Solution Approach 1:
The patent applies universality by developing a generic control algorithm based on characteristic functions that can be applied to various types of fluid conveyors (valves, dampers, actuators) regardless of their specific application. The same algorithm structure works for different devices by simply changing the characteristic curve data, thus achieving multi-functionality without proportionally increasing complexity.
Data Source
AI summary
A valve assembly may include: a valve body with a fluid path extending between the inlet port and the outlet port; a valve member with a closed position blocking the fluid path and an open position; a sensor the fluid flow; an actuator coupled to the valve member; and a controller for the actuator with a set point value and a default flow rate indicative of nominal flow through the fluid path. The controller may: read the sensor; calculate a flow rate; compare the flow rate to a threshold value indicative of substantially zero flow rate; and if the measure of flow rate is below the threshold value, calculate a position of the valve member directly from the set point value and the default flow rate, produce a control signal from the calculated position, and communicate the control signal to the actuator.