Pump Flow Rate Estimation Using Curve Segmentation
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Solution Overview
Problem
Existing methods for estimating the operating point of pumps controlled by frequency converters, such as QH curve-based and QP curve-based methods, face inaccuracies at lower and higher flow rates due to non-monotonic characteristic curves, limiting their reliability and accuracy.
Innovation Solution
A method that combines QH curve-based and QP curve-based estimations, dividing the characteristic curve into regions based on its shape, using the QH curve-based method when accurate and switching to the QP curve-based method in unusable regions to enhance accuracy and reliability across various pump types.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If QH curve-based method is used to estimate pump operating point, then accuracy increases at high flow rates, but accuracy deteriorates at lower flow rates where head curve is flat or non-monotonic
Solution Approach 1:
The characteristic curve is divided into multiple regions based on monotonicity properties. The method segments the flow rate range into regions where the head curve is monotonically decreasing and regions where it is non-monotonic or flat. This segmentation allows selecting appropriate estimation methods for each region, ensuring accuracy across the entire operating range.
Solution Approach 2:
The method dynamically selects between QH curve-based estimation and alternative estimation approaches based on the current operating point's location on the characteristic curve. When the operating point falls in a monotonically decreasing region, QH method is used; when it falls in a non-monotonic region, the method switches to a different estimation strategy, making the system adaptive to varying operating conditions.
2Device complexity
If model-based methods using characteristic curves are used, then device complexity is reduced, but measurement precision deteriorates when curves are non-monotonic
Solution Approach 1:
The method performs preliminary analysis of the characteristic curve's monotonicity properties before conducting the actual flow rate estimation. By pre-dividing the curve into monotonic and non-monotonic regions and storing this information, the system prepares the necessary data structures and selection logic in advance, enabling accurate and efficient estimation without requiring additional sensors during operation.
Data Source
AI summary
A method and arrangement for determining the flow rate (Q) produced by a pump, when the pump is controlled with a frequency converter, which produces estimates for rotational speed and torque of the pump, and the characteristic curves of the pump are known. The method includes determining the shape of a QH curve of the pump, dividing the QH curve into two or more regions depending on the shape of the QH curve, determining on which region of the QH curve the pump is operating, and determining the flow rate (Q) of the pump using the determined operating region of the characteristic curve.