Feed Water Pump Control Device Using Inverter Frequency Error Correction
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Solution Overview
Problem
Existing feed water pump control devices require pressure sensors on the intake side, increasing costs and leading to inefficiencies in energy and water usage due to errors in discharge side pressure control, especially when operating at less than maximum capacity.
Innovation Solution
A feed water pump control device that estimates constant end pressure by controlling the operating speed of the pump using an inverter device, automatically correcting linearized characteristics based on errors in the relationship between output frequency and actual operating conditions without the need for intake side sensors, thereby optimizing discharge side pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pressure sensors are installed on the intake side of the feed water pump to detect boost pressure, then the discharge side pressure can be accurately controlled, but the equipment cost increases and the system complexity increases
Solution Approach 1:
The patent removes the pressure sensor from the intake side of the pump by extracting the boost pressure detection function and relocating it to the discharge side. The discharge side pressure sensor readings are used in conjunction with pump performance characteristics to calculate the required boost pressure, thereby eliminating the need for direct intake side pressure measurement while maintaining control accuracy.
Solution Approach 2:
The patent introduces the pump performance characteristics curve as an intermediary element between the discharge side pressure sensor and the control system. This curve serves as a transfer function that translates discharge side pressure measurements into boost pressure requirements, allowing indirect detection of intake side conditions without physical sensors at that location.
2Reliability
If the feed water pump operates at maximum quantity continuously, then the simple linearized characteristics accurately represent the relationship between operating frequency and discharge side pressure, but energy waste occurs when operating at half maximum quantity or less
Solution Approach 1:
The patent implements dynamic adjustment of the pump's operating characteristics by using the actual discharge side pressure sensor readings to continuously update the required boost pressure calculations. This allows the system to adapt to varying operating conditions and demand levels, optimizing energy consumption across different flow rates rather than relying on fixed linearized characteristics based on maximum capacity operation.
Solution Approach 2:
The patent establishes a feedback control loop where the discharge side pressure sensor continuously monitors actual pressure conditions and feeds this information back to the control system. The control system then adjusts the pump operating frequency based on the difference between actual and required pressure, ensuring energy-efficient operation at varying demand levels while maintaining accurate pressure control.
3Measurement precision
If two sensors (quantity sensor and discharge side pressure sensor) are installed to carry out estimated constant end pressure control, then the control accuracy improves, but the equipment cost and complexity increase
Solution Approach 1:
The patent removes the quantity sensor from the system by extracting the flow rate detection function and replacing it with pressure-based inference. The discharge side pressure sensor readings, combined with pump performance characteristics and operating frequency information, are used to calculate the actual flow rate, thereby eliminating the need for a separate quantity sensor while maintaining control accuracy.
Solution Approach 2:
The patent replaces the mechanical quantity sensor measurement system with a computational approach using pressure measurements and pump performance modeling. Instead of directly measuring flow rate with a mechanical sensor, the system uses the relationship between pressure, frequency, and pump characteristics to infer flow rate, substituting physical measurement with calculation-based detection.
Data Source
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AI summary
The presence or absence of boost pressure is determined from an error between F-P characteristics showing the relationship between the output frequency of an inverter and the power consumption and an actual operating point. When there is boost pressure, an amount of correction of linearized characteristics showing the relationship between quantity and discharge side pressure is automatically calculated based on the error, and the linearized characteristics are corrected. Subsequently, by carrying out a PID control in accordance with a target pressure obtained from post-correction linearized characteristics, the output frequency of an inverter unit is controlled, and an estimated constant end pressure control is carried out. Because of this, a pressure sensor or quantity sensor on a pump intake side is rendered unnecessary, and a simplification and reduction in cost of a feed water pump control device are possible. Also, an estimated constant end pressure control is carried out by controlling the pump discharge pressure to a predetermined value, thus achieving resource saving and energy saving.