Electronic Expansion Valve Control for Heat Pump Superheat Stability
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Solution Overview
Problem
Existing control methods for electronic expansion valves in air source heat pump systems fail to ensure sufficient exhaust gas superheat under extreme working conditions or low-frequency ranges, leading to instability and reliability issues, particularly due to temperature drifts in low-temperature environments.
Innovation Solution
A control method that calculates a target exhaust gas temperature based on compressor frequency and corrects the opening degree of the electronic expansion valve according to the actual superheat degree, ensuring the superheat requirements are met by adjusting the opening degree based on preset values, thereby improving control accuracy and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the electronic expansion valve is controlled according to target exhaust gas temperature in low-temperature heating mode, then the opening degree is reduced to maintain temperature control, but the refrigerant circulation amount becomes insufficient and exhaust gas superheat degree cannot be guaranteed
Solution Approach 1:
The control device continuously monitors the actual exhaust gas superheat degree and compares it with the target superheat degree. Based on the deviation between actual and target values, the control device dynamically adjusts the opening degree of the electronic expansion valve to maintain sufficient refrigerant circulation and ensure adequate exhaust gas superheat, even in low-temperature heating mode.
Solution Approach 2:
The control system transitions from static temperature-based control to dynamic superheat-based control. The opening degree of the electronic expansion valve is continuously adjusted based on real-time feedback of the exhaust gas superheat degree, allowing the system to adapt to varying operating conditions and maintain optimal refrigerant circulation across different temperatures and loads.
2Ease of operation
If the electronic expansion valve is controlled by target opening degree, then the control is simplified, but the sufficient exhaust gas superheat degree cannot be guaranteed in low-frequency ranges
Solution Approach 1:
Instead of using fixed target opening degrees, the control device implements feedback control by continuously measuring the actual exhaust gas superheat degree and adjusting the valve opening accordingly. This ensures adequate superheat across all operating frequencies while maintaining a relatively simple control structure through automated feedback mechanisms.
3Measurement precision
If temperature sensors are used in low-temperature environments, then temperature measurement is enabled, but temperature drift occurs and control accuracy at normal temperature is compromised
Solution Approach 1:
The control device uses feedback from temperature sensors to monitor exhaust gas superheat degree and dynamically adjusts the electronic expansion valve opening to compensate for temperature drift effects. By continuously comparing actual superheat with target superheat and adjusting the valve position, the system maintains accurate control despite sensor drift in low-temperature environments.
Solution Approach 2:
The control system changes the control parameter from absolute temperature to temperature differential (superheat degree). This parameter transformation makes the control less sensitive to absolute temperature measurement accuracy and drift, as it relies on the difference between exhaust gas temperature and evaporating temperature rather than absolute temperature values.
4Device complexity
If the opening degree of the electronic expansion valve is not properly adjusted, then the system operation is simplified, but liquid return occurs and system reliability deteriorates
Solution Approach 1:
The control device implements automated feedback control that continuously monitors exhaust gas superheat degree and adjusts the electronic expansion valve opening accordingly. This prevents liquid return by ensuring adequate superheat is maintained, eliminating the need for manual control adjustments while significantly improving system reliability.
Data Source
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AI summary
The present invention provides a control method and control device for an electronic expansion valve of an air source heat pump system. The control method includes: obtaining (S 1) a frequency of a compressor, calculating a target exhaust gas temperature according to the frequency, and controlling an opening degree of the electronic expansion valve according to the target exhaust gas temperature; and obtaining (S2) an exhaust gas superheat degree of the compressor, and correcting the opening degree of the electronic expansion valve according to a comparison result between the exhaust gas superheat degree and a preset superheat degree value, so that the exhaust gas superheat degree meets superheat degree requirements. According to the present invention, the target exhaust gas temperature is calculated according to the frequency of the compressor, so that the operation load and state of the system can be visually reflected and will not be affected by low-temperature environments, thus, the control accuracy of the electronic expansion valve can be guaranteed, and the problems existing in the prior art are solved. The opening degree of the electronic expansion valve is corrected according to the comparison result between the exhaust gas superheat degree and the preset superheat degree value, so that the superheat degree requirements can be met no matter the compressor operates at a high frequency or a low frequency.