EEV Velocity PID Control for Pulse Drift Correction in VRF Systems
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Solution Overview
Problem
Conventional VRF systems face challenges in accurately controlling the positioning of electric expansion valves (EEVs) over long-term operation, leading to disturbances and complications in refrigeration systems due to inadequate pulse control strategies.
Innovation Solution
A refrigeration cycle system incorporating a velocity PID component, a three-state controller, and a state machine that generates pulse commands based on the EEV's driving state, eliminating the need for position sensors by using stroke time to control the EEV's opening and closing, thereby avoiding zero-resetting and improving operational efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional pulse control strategy is used for EEV positioning, then the system structure is simple, but the positioning accuracy deteriorates after long-term operation
Solution Approach 1:
The patent implements feedback by counting the actual number of pulses sent to the EEV motor and comparing it with the expected pulse count based on operation time. This feedback mechanism detects drift in pulse-position correspondence and triggers corrective actions to restore accurate positioning without adding complex hardware sensors.
Solution Approach 2:
The system performs self-correction by automatically detecting pulse drift and executing recovery procedures using the existing motor and control circuitry. The controller monitors its own operation state and autonomously adjusts pulse counting to maintain positioning accuracy without external intervention or additional sensing components.
2Manufacturing precision
If EEV is reset to zero position after certain operation period, then positioning accuracy is restored, but system disturbance and complexity increase
Solution Approach 1:
Instead of completely resetting the EEV to zero position, the patent applies partial correction by adjusting the pulse count from the drifted position. This partial action restores positioning accuracy without the excessive disturbance of a full reset, maintaining system stability while correcting the positioning error.
Solution Approach 2:
The system performs preliminary detection of pulse drift during normal operation and executes correction before positioning accuracy is severely compromised. This preliminary action prevents the need for disruptive reset operations by maintaining accuracy proactively through continuous pulse counting and periodic correction.
3Speed
If velocity PID control is used for EEV, then dynamic response is improved, but long-term positioning accuracy deteriorates
Solution Approach 1:
The patent merges velocity PID control with pulse counting feedback mechanisms. The velocity PID provides fast dynamic response while the pulse counting feedback continuously monitors and corrects positioning drift over time. This combination integrates the advantages of both control strategies to achieve both rapid response and long-term accuracy.
Solution Approach 2:
The system maintains continuous pulse counting during velocity PID control operations, ensuring that positioning information is continuously updated even during dynamic adjustments. This continuous monitoring allows the system to maintain both fast response capability and accurate positioning by seamlessly combining dynamic control with ongoing position verification.
Data Source
AI summary
A refrigerant cycle of the present invention includes including an outdoor unit, a plurality of indoor units, and a controller for controlling the refrigeration cycle using at least one EEV. The controller comprises a velocity PID component executing a velocity PID control using pulse number for driving an EEV, three-state controller determining a driving state of the EEV and generating pulse commands designating the driving state, and a state machine driving the EEV depending on the pulse commands generated by the three-state controller.