Compressor Motor Housing Temperature Control Using Dual PID Feedback
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Solution Overview
Problem
High thermal inertia in larger compressor motor housings made of materials like cast iron, which generate and retain heat slowly, makes existing temperature control systems less responsive, leading to potential overheating or undercooling issues.
Innovation Solution
A hybrid control system using both stator winding and motor housing temperature measurements to dynamically adjust cooling fluid flow through an electronic expansion valve, with a primary and secondary PID controller to maintain optimal temperature setpoints, effectively addressing the thermal inertia challenge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If larger cast iron motor housings are used in high thermal inertia systems, then heat retention and structural stability are improved, but temperature control responsiveness deteriorates
Solution Approach 1:
The patent implements a dual feedback control system using both stator winding temperature sensors and motor housing temperature sensors. The stator winding temperature provides immediate feedback for rapid response, while the motor housing temperature provides feedback on the actual thermal state of the high thermal inertia system. This dual feedback mechanism allows the controller to anticipate temperature changes and adjust cooling fluid flow proactively, resolving the responsiveness issue in high thermal inertia systems.
Solution Approach 2:
The control system uses stator winding temperature as a leading indicator to initiate cooling actions before the motor housing temperature rises significantly. Since the stator windings heat up faster than the massive cast iron housing, monitoring stator temperature allows the system to take preliminary cooling action, preventing the housing from reaching critical temperatures despite its slow thermal response.
2Device complexity
If traditional PID control based on motor housing temperature is used, then system simplicity is maintained, but control accuracy in high thermal inertia systems deteriorates
Solution Approach 1:
The patent segments the temperature control function into two independent control loops: one controlling stator winding temperature and another controlling motor housing temperature. Each loop uses its own PID controller with appropriate tuning parameters. This segmentation allows each controller to focus on its specific thermal zone, improving overall control accuracy without requiring an overly complex unified controller.
Solution Approach 2:
The patent merges two PID control systems into a unified control architecture that shares common components such as the electronic expansion valve and refrigerant circulation system. The first PID controller regulates stator winding temperature while the second PID controller regulates motor housing temperature, but both control the same cooling fluid flow system, creating an integrated solution that improves accuracy without proportionally increasing complexity.
3Stability of the object's composition
If cooling fluid flow is restricted to maintain low motor housing temperature, then housing temperature stability is improved, but stator winding overheating risk increases in high thermal inertia systems
Solution Approach 1:
The dual PID control system independently monitors both stator winding temperature and motor housing temperature, allowing the controller to detect when housing temperature is stable while stator temperature is rising. The feedback from both sensors enables the system to adjust cooling fluid distribution dynamically, preventing stator overheating even when housing temperature stability is maintained.
Solution Approach 2:
The patent applies different cooling control strategies to different parts of the motor system. The stator winding region receives cooling control based on stator temperature feedback, while the motor housing receives cooling control based on housing temperature feedback. This localized quality approach allows the system to prevent stator overheating without compromising motor housing temperature stability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The hybrid system provides responsive temperature control across varying chiller operating conditions, preventing overheating of the stator and avoiding undercooling, thus extending component life and maintaining stable operation.
Implementation Method 1
the valve operates to expand liquid refrigerant, lowering the pressure and the temperature of the refrigerant
Implementation Method 2
The motor and the motor housing are cooled by a fluid circulated within the motor housing
Data Source
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AI summary
A method and apparatus for controlling temperature of a compressor motor (170) having a motor cooling circuit in a refrigeration system (1014) is provided. The motor cooling circuit includes a second expansion valve (1043) providing fluid communication between the condenser and the compressor motor. The compressor motor (170) is in fluid communication with the refrigeration circuit (1014) between downstream of the first expansion valve (1040) and a compressor inlet. Refrigerant is provided as a cooling fluid to the motor cooling circuit. A primary PID loop (402) and a secondary PID loop (414) are used to control the temperature and the flow of refrigerant to the motor (170).