Compressor control in a vapor compression cooling cycle
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Solution Overview
Problem
Existing vapor compression cooling systems face challenges in controlling compressor speed due to independent expansion valve control and variations in evaporator wall temperature, leading to impaired control capability.
Innovation Solution
Implementing a motor controller that receives expansion valve position signals, analyzes position deltas, and adjusts compressor speed to prevent surge, using sensors and observers to estimate mass flow and calculate target speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If compressor speed is controlled by measuring pressure between the evaporator and the compressor, then the control system is simple, but the control sensitivity is poor due to independent expansion valve control and evaporator wall temperature variations
Solution Approach 1:
The patent introduces an observer as an intermediary component that estimates mass flow rate based on system state variables (pressures, temperatures) and compressor speed. This observer acts as a mediator between the available measurements and the desired mass flow control, providing accurate mass flow estimation without requiring direct mass flow sensors or complex control architecture.
Solution Approach 2:
The patent replaces direct mechanical pressure-based control with a model-based estimation approach. Instead of relying on pressure measurements alone, the system uses a thermodynamic model of the refrigerant cycle to estimate mass flow rate, substituting mechanical measurement limitations with computational estimation that provides superior control sensitivity.
2Ease of operation
If the expansion valve controller is independently controlled, then the valve control is simple, but the compressor speed control capability is impaired
Solution Approach 1:
The patent implements a feedback mechanism where the observer continuously estimates mass flow rate based on system state variables and feeds this information back to the compressor speed controller. The controller adjusts compressor speed based on the estimated mass flow rate to maintain optimal operation, creating a closed-loop feedback system that improves reliability while preserving expansion valve independence.
3Adaptability or versatility
If variations in evaporator wall temperature are allowed, then the system adapts to changing conditions, but the control capability is impaired
Solution Approach 1:
The patent accounts for evaporator wall temperature variations by incorporating temperature measurements into the observer's state estimates. The thermodynamic model uses temperature parameters to calculate refrigerant properties and mass flow rate, allowing the system to adapt to changing thermal conditions while maintaining accurate mass flow estimation and control capability.
Data Source
AI summary
Controllers, system and methods for vapor cycle compressor speed management. A system having a compressor, a condenser, an expansion valve and an evaporator with a circulating refrigerant or refrigerant is managed. A compressor controller uses expansion valve position, a mass flow estimate, or a mass flow measurement to determine desired compressor speed.