Control system for vapour compression cycle and related methods
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Solution Overview
Problem
Existing vapour compression cycle systems, such as refrigeration units, suffer from inefficiencies due to direct motor speed control, which leads to suboptimal operation outside the system's peak efficiency, especially when dealing with temperature fluctuations and varying ambient conditions.
Innovation Solution
A computerized method that dynamically determines cooling or heating power demand based on compartment temperature and prevailing pressures, converting this to a speed demand value for the compressor, allowing finer control and optimizing system efficiency by selecting the most efficient power demand value from a lookup table or model.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If direct motor speed control is used, then the system is simple to operate, but the system operates outside peak efficiency conditions
Solution Approach 1:
The patent introduces an intermediary control layer between the motor speed controller and the compressor. Instead of directly controlling motor speed, the system controls the cooling power demand (Q) as an intermediate parameter, which is then converted to motor speed demands. This intermediary approach allows the system to operate at peak efficiency conditions while maintaining ease of operation through a single control input.
Solution Approach 2:
The patent changes the control parameter from direct motor speed to cooling power demand (Q). By controlling Q and then converting it to motor speed demands, the system can dynamically adjust operating conditions to maintain peak efficiency across varying ambient temperatures and thermal loads, rather than operating at fixed speed points.
2Device complexity
If fixed compressor speeds are used throughout the process, then the control system is simple, but the refrigeration cycle operates outside its optimum operating point
Solution Approach 1:
The patent transforms the static, fixed-speed control system into a dynamic system where motor speed demands are continuously adjusted based on prevailing conditions (ambient temperature, thermal load). The system dynamically converts cooling power demand Q into appropriate motor speed demands, allowing the refrigeration cycle to operate at its optimum operating point under varying conditions while maintaining relatively simple control architecture.
3Ease of operation
If on/off control is used, then the system is easy to control, but the cooling power cannot be modulated to match actual demand
Solution Approach 1:
The patent changes the controlled parameter from binary on/off states to continuous cooling power demand (Q) values. By controlling Q and converting it to motor speed demands, the system can modulate cooling power to precisely match actual thermal demand while maintaining hysteresis-based on/off control logic for temperature bounds, thus achieving both ease of operation and adaptability.
Data Source
AI summary
Computerised methods of controlling a vapour compression cycle system. In a first aspect, the method comprises determining a cooling or heating power demand value based on the prevailing temperature and comparing (730) it with a required set point temperature. The power demand value is converted to a speed demand value according to a model or map (720) and according to evaporating and condensing pressure/temperature, which is sent to the compressor motor speed controller (70). In another aspect, the power demand value for hysteresis control to maintain the temperature is dynamically chosen (710) from a plurality of possible power demand values according to evaporating and condensing pressure/temperature and according to a measure of efficiency calculated for each candidate power demand value. In another aspect, a compressor capacity value is selected (930) by looking up a compressor capacity in a look up table according to evaporating and condensing pressure/temperature.