Compressor Inlet Refrigerant Quality Estimation in EV Thermal Systems
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Solution Overview
Problem
The quality of refrigerant entering the compressor in electric vehicle thermal systems affects performance and efficiency, as it cannot be accurately measured directly from pressure and temperature sensors, leading to inaccurate mass flow rate calculations and potential compressor damage.
Innovation Solution
A control system estimates refrigerant quality at the compressor inlet using a Kalman filter to determine an inlet enthalpy correction factor based on estimated and measured compressor outlet temperatures, and uses this to calculate the refrigerant quality, which is then used to control actuators in the thermal system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If refrigerant quality is measured directly using pressure and temperature sensors, then the measurement process is simple, but the measurement precision is insufficient leading to inaccurate mass flow rate calculations
Solution Approach 1:
The patent uses compressor outlet temperature as an intermediary parameter to indirectly determine refrigerant quality at the compressor inlet. Instead of directly measuring refrigerant quality (which is difficult), the system measures compressor outlet temperature and uses it as a mediator to calculate the inlet refrigerant quality through thermodynamic relationships, thereby improving measurement accuracy without requiring complex direct measurement devices
Solution Approach 2:
The patent replaces direct physical measurement of refrigerant quality with a computational estimation approach. By substituting the mechanical/direct measurement method with a mathematical model that uses readily available sensor data (pressure and temperature measurements combined with thermodynamic equations), the system achieves higher precision without additional complex measurement hardware
2Reliability
If inaccurate refrigerant quality data is used, then the system operation continues, but the reliability decreases due to potential compressor damage
Solution Approach 1:
The system performs preliminary estimation of refrigerant quality using the improved method before making control decisions. By calculating the compressor outlet temperature and estimating inlet refrigerant quality in advance, the system can proactively identify potentially damaging conditions (such as liquid slugging) and take preventive actions before actual damage occurs to the compressor
Solution Approach 2:
The patent implements a feedback control mechanism where the estimated refrigerant quality and compressor outlet temperature are continuously monitored and fed back to the control system. This feedback loop allows the system to adjust operating parameters in real-time based on the estimated refrigerant quality, thereby protecting the compressor from damaging conditions while maintaining optimal system performance
Data Source
AI summary
A system includes a compressor outlet temperature module, a refrigerant quality module, and a correction factor module. The compressor outlet temperature module is configured to estimate a temperature at an outlet of a compressor in a thermal system of an electric vehicle. The refrigerant quality module is configured to estimate a quality of refrigerant at an inlet of the compressor based on an enthalpy at the compressor inlet and an inlet enthalpy correction factor. The refrigerant quality is a ratio of vapor refrigerant mass to total refrigerant mass. The correction factor module is configured to determine the inlet enthalpy correction factor based on the estimated compressor outlet temperature and a temperature measured at the compressor outlet.