## 6 Conclusions  
This study used a semi-empirical compressor simulation model and established a compressor experimental setup to investigate the impact of oil charge on the OCR and the effect of the OCR on compressor performance, considering factors such as evaporation temperature, condensation temperature, and compressor speed variations. Based on the experimental results, a comparison between experimental and simulated data was conducted, leading to the following conclusions:  
1. Oil charge has a significant impact on the system's OCR, and a greater oil charge leads to a higher OCR. A fitting relationship between the oil charge and OCR was obtained. When the OCR is approximately zero, the simulation model aligns well with the experimental values.
2. The OCR increases with increasing compressor speed, decreases with lower evaporation temperatures, and increases with higher condensation temperatures. And the condensation temperature has a greater impact on the OCR than the evaporation temperature.
3. The OCR significantly affects the isentropic efficiency and discharge temperature of the compressor but has a smaller impact on volumetric efficiency. At low compressor speeds, a low OCR leads to a rapid decline in isentropic efficiency. At high compressor speeds, isentropic efficiency tends to be consistent. As compressor speed increases, the discharge temperature first decreases and then gradually levels off. Volumetric efficiency increases with the compressor speed and levels off after surpassing the rated compressor speed. And the OCR shows little impact on volumetric efficiency.
4. The simulation model for volumetric efficiency has the highest accuracy, while isentropic efficiency and the discharge temperature show a notable impact from the OCR. At certain low and high compressor speeds, the impact of the OCR needs to be considered for adjusting the simulation model.  
The variable frequency of electrical vehicle air conditioning compressors has been widely applied due to their precise temperature control, energy efficiency, comfort, and excellent noise and vibration characteristics. However, lubricating oil in the compressor has a significant impact on the reliability of the compressor and the performance of the refrigeration system. Therefore, it is necessary to analyze the mechanism of the oil circulation rate and its effects. From the above analysis, it can be seen that there are three main factors that ensure the best performance of the compressor, such as the oil charge, compressor speed, and appropriate operating conditions (e.g., condensation temperature and evaporation temperature).  
Software, H.C.; data curation, X.L.; Writing--original draft, J.C.; Writing--review & editing, L.H.; Supervision, L.T.; Project administration, X.W. All authors have read and agreed to the published version of the manuscript.  
The project is supported by Shanghai Key Laboratory of Multiphase Flow and Heat Transfer in Power Engineering (13 DZ2260900) and Jiaxing Municipal Science and Technology Plan Project (2023 AD31074).  
Not applicable.  
Data Availability Statement: Data is contained within the article.  
Author [PERSON] was employed by the company Zhejiang Zhongguang Electrical Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.