## 1 Introduction  
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. Lubricating oil in the compressor serves the purposes of cooling, lubrication, and sealing, which has a significant impact on the reliability of the compressor and the performance of the refrigeration system, particularly on the system's pressure drop and heat exchange performance [1]. The lubricating oil content within automotive compressor systems can enhance the performance of compressors within a certain range. However, as compressor lubricating oil enters various components of the system through the discharge pipeline, its presence can lead to a reduction in the heat exchange capacity of the heat exchanger and also greatly affect the flow characteristics of the entire system, thereby impacting the operational stability of the air conditioning system [2]. Therefore, measuring the oil content and oil circulation rate (OCR) is of great importance for system performance and reliability [3]. [PERSON] [4] looked into the potential of low-GWP refrigerant fluids (R152a, R1234 yf, R1234 ze(E), R290, R600a) and assessed their suitability to be utilized as replacements for the historically used R134a. Pressure ratios across the compressor stage were considered in the study. Compared to R134a, R290, R600a, and R152a had higher cooling capacities, although the compression work was notably higher as well. Overall, these refrigerant fluids could act as replacements for R134a. [PERSON] [5] developed a simulation model for the detailed compression process of scroll compressors. A lumped parameter method was adopted to establish energy balance equations, and a recursive method was employed to solve these equations, obtaining parameters such as internal temperature and pressure and ultimately determining power and compressor efficiency. The results allow for the study of factors affecting compressor performance, including the impact of internal leakage and heat transfer losses, and thus provide a theoretical basis for the optimization of compressors. [PERSON] et al. [6] developed the validated zero-dimensional (0-D) and three-dimensional (3-D) simulation model, along with experiments, to investigate the distribution of performance loss and suction compression characteristics in high-speed R290 compressors. The results showed that the R290 compressor exhibits superior volumetric efficiency. However, the combination of increased over-compression loss and motor loss at high speeds resulted in an 11.7% rise in input power, leading to an 8.4% decline in thermodynamic performance for the R290 compressor under standard heating compared to the R32 compressor. [PERSON] [7] developed a performance model for variable frequency compressors, which includes the refrigerant flow rate, power, and COP. With evaporation and condensation temperatures as variables, multi-coefficient models at different frequencies were established. The study also compared the model with test data provided by the compressor manufacturer, and the results showed small relative errors, making the model suitable for frequency conversion systems. Due to the use of a polynomial model, the study also explored issues related to power at 0 frequency and frequency at 0 flow, as well as the relationship between the COP and frequency. [PERSON] [8] used a multilayer neural network to develop a fixed-speed model for scroll compressors with the R410a refrigerant. With evaporation temperatures ranging from \(-\)10 to 55 \({}^{\circ}\)F (\(-\)23.3 to 12.8 \({}^{\circ}\)C) and condensation temperatures from 80 to 150 \({}^{\circ}\)F (26.7 to 65.6 \({}^{\circ}\)C), they derived a ten-coefficient model for the compressor and simulated volumetric efficiency and isentropic efficiency. By adding coefficients, they applied the fixed-speed model to variable frequency compressors.