Study on superheat control methods for refrigerant direct cooling thermal management systems of electric vehicle power batteries

To address the problem of unstable superheat control in refrigerant direct cooling thermal management systems for electric vehicle power batteries, this study proposes a novel superheat regulation method based on the coordinated control of an electronic expansion valve and an electric backpressure valve. By constructing an experimental system and establishing a model for controlling outlet parameters of the power battery cooling plate, the mechanism of superheat fluctuation caused by the controller's over-regulation resulting from the temperature response lagging behind pressure changes is analyzed. The research results indicate that, under variable load conditions, the proposed electronic expansion valve and electric backpressure valve coordinated control method, compared with the conventional electronic expansion valve and compressor coordinated method, reduces the superheat overshoot by approximately 53% (from 17 °C to 8 °C under pressure disturbance), shortens the recovery time by 54% (from 2400 s to 1100 s), and decreases the integral of time-weighted absolute error by over 50% (from above 7000 to below 3000). Under normal-temperature cooling conditions, the superheat overshoot is limited to 23 °C, which is 72% of that of the conventional method. These results significantly enhance the control precision and dynamic stability of refrigerant direct cooling thermal management systems for electric vehicle power batteries.