The electronic expansion valve control of low temperature chiller has significant advantages in suppressing the volatility of evaporation temperature. By optimizing the control strategy, the electronic expansion valve can precisely regulate the flow of the refrigerant, thereby effectively controlling the superheat of the evaporator and reducing temperature fluctuations.

The electronic expansion valve, through its coordinated operation with the compressor, condenser and evaporator, can play a decisive role in the refrigeration capacity and control accuracy of the system. In the traditional configuration, the electronic expansion valve is limited by controlling the superheat at the compressor inlet, resulting in poor cooling capacity output and precision control effect of the system when approaching the target temperature. However, by using the electronic expansion valve as a bypass valve, connecting the compressor outlet to the condenser outlet, and being equipped with a thermal expansion valve, more precise temperature control can be achieved. When the temperature approaches the set target, the controller can directly control the electronic expansion valve to release superheated steam and reduce the refrigeration output, thereby achieving a stable temperature reach the set point while maintaining high precision.

In terms of control design, the PID control strategy and the concept of fuzzy PID control are adopted, which can adapt to different temperature difference change rates, independently adjust PID parameters, and achieve precise control of the opening degree of the electronic expansion valve. The experimental results show that the low temperature chiller system with the above configuration and control design can achieve a control accuracy of ±0.1 degrees Celsius, significantly improving the control performance of the system. Furthermore, the application of the fuzzy control algorithm in low-temperature working conditions also demonstrates its advantages. For instance, in terms of the target superheat tracking performance, the overshoot of the fuzzy logic controller is on average 5.1% lower than that of the PWM control, the regulation time is on average 220 seconds less, the rise time is on average 80 seconds longer, and the absolute error integral is on average 0.55 lower. The average of the integral of time multiplied by absolute error is less than 1295.2.

The control design of the electronic expansion valve also takes into account the regulating performance at low frequencies. Studies show that the increase in the temperature of chilled water widens the regulation range of the electronic expansion valve at low frequencies, effectively improving the regulation performance of the expansion valve. This is because the increase in the temperature of the chilled water raises the evaporation pressure, reduces the suction specific volume of the compressor, and decreases the mass flow rate of the refrigerant. To balance the load of the evaporator, the expansion valve needs a larger adjustment range. This adjustment method can improve the stability and efficiency of the system in practical applications.

The rapid response and precise regulation capabilities of the electronic expansion valve enable it to effectively suppress the evaporation temperature fluctuation in the low temperature chiller system. By optimizing the control strategy and adjustment method, the electronic expansion valve can not only improve the control accuracy of the system, but also maintain good performance under different working conditions.