Research on a Kind of Coolant Pump Working Condition Switching Control Technology

The circulation pump adopts a shielded three-phase AC asynchronous pole-changing motor (hereinafter referred to as the pole-changing motor). During the high-speed to low-speed mode transition and the low-speed to high-speed mode transition, this motor requires an extended power interruption period, resulting in significant drops in both motor speed and process loop flow rate. To address this mode transition challenge, this study proposes a novel bidirectional control strategy for seamless switching between high-speed and low-speed operation modes. First, taking the pole-changing motor of the circulation pump as the analysis object, a simulation model of the pole-changing motor was established based on the pole-changing principle and the mathematical equations of AC asynchronous motors. A simulation model for low-speed and high-speed drive control of the polechanging motor was then constructed. To minimize the flow rate drop during the switching process, with the goal of reducing motor speed drop, the dynamic characteristics of parameters such as the motor's residual electromotive force and speed during mutual switching between high-speed and low-speed modes were investigated. Concurrently, considering the operational constraints during pole-changing motor mode transition, a control strategy for switching from low-speed to high-speed and another for switching from high-speed to low-speed were designed. The proposed control strategies were applied to the development of the frequency converter power supply for the circulation pump. Bench tests demonstrated excellent compatibility between the power supply and the circulation pump. The experimental results confirmed that: Smooth switching between high-speed and lowspeed operation modes were achieved. The system achieves smooth switching between high-speed and low-speed operating modes. During the transition from high-speed to low-speed mode, the speed fluctuation is controlled within 27% (low-speed operation) and the flow fluctuation is maintained within 22.7% (low-speed operation). Conversely, during the transition from lowspeed to high-speed mode, the speed fluctuation is limited to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{2 5. 4 \%}$</tex> (low-speed operation) and the flow fluctuation is kept within 25.5% (low-speed operation). This significantly reduces both speed and flow drop during mode switching. This study successfully resolves