High-Accuracy and Fast Charging Method Based on Multi-Channel Two-Stage Charging Strategy for Surface Nuclear Magnetic Resonance

Abstract

Surface nuclear magnetic resonance (SNMR) technology is widely used in the detection of groundwater. To obtain the large transmission power (450 V, 450 A), SNMR instrument uses large-capacity and high-voltage capacitor as the energy source. Traditional SNMR charging method has a slow speed and low accuracy, which is unfavorable for the efficiency and effectiveness of detection. To solve this problem, we propose a high-accuracy and fast charging method based on a two-stage charging strategy with constant current (CC) first and constant voltage (CV) later. The charging strategy includes a switching rule for smoothly switching between the two stages, and two Proportion Integral (PI) controllers for fast and stable constant current output and constant voltage output respectively. To further speed up the charging process, we propose a multi-channel parallel charging strategy. During the CV process, an average current strategy is applied to ensure automatic current sharing. Theoretical analysis and simulation experiments were conducted to verify the effectiveness of the new method. The simulation results showed that the new method is superior to the traditional method in both charging speed and charging accuracy. Finally, we propose an instrument structure of the transmitter with the proposed charging strategy. The new charging method provides a technical support for ameliorating the charging process of SNMR system.