Design and Experimental Validation of an Integrated Downhole Motor-Drive System

<title>Abstract</title> <p>In mud pulse telemetry for logging-while-drilling (LWD), brushless direct-current motors serve as the key actuators for pressure pulse generation. However, they suffer from large torque ripple, control instability, and limited hardware robustness under extreme conditions. To address these issues, this study presents a high-power, integrated downhole motor drive system. On the control side, simulation-guided design was used to develop a triple-closed-loop proportional-integral-derivative (PID) architecture—comprising position, speed, and current loops. On the hardware side, a compact, integrated motor drive and control circuit based on a dsPIC was implemented. On the software side, embedded control firmware running on the digital signal controller and complementary host-computer software were developed.Experimental results showed continuous operation for more than 200 h at 175°C. The employed position PID scheme limited the current-loop response time to within 15 ms, keeping instantaneous current fluctuations within 0.03–0.13 A, while the position-loop reached a steady state within 70 ms. The incremental PID strategy in the speed loop achieves a 40 ms response time. Furthermore, under a 173.7 mN·m load disturbance, the motor-speed error remained within 1%. Overall, this study provides an integrated, reliable solution for motor drives operating under LWD conditions.</p>