Adaptive Robust Control Strategy for Portable X-Ray Flaw Detectors Under Weak Grid Conditions

Portable industrial X-ray flaw detectors operating in outdoor environments predominantly rely on small diesel generators for power supply. However, the inherent grid frequency drift of such weak grids induces critical phase-shift mismatches in conventional fixed-delay controllers, leading to voltage loss-of-control. This study aims to develop a robust, frequency-adaptive power drive system to overcome these operational challenges. A dynamic zero-crossing capture mechanism is proposed to extract real-time grid frequency variations, enabling instantaneous phase-shift feedforward compensation. This mechanism is integrated with an adaptive incremental proportional–integral–derivative (PID) controller that utilizes grid-condition recognition to dynamically schedule gains and neutralize frequency disturbances. Furthermore, a linear voltage soft-start strategy is incorporated to coordinate downstream constant-current regulation, preventing inrush currents. Concurrently, an offline downtime perception mechanism executes autonomous stepped-voltage conditioning to prevent cold high-voltage breakdowns. Simulation and hardware experimental results demonstrate that under continuous generator frequency drift, the adaptive control maintains a steady-state voltage error below 1%, suppresses the voltage ripple factor to 1.11%, and limits tube current fluctuations to 4.2%. The proposed system effectively mitigates weak-grid instability, ensuring reliable high-voltage generation and extending component lifespan for demanding non-destructive testing (NDT) applications.