Control Strategy to Mitigate Line Voltage Flicker of Commercial High-Power Capacitor Chargers for Pulsed Power Applications

Modern solid-state klystron modulators generate high-voltage, high-power pulses by discharging energy stored in a capacitor bank. Such modulators require at least one capacitor charging unit supplying the energy released in pulsing. Traditional capacitor charging structures rely on AC/DC front-end units based on passive diode rectifiers in conjunction with high-frequency resonant converters. However, being operated in constant-current on-off mode, use of such chargers poses significant challenges when deployed in high-power applications. Most notably, interrupting the charging action implies significant power fluctuation on the grid, generating line voltage flicker. Additional issues include distortion of the line current waveforms and suboptimal power factor. Furthermore, increased demand on accelerator power as well as stricter regulations and standards augment these challenges in view of modern modulator design. From the perspective of power quality, these challenges are most often solved by the integration of both costly and spacious external grid compensators. As an alternative, this paper presents an external controller improving the performance of such commercial capacitor chargers by employing real-time feedback of the capacitor bank voltage. The controller dynamically adjusts the charging current reference through the standard remote interface of the capacitor charger, ensuring continuous charging in greatly reducing line voltage flicker. The manuscript presents a review of the performance characteristics of conventional capacitor chargers, outlines the proposed methodology for flicker reduction, and presents comparative experimental validation on a 1 kV/10 kW charger prototype, demonstrating the feasibility and effectiveness of the proposed solution.