High power, high efficiency, low cost capacitor charger concept and demonstration

A 20-kJ/s, 10-kV, 1-kHz repetition-rate technology demonstrator design and testing are described. The goal of the development was combining high performance and versatility with low-cost design and good manufacturability. This goal was met using an energy-dosing converter topology with smart controls adapting the switching frequency in such a way as to ensure zero-current switching for all possible scenarios, keeping maximum duty cycle for high power. The switching is accomplished at a frequency of up to 55 kHz employing relatively slow IGBTs with low conduction losses. High efficiency allows all-air cooled design that fits into a 19"×10"×24" rack. Design guidelines are reviewed. Comprehensive PSpice models accounting for numerous parasitic parameters and mimicking controls for the frequency variation were developed, and simulation results are presented. Together with analytical tools, they predicted a pulse-to-pulse repeatability (PPR) of ±0.15 %; the measured figures are ±0.4 % and ±0.5 % for short- and long-term operation, respectively, at peak charging and repetition rate. Repeatability analysis is briefed upon here, and to larger extent, in an accompanying paper. Test methods are described. Typical current and voltage traces and results of thermal runs are presented.