HIGH POWER, HIGH EFFICIENCY, LOW COST CAPACITOR CHARGER CONCEPT AND DEMONSTRATION A. Pokryvailo ξ , C. Carp and C. Scapellati Spellman High Voltage Electronics Corporation, 475 Wireless Boulevard Hauppauge, NY 11788 ξ email: Apokryva@spellmanhv.com Abstract 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”x10”x24” 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. I. INTRODUCTION Between numerous capacitor charging applications, a combination of high voltage, high charging rate (tens of kJ/s and higher), high pulse repetition rate (PRR), compactness, high efficiency and good pulse-to-pulse repeatability (PPR) is a serious technological challenge. Putting constraints of low-cost and good manufacturability makes the charger development even more difficult. They restrict use of costly switches, e.g., SiC, exotic cooling schemes and materials, leaving freedom to choose proper circuit topology and control strategy to increase the switching frequency with the purpose of shrinking the size and improving PPR. This paper describes an attempt to satisfy the above contradicting requirements within the constraints of low- cost proven technology. II. MAIN SPECIFICATIONS Input Voltage 400 VAC or % 10 % 14 480 + − VAC , 3Φ 50/60 Hz, frequency % 2 ± Output Voltage 0÷10 kV Average Charging Rate 20 kJ/s PRR Single shot to 1 kHz Efficiency >92 % at full charging rate, >85 % at 30 % of rated power Power factor >0.93 at full charging rate >0.85 at 30 % of rated power Pulse to Pulse repeatability Better than % 5 . 0 ± at 1 kHz, 10 kV, full power; long-term Better than % 4 . 0 ± at 1 kHz, 10 kV, full power; short-term Better than % 1 ± at 1 kHz, 2 kV- 10 kV, short-term. Insulation Air, 10 kV and below Size 10½” (6U)H x 19”W x 24”D rack mount Weight 90 lb (41 kg) Cooling Air III. DESIGN A charger block-diagram is shown in Figure 1. The charger comprises a 3-phase input rectifier with soft start and a smoothing filter, a converter module (CM), an HV divider and control means. Triggered by an external source, the charger charges capacitor Cs that is discharged onto a dummy load via a high-power switch DSw. CM comprises an inverter INV, HV transformer using popular U100/57/25 ferrites, a rectifier R and control means. The CM’s heart is a half-bridge quasi-resonant inverter with energy dosing capacitors (Figure 2) [1]-[3]. Work [2] provides the principle and theory of operation. The benefits of this topology are tight control of the energy transfer and inherent limitation of the short circuit current and voltages across the converter components. The maximum conversion frequency is 55 kHz at low rail voltage. The parasitics of the HV transformer together with capacitors Cdiv form the resonant tank circuit. 801 9781-4244-4065-8/09/$25.00 ©2009 IEEE Authorized licensed use limited to: NORTHERN JIAOTONG UNIVERSITY. Downloaded on May 21,2010 at 01:07:27 UTC from IEEE Xplore. Restrictions apply.