DESIGN OF A RESONANT SOFT SWITCHING POWER SUPPLY FOR STABILIZED DC IMPULSE DELIVERY by Andrew H. Seltzman A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science (Electrical Engineering) at the UNIVERSITY OF WISCONSIN-MADISON 2012 APPROVED By Adviser Signature: ______________________________________ Adviser Title:_________________________________________ Date:__________________ i Abstract This thesis addresses the issues involved in the design and construction of a multi- phase resonant switching power supply for delivery of a high voltage, high current stabilized DC impulse. Such a power supply may be used in place a pulse forming network (PFN) to drive a high power klystron amplifier, which typically requires voltages near -100kV at 10s of amps of current. Unlike an LC PFN, a switchmode power supply (SMPS) allows greater control over pulse duration while still allowing generation of longer duration pulses on the order of 10ms with constant output voltage by use of feedback regulation. Specifically, the thesis documents the results from the design of a loosely coupled boost transformer with a parallel LC resonator on the secondary, a microcontroller based control system for feedback stabilization and techniques of harmonic mitigation to reduce switching noise on the output waveform. iii Acknowledgements I would like to thank Giri Venkataramanan, Paul Nonn, Bob Ganch, Jason Kauffold and Jay Anderson for assisting with this project. I would also like to thank the UW Madison Department of Physics, and Los Alamos National Lab (LANL) for providing support for this research. iv Table of Contents Abstract ............................................................................................. i Acknowledgements ......................................................................... iii Table of Contents ............................................................................ iv List of Figures ................................................................................. ix List of Tables ................................................................................. xiv Nomenclature ................................................................................. xv Introduction ...................................................................................... 1 0.1 Overview ........................................................................................................ 1 0.2 Research Contributions .................................................................................. 3 0.3 Overview of Chapters .................................................................................... 4 Chapter 1 State of the Art Review ................................................. 6 1.1 High power SMPS Design and Topologies ................................................. 7 1.2 Loosely Coupled Transformers ................................................................... 9 1.3 Resonant SMPS Power Converters ........................................................... 10 v 1.4 Harmonic Mitigation.................................................................................. 20 1.5 Summary .................................................................................................... 22 Chapter 2 Power Supply Design Overview ................................ 23 2.1 Design Requirements and Constraints ....................................................... 24 2.2 Summary .................................................................................................... 26 Chapter 3 Power Supply Design ................................................ 27 3.1 Overview and Block Diagram ................................................................... 29 3.2 Capacitor Charging Power Supply ............................................................ 31 3.3 Testing Capacitor Bank ............................................................................. 33 3.4 Long Pulse Capacitor Bank ....................................................................... 35 3.4.1 Electrolytic Capacitors ................................................................... 36 3.4.2 Capacitor Fuses .............................................................................. 36 3.4.3 Capacitor Bank Bus Plates ............................................................. 37 3.4.4 Capacitor Bank Interconnect Cables .............................................. 38 3.5 Switching Network Design ........................................................................ 39 3.5.1 Topology ........................................................................................ 39 3.5.2 Cable Interconnects From Capacitor Bank .................................... 40 3.5.3 Low ESL Stiffening Capacitor Bank ............................................. 41 3.5.4 Low Inductance Relay.................................................................... 42 3.5.5 Low Inductance IGBT Busbars ...................................................... 43 vi 3.5.6 IGBTs and Gate Drivers................................................................. 46 3.5.7 Transformer Connections ............................................................... 47 3.6 Transformer Design ................................................................................... 48 3.6.1 Overview ........................................................................................ 48 3.6.2 Nano-crystalline Iron Core ............................................................. 50 3.6.3 Primary Winding ............................................................................ 51 3.6.4 Secondary Winding Enclosure ....................................................... 52 3.6.5 Secondary Winding ........................................................................ 53 3.6.6 Oil Tank Feedthroughs ................................................................... 54 3.6.7 Parallel Resonator Capacitor .......................................................... 57 3.6.8 Variation of Frequency, Turns Ratio, and Load Resistance .......... 58 3.7 Doubling 3 Phase Rectifier ........................................................................ 67 3.7.1 Rectifier Stack Design.................................................................... 67 3.7.2 Doubling Configuration ................................................................. 68 3.8 Harmonic Mitigation.................................................................................. 70 3.8.1 Capacitive Loading ........................................................................ 70 3.8.2 Parallel LC Harmonic Filter for 6th Harmonic Mitigation ............ 70 3.9 Safety Systems ........................................................................................... 72 3.9.1 LR Snubber .................................................................................... 72 3.9.2 Crowbar Spark Gap ........................................................................ 73 3.10 Summary .................................................................................................... 76 vii Chapter 4 Control System Design .............................................. 77 4.1 Overview .................................................................................................... 78 4.2 dsPIC Microcontroller ............................................................................... 79 4.3 Analog Input Galvanic Isolation ................................................................ 82 4.4 Feedback Voltage Dividers ........................................................................ 84 4.5 Current Measurement ................................................................................ 85 4.6 Fiber Optic I/O ........................................................................................... 86 4.7 Microcontroller Code Design .................................................................... 88 4.8 Summary .................................................................................................... 92 Chapter 5 Power Supply Testing ................................................ 93 5.1 Spice Simulation Model............................................................................. 94 5.2 Open Loop Testing .................................................................................... 99 5.3 Feedback Controller Testing .................................................................... 104 5.4 Filter Testing ............................................................................................ 106 5.5 Output Arc Fault Simulation and Testing ................................................ 113 5.6 Summary .................................................................................................. 118 Chapter 6 Conclusions and Recommendations ........................ 119 6.1 Summary of Research .............................................................................. 120 6.2 Conclusions .............................................................................................. 122 viii 6.3 Future Work ............................................................................................. 124 Bibliography ................................................................................. 125 Appendix ........................................................................................... 1 A CM1200HB-66H IGBT ................................................................................... 1 B Hipotronics