Session 4b Staines II High-Megawatt Converter Technology Workshop Capacitor Technology for High-Megawatt Power Conversion Dr Geoff Staines General Atomics – Electronic Systems Inc 24 Jan, 2007 • Depending on frequency, capacitors can be the largest component in the system • Requirements are – Low inductance – High rms current capability – Low loss – 100% reversal – High energy density – GA-ESI paper/polypropylene capacitors developed for SNS [Figure: IGBT switch plate assembly (LANL SNS modulator)] • Long DC life at high energy density • High-temperature Polymers • Novel construction technique for high current and high energy density • Improved metallized electrodes for self-healing and low ESR • Packaging for high temperature and thermal management • Thin film winding for low voltage applications • Polypropylene film capacitors have highest energy density at low temperature • Performance degrades rapidly above 40°C • Investigating high-temperature films including – Polyphenyl sulfide (PPS) – Polyetheretherketone (PEEK) – Polyetherketoneketone (PEKK) • Self-healing capacitors use thin metallization deposited on dielectric films instead of foil • Fault current causes vaporization of metallized layer, quenching the fault discharge • Thin (~300Å) metallization limits current and thermal dissipation • Challenge is to improve thermal conductivity without sacrificing self-healing properties • Self-healing allows operation up to limit of film breakdown voltage for higher energy density • High energy density passive components reduce the need for high frequency switching • Reduces switching loss and switch stress • Could use cheaper, more mature switch technology without prohibitive size, weight • Metallized film capacitors fail gracefully • Capacitor monitoring could identify when maintenance required to avoid failures • Depending on frequency, capacitors can be the largest components in power converters • Future development to focus on – Increasing energy density – Reducing loss – Improving thermal management • Significant improvements in fast capacitor technology expected from improved engineering using proven film technology • Smaller passive components may reduce requirement for high switching speeds