HV Storage Capacitors for High Current Pulse Power Applications

Solid-state power electronic circuits that incorporate switching devices such as IGBTs, IGCTs and MOSFETs can now operate at voltages as high as 3KV to 6.0+KV with peak currents of 0.5-6.0+KA. Modulators built with various topologies require high voltage, energy storage capacitors, that can operate at the same voltage and current as the switching devices. Presently such capacitors are large, costly and cannot be integrated onto the same boards as the rest of the power electronic components. This SBIR program addresses the development of solid-state Polymer-Multi-Layer (PML) capacitors, for use in high ripple current and dV/dt pulse power applications. PML capacitors comprise thin high temperature polymer dielectrics with breakdown strength greater than 1000V/m. A large area mother capacitor material with thousands of capacitor layers is formed, which is segmented into capacitor chips that have low ESR and ESL and can withstand temperatures & gt;260oC. The Phase I development demonstrated PML capacitors with 2,000 to 3,000 layers, with excellent capacitance and dissipation factor stability in the temperature range of -60oC to 160oC. 10F parts were successfully tested with multiple discharges up to 1100V, discharging 2KApeak current at di/dt & gt;1000A/s. PML capacitors with such pulse power capacity have an energy density of 1.8J/cc, which is approximately 100X improvement over state of the art pulse capacitors, which utilize a lower temperature polypropylene film dielectric with double metallized polyester film electrodes. The Phase II development will focus on solving interconnection problems identified in the Phase I work, when several capacitors are connected in series using a bifilar configuration, as well as termination damage when attaching leads to the first and last capacitors. PML capacitors with internal series connections will be produced, which will eliminate the need for external series connections. Instead, capacitor chips with a voltage rating of 1KV to 5KV will be stacked in parallel configuration to form a small surface mounted capacitor block. Commercial Applications and Other Benefits: Commercial applications include inverter DC-Link capacitors for hybrid and electric vehicles, wind power generators, large-scale PV installations, electric trains, elevators and industrial power supplies. DC-link capacitors currently produced using polypropylene film dielectrics are one of the largest, costliest and most failure prone components in an inverter. Cost, weight, and volume improvements in automotive inverters, will improve the competitiveness of U.S. automotive power electronic OEMs and will have a direct impact in oil consumption and overall dependence on foreign energy imports.