A fault recovery method for multiphase power converters enables delivery of reduced output power of as much as 66% of normal power in the event of a shorted power switch component. The need for redundant power converters in conventional multi-phase space power systems is reduced, if not eliminated. Fault recovery includes detecting a shorted power switch fault, providing short circuit current protection, providing isolation of the shorted power switch, and reconfiguring the remaining undamaged power switches.

Three-phase power switching systems are employed in DC power generators for gridded ion engines and Hall thrusters installed on satellites. These DC power generators must be lightweight and exhibit exceptional redundancy in environments in which silicon power switches may be damaged by radiation, typically by heavy ion bombardment. A typical satellite electric propulsion system contains at least two gridded ion engines or Hall thruster units, each having its own DC power processing unit (PPU). Each PPU is paired with an electric thruster with no redundancy other than the other PPUthruster pair. One of the PPUs is typically operational while another is redundant and used only when the first one is no longer operational due to failure of a component.

The three-phase resonant converter includes a switch fault detection circuit and a switch controller that together can detect and isolate shorted switch components. The switch controller provides the electronic drive to the switches, each pair of which comprises one of the three halfbridge inverters. Each of the switching devices includes a conventional electronic switch such as a transistor, and may also include a conventional freewheeling diode, connected in an anti-parallel manner, and a blocking diode in series with the electronic switch. The switching devices are operated by the switch controller that conventionally controls threephase- shifted half-bridges.

Conventional DC power is applied to the three-phase resonant converter. A capacitor provides voltage filtering for the converter’s input power, and provides current to the fault detector during a switch fault. The switch controller controls all six switches through control lines. The three square waves are applied to the resonant circuit through capacitors. The three-phase transformer provides the needed voltage isolation, winding ratios, and resonant inductive components. The output of the transformer is connected to the full wave rectifier diodes. The output from the rectifier diodes is a DC voltage that is presented at the output terminals.

This work was done by Geoff Drummond and Vlad Shilo of Colorado Power Elec tronics for Glenn Research Center. NASA invites and encourages companies to inquire about partnering opportunities. Contact NASA Glenn Research Center’s Technology Transfer Program at This email address is being protected from spambots. You need JavaScript enabled to view it. or visit us on the Web at https://technology.grc.nasa.gov/ . Please reference LEW-19299-1.

NASA Tech Briefs Magazine

This article first appeared in the November, 2015 issue of NASA Tech Briefs Magazine.

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