Hybrid Direct Drive PPU with Extended Operating Range

High-power electric propulsion with Hall thrusters has been proposed as a strong candidate for Electric Path missions, but conventional power processing units (PPUs) are complicated and the mass of the discharge power converters needs to be reduced. Direct Discharge Power Processing Units (DDUs) have been proposed as an alternative due to their simplicity and low mass, but the achievable operating range of thrust and ISP is significantly limited because power regulation for DDUs is only achieved through gas flow control, array offpointing or shunting. This proposal presents a compromise between PPUs and DDUs called a Hybrid Direct Drive Power Processing Unit (HDDU) that provides a wider operating range than DDUs while reducing the mass and increasing the efficiency compared to conventional PPUs. An HDDU provides filtering like a DDU, but it can additionally raise or lower the discharge voltage over a limited range. An HDDU only processes the power necessary to raise or lower the discharge voltage. Several different converter circuits can be used in an HDDU. One approach uses an isolated high-efficiency resonant DC-DC converter with connections that can be configured through a set of electromechanical relays. Another approach uses a novel soft-switching non-inverting buck-boost circuit that requires no relays, but is a little less efficient than resonant circuits. Straight-through direct drive operation is possible with either type of converter. The proposed HDDU would operate from an input voltage of 150 V to 300 V, and would provide 10 kW output power over a limited range such as from 150 V to 500 V. The HDDU approach is readily scalable by connecting modules in parallel because both proposed circuits naturally share output currents. The modular approach and enhanced operating range increase design re-use and reduce life-cycle costs. A Phase II project could include making a more flight-like discharge supply and adding heater, keeper and magnet supplies.

Hybrid Direct Drive Power Processing Units are well-suited for both manned and unmanned Electric Path missions, and can be readily scaled to hundreds of kilowatts through parallel-connected modules. With presently-available semiconductors, the optimum power level per module is probably around 10 kW, but higher-power semiconductors are expected to become available in the near future. The power converters used in the HDDUs could be re-purposed for a variety of power conversion applications such as fuel-cell output converters and solar array simulators. The primary market for this technology is for high-power low-cost electric propulsion systems where Hall thrusters are likely to be used. It is anticipated that the CPE HDDU will have a lower cost than state-of-the-art PPU designs. Additionally, the high specific mass and high efficiency will reduce the overall system cost. The enhanced operating range capabilities compared to a pure direct drive can help enable missions where shifts between high thrust for short-term maneuvers and high ISP for long-term operation are desirable. The wide-range capabilities and a modular design also enable one HDDU design to be used in a variety of different applications.

Hybrid Direct Drive Power Processing Units could be used for commercial and military satellites, both for station keeping and orbit lifting. The advantages outlined for NASA applications also apply here. One specific non-NASA application is for Aerojet thrusters that are being developed for geosynchronous satellite use. Commercial non-flight applications include laboratory bench power supplies. A path to high volume sales may be achieved by using the converters refined in this SBIR for general purpose scientific equipment. The power converters used in the HDDUs could be re-purposed for a variety of power conversion applications such as fuel-cell output converters, solar array simulators and hybrid vehicles.

This is early/mid-stage (TRL 4) — the most realistic path in is NASA SBIR/STTR, which funds small businesses and research institutions to develop technology aligned with NASA's needs (equity-free, phased funding). Check whether a current SBIR/STTR solicitation topic overlaps with this project's technology area, or contact the project directly (above) to ask.

None of these are guaranteed paths for this specific project — TechPort itself doesn't have an "apply" button. Reaching out to the contact(s) above with a specific question is usually the fastest way to find out what's actually open.