A Maximum Power Tracker for Improved Thermophotovoltaic Power Generation

Radioisotope Power Systems (RPS) are critical for future flagship exploration missions in space and on planetary surfaces. Small improvements in the RPS performance, weight, size, and/or reliability can have a dramatic effect on the scientific capability of the vehicle and the overall mission costs. Radioisotope Thermophotovoltaic (RTPV) energy converters are a particular type of RPS that directly converts the heat produced by a General Purpose Heat Source (GPHS) to electrical power using a specialized Photovoltaic (PV) cell. A key element in an RTPV system is the power conversion electronics system that efficiently converts the low-voltage current from each PV cell into useable, stable bus voltage for powering spacecraft systems despite issues such as non-uniform illumination, PV cell degradation, and decay of the GPHS source. In this project, Creare and the Massachusetts Institute of Technology (MIT) propose to develop an advanced, multi-channel maximum power point tracking module (MPPT) that is optimized for RTPV systems. The converter will provide stable output voltage from a 16-cell PV array that, when coupled with advanced PV technology of the RTPV system, will provide high system efficiency. In Phase I, we will design a prototype power tracking module, which will be fully characterized for conversion efficiency. We will also assess the impact of this new MPPT on the overall RTPV system design and performance.

Radioisotope power systems are used for a number of military applications. RTPV based systems would be a viable alternative to the current thermoelectric-based systems. There is also current interest in small nuclear powered batteries based on RTPV. The power-conversion technology developed on this project could be readily applied in both these military applications. TPV with combustion-based heat sources has long been considered for a number of industrial and consumer applications. The technology developed on this project would have potential application in many of these systems if a commercial TPV system were ever marketed. Most likely, this would be a low power energy scavenging application(s) (e.g., self-powered sensors).

Exploration missions that extend much beyond the earth's orbit around the sun are severely limited by the amount of power that can be generated by conventional solar panels. Radioisotope power systems are, therefore, required to enable flagship missions to the outer solar system and in some cases to the inner solar system (e.g., the lunar poles). RTPV systems offer the potential for high specific power and high efficiency, both of which can lead to vehicles with more science capability at lower cost and lower launch mass. RTPV offers the potential reliability and low vibration of a static conversion process like thermoelectrics with efficiency approaching that of dynamic systems like Stirling and Brayton energy converters. RTPV could, therefore, be a viable alternative for any NASA exploration mission requiring an RPS.

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