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The DC Source Emulator methodology combines impedance characterization, custom filter design, and external control implementation to replicate any DC power source using standard laboratory equipment. Engineers first identify the system requiring verification and determine the impedance characteristics of the power source at the interface through hardware testing, simulation, or circuit analysis. Using this impedance data, they design a filter network that matches the target characteristics as seen from the interface. This custom filter connects to the output of a commercially available dynamic DC power supply or linear amplifier. External voltage and current sensing circuits work with external controllers to command the power supply output to respond identically to the physical hardware being emulated. The supply must be capable of changing its output voltage and current in response to external inputs. Transient load step response, impedance response, and ripple characteristics can all be verified to match the target system. Controllers such as PI or PID configurations command the supply output, capturing small signal response for minor variations and transient response for sudden changes. An optional ripple injection stage using an amplifier can be added for increased emulation accuracy. Once configured, the emulated system can be tested for stability across all loading conditions without requiring actual power source hardware. The methodology shapes impedance on a target impedance plot while using high-bandwidth power supplies in either current or voltage mode. The same equipment can be dynamically reconfigured for different emulation targets by changing the output filter and controller parameters, making it highly adaptable across various DC power architectures including converters, batteries, fuel cells, and complex multi-source systems. The DC Source Emulator is available for patent licensing.

NASA’s Universal Modular Interface Converter (UMIC) is a bidirectional, modular power electronics converter that transfers power between a 120 V DC space power bus, and a medium-to-high-voltage, three-phase AC power grid. The UMIC system contains multiple parallel AC/DC UMIC modules that convert between 120 V DC and low voltage AC, as well as one or more transformers that convert power from the low voltage AC bus to the grid voltage. The UMIC module consists of multiple subsystems, including the power stage, gate driver, Field Programmable Gate Array (FPGA)-based controller, output filter, signal conditioning and sensing circuits, and thermal management subsystems. An FPGA-based controller is included within each AC/DC module and is used to regulate desired power system variables; synchronize power switching events and share load current between modules; synchronize the modules with existing service on the grid; receive commands; and share telemetry. The FPGA-based controller subsystem includes the FPGA Integrated Circuit, associated flash memory, and a controller area network (CAN) transceiver. It is envisioned that future UMIC designs can support lunar grid expansions, a Mars surface grid, or large space stations. These applications may necessitate different grid voltages or frequencies, or different control logic and communication systems. However, the core UMIC architecture and functionality will remain the same. The related patent is now available to license. Please note that NASA does not manufacture products itself for commercial sale.

Combining a dynamic load emulation technique with a PWM dithering technique, NASA’s technology provides a more efficient, cost-effective, and practical method to emulate complex loads. While there are commercially available electronic device loads on the market that meet basic emulation needs, these devices are limited; they are limited with respect to small input voltage changes, and to feedback signals from the device’s power system, which may lack the strength and resolution needed to emulate accurately. A common solution for the bus emulation limitation is to construct a model of an actual microgrid using representative loads and connections. But this can be complex, costly, and have limitations in performance. NASA’s approach addresses these challenges without creating an actual model microgrid to replicate the systems. As opposed to stand-alone COTS electronic load devices or model microgrids using representative loads and connections for a given test, NASA’s technology is a system constructed of an input power filter, a COTS electronic load device or load subsystem, and a power control circuit. The input power filter is designed to emulate load or bus performance at the medium to high frequency range. The power control circuit combined with the electronic load or load subsystem emulates lower frequency and constant power dynamics of the system. Lastly, the power control circuit linearizes digitization and quantization issues present with digitally controlled COTS electronic loads. The power control circuit can be set to measure a load voltage, which is divided by a determined value for power, and combined with a triangle wave dither (the power control circuit block image demonstrates how to integrate a triangle wave dither). This dither dynamically adjusts the electrical current or power to keep it constant within the commercially purchased load device, enabling accurate emulation of complex DC microgrid systems.