Enhanced DC Bus Emulator

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. DC bus emulators are verification testing tools that emulate power load dynamics of entire power systems, subsystems, and individual loads. Due to limitations of commercial-off-the-shelf (COTS )hardware, it is challenging and costly to evaluate the loads of complex systems using hardware alone. Innovators at NASA’s Glenn Research Center developed an easily implementable enhancement to existing DC bus emulators that overcome these limitations. The inspiration for this technology arose because NASA designs power systems for a variety of loads, from spacecraft and aircraft to future lunar outputs. The busses that power these loads may include simple, individual DC-to-DC power converters, or complex, integrated systems, such as robots, propulsors, refueling equipment, and habitation hardware. Each load and each system are key to an application’s function, making them critical to assess. However, using COTS DC loads it is not possible to fully, dynamically replicate power systems, subsystems, or individual loads on a small-signal basis. Further, this replication method is costly and time-consuming because hardware copies are needed to recreate each individual load that will be assessed in a DC microgrid. In contrast, using a mixture of representative filters, a Pulsed Width Modulator (PWM) dithering technique, and COTS loads, this technology provides a collaborative way to integrate individual, sub-system, and entire power systems loads.