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ASNE Day 2016 - Technical Paper Session 5 : Thursday, March 3, 2016 1330-1500

Current Trends in Naval Applications


Authors: John Herbst, Robert Hebner, Angelo Gattozzi, Douglas Wardell, Jon Hahne

Title: Integration of Large Pulsed Loads into a Naval Power Systems Testbed


The University of Texas at Austin implemented a MW-scale microgrid laboratory at its Center for Electromechanics to support the development of advanced naval power systems. The microgrid laboratory provided important technical information to a collaborative Project Arrangement between the U. S. Navy and the Royal Navy of the United Kingdom. UT’s microgrid was used to validate of high fidelity power system simulation models by successfully demonstrating power management with multiple loads and sources and the use of energy storage to support large transient loads. The microgrid laboratory is being upgraded with the addition of ten Semikron 1.4 MW power conversion modules. The microgrid laboratory is currently being upgraded with the following additional capabilities:

• Ten Semikron 1.4 MW power conversion modules and 100 bus capacitors each rated at 2 kV 500 μF, which add flexibility and reconfiguration options to the present architecture.
• A Multi-purpose Real Time Simulator (MRTS) that extends the capabilities of the
test bed and make it more adaptable as a Hardware-In-the-Loop/Power-Hardware-In-the-Loop
(HIL/PHIL), or hybrid validation tool.
• The incorporation of an existing 12 MJ capacitor-based pulse forming network
and 4 m long x 54 mm bore electromagnetic launcher.

The addition of ten programmable power conversion modules, an advanced simulation/control platform, and a functional high voltage capacitor-based PFN and rail gun expand the flexibility of the microgrid with broad options for reconfiguration which will facilitate HIL testing and its related PHIL testing. The new configuration enables testing and model validation of a distributed microgrid system at relevant power levels, combining the performance of power components, control systems, and an EMRG system.

As computational hardware and software tools have improved, modeling and simulation have become effective methods to evaluate naval power system designs. High fidelity simulation models can accurately represent almost all aspects of the power system that are known to the modeler; however, these are dynamic distributed systems and many parameters and complex dynamic interactions may not be well defined. Experimental validation at relevant scales is required to fully characterize the power system performance models and identify unexpected behaviors. The UT microgrid laboratory was designed to be a flexible power system testbed and has successfully demonstrated experimental validation of power system performance and control strategies at significant power levels.

Emerging high-power electric weapons and sensors are creating significant challenges for naval power systems. Currently, the Electromagnetic Railgun is the single most challenging mission system, with the current architecture requiring repetitive charging of the capacitor-based pulse forming network at multi-megawatt power levels. To provide engineering data need for integration of an electromagnetic gun into a ship power system, UT is leveraging related research and re-configuring the microgrid to incorporate an existing 12 MJ capacitor-based pulse forming network and 4 m long x 54 mm bore electromagnetic launcher. A novel feature of the UT installation is that the electromagnetic launch system features a soft-catch capability that enables experiments on electronic circuits exposed to the extreme acceleration and dynamic in-bore magnetic fields. The physical interface between the two systems is through a power conversion module configured as a dc power supply to charge the capacitive energy store. Approaches to buffering this large transient load are being explored but most solutions require some form of energy storage to balance the load seen by the ship’s power system. When fully commissioned, the upgraded microgrid will also include improved dynamic load control and more accurate emulation of power sources and energy storage technologies to explore holistic, system-level strategies to mitigate the impact of large pulsed loads.

The UT microgrid has a distributed control network designed to emulate ship environments. Each local controller is capable of operating in safe mode in the event that communication is lost from the supervisory controller. A supervisory controller is responsible for system-level management of the microgrid and provides a graphical user interface (GUI) for the microgrid operator. The microgrid uses a desktop PC as a supervisory controller with a variety of local control platforms. These include National Instruments (NI) PXI controllers, NI cRio controllers, and NI sbRio controllers. The microgrid control network communicates over a fiber optic ethernet network. To synchronize controllers and enable deterministic communication over the Ethernet network, the control system employs IEEE 1588 precision timing protocol. The supervisory controller sends and receives communication updates from the local controllers at 17 ms rate. Each local controller operates at control rates appropriate for the function it is performing and range from 33 µs to 1.7 ms. The NI cRio and NI sbRio controllers each have a microprocessor and field-programmable gate array (FPGA). Having the range of computational speeds in the controller allows mixed rate control. Communication and slower control loop rates are performed on the microprocessor and critical high-speed controls are performed at the FPGA level with control loop rates as high as 25 ns. The FPGA is typically used to control power electronic switching events but can also be configured to perform real-time simulation of power system components to enable emulation of multiple power system elements. The experimental microgrid allows the study key power system performance from communication and energy management protocols to power converter control algorithms. The distributed, multi-rate control system of the microgrid also provides a platform for assessing novel control strategies in a “real-world” distributed power system.

The microgrid has successfully been used to validate predicted performance using propulsion loads, hotel loads, and large block loads. This development replaces the block load approach with a functional electromagnetic launch system to assess the need for refinements in the simulation approach.

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