DMC worked with the client to model, simulate, and physically emulate their battery pack. This allowed them to validate and assess their Battery Management System (BMS) and find the best way to deliver goods to customers safely using drones.
DMC developed a power Hardware in the Loop (HIL) simulator, which allows the client to safely simulate different battery conditions that are difficult and potentially dangerous to do with a real battery pack. The system allows the client to do a variety of testing to validate the design of their BMS before using it for full scale vehicle testing.
When the client runs a simulated flight with their drone, the DMC system simulates the battery pack operation throughout that flight, allowing the client to simultaneously test the BMS and power electronic system's response to that battery during the simulated flight. Optionally, the client can simulate the occurrence of specific battery fault conditions (open/short/reversal) during a simulated flight, to ensure the BMS and flight systems detect, report, and manage the fault appropriately.
The developed HIL system is a complex but modular assortment of off-the-shelf and DMC custom hardware. To simulate the voltages of all the individual cells in the battery pack, DMC used a Pickering LXI Chassis loaded with Pickering PXI Battery Cell Simulators. We also used Pickering PXI cards in the LXI Chassis to simulate the battery pack’s internal temperature sensors/pack current sensors were simulated using NI c-series modules located in a cRIO Chassis.
While the individual cell voltages to be monitored by the client’s BMS were simulated by the Pickering PXI cards, they do not provide sufficient power to supply the drone’s power electronics and motors. The actual battery stack voltage, current, and power sufficient to drive the drone’s power electronics and motors is provided by Keysight RP7900 Series Regenerative Power Supplies. The DMC power HIL system synchronized the voltages of the Pickering Cell simulators with the Keysight power supplies within a few milliseconds, even under various faulted conditions.
While the hardware listed above is capable of completely simulating the battery pack, the client required the ability to simulate several faults that could occur during assembly of the pack or during vehicle operation. This capability would allow them to conduct tests to ensure the drone safely handled all faults prior to putting it in the air.
To provide this functionality, DMC designed and developed three custom fault injection boxes. DMC’s Test and Measurement team specified the control system, modular interface, and functionality of these boxes. DMC’s Embedded team designed the custom circuit boards required for the fault boxes to simulate different fault conditions for the battery cells. With this subsystem, the client can select to place any combination of cells into one of four states: no fault condition, cell reversed, cell short circuited, or cell open circuit.
For the control system of the power HIL system, DMC chose NI VeriStand. VeriStand is a powerful, but user-friendly platform for HIL systems and provides simple and robust control of all the required hardware. VeriStand uses an industrial PC running the Windows operating system to act as the system HMI and programming console. The VeriStand control model runs on an embedded real-time controller (NI cRIO), so it can easily handle the high-speed I/O and simulation loops required in this system. The client also made skillful use of the basic sequence editor built into VeriStand, allowing them to create simple sequences for their testing needs: such as injecting faults on specific cells or performing manual control of outputs.
DMC created a simple electric circuit model for VeriStand so that the battery voltages would respond to the current draw of the client’s power electronics in exactly the same manner as the actual battery cells. This allows the client to simulate scenarios such as terminating a flight based on a low battery pack state of charge (i.e. running out of fuel).
The model also adjusts the simulated temperature of the cells based on the measured battery usage, so the simulated thermistor outputs react exactly as expected when the battery is charged and discharged. This allows the client to test conditions in which the battery temperature goes out of range. The battery model parameters are adjustable by the clients, so any change in cell chemistry can be handled by simply entering new parameters in VeriStand and restarting the simulation.
To house all the hardware needed for the test stand, DMC’s test and measurement team completed a small rack enclosure design for housing the various components in a manner that allows ergonomic use of the test system and easy access to components for any required service.
DMC’s Control Panel Design and Fabrication experts from the DMC Fabrication Studio assembled the test system’s rack, subsystem components, and custom fault boxes. They also completed the final wiring of the system. Building the test stand in-house allowed for an efficient assembly, and quick resolution of any issues that required alterations and/or adjustments during IO checkout and Factory Acceptance Testing.
DMC’s experience with custom circuit board building and the use of our Fabrication Studio allowed us to provide the client with quick assembly of the test stand and a quick turnaround time when making improvements, modifications, or adjustments.
Our client can now simulate and emulate the performance of their battery pack under a full range of normal and faulted conditions, allowing them to fully test and validate the safe operation of their autonomous air delivery vehicle.
Learn more about our Battery Pack and BMS Test Systems expertise and contact us today for your next project.