Unmanned Systems Technology Dec/Jan 2020 | Phoenix UAS | Sonar focus | Construction insight | InterGeo 2019 | Supacat ATMP | Adelan fuel cell | Oregon tour | DSEI 2019 | Copperstone Helix | Power management focus

88 T he design of the power management systems in unmanned platforms is increasingly having to account for the safety, reliability and security issues that come to the fore when there is no driver or operator. These add cost and complexity though, which developers are looking to reduce while at the same time improving the efficiency and range of vehicles. There are three decisive factors when it comes to installing the power electronics – space, weight and efficiency. New wide-bandgap materials such as silicon carbide (SiC) and gallium nitride (GaN) are starting to replace silicon insulated gate bipolar transistors (IGBTs) in inverter designs, as they have demonstrated their reliability over the past five to 10 years, and new packaging technologies are being developed to improve the power management of such devices. Researchers are also looking at new devices such as a GaN-on-SiC and aluminium nitride (AlN) to increase the efficiency of power conversion. Safety Safety is an increasingly important design issue for power management in unmanned systems. If a fault occurs in the battery pack of a driver-operated EV, for example, the system can, ideally, gradually shut down to avoid a fire. With no driver or operator, dual redundant systems are needed to ensure that the vehicle is as safe as possible and allow time for the vehicle to stop safely. That means using two separate and different measurement and reporting systems for each battery cell, which creates a major measurement challenge. Different structures are used to ensure that the signal chains do not fail in the same way. Developers are looking for the maximum accuracy when measuring each cell to give the best possible range, but having to use two separate measurement chains reduces the accuracy. For an autonomous vehicle, the electronics managing the battery must know to a very high standard if there are any faults in the system – 99.9% of potential faults are detected by the electronics. That is achieved by using redundancy within the measurement chips. There are two distinct ways of making every measurement with two separate paths to give a high level of redundancy. However, this leads to a lower accuracy for the safety element in the two measurement schemes when compared to the maximum possible performance Nick Flaherty explains the key issues in power management in unmanned systems and explains how they are being addressed December/January 2020 | Unmanned Systems Technology On the safe side Dual redundant high-precision battery management systems are key to making sure EVs are as safe as possible (Courtesy of Rimac Motors)