Increasing Battery Performance with Ohmic Drop Compensation for an Electric Drone

Abstract

Lithium-ion batteries are now widely used in a wide variety of applications ranging from powering mobile equipment to electric vehicles (EV), through stationary electrical energy storage systems or the electrification of flying devices such as drones. The main reason for the rapid growth of this type of batteries in the market is their high specific energy (Wh/kg) and/or specific power density (W/kg) compared to older chemistries. In the case of drones, weight optimization requires that the battery not be oversized for the mission it must perform.. Moreover, batteries can be subjected to deep discharges and high currents during the mission. One of the phenomena that leads to a drop in energy at high power is the ohmic drop phenomenon. Thus a ohmic drop compensation method has been applied to the discharge of lithium batteries. In this study, four different types of NMC Li-ion batteries (18650 type) were compared; two cells typed "energy" and two cells typed "power". We have shown that the ohmic drop compensation method applied to the discharge is capable for one of the "energy" cells of greatly increasing its available capacity at high power: 21% at 4C.A simplified electric Vertical Take-Off and Landing (e-VTOL) mission profile was applied to this energy cell. We have demonstrated, without a doubt, the interest of using this type of protocol in this case. This ohmic drop compensation method makes it possible either to extend the duration of the flight without increasing the embedded capacity of the battery (about 50% time as shown in figure 1), or to consider an emergency diversion scenario. Finally, a preliminary aging study was also carried out for this cell: the use of ohmic drop compensation has no effect on the decrease in low power performance during aging and a moderate impact on the performance at high power. Figure 1