14 AUTOMOTIVE POWER www.lem.com Issue 4 2023 Power Electronics Europe www.power-mag.com Battery management systems and the role of the sensor in EV driving range and safety The latest sensors used in electric vehicles (EVs) not only help to prevent on-board fires but also contribute to tackling the driving range challenges, says Jérémie Piro, Global Product Manager BMS at LEM Whenever EVs are discussed, the number one topic raised is range - the distance that they are capable of travelling on a single charge. Even though distance travelled on a full tank is usually a long way down the list of criteria for most people buying a petrol or diesel vehicle, for EVs it is at the very top. Despite the average car journey being around 10 miles, drivers insisted in a recent survey that what they expected from an EV was the ability to drive around 375 miles on a single charge. Of course, the reality (at the time of writing) is that most drivers will not be able to travel anywhere near that distance on a fully charged EV lithium-ion (Li-Ion) battery. This highlights a clear dilemma for the automotive sector. The technology used in EVs is completely different to what customers are familiar with and comparisons with the internal combustion engine (ICE) are erroneous. There is another criterion that is increasingly governing people’s choice of electric vehicles – safety, in particular from the risk of fire. This topic is expected to take on even greater importance in the coming years. Why has safety become such a major issue? Simply because as modern EVs need to be designed to charge faster in order to satisfy the demands described earlier, on-board systems are going to have to deal with higher current and higher voltage and this will require greater isolation. There is a genuine concern in the automotive sector – whether among OEMs, manufacturers of EV chargers or charge point operators – that while it is vital to deliver all the benefits drivers are looking for, there has to be an absolute priority given to avoiding any possibility of leakage or fire within vehicles. State of charge, state of health The battery management system (BMS) installed in every EV is the main component of a vehicle’s battery pack. It fulfils two essential requirements for the driver. Firstly, it evaluates the state of charge (SoC), which is the level of charge of an EV battery relative to its capacity. This dictates the driving range that the vehicle can achieve. Secondly, the BMS manages the battery pack’s state of health (SoH) with an on-board safety function designed to prevent leakage or fire. The more accurate these evaluations are, the happier motorists will be in terms of addressing driving range anxiety as well as concerns over safety. For a BMS to deliver these vital functions, it has to incorporate reliable sensing elements. Not surprisingly current sensors are key components of any BMS and these devices have gone through significant changes as demands increase from the EV sector. LEM has recently developed the third generation CAB series of transducers for delivering SoC figures with optimum accuracy. The premium CAB range was first developed for battery management systems 12 years ago and has evolved as customer requirements have altered. The first model represented a breakthrough technology that made it possible to achieve more accurate current measurements by eliminating magnetic offset and delivered contactless current Figure 1: In the CAB 1500, the fluxgate sensing head’s induction coil ensures rapid transition between linear and saturated state.
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