E-Mobility Engineering 015 l EMotive Scarab off-road truck dossier l In Conversation: Giulio Ornella l Hall effect and magnetic sensors focus l Challenge of batteries for heavy-duty EVs l Alpha Motor Corporation digest l Automated charging insight l HVAC systems focus

engineering departments for them. That has changed with EVs though, in that the need for precise thermal management of the battery, and the relative scarcity of energy, requires close contact between the coolant and refrigerant loops. Integrating these systems, and the need for precise control of the flow of energy between them via an array of pumps, valves and heat exchangers with a large number of operating modes brings much greater complexity, our expert argues. It is therefore vital to characterise the system early in a vehicle’s development, he stresses, adding that a lot of virtual calibration and validation is needed to make sure all the modes run smoothly and result in a well-balanced system. The expert from the HVAC, battery and charging systems supplier says it is also important to make the most of ‘free’ energy such as waste heat for HVAC, even though there is less of it available in EVs than in IC-engined vehicles. One way to minimise the system’s demand for energy from the battery, he points out, is pre- conditioning both the battery and the cabin during charging, so the energy to do that comes from the grid. Just as the absence of an IC engine enables EV designers more cabin space and flexibility with interior configurations, it also creates opportunities to relocate thermal systems, the HVAC systems builder points out. For example, some automakers might opt to move some or all of the HVAC equipment to the powertrain electronics bay – formerly the engine bay. EV thermal management systems consist of different sub-loops, the automotive electrification specialists note, and in most of them the HVAC system plays a role in battery cooling. This is usually indirect cooling, in which the HVAC and battery cooling/ heating circuits are coupled with a heat exchanger, while in a few cases the HVAC system is combined with a heat pump function. While HVAC compressors and cooling system pumps in most IC- engined vehicles are mechanically coupled to the engine, and are either on or off, their electrically driven counterparts in EVs can be commanded to run at any speed to meet cooling, defogging and heating demands, they explain. Because the heat in EV powertrains tends to be concentrated in the traction inverter and the battery pack, a good first rule of the thumb is to distribute cold/heat generation and use a set of diversified technologies for each case, according to an expert from a control software and hardware provider. Heat pumps are attractive, he adds, because they can be managed with very efficient field-oriented control (FOC) algorithms. Used in high-performance motors of both AC and DC types, FOC is a means of decoupling the magnetising flux and the torque-producing flux generated by the stator current so that torque and therefore speed can be controlled independently. It enables motors to run smoothly over a wide speed range, generate maximum torque from zero rpm, and accelerate and decelerate quickly. The power electronics to drive pumps consist of optimised three-phase inverters with efficient power stages made from IGBT and SiC switches, the expert explains. As HVAC moves towards higher bus voltages with faster control loops and motor speeds, the use of SiC is increasing. For comfort features such as car-seat cooling and heating, a smaller dedicated heat pump can be placed in the seat. Less expensive alternatives include PTC devices switched via simple silicon-based relays with accurate current control. Although such devices tend to be more power-hungry, there are ways of minimising the impact of that. For example, resistors are typically used for defrosting windows, because they work quickly, so normally they are powered up for only a very short time. Together with distributed cooling and heating, new materials with better insulation and heat transfer properties are playing an increasingly important role in overall thermal management within EVs. Control electronics typically consist of a system controller, microprocessor and motor driver, the expert from the HVAC control hardware developer explains. He adds that the company also offers solutions in which the motion control algorithm is integrated, eliminating the need for a microprocessor. Motor drivers with integrated algorithms are well-suited to systems with external ECUs, he continues, Focus | HVAC systems With an air source heat pump, an EV HVAC system can warm the vehicle with heat drawn even from cold air outside (Courtesy of Hanon Systems) 66 Autumn 2022 | E-Mobility Engineering