E-Mobility Engineering 019 | In conversation: Stephen Lambert l WAE EVR l Battery case materials focus l Quality control insight l Clipper Automotive Clipper Cab digest l Optimising battery chemistries insight l Powertrain testing focus

10 May/June 2023 | E-Mobility Engineering 800Vpowertrains SiC isolator Sensor aims to boost range of EVs N ovosense Microelectronics has developed a capacitive technology for 800 V powertrains based on SiC chips (writes Nick Flaherty). Isolating EVs is a key requirement for personal and equipment safety at 800 V, as well as protecting electronic control units and other sensitive electronics devices. Isolation and driver chips aremainly used inOBCs, DC-DC converters, mainmotor drivers, BMSs and thermal management systems. These applications require a common ground that needs to use the isolation device to realise the level conversion function as well as high noise resistance requirements to achieve higher common mode transient immunity (CMTI) and avoid large noise interference. SiC transistors switch at a higher frequency, typically 100 kHz, compared with silicon devices which operate at 10 kHz, causing relatively large dv/dt noise. Creepage, which represents the L EM has developed a current sensor with a resolution of 0.1% that can boost the range of EVs (writes Nick Flaherty). The CAB 1500 uses an open-loop fluxgate transducer to deliver that resolution and a total error of 0.5%. This provides reliable coulomb counting to measure the discharging current of lithium-ion batteries to estimate their SoC more accurately and hence provide more range. The low-frequency fluxgate transducer is made of a wound core that saturates under low induction. A current-chopper switches the winding’s current to saturate themagnetic core at themaximum magnetic field with a fixed frequency, distance from the chip packaging’s surface that can result in flashover or breakdown, is also a safety compliance requirement. The common creepage distance in the HV battery, motor and electric control system of EVs is 8 mm. With the upgrading of the battery, motor and electric control system to 800 V, the creepage distance will also increase. CMTI, wide grid voltage swings, large peak output currents, fast rise and fall times, fast short-circuit protection and soft shutdown are the key factors when selecting suitable SiC driver chips. Novosense uses capacitive isolation technology based on capacitance coupling. In a capacitive isolation chip, the isolation capacitors are located on two separate bare chips. Two capacitive plates with a layer of silicon dioxide in between are connected in series to achieve isolation. The withstand voltage of each micron of isolation can reach more than 400 V, which is five to six times that which for the CAB-1500 is 20 Hz. Fluxgate transducers use the change of the saturation’s point symmetry to of the epoxy resin used for isolation by an optical coupler. Theoretically, an isolation grid with a thickness of 30 microns can reach an isolation voltage of more than 10 kV, and the measured 60-second withstand voltage can be up to 12 kV. Using a capacitance-isolated differential transmission architecture with isolation on each channel also helps to improve common-mode noise suppression. For that, modulation of the signal is needed. The prevailing approach is usually to use OOK encoding, whichmodulates an input signal on a 400MHz carrier signal and then transmits it between the capacitors. Novosense has patented an adaptive OOK coding scheme that further improves the capability of the isolator to resist common-mode noise. Compared with the other two approaches, OOK coding has a strong resistance to common-mode suppression. measure the primary current so that all electric and magnetic offsets are cancelled out, providing the accurate measurement. Current ripples on the HV DC lines could be induced during power conversion from devices such as the DC-DC converter, inverter or the OBC. However, the ripples have a negative impact on the health of lithium-ion batteries, and could cause malfunctions in the CAB transducer. The sensor can be mounted on a busbar or panel, and has a current range of up to ±1500 A and compatibility with 800 V applications to the IEC 60664-1 standard, plus full galvanic isolation of up to 2.5 kV. VEHICLE SAFETY CURRENT SENSING LEM’s CAB 1500 current sensor has a range of ±1500 A