E-Mobility Engineering | March/April 2024 65 Inverters | Focus Naturally, there is significant scope for improvement through software, particularly in the realms of control algorithms and optimisation, says the advanced semiconductor and control algorithm developer. This enhances efficiency, improving thermal management and dynamic adaptation to varying load conditions. “Depending on how much torque or speed is needed from the motor at a given moment, the software can switch how the motor is driven,” our powerswitching, motor control and software expert notes. “What we are seeing is that you get improvement in efficiency, and it also reduces switching noise and eddy currents in the motor. That means you heat up the motor less.” This, he says, simplifies thermal management. Gate drivers Microcontrollers lack the electrical punch required to switch the IGBTs or MOSFETs directly, so they rely on gate drivers. “High-performance gate drivers are crucial for controlling the latest inverters, especially those using wide-bandgap semiconductors, such as SiC and GaN, says our developer of advanced semiconductors and control algorithms. “They ensure precise control over switching operations, minimise switching losses, and protect against over- and under-voltage conditions. Fast, accurate gate drivers are essential for achieving the full performance and efficiency benefits of modern semiconductors.” They can also simplify inverter design by achieving safety-related functions, and help protect the health of the motor, says the specialist in electric machines, power electronics and control. Motors operating at 800 V and above are more prone to partial discharge, says a traction inverter and BMS developer, compromising the motor’s electrical isolation and, consequently, its durability. “The higher the voltage overshoot, the higher the risk of partial discharge. And the higher the switching frequency, the faster that occurs. Fast-switching SiC inverters are provoking this problem, which the industry is working to resolve,” the expert says. The company has developed and implemented gatedriver functions to control the voltage overshoot dynamically and prevent problems such as partial discharge. The expert from our traction inverter developer notes that to control a SiC MOSFET, gate drivers need to meet two basic criteria. “It has to have the pulsecurrent capacity to be able to charge the gate capacitors in the amount of time that you want them to, and, conversely, to discharge them,” he says. “The gate driver has to have a fairly low output impedance so that it is not influenced by other devices to cause spurious turn-on, for example.” Gate drivers are also relied upon to handle anomalies arising from high switching speeds, very efficient energy delivery to the motor, and increased sensitivity to over-current and overvoltage conditions. These can lead to motor runaways in permanent magnet machines that cannot be controlled by switching the current off, because the motor converts its own kinetic energy into current to drive itself. While the inherent losses in this process will eventually stop the motor, this can take a dangerously long time. “So, we have a whole raft of protection measures in place within the gate drivers to prevent runaway events,” says the expert from our power-switching, motor control and software company. Future trends Looking ahead, our experts anticipate the expanded adoption of wideband semiconductors, higher voltages, further efficiency improvements, advanced cooling solutions and better control algorithms. Some expect pressure for more efficiency from inverters and e-machines to increase range before new battery technologies come to the fore, instead of fitting ever larger batteries. More electromagnetic compatibility challenges are likely to result from these efficiency improvements, says the global automotive technology company expert, who also expects increased integration of the inverter into the EDU. There will also be further integration of inverters with other power electronic systems, such as DC-DC converters and onboard chargers, according to our traction inverter and BMS developer. Acknowledgements The author would like to thank the following people for their help with this article: Carsten Himmele, technical sales engineer at Allegro Microsystems; Mike Sandyck, marketing director at Cissoid Power Semiconductors; Francois Dube, senior manager, traction inverter product engineering at Dana; Jon Duroudier, CTO at EPowerlabs; Eric Hustedt, CTO at Exro Technologies; and Ben DeLand, director of electrical hardware engineering at GKN Automotive. The Coil Driver family of series/parallel switching inverters is designed to optimise power, torque and efficiency dynamically (Image courtesy of Exro Technologies)
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