ISSUE 012 Winter 2021 Sigma Powertrain EMAX transmission dossier l In conversation: David Hudson l 48 V systems focus l 2021 Battery Show North America and Cenex-LCV reports l Everrati Porsche 911 digest l Switching insight l Motor laminations focus

patterns that are pre-computed offline to reduce switching losses in the iron and copper of the motor using precisely pre-calculated switching angle positions. The duration and position of the pulses are determined from the voltage modulation ratio and e-motor speed. Combined with voltage phase compensation, the optimal operating range of the electric motor can be extended, reducing losses, torque ripple and total harmonic distortion, thus improving the overall system’s efficiency. Traditional space vector PWM (SVPWM) is based on fixed switching frequencies, where only the PWM duty cycle varies, while the number of switches per time period is fixed. Improving the quality and efficiency of an SVPWM-controlled inverter means finding an optimal switching frequency, which is a compromise between losses in the inverter and the quality of the sinusoidal phase currents. Increasing the frequency of the SVPWM increases the quality of the output currents, but at the expense of a dramatic increase in the inverter’s switching losses. Instead of modulating a duty cycle at a fixed time interval (frequency), OPP is based on periodic switching patterns that are generated as a function of the position of the electric motor. However, OPP execution demands a huge real-time processing capability. As an example, for a six pole-pairs electric motor rotating at 20,000 rpm, controlled with modulation over 32,768 cycles, a software implementation of OPP would require 65,536,000 interrupts/second. A software-based implementation in a processor cannot properly support such a modulation. Currently, the field-programmable control unit (FPCU) from OLEA is the only automotive-qualified system- on-chip powerful enough to run the algorithm, while also ensuring the ISO 26262 safety ASIL D level. an integrated boost converter – and traditionally uses a hysteresis-based controller. The unidirectional design means it is more suited to on-street or parking chargers, and the architecture can support higher power such as 350 kW fast-charging designs. Modules Having discrete transistors gives designers more flexibility in implementing whichever switching topology suits the design, but this is more complex in terms of assembly and cooling. Suppliers increasingly provide the transistors in modules on specialist substrates, which allows the inductance and parasitic capacitance of the connections to be minimised, helping to reduce the switching losses and boost the efficiency. The modules started off as full-bridge and half-bridge implementations, with superjunction or SiC MOSFET transistors as the most flexible design option, but more are being developed to support a totem pole topology for the PFC stage in an OBC for example. “Modules limit the choice of topologies, but with the module you have multiple dies in a particular configuration in the package so you can save on system cost, so instead of using 36 discrete devices, it’s one package,” says Nagle. “The way the modules are pinned out allows us to connect the module to the DC busbar, and that gives the advantage of reducing the interconnect inductances.” Switching controllers New switching techniques are also being developed to boost the efficiency of inverters using IGBTs and SiC MOSFETs from low to high loads. One of these, optimised pulse pattern (OPP) modulation, is used to increase the efficiency of the inverter and the permanent magnet synchronous drive motor by reducing switching losses in the inverter, and copper and iron losses in the electric motor. This is achieved by dynamically switching the control of the modulation between speed/torque operating set points using several optimisation criteria but requires a high-performance controller. This can reduce losses by 2 to 5 percentage points in the motor and inverter. OPP is based on field-oriented control of the current/torque regulation and adaptive PWM control of the modulation. Depending on the motor’s operating conditions, the controller can switch between different types of modulation techniques to provide the optimal modulation for the targeted set point. OPP uses a set of switching (pulse) ;Oe =ienna rectifier (Courtesy of ;e_as 0nstruTents) 60 Winter 2021 | E-Mobility Engineering