Efficiency is the key goal of electric vehicle development. This is especially true of power electronics, where one increasingly adopted approach is to integrate multiple functions into the same package. For automotive OEMs, this can result in reductions in overall weight to increase the efficiency of the vehicle while also reducing the cost of production. The power electronics of an electric vehicle have well-defined functions. The traction inverter transforms current from the high-voltage battery to the three-phase alternating current (AC) required to drive the electric motor. The onboard charger takes AC electricity from the grid to direct current (DC) to charge the high-voltage battery. The DC-DC converter takes high-voltage DC-DC and steps it down to the standard level (currently 12V and sometimes 48V), which can be used to power auxiliary functions in an electric vehicle: infotainment, sensors, lighting, steer-by-wire, and most things outside of the main drivetrain of the vehicle.
With the EV supply and manufacturing chains starting to mature, one of the key ways automotive OEMs and tier-one suppliers seek to reduce costs and weight without sacrificing performance is by integrating power electronics. That is, combining multiple power electronics functions under one mechanical housing. IDTechEx’s report, “Power Electronics for Electric Vehicles 2025-2035: Technologies, Markets, and Forecasts”, provides insights and analysis of the methods and advantages of integrating power electronics in a vehicle.
Integrated inverters
The first way to integrate power electronics is by combining two inverters in one housing. The market is seeing a trend towards dual, tri, and quad motor configurations in electric vehicles, especially in the US. In these vehicles, two motors can exist on one axle and an inverter will be required to drive each motor. A straightforward approach is to have two inverters share the same housing by integrating the circuitry for each inverter: power switching modules (Si IGBT or SiC MOSFET), passive elements, and control boards. One example is the Rivian R1T, whereby two inverters share a housing, control board, and capacitor bank. Conversely, Tesla uses single inverter housings for its models, taking advantage of the modularity of its well-known inverter.
Integrated onboard charger and DC-DC converters
A solution that many OEMs and tier-one suppliers turn to is the integrated onboard charger and DC-DC converter. Bosch, Vitesco, and Eaton are tier-one suppliers offering such solutions, and BYD’s 8-in-1 powertrain also combines the OBC and DC-DC converter in one housing.
IDTechEx estimates that this solution could result in a cost saving of up to 25% when compared to two separate units. The amount of savings depends on the level of integration, including the mechanical housing, passive elements such as the capacitor, wiring (reducing the total copper content in the vehicle), control circuits, and cooling systems. The sharing of these elements will also result in a weight reduction, which can yield a marginal increase in vehicle range, although this is unlikely to be significant with current integration methods. Higher levels of integration bring engineering challenges, including thermal management, electromagnetic interference (EMI), and galvanic isolation. IDTechEx predicts that further mechatronic integration will drive costs down over the coming 10 years. Integrated systems may currently only significantly affect the mechanical housing and overall wiring, revealing further potential for weight and cost savings through higher levels of integration.
Traction-integrated onboard chargers
A key driver to adopting 800V architectures is faster and more efficient charging. The greatest charging power for 400V vehicles is 250kW, whereas for 800V vehicles, this can increase to 350kW and beyond. However, if the vehicle is 800V, but the charging station natively charges at 400V, these greater powers cannot be accessed. Therefore, some vehicles are equipped with an extra DC-DC converter that steps up the voltage from the charging station to 800V, unlocking faster charging. However, this extra unit then requires its own housing, connectors, transistors, circuits, and cooling, adding cost and weight to the vehicle. This technology is already in the mass market, primarily in the form of the Hyundai IONIQ 5 and 6 and the Kia EV9.
An innovative solution comes in the form of the traction-integrated onboard charger. This adds boost converter functionality to the inverter unit: the motor windings act as filter inductance, and the power switches are used to step up from 400V from the charging station to 800V in the vehicle. The ingenuity of such a system lies in the fact that the inverter and boost converter will never be operating at the same time, as the boost converter operates when the vehicle is stationary and the inverter when the vehicle is moving.
The result of traction-integrated onboard chargers is faster charging, but it is still not as fast as a native 800V charging station. For example, the Hyundai IONIQ 5 charges at an average power of 149kW when on a 400V (rated 150kW) DC fast charger, but when on a native 800V (rated 300kW) DC charger, it can charge at an average power of 200kW, representing a 33% increase in charging power. The integrated unit is bulkier than a typical inverter, but costs can be reduced by up to 30% compared to having a separate inverter and boost converter. IDTechEx examines this and other pathways to 800V EVs, such as three-level inverters and battery splitting, in its “Power Electronics for Electric Vehicles 2025-2035: Technologies, Markets, and Forecasts” report.
Conclusions
As previously highlighted, the integration of power electronics can yield technical challenges, such as thermal management and electromagnetic interference. OEMs will also need to consider where to install the larger integrated units. Some internal restructuring may be required to find the space in the vehicle to install the integrated unit. These installations may also need to be different for front-wheel drive configurations. Therefore, an integrated unit will likely have a knock-on effect on the internal structure of the vehicle.
However, the weight, volume, and, most importantly, cost reductions make integrated power electronics an attractive solution for automotive OEMs. IDTechEx is observing an increased adoption of integrated power electronics and a wider product offering from many tier-one suppliers. This is a key trend in the electric vehicle power electronics industry, with an integration of the inverter, onboard charger, and DC-DC converter all in one unit potentially arriving by 2025. More technical analysis of integrated power electronics, 3-level inverters, traction-integrated onboard chargers, and many other factors are introduced in IDTechEx’s report, “Power Electronics for Electric Vehicles 2025-2035: Technologies, Markets, and Forecasts”.
