What kind of main drive inverter do new energy vehicles need? How do automobile manufacturers choose the appropriate main drive solution?

With the development of new energy vehicles, the key component of main drive inverter is becoming more and more important. What are the core requirements of the market for main drive inverter? Under different requirements, what are the popular main drive technology solutions in the market? How do automobile manufacturers choose a suitable main drive solution?

In recent years, new energy vehicles have made great progress in major mainstream automobile markets around the world. According to data from the European Automobile Manufacturers Association ACEA, the cumulative registrations of new energy vehicles (BEV+PHEV) in EU countries from January to October 2023 were approximately 1.94 million, a year-on-year increase of approximately 32%, and the penetration rate exceeded 20%; and according to data released by the China Passenger Car Association, the domestic retail sales of new energy vehicles in the same period reached 5.962 million units, a year-on-year increase of 34.7%, and the penetration rate was as high as 34.5%.

With the expansion of the market and the maturity of the relevant industrial chain, new energy vehicles have long since changed from being policy-driven to being product-driven. From the new energy vehicle products in recent years, we can also see that there have been great improvements in terms of autonomous driving, intelligent cockpit, cruising range, and electric drive system performance.

The main drive inverter is a key component for controlling the main drive motor. It converts the DC power of the battery pack into the AC power of the drive motor. The efficiency of the conversion largely determines the energy consumption performance of the vehicle. At the same time, the peak power of the main drive inverter combined with the high-performance main drive motor also determines the overall performance of the vehicle.

Development trend of main drive inverter

The main development direction of new energy vehicles today is to have longer and longer driving range and stronger performance. For example, this year a driving range of more than 500 km has become the standard for mainstream BEVs (pure electric vehicles); many HEVs (hybrid electric vehicles) have a driving range of more than 1,000 km, and some BEV models even have a CLTC (China Light Vehicle Driving Condition) range of more than 1,000 km.

Of course, the range can also be improved by increasing the battery pack capacity. However, the current battery energy density is limited by factors such as materials and cannot be greatly improved. Therefore, while increasing the battery pack capacity, not only is the cost higher, but it will also significantly increase the vehicle weight, thereby increasing the driving energy consumption. That is, the actual range increase will be smaller than the battery capacity increase.

Therefore, the key to improving the cruising range of new energy vehicles can actually be seen as the balance between battery pack capacity and drive energy consumption. At present, when battery costs are high and energy density increases slowly, optimizing the operating efficiency of the main drive inverter is of paramount importance.

In terms of performance, on the one hand, the power of a single motor is getting higher and higher, and the peak power of the main drive motor can exceed 300kW; on the other hand, the number of drive motors is increasing. Following the dual-motor and triple-motor models, several four-motor models have appeared this year, which will require higher power density of motors and supporting equipment such as inverters.

Looking at the development of main drive inverters in recent years, first of all, under the demand for the range of new energy vehicles, more efficient main drive inverters have become the mainstream demand;

Secondly, in the era of electric vehicles, motor power is getting bigger and bigger. At the same time, the peak power that the main drive inverter needs to support is also getting bigger. In the limited space of the vehicle, a main drive inverter with higher power density is needed.

In addition, as the new energy vehicle market continues to expand, it is necessary to continuously reduce vehicle costs. As one of the core components of the vehicle, the main drive inverter will inevitably have a greater demand for cost reduction and efficiency improvement;

Finally, with the overall technology iteration speed being relatively fast, how to ensure the overall stability and reliability of the main drive inverter is also one of the points that users are most concerned about.

Therefore, we can simply summarize the development trend of main drive inverters into four points: higher efficiency, higher power density, safety and reliability, and low cost.

However, it is not easy to achieve these goals. To improve the conversion efficiency of the main drive inverter, many aspects need to be optimized, from devices and chips to drive circuit design and heat dissipation design. For example, use power devices and gate drive ICs with lower losses, or enhance the heat dissipation performance of power modules.

From IGBT to SiC, from 400V to 800V platforms,

Continuous evolution of technical solutions

In the main drive inverter, due to the cost advantage, the current mainstream solution is based on silicon-based IGBT. With the widespread application of SiC, the main drive voltage level is also accelerating from the current 400V to 800V.

The reason behind the technology replacement is actually to meet the needs of high efficiency and high power density. Compared with silicon-based IGBT, SiC MOSFET has a smaller tail current when the device is turned off, and the switching loss of the device is also smaller; at the same time, under daily low-load conditions of electric vehicles, the current required to be output by the main drive inverter is much lower than the rated current value, and the conduction loss of SiC MOSFET at medium and low currents is much lower than that of IGBT, which has a significant efficiency improvement in the overall system.

In terms of power density, SiC MOSFET can operate at a higher switching frequency with lower losses, so it has lower heat dissipation requirements and can effectively reduce the weight and volume of drive components and water-cooling components. At the same time, high switching frequency also reduces the size and cost of passive components, so the volume of SiC main drive inverter can be greatly reduced at the same power.

However, under the 800V platform, due to the doubling of voltage, in addition to the IGBT, SiC MOSFET, etc. in the main drive inverter, which need to generally upgrade the withstand voltage to 1200V, there are also a variety of devices, including MCU, gate driver, current sensor, etc. that require higher performance.

In general, today's new energy vehicle models include BEV, HEV and PHEV, and the traction inverter solutions they adopt are rich and diverse. For example, due to cost considerations, dual-motor models choose to use SiC in the main drive inverter and silicon-based IGBT in the auxiliary drive inverter; the motor layout includes front and rear dual motors, two rear and one front motor, rear single motor, front single motor, etc.; and the current drive solutions for HEV and PHEV are even more diverse, such as engine series connection, parallel connection, hybrid connection, extended range, etc., and a variety of drive solutions are extended according to the motor distribution and whether the engine has a direct drive part.

Therefore, in the case of diverse driving solutions, chip manufacturers who can provide complete chip selection and traction inverter solutions for different solutions are very important for Tier 1 and OEMs.

Infineon's one-stop traction inverter solution

As a global automotive chip giant, Infineon's products cover almost all components of automotive traction inverters and provide one-stop application solutions. It is understood that Infineon provides core components of main drive inverters including AURIXTM MCU, EiceDRIVERTM coreless isolation driver chip, OPTIREGTM PMIC, XENSIVTM current sensor, IGBT/SiC single tube and module, and its application range covers various needs of hybrid vehicles and electric vehicles.

In the main drive inverter, the MCU can be regarded as the brain of the system. The MCU is responsible for executing the driver's operating instructions in the inverter, determining the motor working status through signals such as current sensors, and using the FOC algorithm to send control pulses PWM to the gate driver. The MCU continues to determine the motor position and speed based on sensor data to achieve precise control.

In automotive applications, safety and reliability are undoubtedly the most important factors for users. Infineon's AURIXTM series MCU provides a high-performance architecture with up to six cores for the main drive inverter, supporting the highest ASIL-D functional safety standard. At the same time, Infineon's OPTIREGTM PMIC can be used with the AURIXTM series MCU to power the main drive inverter MCU and peripheral current sensors and other chips while monitoring the MCU and system working conditions as the last safety barrier.

The EiceDRIVERTM coreless isolation driver chip is used to drive power devices and modules such as IGBT and SiC MOSFET. Its main function is to amplify the logic signal of the MCU to achieve fast shutdown and conduction of the power device. As the name implies, the isolation driver chip integrates the function of electrical isolation while driving the power device, electrically isolating the high voltage of the power device from the low voltage circuit of the MCU to ensure system safety. The use of the EiceDRIVERTM driver chip in the main drive inverter can reduce the use of additional devices and reduce system costs. At the same time, it has strong compatibility with Infineon power devices, and its ease of use and operational stability are guaranteed.