August 2025 Electric & Hybrid Vehicle Corner

By Curt Ward, Professor at Joliet Junior College

Teaching the Operation of the Electric Drive Unit Inverter

As I write this article, the summer semester is almost finished, and an exciting and informative NACAT conference has come and gone for another year. It was great to fellowship with my NACAT family and attend some of the best technical training of the year. Over the past few years, I have shared information on a variety of different hybrid and electric transmissions. When teaching these transmissions in our hybrid and electric vehicle curriculum, it has become very clear that our students sometimes struggle to understand the electrical operation of the inverter and the way it controls the electric motors in these drive units. This month, I will share some of what I recently explored and how I hope it helps to improve understanding.

Earlier this spring, I had the opportunity to be part of a group that disassembled a front drive motor assembly from a Rivian dual-motor system. The inverter is housed within the drive unit and converts the battery’s DC power into AC power to operate the motor. After disconnecting the high voltage cables, the inverter easily unbolted, as an assembly, from the drive unit (See Figure 1 – Inverter)

Figure 1: Inverter

The unit is very modular in design, for use in a variety of applications, and is easy to disassemble. The main control board, the capacitors, and the filter are easily visible with the inverter lying on its cover. The capacitors allow the vehicle to operate with a smaller high voltage battery by providing boost power when needed. They also smooth the current being generated by the drive motor during regeneration.

The main control board was easily removed after unplugging the two electrical connectors and removing the eleven retaining screws. Under the main control board was the first of two heat sinks that is used to both support the main control board and protect it from operational heat of the insulated gate bipolar transistors (IGBTs) (See Figure 2 –Heat sink). Once the support was removed, the IGBT control board was visible. This board contains all the logic needed to operate the drive motor (See Figure 3 – IGBT Control Board).

Figure 2: Heat Sink

Figure 3: IGBT Control Board

After the IGBT control board was removed, the transistors and the current senor were visible (See Figure 4 – IGBTs). The transistors are mounted on a heat sink that is cooled directly with coolant circulating through the power electronics cooling system. The current sensor assembly monitors each phase of the drive motor operation. Once the assembly was removed from the inverter, we were able to test the functionality of the IGBTs using the small voltage from the diode check feature of a digital multimeter (See Figure 5 – Multimeter).

Figure 4: IGBTs

Figure 5: Multimeter

The ease that this unit came apart makes it ideal for student learning. The only area of caution was the care needed to ensure small pins that went through multiple control boards were not damaged during disassembly. After some brief instructions in the classroom, and then armed with specific disassembly instructions, the students should be able to identify each of the components, better understand the unit operation, and test the operation of the IGBTs. This should improve the students’ overall understanding of the inverter operation and how the drive motor controls operate. My hope is to discover additional inverters that are equally modular to provide a greater number of student learning opportunities.

I will finish this article with the same offer I make after each of my presentations. If you are interested in getting started in the process of adding hybrid and electric vehicles to your curriculum or want more information, please feel free to reach out. I am more than willing to sit down in-person or online and share my experiences. Are you looking for a classroom textbook? Reach out to Pearson and ask for a review copy of the all-new Electric and Hybrid Electric Vehicle text that Jim Halderman and I co-authored. It is a comprehensive text covering all the latest information on the subject.