Multifunctional electric equipment with fewer components increases EV efficiency
Powertrain integration, standardization and modularization simplify design
Achievable integration of magnetic components with the same rated voltage


Automotive applications that perform more functions with fewer parts reduce vehicle weight and cost, and increase safety. This is why the design of electric vehicles (EVs) or hybrid electric vehicles (HEVs) is being integrated. Powertrain integration refers to the integration of powertrain end devices such as onboard chargers (OBCs), high-voltage DC/DCs, inverters, and power distribution units (PDUs), which can be applied at the mechanical, control, or powertrain levels, as shown in Figure 1.

So why is powertrain integration useful for HEVs/EVs? Integrating powertrain end-unit components can increase power density and reliability, while also reducing cost. Additionally, standardization and modularization enable simplified design and assembly.

There are many approaches to powertrain integration; Figure 2 illustrates four common approaches to achieving high power density when combining powertrain, control circuits, and mechanical devices, using OBC and DC/DC integration as examples.

△Option 1 is a method using an independent system. This method is not as popular today as it was a few years ago. △Option 2 can be divided into two stages. The mechanical housing of the DC/DC converter and the OBC are shared, but the independent cooling system is separated, or both the housing and the cooling system are shared. The latter is the most common choice.

Next, △Option 3 is a method of integrating the control stage. This method is evolving into Option 4. △Option 4 has the highest cost advantage because it requires fewer power switches and magnetic components in the power circuit, but its control algorithm is the most complex.

Table 1 briefly describes the combo box architectures currently in use on the market.

Figure 3 is a powertrain block diagram that shares power switches and integrates magnetic components. Since both the OBC and the high-voltage DC/DC converter are connected to the high-voltage battery, the full-bridge rated voltage for the onboard charger and the high-voltage DC/DC is the same. Therefore, the full-bridge and power switches can be shared for the onboard charger and the high-voltage DC/DC.

In addition, magnetic component integration can also be achieved by integrating two transformers. This is possible because these components have the same rated voltage on the high voltage side, resulting in a three-terminal transformer.

Figure 4 shows how to integrate a buck converter to improve the performance of the low-voltage output. When this integrated topology operates under high-voltage battery charging conditions, the high-voltage output is accurately controlled. However, the performance of the low-voltage output is limited because the two terminals of the transformer are coupled. A way to improve the performance of the low-voltage output is to add a built-in step-down converter. However, this method entails additional cost.

As with the OBC and high-voltage DC/DC integration, the voltage ratings of the onboard charger and the power factor correction stage in the three half-bridges are very close. This allows for three half-bridges and power switch sharing by two end device components, as shown in Figure 5, to reduce cost and increase power density. Since a motor typically has three windings, magnetic component integration can be achieved by sharing the windings with the power factor correction inductor in the OBC.

◇ Flexibility, the key to powertrain integration

The evolution of integration continues, from low-level mechanical integration to high-level electronic integration. Flexibility is key to powertrain integration, with engineers able to explore the above-mentioned designs at any level using four or more different options.

Meanwhile, engineers looking to integrate diverse architectures into a single system should keep in mind that: △ careful magnetic component integration design is required to achieve the best performance; △ control algorithms will become more complex in integrated systems; and △ highly efficient cooling system design will be required to dissipate all the heat within a smaller system.



This article is a summary of the article titled “Reduce EV cost and improve drive range by integrating powertrain systems” by Weijie Cao, an engineer with TI Shanghai CFT team.