Reduce the cost of electric vehicles and increase driving range through integrated powertrain systems

“Using fewer devices to achieve more automotive applications can not only reduce vehicle weight, reduce costs, but also improve reliability. This is the idea behind the design of integrated electric vehicles (EV) and hybrid electric vehicles (HEV).

“

Using fewer devices to achieve more automotive applications can not only reduce vehicle weight, reduce costs, but also improve reliability. This is the idea behind the design of integrated electric vehicles (EV) and hybrid electric vehicles (HEV).

What is an integrated powertrain?

The integrated powertrain is designed to combine terminal equipment such as on-board chargers (OBC), high-voltage DC/DC (HV DCDC) converters, inverters, and power distribution units (PDUs). The mechanical, control or powertrain level can be integrated, as shown in Figure 1.

Figure 1: Overview of a typical architecture of electric vehicles

Why is powertrain integration beneficial to hybrid/electric vehicles?

Integrated powertrain terminal equipment components can achieve the following advantages:

・ Improve power density.
・ Improve reliability.
・ Optimize costs.
・ Simplify design and assembly, and support standardization and modularization.

Market application status

There are many ways to achieve an integrated powertrain. Figure 2 takes the integration of an on-board charger and a high-voltage DC/DC converter as an example, and briefly introduces four common methods used to achieve high power density when combining powertrains, control circuits, and mechanical components. they are, respectively:

・ Method 1: Form an independent system. This method is not as popular as it was a few years ago.
・ Method 2: It can be divided into two steps:
・ The DC/DC converter and the on-board charger share a mechanical casing, but have their own independent cooling system.
• Share the housing and cooling system at the same time (the most commonly used method).
・ Method 3: Perform control-level integration. This method is evolving into the fourth method.
・ Method 4: Compared with the other three methods, this method has a greater cost advantage due to the reduction of power switches and magnetic components in the power circuit, but its control algorithm is also more complicated.

Figure 2: Four common methods of integration of on-board chargers and DC/DC converters

Table 1 summarizes the integration architecture currently on the market:

Table 1: Three successful realizations of integrated powertrain

Powertrain integration block diagram

Figure 3 is a block diagram of a powertrain that implements an architecture of power switch sharing and magnetic integration.

Figure 3: Power switch and magnetic component sharing in an integrated architecture

As shown in Figure 3, both the on-board charger and the high-voltage DC/DC converter are connected to the high-voltage battery, so the full-bridge rated voltages of the on-board charger and the high-voltage DC/DC converter are the same. In this way, the on-board charger and the high-voltage DC/DC converter can share the power switch through the full bridge.

In addition, integrating the two transformers shown in Figure 3 can also achieve magnetic integration. This is because they have the same rated voltage on the high-voltage side and can finally form a three-terminal transformer.

Performance improvement

Figure 4 shows how the built-in step-down converter can help improve the performance of the low-voltage output.

Figure 4: Improve the performance of low-voltage output

When this integrated topology works under high-voltage battery charging conditions, the high-voltage output can be precisely controlled. However, because the two terminals of the transformer are coupled together, the performance of the low-voltage output will be limited. There is a simple way to improve low-voltage output performance, and that is to add a built-in buck converter. But the price of doing so is that it will lead to increased costs.

Shared components

Like the integration of an on-board charger and a high-voltage DC/DC converter, the power factor correction stage in the on-board charger is very close to the rated voltages of the three half-bridges. In this way, power switch sharing can be achieved through three half-bridges shared by two terminal equipment components, as shown in Figure 5. This can reduce costs and increase power density.

Figure 5: Component sharing in powertrain integrated design

Since a motor generally has three windings, these windings can also be used as power factor correction inductors in on-board chargers to achieve magnetic integration. This also helps reduce design costs and increase power density.

Concluding remarks

From low-level mechanical integration to high-level Electronic integration, the development of integration continues. As the integration level increases, the complexity of the system will also increase. However, each architecture variant brings different design challenges, including:

・ In order to further optimize the performance, the magnetic integration must be carefully designed.
・ When using an integrated system, the control algorithm will be more complicated.
・ Design an efficient cooling system to meet the heat dissipation needs of smaller systems.

Flexibility is the key to powertrain integration. There are many methods for you to choose, and you can explore various levels of integrated design at will.