Powertrain integration is beneficial for hybrid/electric vehicles, mainly in the following aspects:
Increase power density: By integrating the powertrain system, the number of components can be reduced and the power density of the system can be increased, thereby improving the overall performance of electric vehicles.12
Cost optimization: Integrated design can reduce the number of components and assembly steps, thereby reducing manufacturing costs and improving economic efficiency.12.
Improved reliability: Integrated design reduces interfaces and connections between components, lowers the failure rate, and improves the overall reliability of the system.<sup>12</sup>
Simplified design and assembly: Integrated design supports standardization and modularity, simplifying the design and assembly process and improving production efficiency.<sup>12</sup>
Lightweighting: Integrated design reduces system weight, which helps to achieve vehicle lightweighting, thereby improving fuel economy and driving range.34
Specific application cases and future development trends
BYD's three-in-one powertrain: BYD's three-in-one drive system, which integrates motor, electronic control and transmission, achieves advantages such as small size, light weight and high power density through integrated design, which significantly improves the efficiency and cost-effectiveness of the electric drive system.
Wide bandgap semiconductor devices: The application of new materials such as silicon carbide (SiC) and gallium nitride (GaN) has further improved the efficiency and power density of electric vehicles and promoted the development of powertrain integration technology.
What is an integrated powertrain?
The integrated powertrain aims to combine terminal equipment such as the on-board charger (OBC), high-voltage DC/DC (HV DC-DC) converter, inverter, and power distribution unit (PDU). Integration can be achieved at the mechanical, control, or powertrain level, as shown in Figure 1.
Integrated powertrain end-equipment components offer the following advantages:
• Increase power density.
• Improve reliability.
• Optimize costs.
• Simplify design and assembly, and support standardization and modularity.
Current Status of Market Applications
There are many methods for achieving integrated powertrains. Figure 2 briefly illustrates four common methods for achieving high power density when combining powertrain, control circuitry, and mechanical components, using the integration of an on-board charger and a high-voltage DC/DC converter as an example. These are:
Method 1: Form an independent system. This method is not as popular as it was a few years ago.
Method 2: This can be divided into two steps:
The DC/DC converter and the vehicle charger share a mechanical housing but have their own independent cooling systems.
• Sharing both the outer casing and the cooling system (the most common method).
• Method 3: Perform control-level integration. This method is evolving into a fourth method.
• Method 4: Compared to the other three methods, this method has a greater cost advantage because it reduces the number of power switches and magnetic components in the power supply circuit, but its control algorithm is also more complex.
Why is powertrain integration beneficial for hybrid/electric vehicles?
Table 1 summarizes the current integration architectures on the market:
High-voltage three-in-one integration to reduce electromagnetic interference (EMI): integration of on-board charger, high-voltage DC/DC converter and power distribution unit (Method 3) Integrated architecture: integration of on-board charger and high-voltage DC/DC converter (Method 4) 43kW charger design: integration of on-board charger, traction inverter and traction motor (Method 4)
· 6.6kW vehicle charger
· 2.2kW DC/DC converter
• Power distribution unit
*Third-party data reports indicate that this design can reduce size and weight by approximately 40% and increase power density by approximately 40% for a 6.6kW car charger.
· 1.4kW DC/DC converter
· Magnetic integration
Shared power switch
• Shared control unit
(A power factor correction stage controlled by a microcontroller [MCU], a DC/DC stage controlled by a microcontroller, and a high-voltage DC/DC converter) • AC charging power up to 43kW
Shared power switch
Shared motor windings
Furthermore, integrating the two transformers shown in Figure 3 together can also achieve magnetic integration. This is because they have the same rated voltage on the high-voltage side, ultimately forming a three-terminal transformer.
Performance improvement
Why is powertrain integration beneficial for hybrid/electric vehicles?
When this integrated topology operates under high-voltage battery charging conditions, the high-voltage output can be precisely controlled. However, the performance of the low-voltage output is limited because the two terminals of the transformer are coupled together. A simple way to improve the low-voltage output performance is to add a built-in buck converter. But this comes at the cost of increased cost.
Shared components
Similar to the integration of on-board chargers and high-voltage DC/DC converters, the power factor correction stage and the rated voltages of the three half-bridges in an on-board charger are very close. This allows for power switch sharing via three half-bridges shared by two terminal device components, as shown in Figure 5. This reduces cost and increases power density.
Why is powertrain integration beneficial for hybrid/electric vehicles?
Since a motor typically has three windings, these windings can also be used as power factor correction inductors in on-board chargers, thereby achieving magnetic integration. This also helps reduce design costs and increase power density.
Conclusion
The evolution of integration continues, from low-level mechanical integration to high-level electronic integration. As the level of integration increases, so does the complexity of the system. However, each architectural variant presents different design challenges, including:
• To further optimize performance, magnetic integration must be carefully designed.
• When using an integrated system, the control algorithm becomes more complex.
• Design efficient cooling systems to meet the heat dissipation needs of smaller systems.
Flexibility is key to powertrain integration. Numerous approaches are available, allowing you to explore various levels of integration design.
As more and more hybrid electric vehicles (HEVs) and electric vehicles (EVs) debut, automakers are increasing the electrification of their vehicle powertrains. Driven by global regulations limiting CO2 emissions, sales are growing at a rate of 20% to 25% per year[1] and are projected to account for 20% to 25% of total vehicle sales by 2030[2]. In addition, as consumers become more accepting of hybrid vehicles, there is also a greater demand for fuel-efficient, robust and compact systems with better performance and longer driving range.
One of the main concerns in this area is how to make hybrid/electric vehicles more affordable, promote mass market adoption, and address the current lack of profitability for automakers. Currently, the average price of a small to mid-sized electric vehicle is about $12,000 higher than that of a comparable internal combustion engine vehicle.[3]
Initially, it was thought that battery cost was the only reason for the price difference. Indeed, battery cost may decrease significantly in the future. However, detailed business models have recently shown that other options can also reduce costs[3] and shorten the time it takes for original equipment manufacturers (OEMs) to make hybrid/electric vehicle sales profitable. One option is Design-to-Cost (DTC), which focuses on powertrain integration, i.e., placing power electronic components more compactly, reducing the number of components, and integrating them into fewer boxes.
In this white paper, I will explain how applying DTC to power electronics products enables OEMs to achieve mass market adoption. First, I will explain why advancements in power electronics technology can alleviate consumers' "range anxiety" while efforts are made to reduce DTC in powertrain systems. Then, I will introduce system-level integrated powertrain solutions designed to incorporate DTC, with a particular focus on optimizing semiconductors (ICs) and power devices.
Solving range anxiety
Range anxiety has always been a top concern for consumers when buying hybrid and electric vehicles. In 2020, several electric vehicles with a range of over 200 miles[4] are expected to be released on the market. Even across different OEMs, these electric vehicles share a common feature: they all feature a completely new powertrain platform design that optimizes battery stacking and packaging to achieve high range. Higher battery stacking translates to higher voltage and more horsepower.
Modern electric vehicles typically have battery voltages of around 400V, but to achieve greater horsepower, the voltage needs to be increased to 800V, especially in high-end electric vehicles. Higher voltage translates to greater horsepower from the same current. Optimization of battery stacking and packaging enables compact space and lower DTC (Discharge Tolerance).
Furthermore, at the same power, higher voltage improves efficiency because it eliminates the need for higher current, thus reducing heat dissipation. Smaller cable diameter and lower weight, in turn, reduce DTC (Dissipated Tolerance).
