How to optimize automotive HVAC design to stay ahead in the growing hybrid and electric vehicle markets

As the number of hybrid electric vehicles (HEVs) and electric vehicles (EVs) continues to grow around the world, automotive developers are innovating to stay ahead. While HEV/EV powertrain differentiation has historically been an area of ​​focus, today HEV/EV thermal management or heating, ventilation and air conditioning (HVAC) system differentiation is also an area that cannot be ignored by market leaders. The thermal management system consumes the second most power in an HEV/EV (after the powertrain) and has a direct impact on driving range.

Internal combustion engines (ICE) have been powering cars and their HVAC systems for decades. In hybrid/electric vehicles, size restrictions or the absence of ICEs necessitate the introduction of two additional components that play key roles in the HVAC system:

● A brushless DC (BLDC) motor is a DC motor that rotates the air conditioner compressor instead of the engine.

● A positive temperature coefficient (PTC) heater or heat pump heats the coolant instead of the engine. In the case of a heat pump, battery thermal management transfers heat from the battery to the vehicle interior. An integrated heat pump can reduce weight, extend range, and reduce costs.

See Figure 1.

Figure 1 Heating and cooling systems in hybrid and electric vehicles

In this article, we will outline the design challenges associated with these electronic HVAC applications and explore how to address these challenges in terms of real-time control performance, scalability, and cost.

Reliable real-time control performance

High starting torque, high efficiency, low audible noise and low electromagnetic interference (EMI) are the main characteristics of a good electric compressor system.

Let’s take a look at the important factors that influence HVAC performance and why they matter:

● High starting torque: High inertia systems such as electric compressors require high starting torque so that the compressor motor can reach the optimal operating speed as quickly as possible, thereby improving the end-user experience of the HVAC system.

● High efficiency: With the exception of the HEV/EV powertrain system, the electric compressor system consumes the highest power in an EV/HEV, about 5kW. Therefore, power savings through improved efficiency to extend driving range is a matter of great concern to HEV/EV developers and consumers.

● Low audible noise and low EMI: In ICE vehicles, the noise of the HVAC system is negligible compared to the noise of the engine. However, EVs and HEVs are susceptible to audible noise, which is particularly prominent in quiet vehicles without engines. HEVs and EVs are also susceptible to EMI from the BLDC motors and electronics required for the electric compressor. The electric compressor components in HEVs and EVs should not introduce noise that affects the existing system or the consumer driving experience.

● While the quality of electric compressor products is directly affected by the real-time control performance of the system, traditional PTC heaters can work completely without electric compressors, and designers mainly rely on cost to differentiate these products. PTC heaters control the temperature inside the vehicle by measuring and controlling the current flowing through the system (using a single resistor).

● Considering the integration of multiple motors on a single system, heat pumps rely on strong real-time control performance. System and microcontroller (MCU) architecture play an important role in achieving efficient and cost-effective integrated heat pump system control.

The block diagram in Figure 2 shows how the architecture and peripherals of a TI C2000™ real-time MCU enable a heat pump system with multi-motor control.

Figure 2 Heat pump system controlled by C2000 real-time MCU

Scalability

鉴于全球汽车原始设备制造商存在的不断发展的趋势和不同的需求，当下迫切需要利用兼容平台来扩大不同应用需求的能力。基于平台的汽车 HVAC 压缩机、PTC 加热器和热泵设计方法有助于显著缩短开发时间并降低开发成本。特别是对于 MCU，封装类型、引脚数、闪存、温度、功能安全性（汽车安全完整性等级 B）、网络安全、通信接口和成本方面的广泛选择对于帮助汽车 HVAC 设计人员开发可扩展平台至关重要。

cost

System bill of materials, development resources, and time to market are significant costs for automotive HVAC developers. Cost-effective components (including MCUs), the ability to leverage scalable platforms, and reference designs can help address these issues.

TI High Voltage EV/HEV e-Compressor Motor Control Reference Design is a high voltage 5kW reference design built for EV/HEV e-compressor applications controlled by a C2000 TMS320F2800157-Q1 real-time MCU. This reference design demonstrates solutions to some of the HEV/EV e-compressor design challenges in terms of performance, scalability and cost.

Conclusion

Hybrid and electric vehicles will become more and more popular in the coming decades, and so will electronic solutions for HVAC control. The components required for automotive HVAC subsystems in these cars present design challenges such as reliable real-time control, scalability, and cost. With the help of C2000 real-time MCUs and reference solutions, you can smoothly transition from ICE to hybrid and electric vehicle HVAC systems.