How to design heating and cooling systems for hybrid vehicles

For decades, internal combustion engines (ICE) have been powering automobiles and heating and cooling systems. As the automotive industry electrifies and transitions to hybrid vehicles with small internal combustion engines or fully electric vehicles without engines at all, how will HVAC systems work?

For decades, the internal combustion engine (ICE) has been powering cars and heating and cooling systems. As the automotive industry electrifies and transitions to hybrid vehicles with small internal combustion engines or fully electric vehicles without engines at all, how will HVAC systems work?

We will introduce new heating and cooling control modules in 48V, 400V or 800V hybrid vehicles and electric vehicles. Among them, you will learn about the unique subsystems in these modules through examples and system diagrams, and finally we will help you start planning and implementation by reviewing the functional solutions of these subsystems.

How internal combustion engines work in HVAC systems

In vehicles equipped with ICE, the engine is the basis of the heating and cooling system. Figure 1 illustrates this concept. During cooling, the air from the fan enters the evaporator, where the refrigerant cools the air. Then, the air conditioner compressor driven by the engine compresses the refrigerant leaving the evaporator. Similarly, when heating the air, the heat generated by the engine is transferred to the coolant. This hot coolant enters the heater core, which heats the air that will be blown into the passenger compartment. In this way, the engine plays a fundamental role in the heating and cooling of the cabin.

How to design heating and cooling systems for hybrid vehicles
Figure 1. The engine plays a fundamental role in the heating and cooling system of an ICE vehicle.

Hybrid electric vehicles and electric vehicles realize heating and cooling methods

In hybrid/electric vehicles, due to size limitations or the lack of internal combustion engines, two additional components need to be introduced. These components play a key role in the HVAC system, as shown in Figure 2:

How to design heating and cooling systems for hybrid vehicles

How to design heating and cooling systems for hybrid vehicles

Except for these components, the rest of the heating and cooling system infrastructure is the same as that of the vehicles using ICE. As mentioned earlier, in the absence of an engine, it is necessary to use a BLDC motor and a PTC heater or heat pump, which respectively pose challenges for power consumption, motor and resistance heater control, and overall HVAC control.

Electronics to control BLDC motors and PTC heaters

In high-voltage hybrid vehicles/electric vehicles, both BLDC motors and PTC heaters use high-voltage power supplies. Air-conditioning compressors may require up to 10kW of power, while PTC heaters may consume up to 5kW. Figures 3 and 4 are block diagrams of the air-conditioning compressor BLDC control module and PTC heater control module, respectively. Both block diagrams show that the air-conditioning compressor BLDC motor and PTC heater are powered by high-voltage batteries. In addition, these modules all use insulated gate bipolar transistors (IGBT) and corresponding gate drivers to control the power of the BLDC motor and PTC heater.

Figures 3 and 4 also illustrate the similarities between the remaining subsystems of these two control modules. Both systems include a power subsystem, a gate driver bias power supply, microcontroller (MCU), communication interface, and temperature and current monitoring devices.

Many of the subsystems used in these control modules (such as transceivers for communication and amplifiers for current measurement) are similar to those used in other heating and cooling control modules. However, the power supply subsystem and the gate driver subsystem are unique to these control modules in the vehicle heating and cooling system. These subsystems are connected to the low-pressure domain and the high-pressure domain.

Later in this white paper, we will discuss functional block diagrams of circuit topologies for these subsystems. Please note that the choice of circuit topology must meet the subsystem functions and system design requirements, such as efficiency, power density, and electromagnetic interference (EMI).

How to design heating and cooling systems for hybrid vehicles
How to design heating and cooling systems for hybrid vehicles

Heat pump

An alternative to using high-power PTC heaters to heat the cabin is to use the cooling circuit as a heat pump as shown in Figure 5. In this mode, the reversing valve reverses the flow of refrigerant. In addition, there may be other valves in the system for regulating the flow of refrigerant. For example, a stepper motor is used to control a valve in a heat pump.

How to design heating and cooling systems for hybrid vehicles

In heating and cooling systems based on heat pumps, the following types of valves are used:

• Expansion valve, used to control refrigerant flow. They help promote the transition from high-pressure liquid refrigerant in the condensing device to low-pressure gaseous refrigerant in the evaporator. Electronic expansion valves generally benefit from faster and more accurate response to load changes, and can more accurately control refrigerant flow, especially when stepping motors are used to control the expansion valve.

• Shut-off valves and reversing valves are used to change the direction or path of the refrigerant, thereby realizing reverse circulation and bypassing certain components in heating and cooling modes. Solenoid drivers or brushed DC motors can both control shut-off valves and reversing valves.

It can be inferred from Figure 5 that the heat pump system still uses the air-conditioning compressor module, which has been discussed in the previous section. In addition, the heat pump system also uses a motor driver module to drive the valve. This adds to the additional design challenge of driving the valve to control the refrigerant flow.

Figure 6 shows a typical block diagram of the motor driver module used to drive the valve. This block diagram shows a stepper motor driver. If the motor is a brushed DC motor, the brushed DC motor driver in this block diagram will replace the stepper motor driver. The design requirements of the motor driver module include power density and EMI.

How to design heating and cooling systems for hybrid vehicles

HVAC control module

Figure 7 is a typical block diagram of the HVAC control module. The HVAC control module controls the high-voltage contactor, which is used to connect and disconnect the high-voltage battery to the BLDC motor and the PTC heater. The block diagram also shows the damper motor controller, defrost heater, communication interface, and power subsystem.

How to design heating and cooling systems for hybrid vehicles

How to design heating and cooling systems for hybrid vehicles

Typical functional block diagram of the unique HVAC subsystem

As mentioned earlier, other control modules in the new heating and cooling system of hybrid/electric vehicles include subsystems unique to these control modules-power supply, gate driver, and stepper motor valve driver for controlling refrigerant flow. In this section, we will explore a typical functional block diagram of the circuit topology of these subsystems in the high-voltage air-conditioning compressor and PTC heater control module. These topologies must address the unique challenges in hybrid/electric vehicles (including isolation barriers and EMI), which we will discuss in the next section.

power supply

For hybrid/electric vehicles, there are high-power heating and cooling subsystems, such as BLDC motors or PTC heaters. But the rest of the subsystems in the module are usually low power consumption, such as MCU, gate driver, temperature sensor and other circuits. The typical method is to directly supply power to the load requiring high power consumption through the available higher voltage (800V, 400V or 48V), and to supply power to the circuit on the board through the 12V voltage rail, as shown in Figure 8.

How to design heating and cooling systems for hybrid vehicles

In 48V systems, critical systems (such as starters/generators or traction inverters) usually require the use of O-rings between the power provided by the 12V and 48V voltage rails. The heating and cooling subsystems usually do not need this O-ring. Figure 8 also shows an isolation barrier. In systems with high voltages (such as 800V and 400V), isolation is always required between the 12V side and the high voltage side. However, in 48V vehicles, the answer is not so straightforward. Due to the low voltage, electrical isolation may not be required between the 12V system and the 48V system in the vehicle. In practical situations, it is most likely to use functional isolation between the 12V domain and the 48V domain (so that the system can work normally without isolation for electric shock protection).

The isolation barrier can be placed at the input or output of the system. Figure 8 shows the isolation barrier at the input of the system, where most of the system components are on the high-voltage side. In this case, isolation components are required for the 12V power supply and the communication interface. Conversely, if the isolation barrier is to be placed at the output of the system, most of the circuit components should be on the low-voltage side. In this case, the module will use an isolated gate driver to drive the transistor, as shown in Figure 9.

How to design heating and cooling systems for hybrid vehicles

The automotive high-voltage and high-power motor driver reference design for HVAC compressors shows an example of using the LM5160-Q1 isolated Fly-Buck-Boost converter, which provides 16V for the gate driver, and provides the MCU and operational amplifiers. And all other logic components provide 3.3V (5.5V followed by a low voltage buck). This method is relatively simple and compact (using a single converter and transformer to generate two voltages), and has good performance.

Gate driver

You can use a three-phase bridge driver integrated circuit (IC) to drive the inverter stage transistors. However, due to the low drive strength (

How to design heating and cooling systems for hybrid vehicles

From the perspective of the gate driver, EMI is usually related to gate overshoot. The half-bridge gate driver approach shown in Figure 10 helps to remove redundant components and reduce the complexity of the PCB layout, because you can place the driver very close to the transistor while also restricting the switching node to a minimum. These operations will reduce EMI challenges. In addition, the half-bridge gate driver does not need to use an external boost stage to amplify the gate drive current, because the IC can achieve large current sourcing and sinking. Half-bridge drivers can usually implement interlocking and dead-time functions to prevent the two output terminals from being turned on at the same time and provide sufficient margin to effectively drive the transistors, thereby preventing half-bridge breakdown.

Stepper motor driver

If a stepper motor driver drives a valve in a heat pump system, an important function that the stepper motor driver should have is stall detection, that is, the driver electronics detects that the motor has stopped running (because it hits a mechanical block, especially in When the motor is micro-stepping). Microstepping can achieve very precise valve position control. Since motor coils are driven by pulse width modulation (PWM) signals, EMI can indeed become a problem. The stepper motor driver must also be able to drive the load torque. Devices such as DRV8889-Q1 integrate motor current sensing and advanced circuitry to help detect stalls during microstepping. DRV8889-Q1 also includes programmable slew rate control and spread spectrum technology to help reduce EMI.

Summarize

The new HVAC control module introduced due to the higher voltages in hybrid/electric vehicles brings new challenges such as power isolation, EMI, and stalls during microstepping. By combining typical circuit topologies with products such as isolated Fly-Buck-Boost converters, gate drivers, and stepper motor drivers, you can smoothly transition from ICE HVAC systems to hybrid/electric vehicle HVAC systems.

For decades, internal combustion engines (ICE) have been powering automobiles and heating and cooling systems. As the automotive industry electrifies and transitions to hybrid vehicles with small internal combustion engines or fully electric vehicles without engines at all, how will HVAC systems work?

For decades, the internal combustion engine (ICE) has been powering cars and heating and cooling systems. As the automotive industry electrifies and transitions to hybrid vehicles with small internal combustion engines or fully electric vehicles without engines at all, how will HVAC systems work?

We will introduce new heating and cooling control modules in 48V, 400V or 800V hybrid vehicles and electric vehicles. Among them, you will learn about the unique subsystems in these modules through examples and system diagrams, and finally we will help you start planning and implementation by reviewing the functional solutions of these subsystems.

How internal combustion engines work in HVAC systems

In vehicles equipped with ICE, the engine is the basis of the heating and cooling system. Figure 1 illustrates this concept. During cooling, the air from the fan enters the evaporator, where the refrigerant cools the air. Then, the air conditioner compressor driven by the engine compresses the refrigerant leaving the evaporator. Similarly, when heating the air, the heat generated by the engine is transferred to the coolant. This hot coolant enters the heater core, which heats the air that will be blown into the passenger compartment. In this way, the engine plays a fundamental role in the heating and cooling of the cabin.

How to design heating and cooling systems for hybrid vehicles
Figure 1. The engine plays a fundamental role in the heating and cooling system of an ICE vehicle.

Hybrid electric vehicles and electric vehicles realize heating and cooling methods

In hybrid/electric vehicles, due to size limitations or the lack of internal combustion engines, two additional components need to be introduced. These components play a key role in the HVAC system, as shown in Figure 2:

How to design heating and cooling systems for hybrid vehicles

How to design heating and cooling systems for hybrid vehicles

Except for these components, the rest of the heating and cooling system infrastructure is the same as that of the vehicles using ICE. As mentioned earlier, in the absence of an engine, it is necessary to use a BLDC motor and a PTC heater or heat pump, which respectively pose challenges for power consumption, motor and resistance heater control, and overall HVAC control.

Electronics to control BLDC motors and PTC heaters

In high-voltage hybrid vehicles/electric vehicles, both BLDC motors and PTC heaters use high-voltage power supplies. Air-conditioning compressors may require up to 10kW of power, while PTC heaters may consume up to 5kW. Figures 3 and 4 are block diagrams of the air-conditioning compressor BLDC control module and PTC heater control module, respectively. Both block diagrams show that the air-conditioning compressor BLDC motor and PTC heater are powered by high-voltage batteries. In addition, these modules all use insulated gate bipolar transistors (IGBT) and corresponding gate drivers to control the power of the BLDC motor and PTC heater.

Figures 3 and 4 also illustrate the similarities between the remaining subsystems of these two control modules. Both systems include a power subsystem, a gate driver bias power supply, microcontroller (MCU), communication interface, and temperature and current monitoring devices.

Many of the subsystems used in these control modules (such as transceivers for communication and amplifiers for current measurement) are similar to those used in other heating and cooling control modules. However, the power supply subsystem and the gate driver subsystem are unique to these control modules in the vehicle heating and cooling system. These subsystems are connected to the low-pressure domain and the high-pressure domain.

Later in this white paper, we will discuss functional block diagrams of circuit topologies for these subsystems. Please note that the choice of circuit topology must meet the subsystem functions and system design requirements, such as efficiency, power density, and electromagnetic interference (EMI).

How to design heating and cooling systems for hybrid vehicles
How to design heating and cooling systems for hybrid vehicles

Heat pump

An alternative to using high-power PTC heaters to heat the cabin is to use the cooling circuit as a heat pump as shown in Figure 5. In this mode, the reversing valve reverses the flow of refrigerant. In addition, there may be other valves in the system for regulating the flow of refrigerant. For example, a stepper motor is used to control a valve in a heat pump.

How to design heating and cooling systems for hybrid vehicles

In heating and cooling systems based on heat pumps, the following types of valves are used:

• Expansion valve, used to control refrigerant flow. They help promote the transition from high-pressure liquid refrigerant in the condensing device to low-pressure gaseous refrigerant in the evaporator. Electronic expansion valves generally benefit from faster and more accurate response to load changes, and can more accurately control refrigerant flow, especially when stepping motors are used to control the expansion valve.

• Shut-off valves and reversing valves are used to change the direction or path of the refrigerant, thereby realizing reverse circulation and bypassing certain components in heating and cooling modes. Solenoid drivers or brushed DC motors can both control shut-off valves and reversing valves.

It can be inferred from Figure 5 that the heat pump system still uses the air-conditioning compressor module, which has been discussed in the previous section. In addition, the heat pump system also uses a motor driver module to drive the valve. This adds to the additional design challenge of driving the valve to control the refrigerant flow.

Figure 6 shows a typical block diagram of the motor driver module used to drive the valve. This block diagram shows a stepper motor driver. If the motor is a brushed DC motor, the brushed DC motor driver in this block diagram will replace the stepper motor driver. The design requirements of the motor driver module include power density and EMI.

How to design heating and cooling systems for hybrid vehicles

HVAC control module

Figure 7 is a typical block diagram of the HVAC control module. The HVAC control module controls the high-voltage contactor, which is used to connect and disconnect the high-voltage battery to the BLDC motor and the PTC heater. The block diagram also shows the damper motor controller, defrost heater, communication interface, and power subsystem.

How to design heating and cooling systems for hybrid vehicles

How to design heating and cooling systems for hybrid vehicles

Typical functional block diagram of the unique HVAC subsystem

As mentioned earlier, other control modules in the new heating and cooling system of hybrid/electric vehicles include subsystems unique to these control modules-power supply, gate driver, and stepper motor valve driver for controlling refrigerant flow. In this section, we will explore a typical functional block diagram of the circuit topology of these subsystems in the high-voltage air-conditioning compressor and PTC heater control module. These topologies must address the unique challenges in hybrid/electric vehicles (including isolation barriers and EMI), which we will discuss in the next section.

power supply

For hybrid/electric vehicles, there are high-power heating and cooling subsystems, such as BLDC motors or PTC heaters. But the rest of the subsystems in the module are usually low power consumption, such as MCU, gate driver, temperature sensor and other circuits. The typical method is to directly supply power to the load requiring high power consumption through the available higher voltage (800V, 400V or 48V), and to supply power to the circuit on the board through the 12V voltage rail, as shown in Figure 8.

How to design heating and cooling systems for hybrid vehicles

In 48V systems, critical systems (such as starters/generators or traction inverters) usually require the use of O-rings between the power provided by the 12V and 48V voltage rails. The heating and cooling subsystems usually do not need this O-ring. Figure 8 also shows an isolation barrier. In systems with high voltages (such as 800V and 400V), isolation is always required between the 12V side and the high voltage side. However, in 48V vehicles, the answer is not so straightforward. Due to the low voltage, electrical isolation may not be required between the 12V system and the 48V system in the vehicle. In practical situations, it is most likely to use functional isolation between the 12V domain and the 48V domain (so that the system can work normally without isolation for electric shock protection).

The isolation barrier can be placed at the input or output of the system. Figure 8 shows the isolation barrier at the input of the system, where most of the system components are on the high-voltage side. In this case, isolation components are required for the 12V power supply and the communication interface. Conversely, if the isolation barrier is to be placed at the output of the system, most of the circuit components should be on the low-voltage side. In this case, the module will use an isolated gate driver to drive the transistor, as shown in Figure 9.

How to design heating and cooling systems for hybrid vehicles

The automotive high-voltage and high-power motor driver reference design for HVAC compressors shows an example of using the LM5160-Q1 isolated Fly-Buck-Boost converter, which provides 16V for the gate driver, and provides the MCU and operational amplifiers. And all other logic components provide 3.3V (5.5V followed by a low voltage buck). This method is relatively simple and compact (using a single converter and transformer to generate two voltages), and has good performance.

Gate driver

You can use a three-phase bridge driver integrated circuit (IC) to drive the inverter stage transistors. However, due to the low drive strength (

How to design heating and cooling systems for hybrid vehicles

From the perspective of the gate driver, EMI is usually related to gate overshoot. The half-bridge gate driver approach shown in Figure 10 helps to remove redundant components and reduce the complexity of the PCB layout, because you can place the driver very close to the transistor while also restricting the switching node to a minimum. These operations will reduce EMI challenges. In addition, the half-bridge gate driver does not need to use an external boost stage to amplify the gate drive current, because the IC can achieve large current sourcing and sinking. Half-bridge drivers can usually implement interlocking and dead-time functions to prevent the two output terminals from being turned on at the same time and provide sufficient margin to effectively drive the transistors, thereby preventing half-bridge breakdown.

Stepper motor driver

If a stepper motor driver drives a valve in a heat pump system, an important function that the stepper motor driver should have is stall detection, that is, the driver electronics detects that the motor has stopped running (because it hits a mechanical block, especially in When the motor is micro-stepping). Microstepping can achieve very precise valve position control. Since motor coils are driven by pulse width modulation (PWM) signals, EMI can indeed become a problem. The stepper motor driver must also be able to drive the load torque. Devices such as DRV8889-Q1 integrate motor current sensing and advanced circuitry to help detect stalls during microstepping. DRV8889-Q1 also includes programmable slew rate control and spread spectrum technology to help reduce EMI.

Summarize

The new HVAC control module introduced due to the higher voltages in hybrid/electric vehicles brings new challenges such as power isolation, EMI, and stalls during microstepping. By combining typical circuit topologies with products such as isolated Fly-Buck-Boost converters, gate drivers, and stepper motor drivers, you can smoothly transition from ICE HVAC systems to hybrid/electric vehicle HVAC systems.

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Author: Yoyokuo