EV Technology Introduction 10 – Heat Pump Function

The most concerning issue for electric vehicles is range, especially in winter. In addition to powering the drive motors (which may use 3-phase BLDC motor controllers), the battery must also provide cabin heating since EVs don’t have traditional HVAC systems (unlike those with HVAC circuit boards). This heating demand significantly drains battery capacity, reducing range. A new technology – the heat pump – helps reduce this energy loss and maintain driving distance.

Heat Pump Working Principle

Without a heat pump system, EVs rely on direct heating from the battery powering electric heaters (similar to how some industrial DC motor controllers operate):

Battery (like those managed by brushless DC motor controllers)

Electric heater

Cabin heating

(Fig. 1 Direct Electric Heating)

The heat pump system recovers waste heat not only from power electronics (including drive motors, onboard chargers, and inverters that may use sensorless BLDC controllers), but also from the battery pack and slow charger. The system uses heat from these components to vaporize refrigerant from liquid to gas. The high-pressure gas from the compressor is forced into the condenser where it returns to liquid, generating additional heat that can be recovered by the heat pump for cabin heating.

Waste heat (like that from variable frequency drive air compressors)

Evaporator

Compressor (similar to those in VRF air conditioning systems)

Condenser

Cabin heating

Efficiency improvement

(Fig. 2 Heat Pump)

This process is essentially the same as conventional air conditioning (like those using PFC power supplies), but utilizes waste heat through evaporation and condensation to save battery power and extend range.

(Fig. 3 Heat Pump Equipment in EVs)

Compressor (potentially controlled by a compressor driver board)

Condenser

Electronic control module (similar to heat pump control boards)

Waste heat exchanger

Battery

Inner condenser

In cold winters when outside temperatures are low, refrigerants with lower temperature coefficients can be used. Following the Second Law of Thermodynamics, heat flows from high to low temperature areas, allowing heat to be extracted from outside air. The compressor pressurizes this heat into the cabin, where refrigerant evaporation releases heat to warm the interior.

Typical Applications

(Fig. 4 Tesla Model 3 Cooling System)

High temp coolant

Low temp coolant

Medium temp coolant

Pump (similar to those in inverter heat pumps for swimming pools)

Restrictor

CR coolant reservoir valve

Chiller

Radiator

(Fig. 5 Tesla Model 3 Cooling System Schematic)

(Fig. 6 Audi Thermal Management System)

High-voltage compressor

Gas cooler

Coolant radiator

High-voltage auxiliary heater (like those using power supply PCB boards)

Front/rear electric motor with power electronics (possibly using BLDC FOC controllers)

Low temperature circuit

Onboard charger

DC-DC converter

Medium temperature circuit

Evaporator

High-voltage heater

Refrigerant circuit