Electric Vehicle Thermal Management
This example models the thermal management system of a battery electric vehicle (BEV). The system consists of two liquid coolant loops, a R-134a refrigerant loop, and a cabin air HVAC loop. The thermal loads are the batteries, the power electronics, and the cabin.
You can join the two coolant loops together in serial mode or keep them separate in parallel mode using the parallel-serial mode 4-way directional valve. In cold temperatures, the coolant loops operate in serial mode so that heat from the motor warms the batteries. If necessary, a heater can provide additional heat. In moderate temperatures, the coolant loops remain in serial mode and the radiator cools both the batteries and the power electronics. If the environment temperature or coolant temperature rises above 35 degC, the coolant loops switch to parallel mode and separate. One loop cools the power electronics using the radiator. The other loop cools the batteries by using the chiller in the refrigerant loop.
The refrigerant loop provides cooling to the cabin and batteries. It consists of a compressor, a condenser, a liquid receiver, two expansion valves, a chiller, and an evaporator. The chiller expansion valve meters refrigerant to the chiller to cool the coolant. The evaporator expansion valve meters refrigerant to the evaporator to cool and dehumidify the cabin air. The controller adjusts the compressor such that the condenser can dissipate the heat absorbed by either or both the chiller and the evaporator.
The cabin air HVAC loop consists of a blower, an evaporator, a positive temperature coefficient (PTC) heater, and the vehicle cabin. The evaporator provides air conditioning in hot weather. The PTC heater provides heating in cold weather. The blower maintains the cabin temperature at a controlled setpoint.
The model has three possible scenarios:
The drive cycle scenario simulates driving conditions in 30 degC weather with air conditioning on. The vehicle speed is based on the New European Drive Cycle (NEDC) followed by 30 min of high speed to increase the battery heat load. The coolant loop starts off in serial mode but switches to parallel mode when the battery is generating a lot of heat.
The cool down scenario simulates a stationary vehicle in 40 degC weather with air conditioning on.
The cold weather scenario simulates driving conditions in -10 degC weather, which requires the battery heater and PTC hater to warm up the batteries and cabin, respectively.
The total refrigerant charge is the same for each scenario despite the different initial conditions because the model uses the function refrigerantChargeProperties to calculate the initial refrigerant pressure and vapor quality corresponding to the desired charge and environment temperature.
For more information on electric vehicle thermal management with a heat pump for cabin heating, see Electric Vehicle Thermal Management with Heat Pump.
For more information on electric vehicle thermal management with a transcritical CO2 heat pump, see Electric Vehicle Thermal Management With CO2.
Model
Scenario Subsystem
This subsystem sets up the environment conditions and inputs to the system for the selected scenario. The battery current demand and power electronics heat load are a function of the vehicle speed based on tabulated data.
Controls Subsystem
This subsystem consists of all of the controllers for the pumps, compressor, fan, blower, and valves in the thermal management system.
Parallel-Serial Mode Valve Subsystem
The 4-way valve in this subsystem controls whether the coolant loop operates in parallel mode or serial mode. When ports A and D are connected and ports C and B are connected, it is in parallel mode. The two coolant loops are separated with their own coolant tanks and pumps. When ports A and B and ports C and D are connected, it is in serial mode. The two coolant loops are joined together and the two pumps are synchronized to provide the same flow rate.
Motor and Battery Pump Subsystems
The motor pump and battery pump subsystems are the same. The motor pump is shown below. The motor pump drives the coolant loop that cools the charger, motor, and inverter. The battery pump drives the coolant loop that cools the batteries and DC-DC converter.
Motor, Charger, Inverter, and DCDC Subsystems
The motor, charger, inverter, and DCDC subsystems are the same. The motor is shown below. Each of the four subsystems models a coolant jacket around the motor, charger, inverter, or DC-DC converter, represented by a heat flow rate source and a thermal mass.
Battery Subsystem
The batteries are modeled as four separate packs surrounded by a coolant jacket. The battery packs generate voltage and heat based on the current demand. The model assumes that the coolant flows in narrow channels around the battery packs.
Pack 1 Subsystem
Each battery pack model contains a stack of lithium-ion cells coupled with a thermal model. The power losses in the cells correspond to the generated heat.
Radiator Subsystem
The radiator is a rectangular tube-and-fin type heat exchanger that dissipates coolant heat to the environment air. The air flow passes through the condenser before the radiator. The vehicle speed and the fan located behind the radiator drives the air flow.
Radiator Bypass Valve Subsystem
This 3-way valve directs coolant to the radiator to reject heat. In cold weather, the valve bypasses the radiator so that heat from the power electronics can help warm the batteries.
Chiller Bypass Valve Subsystem
The chiller operates in an on-off manner depending on the battery temperature. This is controlled by a 3-way valve that either directs coolant to the chiller or bypasses the chiller.
Heater Subsystem
The battery heater model contains a heat flow rate source and a thermal mass. The battery heater turns on in cold weather to bring the battery temperature above 5 degC.
Compressor Subsystem
The compressor drives the flow in the refrigerant loop. It is controlled to maintain a pressure of 0.3 MPa in the chiller and the evaporator, which corresponds to a saturation temperature of around 1 degC.
Condenser Subsystem
The condenser is a rectangular tube-and-fin type heat exchanger that either transfers heat from the refrigerant to environment air. The vehicle speed and the fan located behind the radiator drives the air flow. The liquid receiver provides storage for the refrigerant and permits only subcooled liquid to flow into the expansion valves.
Chiller Expansion Valve Subsystem
This expansion valve provides the pressure drop needed to vaporize the refrigerant entering the chiller. It is a simple thermostatic expansion valve that meters the refrigerant flow based on the measured chiller outlet temperature.
Chiller Subsystem
The chiller is a shell-and-tube type heat exchanger that transfers heat from the coolant to the refrigerant.
Evaporator Expansion Valve Subsystem
This expansion valve provides the pressure drop needed to vaporize the refrigerant entering the evaporator. It is a simple thermostatic expansion valve that meters the refrigerant flow based on the measured evaporator outlet temperature.
Evaporator Subsystem
The evaporator is a rectangular tube-and-fin type heat exchanger that transfers heat from the cabin air to the refrigerant. It also dehumidifies the air when the air is humid.
Blower Subsystem
The blower drives the air flow in the cabin HVAC loop. It is controlled to maintain the cabin temperature setpoint. The source of air can come from the environment or from recirculated cabin air.
Recirculation Flap Subsystem
The recirculation flap is modeled as two restrictions operating in the opposite manner to send either environment air or cabin air to the blower.
PTC Subsystem
The PTC heater model contains a heat flow rate source and a thermal mass. The PTC heater turns on in cold weather to provide heating to the vehicle cabin.
Cabin Subsystem
The vehicle cabin is modeled as a large volume of moist air. Each occupant in the vehicle is a source of heat, moisture, and CO2.
Cabin Heat Transfer Subsystem
This subsystem models the thermal resistances between the cabin interior and the external environment.
Simulation Results from Scopes
The following scope shows the vehicle speed, heat dissipation, cabin temperature, component temperatures, and control commands for the drive cycle scenario. For the Parallel Serial Mode valve command:
0 = parallel mode
1 = serial mode
At the beginning, the coolant loop is in serial mode. After about 1100 s, it switches to parallel mode and the chiller is used to keep the batteries below 35 degC. As the chiller bypass valve periodically directs coolant to the chiller, the compressor ramps up and down, respectively, to adjust to the thermal load of the batteries.
Simulation Results from Simscape Logging
This plot shows the power consumed by the thermal management system to cool the vehicle components and cabin. The largest power consumption occurs in the refrigerant compressor when the chiller bypass valve directs coolant to the chiller to cool the batteries.
