Automotive Engineering - September 2023 - 30

Sensing to solve EV thermal challenges
The complex HVAC
required by EVs depends
on leading-edge
sensors, actuators, and
controllers to assure
that the vehicles operate
at peak performance
in all ambient thermal
conditions.
The complexities of electric-vehicle HVAC require new sensing solutions.
An expert at TDK explains.
by Jeroen Van Ham
A
common criticism of electric vehicles (EVs) is that extremes
of heat and cold adversely affect their performance, particularly
range. OEMs have been aware of the issue and
have innovated and iterated technologies to solve it. EVs
increasingly are being engineered with sophisticated heating, cooling
and ventilation (HVAC) systems based on some of the most advanced
and robust sensors and actuators available.
These systems mitigate against the effects of thermal extremes that,
admittedly, still challenge IC-engine vehicles on an infrequent basis.
But there are tradeoffs. The ICE vehicle's HVAC is a relatively simple
affair involving air cooling, a coolant (water ethylene glycol, or WEG),
heaters, and heat exchangers (including air conditioners). HVAC systems
for EVs by necessity are far more complex. Understanding the
details is important to designing an effective system.
EV HVAC differences
An EV HVAC system has multiple temperature-sensitive subsystems
and components, all with different optimal temperature ranges that
only sometimes overlap. Specifically:
* Magnetic elements in the motor must be kept below 80° C (176° F)
to keep them from demagnetizing.
* Motor inverter and charging electronics must be kept at less than
120° C (248° F)
* Lithium-ion batteries must operate between 10° C and 40° C (50° F
and 104° F).
30 September 2023
* A hydrogen fuel cell may need to run somewhere
between 100° C and 200° C (212° F and 392° F, depending
on the fuel-cell stack technology)
* Passengers in any vehicle tend to be most comfortable
within a few degrees of 20° C (68° F).
EV HVAC complexity derives from having to satisfy
all requirements, often simultaneously. The complexity
begins with the three distinct heating/cooling loops
that are part of every EV. The battery system, power
system and the passenger space each have a dedicated
loop. Handling so many systems that operate in
different temperature ranges requires careful management.
For example, EV manufacturers had to devise a
means of handling both power electronics (operable
to 120° C) and the batteries (operable to 40° C).
EV engineers divide what would have been a single
thermal loop covering both the power electronics and
the battery into two channels to take advantage of the
existence of the vehicle's air-conditioning unit.
In one channel of the thermal loop, WEG cycles
through power electronics and radiator at some temperature
between 40° C and 100° C, while in the other
channel of the loop, the WEG is chilled below 40° C by
an air-conditioning system. This is done with a chiller
that transfers the heat from the battery loop WEG to
the air-conditioning refrigerant.
AUTOMOTIVE ENGINEERING
TDK-MICRONAS
Automotive Engineering - September 2023

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