■ In Inverters, Heat and EMI Exist at the Same Time
When power semiconductors switch at high speed,
electromagnetic noise is generated.
That is why
● EMI shielding
● Conductive materials
● Grounding components
are also needed.
On the other hand, those metal components also conduct heat.
In other words, thermal management and EMI countermeasures may relate to the same component.
■ Metal Foils May Have Multiple Functions
Copper foil and aluminum foil can play multiple roles:
● Conduction
● EMI shielding
● Heat spreading
For example, the idea is
to spread heat around power semiconductors sideways
while also using it for EMI countermeasures.
However, it is necessary to consider
where to connect it electrically
and whether the insulation distance is sufficient.
■ Busbars Also Generate Heat
Busbars carrying large currents also have resistance.
Where there is resistance, heat is generated.
In particular, at
● Connections
● Bends
● Bolted joints
local heat generation can increase depending on the contact condition.
In other words,
large-current paths themselves also become heat sources.
■ Contact Resistance Creates Local Heat Generation
Terminals are not in sufficient contact with each other.
Fastening force is insufficient.
Surfaces oxidize.
Then contact resistance increases.
Where large currents flow,
even small differences in resistance lead to large heat generation.
In other words, in energy equipment,
electrical contact quality connects directly to heat problems.
■ In ESS, Both Batteries and Power Electronics Are Heat Sources
In ESS,
it is not enough to cool only the batteries.
To control the power going in and out of the batteries, there are also
● PCS
● Inverters
● Converters
● Power supplies
In other words, ESS require both battery thermal management and power semiconductor thermal management.
■ In ESS, Scaling Up Makes Heat Problems Harder
Small batteries can be cooled one by one.
In large-scale ESS, however, many cells, modules and power devices gather.
That is why temperature differences arise between
● The center and the periphery
● Upper and lower tiers
● Cooling inlets and outlets
In other words, it is necessary to consider
the temperature distribution of the entire facility.
■ In ESS, Heat Propagation in Abnormal Situations Is Also Important
In normal operation, you want to release heat efficiently.
But if abnormal heat generation occurs in one cell,
you do not want to transfer heat to the neighboring cells.
In other words, there is the contradiction of
heat dissipation in normal times
thermal insulation in abnormal times
That is why
● Thermally conductive materials
● Thermal insulation materials
● Flame-retardant materials
must be used selectively.
■ Renewable Energy Also Requires Power Conversion
In solar power generation, DC power is converted into AC.
In wind power too, conversion is needed to match generated power to the grid.
In other words,
the spread of renewable energy
leads to an increase in power electronics equipment.
And as power semiconductors increase, thermal management components are also needed.
■ In Solar Power Generation, the Outdoor Environment Is Also a Problem
Power conversion equipment for solar power is sometimes installed outdoors.
Then it is affected by
● High temperatures
● Low temperatures
● Solar radiation
● Humidity
● Rain
● Dust
That is why not only heat, but waterproofing and dustproofing are also important.
■ Waterproofing Makes It Harder for Heat to Escape
Sealing outdoor equipment
makes it easier to prevent the intrusion of water and dust.
But it also makes it harder for air to pass.
In other words,
the higher the waterproof performance, the harder air cooling becomes.
So a structure that
transfers internal heat to the enclosure
and releases it outside from the enclosure surface becomes important.
■ Considering Seal Materials and Heat Dissipation at the Same Time
Around the outer perimeter of the enclosure,
● Gaskets
● Foam seals
● Adhesive seals
are used.
If these enter the heat path, they can affect the flow of heat.
In other words,
waterproofing components are not unrelated to thermal design either.
■ EV Charging Equipment Is Also Increasing in Power
Fast chargers handle large amounts of power in a short time.
That is why
● Power semiconductors
● Cables
● Connectors
● Power supply circuits
generate heat.
The faster the charging speed, the bigger the heat problem.
In other words,
charging performance and cooling performance are connected.
■ Cables Themselves May Also Be Cooled
Charging cables carrying large currents become thick and heavy.
So, to handle higher currents, methods that give cables internal cooling mechanisms are also conceivable.
Then it becomes a composite structure of
power line + coolant + insulation + sealing.
Here too,
heat,
insulation,
and liquid
must be managed at the same time.
■ Thermal Management Also Exists in Hydrogen-Related Equipment
In hydrogen-related equipment too, heat is generated in
● Fuel cells
● Electrolyzers
● Power conversion equipment
In fuel cells, heat is produced during power generation.
How to remove this heat.
Or whether to use it for another purpose.
These are important.
In other words, in energy facilities, not only cooling but also waste heat use is important.
■ Using Heat Instead of Discarding It
In large-scale energy facilities, the amount of waste heat is also large.
If that heat can be used for
● Heating
● Hot water supply
● Factory processes
the energy efficiency of the entire facility can be increased.
In other words, it is necessary to look not only at
power conversion efficiency,
but at overall efficiency including heat.
■ Temperature Monitoring by Sensors Is Also Important
In energy facilities, the temperatures of
● Power semiconductors
● Batteries
● Busbars
● Terminals
are monitored.
If local temperature rises can be detected early,
● Failures
● Poor contact
● Degradation
may be discovered early.
In other words,
temperature is something to be cooled, and at the same time,
information that indicates the condition of the equipment.
■ The Fixing Condition of Temperature Sensors Also Affects Measured Values
If temperature sensors
● Lift
● Shift position
● Change in contact pressure
the measurement results may change.
In other words,
sensor fixing components
also relate to equipment reliability.
Here,
● Thin-film adhesives
● Insulating materials
● Thermally conductive materials
may be used.
■ Energy Equipment Is Required to Have a Long Life
Energy facilities are often premised on use not for a few years, but for long periods.
That is why
having high initial performance
is not enough.
Even after long-term exposure to
● High temperatures
● Low temperatures
● Temperature cycling
● Humidity
● Voltage
● Vibration
performance must be maintained.
In other words, not only initial quality at volume production,
but performance after aging is important.
■ Adhesives Also Need Long-Term Reliability
When adhesives are used to fix insulating films or sensors,
long-term use at high temperatures may cause
● Creep
● Peeling
● Hardening
● Softening
That is why there are cases where the perspective needed is not whether it could be applied,
but whether it will still be there in 10 years.
■ Even in Large Equipment, Small Components Become Weak Points
Large PCS.
Large ESS.
Huge inverters.
The equipment as a whole is very large.
However, the cause of failure may be
a small insulating film,
a small TIM,
a small seal,
or a small sensor fixing component.
In other words,
the larger the equipment, the more important the reliability of small functional components becomes.
■ Processing Accuracy Also Affects Long-Term Performance
The insulating material shifts slightly.
Part of the TIM lifts.
The gasket width is narrower in just one place.
There are burrs on the metal foil.
Even if there is no problem initially,
they can become weak points through repeated temperature cycles and vibration.
In other words,
small processing differences at the start
may lead to large differences in long-term reliability.
■ A Good Match for Composite Functional Components
Energy equipment needs many functions, such as
● Thermal conduction
● Insulation
● EMI
● Waterproofing
● Fixing
If all of these are assembled as separate components,
● Number of parts
● Man-hours
● Misalignment
increase.
Depending on the application, there is value in
integrating multiple functions into a single component.
■ For Example, "Heat + Insulation + Adhesion"
Suppose thermal conduction,
insulation,
and fixing
are needed between a power semiconductor and a cooling component.
Rather than putting in separate components for each, if they can be integrated as
an insulating thermally conductive material + adhesive layer,
processes may be reduced.
However, there are also effects such as
the adhesive layer becoming thermal resistance,
and thickness increasing.
The optimal configuration must be considered.
■ "Heat + EMI + Insulation" Is Also Conceivable
Around inverters,
heat,
high voltage,
and noise
exist at the same time.
So
● Metal foil
● Insulating film
● Adhesive
are laminated in the required positional relationships.
In other words, value arises in supplying components that combine functions, rather than selling materials one sheet at a time.
■ Automation Is Also Important
Energy equipment is also mass-produced.
EV chargers.
PCS.
Inverters.
ESS modules.
In such products,
insulating films,
TIM,
and seal materials
are more stable with automated application than if people keep applying them by hand.
■ Automating Processes with Reel Supply
Small and medium components are arranged at a constant pitch on a carrier.
Equipment automatically
peels,
picks up,
and applies them.
This may lead to
● Reduced man-hours
● Improved positional accuracy
● Less foreign matter
● Stable quality
In other words, in energy equipment too, it is important to design components including their supply format.
■ The Researcher's Perspective: In Energy Equipment, "Efficiency" and "Heat" Are Two Sides of the Same Problem
Energy lost in power conversion becomes heat in many cases.
In other words,
generating a lot of heat
also means
large energy loss.
That is why higher efficiency has meaning not only for
● Electricity costs
● Energy saving
but also for reducing the cooling load.
■ The Shop-Floor Perspective: Cooling Performance Alone Cannot Prevent Failure
The cooling plate is normal.
The fans are also running.
Even so, only one part becomes hot.
In this case, it is necessary to check
● TIM lifting
● Insulating material thickness
● Connection terminal resistance
● Busbar contact
● Sensor position
In other words,
heat problems are not only a problem of cooling equipment.
It is necessary to look as far as
electrical connections,
insulation,
processing,
and assembly.
■ Things to Check at the Design Stage
In thermal management for energy equipment, at least the following need to be checked.
Power semiconductors
● How much heat is generated?
● How high is the heat generation density?
● What is the cooling method?
● Where are the hot spots?
Interface
● Is the TIM appropriate?
● Is contact pressure sufficient?
● Are there air bubbles or lifting?
● Will it change with long-term thermal cycling?
Insulation
● What withstand voltage is required?
● Is the insulating material thickness appropriate?
● Are there effects from burrs or foreign matter?
● Is thermal resistance being increased too much?
Thermal cycling
● How large is the maximum temperature difference?
● How many times is it repeated?
● Will dissimilar materials delaminate?
● Will warping occur?
EMI
● Is there high-speed switching noise?
● Can metal foil be used?
● Do heat paths and electrical paths interfere?
Waterproofing and sealing
● Is it used outdoors?
● Where will heat go after sealing?
● Can seal materials withstand temperature cycling?
● Is there a risk of moisture intrusion?
Volume production
● Can components be integrated?
● Can they be applied automatically?
● Can they be supplied on reels?
● Has processing variation been considered all the way to long-term reliability?
In energy equipment, heat, insulation, electricity, sealing and long-term reliability
must be considered as a single system.
■ OTIS's Perspective: Energy Equipment Is a Representative Market for "Heat + Insulation"
OTIS is
not an inverter manufacturer.
Not a PCS manufacturer.
Not a power semiconductor manufacturer.
Not an ESS manufacturer.
However, inside energy equipment there are many functional components, such as
● TIM
● Thermally conductive sheets
● Insulating films
● Ceramic-based sheets
● Copper foil
● Aluminum foil
● EMI materials
● Adhesives
● Seal materials
● Sensor fixing components
In particular, the challenge of heat + insulation is very common.
This has a strong connection with OTIS’s processing technologies.
■ Where OTIS Should Aim
Not the finished energy facility itself.
What to target are the functional components that exist
between power semiconductors and cooling components
between high-voltage parts and metal enclosures
at the seals of outdoor enclosures
For example,
● Insulating TIM for power semiconductors
● Insulating components around inverters
● Metal foil heat-spreading and EMI components
● Insulating and thermal insulation materials for ESS
● Seal materials around cooling plates
● Insulating components around busbars
● Temperature sensor fixing components
● Waterproof seal materials for outdoor equipment
■ Turning Material Performance into "Component Performance"
Material manufacturers develop
high thermal conductivity materials,
high insulation materials,
high heat-resistant adhesives,
and high-performance seal materials.
OTIS’s role is to take them and
process them into the required shapes.
Laminate them in the required positions.
Align them to the required thicknesses.
Make them into supply formats that can be used automatically.
In other words,
turning material performance into volume-produced component performance.
■ What OTIS Can Do
At OTIS, through
● TIM processing
● Thermally conductive sheet processing
● Insulating film processing
● Copper foil processing
● Aluminum foil processing
● EMI material processing
● Thermal insulation material processing
● Flame-retardant material processing
● Adhesive processing
● Seal material processing
● Sensor fixing component processing
● High-precision die-cutting
● Microfabrication
● Thin-film processing
● High-precision lamination
● Lamination of dissimilar materials
● Partial lamination
● Half-cutting
● Reel-to-reel processing
● Supply formats for automated application
● Integration of multiple functional components
● Image inspection
● Volume production stabilization
we may be able to contribute to
turning functional materials used in energy equipment into volume-produced components that take long-term reliability into account.
■ Outside OTIS's Expertise
OTIS is not a company that specializes in
● Design of power semiconductors themselves
● Inverter circuit design
● Overall PCS design
● Overall ESS design
● Design of entire cooling systems
● Renewable energy facility design
● Hydrogen system design
● Dedicated CFD analysis
As needed, collaboration with
● Power semiconductor manufacturers
● Power supply equipment manufacturers
● Material manufacturers
● Cooling equipment manufacturers
● Equipment manufacturers
is necessary.
■ Markets Where This Technology Will Be Important
★★★★★ Power electronics
★★★★★ ESS
★★★★★ PCS for solar and wind power
★★★★★ EV fast chargers
★★★★★ Industrial inverters
★★★★☆ Power conversion equipment
★★★★☆ Fuel cells and hydrogen equipment
★★★★☆ Data center power supplies
★★★★☆ Smart grid equipment
■ Summary
Thermal management for energy equipment is the technology of “stopping electricity while releasing heat”
Energy equipment is moving in the direction of handling
larger amounts of power,
in smaller equipment,
with higher efficiency.
At its center are
power semiconductors,
inverters,
batteries,
and power supplies.
However, the higher the output,
the more heat increases.
Heat generation density also rises.
And the higher the voltage,
the stricter the insulation requirements become.
In other words, the more
higher output
miniaturization
higher voltage
advance at the same time, the harder achieving both heat and insulation becomes.
That is why, in energy equipment, multiple requirements must be met at the same time:
releasing heat to the cooling plate,
but not letting electricity flow to the metal enclosure,
suppressing EMI,
keeping water out if outdoors,
not peeling even after repeated temperature cycles,
and maintaining performance for years of use.
What is used for this are thin functional components such as
TIM,
insulating films,
metal foils,
EMI materials,
adhesives,
seal materials,
and thermal insulation materials.
Within large energy facilities, these are very small.
However,
insulation failure of a small component,
lifting of a small TIM,
a small seal failure,
may stop the entire facility.
That is why what matters in energy equipment is not only choosing high-performance materials.
It is processing those materials into the required shapes, thicknesses and positions, in a state that is stable over long periods.
What OTIS should target is not the power generation facility itself.
Nor the inverter itself.
It is the challenges that commonly exist within them:
heat, insulation, EMI, sealing, thin films, long-term reliability and automation.
The larger the power becomes, what is ultimately asked is
“Can that heat be released while insulating safely?”
Column Supervisor: Koji Kakumoto (President, OTIS Co., Ltd.)
After studying abroad and working in planning and development at a trading company, he joined OTIS Co., Ltd. in 2011. While primarily working in the Corporate Planning Department, he has also served concurrently in manufacturing and technical divisions, and since 2018 has served as President, working to drive business growth and strengthen the organization.
This article is a general technical explanation intended for educational purposes and does not refer to any specific company, product, or technology.
