SOLUTTIONS
ISSUE 1, SECOND QUARTER 2020, TRANSPORTATION
INNOVATION AND IDEAS IN ELECTRONICS
1 SUPERCAPACITORS AS LONG-LIFE SOLUTIONS IN BATTERY POWERED APPLICATIONS BY FELIX CORBETT
2
TEMPERATURE SENSORS AND THE HYBRID/ELECTRIC VEHICLE MARKET BY ROS KRUGER
3
DEALING WITH EMC FILTERING IN TODAY’S ELECTRIC & HYBRID VEHICLES BY JOSEPH PULOMENA
WELCOME TO SOLUTTIONS ISSUE 1, FIRST QUARTER 2020, TRANSPORTATION
CONTENT 1
SUPERCAPACITORS AS LONG-LIFE SOLUTIONS
IN BATTERY POWERED APPLICATIONS
BY FELIX CORBETT
2
TEMPERATURE SENSORS AND THE HYBRID/ELECTRIC VEHICLE MARKET BY ROS KRUGER
3
DEALING WITH EMC FILTERING IN TODAY’S ELECTRIC & HYBRID VEHICLES BY JOSEPH PULOMENA
SoluTTIons is a regular publication of TTI, designed to bring clear, current information about the rapidly changing world of electronic design to engineers and procurement professionals in the electronics industry. Sourced from industry insiders and thought leaders, these case studies, white papers and marketing intelligence overviews are selected to be informative and thought provoking. Specific focus is given to transportation and industrial market categories.
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SUPERCAPACITORS
As a Long-Life Solution in Battery Powered Applications By Felix Corbett, Director, Supplier Marketing TTI Europe
1
Supercapacitors have long been used for supplying a peak power demand in many consumer electronics devices such as a flash function on a smartphone to deliver large amounts of current quickly and reliably. New materials and structures have expanded their use beyond small coin-cell sized devices into larger supercapacitor cells and modules with a wider supply voltage range. This has seen the benefits of supercapacitors integrated into a broader range of applications as part of the power supply. They can deliver the peak-power demand of a wide range of battery powered applications, and, in the process prolong the life of the battery, and by not having to specify a larger battery, save both physical space and cost. Using electrostatic technologies in supercapacitors rather than the electrochemical technology of battery cells provides another level of control and reliability for all kinds of power sub-systems, overcoming the limited lifetime of batteries, particularly in industrial and transportation applications. This article looks at the basics of supercapacitors, and those that are available for a range of higherpower industrial examples such as powering the startup-surge demand of electric vehicles.
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CAPACITOR TECHNOLOGY
Ceramic, Film
Aluminium, Tantalum
Electrostatic
Electrolytic
d
Supercapacitor values range from several millifarads to 1,000s of farads. They typically store 10 to 100 times more energy per unit volume or mass than electrolytic capacitors, can accept and deliver charge much faster than batteries, and tolerate many more charge and discharge cycles than rechargeable batteries.
d
A
AI2O3
+-
+
er C= E=
The most common type is the electrostatic double-layer capacitors (EDLCs), which use carbon electrodes (in the form of graphene or 3D structures) with much higher electrostatic double-layer capacitance than electrochemical pseudocapacitance. The separation of charge is of the order of 0.3 to 0.8 nm, much smaller than in a conventional capacitor. Hybrid capacitors, such as the lithiumion capacitor, use electrodes with both techniques, combining electrostatic capacitance and electrochemical.
-
er
d V d V
V
The hybrid electrochemical pseudocapacitance-type devices are largely based on activated carbon that amplifies the surface area, A, of the electrode, d, that is defined by the diameter of the salt ion in the electrolyte between the electrodes. The voltage is a function of the ionic breakdown of the salt ion, and so is a function of temperature and voltage. See Figure 1.
dx
E
E d
d
d
SuperCaps
+
Electrochemical Double-layer (EDLC)
+
+
-
-
+ +
+
-
-
+
Electrode
Separator Activated Carbon
Figure 1: Different capacitor technologies – Source (AVX)
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SUPERCAPACITOR APPLICATIONS Supercapacitors can be used in a wide range of applications, from pulse power for wireless transceivers, to power hold-up sub-systems to provide a ‘dying gasp’ to allow memory systems to shut down reliably in the event of a power failure. They can also be used in energy harvesting systems to give power controllers the boost they need to start operating in the Internet of Things and even as a complete replacement for a battery. As a result, the market for these devices is expected to grow from $700M in 2016 to over $2B by 2019, a dramatic increase over a short period of time. This growth is driven by the wide range of applications. Data storage systems such as solid state disks need high currents for a short time to shut down safely, and in case of interruption of the 230Vac main power, a smart meter needs to provide a ‘dying gasp’ message. This is done via an RF module using the energy stored in a supercapacitor bank. See Figure 2. A 3-phase static uninterruptible power supply (UPS) recently installed in a print factory uses a 600F supercapacitor board to provide up to 60kW for a maximum of 20 seconds in order to allow a data system to shut down safely in the event of a power failure, but it can also be used to compensate for voltage sags and micro interruptions in facilities that can create data errors. Supercapacitors can also be used to capture energy from vehicles. Regenerative braking systems take the energy from brakes in electric cars or forklift trucks and convert it to electricity. Storing it directly in a battery creates problems of charging and battery lifetime, so a supercapacitor is used instead. As it uses electrostatic forces, it has a dramatically longer lifetime and the captured energy can be easily stored and then used by the electric
Main Power 230Vac/50Hz
Smart Meter
00000000000
Digital Circuit Power Supply
Supercap Bank 3 x 3.3F
RF Module
Figure 2: Using a supercapacitor to allow a smart meter to send a ‘dying gasp’ message in the event of a power failure (Source Eaton)
subsystem in the vehicle, for example to power the stop-start operation. Hybrid double-decker busses used by London Transport are using AECQ automotive qualified supercapacitor modules to store and release mild hybrid drivetrain regenerated energy and contribute to the hybrid drive’s efficiency in a 48V powertrain. Parallel connections ensure the required capacity for the drive cycles.
stops to recharge the supercapacitor banks quickly while taking on more passengers, delivering enough charge quickly to get the bus to the next stop. This can reduce the weight of the bus and the cost of replacing the batteries, which is significant.
Supercapacitors are even replacing batteries entirely in some specific applications. Busses on dense urban routes in Switzerland, where the bus stops every few minutes, are using those ISSUE 1 | FIRST QUARTER 2020 | TRANSPORTATION 6
SUPERCAPACITOR VS BATTERY An electrochemical battery using lithium, manganese or nickel, or even lead-acid, can store energy for a substantial amount of time but needs careful charging over time and has a relatively limited number of cycles. For example 500 for a lithium ion battery see Figures 3 & 4. In contrast, the supercapacitor charges simply like a capacitor and supports millions of cycles, delivering large amounts of power in a short time that would make a battery catch fire by over discharging. The challenge is the output voltage and the time it retains the charge, which can be measured in minutes rather than months. Direct Comparison
Pros
Cons
Long Life Cycle
Low Specific Energy
High Load Currents
Slightly Higher Self-Discharge
Fast Charging Times
High Cost Per Wh
Supercapacitors
Batteries High Energy Density
Limited Life Cycle
Better Leakage Current
Long Charging Times Very Temperature Sensitive
Figure 3: A comparison of supercapacitor and battery technologies
Characteristic Comparison
Supercapacitors
Li-ion Battery
1 - 10 secs
10 - 60 mins
Charge Time Life Cycle Cell Voltage
1 million
500+
2.1V - 3.3V
3.6V - 4.2V
Specific Energy
5
100 - 200
Specific Power
~10,000
1,000 - 3,000
> $10
$0.50 - $1
Cost Per Wh Service Life in Automobile
10+ years
5-10 years
Charge Temperature
-55°C to +90°C
0°C to +45°C
Discharge Temperature
-55°C to +90°C
-20°C to +60°C
Figure 4: The different electrical characteristics of supercapacitors and batteries
Figure 5: Combining batteries and supercapacitors (Source Eaton)
Power On Demand
Algorithm for portunity charging Battery Energy Storage
For example, a supercapacitor-powered automatic guided vehicle or warehouse shuttle completing a defined mission normally in 100-200 seconds can be followed by a 10 second recharge before starting again. This is a costefficient solution compared to batteries, and can be used in cold environments such as refrigerated warehouses where batteries become sluggish. However supercapacitors have voltage limits. While the electrostatic capacitor can be made to withstand high voltages, the supercapacitor is confined to 2.5–2.7V. Voltages of 2.8V and higher are possible, but with a reduced lifetime. To get higher voltages, supercapacitors are connected in series but this reduces the total capacitance and increases the internal resistance, or Equivalent Series Resistance (ESR). Like batteries, putting three or more supercapacitors together in a string needs voltage balancing to prevent any cell from going into over-voltage. The discharge curve is another key difference. While a battery provides a steady voltage until discharged, the voltage of the supercapacitor decreases linearly. This means the supercapacitor has to be carefully chosen to ensure that it provides the required voltage for the right amount of time to provide the power needed. This means the two technologies are often used together.
Electronic Unit Peak Pulse Power Demand
SuperCap
This means that the high power, high current capability of supercapacitors is increasingly used alongside batteries to provide instantaneous power. Interestingly, the safe, fast charging properties supercapacitors are even replacing batteries entirely.
Primary Battery
Super Cap
Battery Powered Equipment Requiring High Current Pulses
Continuous Power Usage
Continuous low power energy meet average power requirements ISSUE 1 | FIRST QUARTER 2020 | TRANSPORTATION 7
SELECTING THE RIGHT SUPERCAPACITOR A key factor in selecting the right supercapacitor is identifying the operating temperature range and the operating voltage of the application. The key equations are shown in figure 6: where Vo is the nominal operating voltage, ΔV is the Cut-off voltage, I is the peak current and Δt is the duration of the energy pulse required. The equivalent series resistance (ESR) and leakage current (LC) in the design are key considerations. The ESR can double over the lifetime of the supercapacitor, and the nominal capacitance can drop by 30%, so that combination requires more careful sizing of the device or devices for the design. Understanding the application is also essential. Energy harvesting as very different current requirements from pulse power or power hold-up, so specifying the right device needs a good understanding of the design. What will the peak current requirement be, and how long will it be required. Power hold up will need a longer current retention time that pulse power, for example.
∆V ___
I = C ∆t
∆Vtotal = I*ESR + I*∆t/C
1 __ E = 2 CV 2
Figure 6: Key Equations
High Power Density, Low ESR The DGH series includes 21 different value/voltage combinations and offers massive energy storage. They have the ability to provide instantaneous bursts of power to smooth power interruptions, supplement batteries or even be used in place of batteries in certain applications. • Standard values from 0.5 to 470 Farad and 2.7V or 5.5V • Radial leaded or Snap-In mount • Operating life is rated at 10 years with 500,000 cycles
1.800.CALL.TTI ttiinc.com
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LIFETIME
CONCLUSION
The lifetime of a supercapacitor is a function of voltage and temperature. From internal testing and “rule of thumb,” the life time doubles for every 10°C lower operating temperature, and again doubles for every 0.1-0.2V lower operating voltage, so the system specification relates directly to the reliability.
There are many differences between supercapacitors and batteries, and the supercapacitor technology is often misunderstood. The fast charging and pulsed current delivery make the devices suitable for a wide range of power applications, from holding up a storage system to ensure a reliable shutdown while providing a cleaner voltage, to powering busses or automated vehicles in factories. Supercapacitors can run in the cold environments where many batteries cannot, and can even replace batteries entirely in certain applications.
FORM FACTOR Supercapacitors come in a wide range of form factors, from cylindrical devices that look like capacitors to rectangular blocks, prismatic cells or even pouch cells. The BestCap range from AVX is a low ESR pulse Supercapacitor in a low profile design based on the nonhazardous proton activated polymer system This has a capacitance range of 4.7mF to 1F across 2.0V to 20V and an ESR of 25mΩ to 600mΩ. The operating temperature range: -20°C to +70°C (selected values offer -40°C to +75°C) Cylindrical supercapacitors provide a capacitance range of 1F to 3,000F with an operating temperature range of -40°C to +85°C at voltages from 2.7V at 65°C, derating to 2.3V at 85°C (3.0V Series up to 65°C). These can provide a high pulse power capability. SCM Series-connected (2 or 3 cells) standard Supercapacitor modules feature very high capacitance, low ESR, and low leakage current with a capacitance range of 0.33F up to 15F. With the series connection these can provide a voltage range of 5.0V to 9.0V and are available in balanced or unbalanced versions.
to 155x85mm in size but crucially have a low profile design down to 0.5mm thickness and range from 1F to 500F with a voltage range of 2.1V at 70°C derating to 1.1V at 90°C, and operate down to -55°C. A key feature of these supercapacitors is a leakage current down to 10µA. With many devices aimed at 2.7V operation, improvements in technology by Eaton have meant that 3.0V supercapacitors are becoming increasingly popular. These are drop in replacements but the relatively small change in operating voltage delivers twice the expected operating life at same working voltage and can handle higher power than the 2.7V version. The smaller size also supports high cell count designs, with 10 to 20% fewer cells needed for the same operating voltage.
However, the linear discharge means that these devices have to be carefully sized for a design to ensure that they can deliver the current that is actually required over the right time, which can be challenging. Innovation in the design of the electrodes mean that the energy density is always increasing, providing more power in smaller form factors for a wider range of applications and increasing in voltage to improve the system performance even further.
The operating temperature range is -40°C to +85°C and these are available with Epoxy filled plastic packaging for a longer lifetime in humid environments. Prizmacap prismatic electrolyte supercapacitors range from 25x21mm ISSUE 1 | FIRST QUARTER 2020 | TRANSPORTATION 9
TEMPERATURE SENSORS
Are Enabling the Continued Transition to Hybrid and Fully Electric Vehicles By Ros Kruger, Director, Supplier Marketing TTI Europe – Sensors, E/Mech and Power
2
According to the International Energy Agency (IEA) there are now more than 3 million electric vehicles on the roads worldwide, 1 million of which were sold in 2017. Over half of that 1 million were purchased in China, but other nations are breaking records, too. In some counties the revolution is still nascent; in 2017 Bulgaria saw over a 700% increase in the number of electric vehicles on its roads, but in real terms that still only equates to just over 100. Norway continues to dominate in absolute figures, now with well over 60,000 electric vehicles in operation. These figures point to the increased adoption of Electric Vehicles (EVs) and Hybrid Electric Vehicles (HEVs) in general, while the continued downwards pressure on battery price, coupled with an upward trend in capacity and energy density, is seeing the increased adoption of commercial electric vehicles such as busses for mass transport, delivery vehicles for logistics and industrial applications such as fork-lift trucks. This Whitepaper provides an overview of the EV/HEV market and takes a deeper dive into the sensor technologies being developed and deployed in EV/HEV vehicles. It will highlight the need for temperature measurement in EVs and focus on the need for Battery Thermal Management Systems (BTMS) and the temperature sensors being developed to support them.
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Others
United States
Europe
China
BEV
BEV + PHEV
3.5
Electric stock (millions)
3.0 2.5 2.0 1.5 1.0 0.5 0.0
2013
2014
2015
2016
2017
Notes: The electric car stock shown is primarily estimated on the basis of cumulative sales since 2015. Where available, stock numbers from official national statistics have been used (provided that the data can be shown to be consistent with sales evolutions). Sources: IEA analysis based on country submissions, complemented by ACEA (2018); EAFO (2018a).
Figure 1: Global electric car stock, 2013-2017
EVOLUTION OF THE ELECTRIC CAR MARKET With around 3 million electric cars now on our roads, it may seem like it’s just a drop in the ocean, but considering that 1 million of those were sold in 2017 – a growth of over 50% from 2016 – it would suggest that the rate of adoption is increasing rapidly. Figure 1 represents the evolution of the global electric car market between 2013 and 2017. The global market for electric commercial vehicles is expected to grow at around 40% per year between now and 2025, which covers all types of propulsion including battery, hybrid, plug-in hybrid and fuel cell. The adoption of electric propulsion for busses and vans is, in particular, driving this growth, due in large part to various governments’ legislation against pollution. The region expected to account for the majority of electric commercial vehicle sales is Asia Pacific, where urban pollution is of particular concern. Of all propulsion types, battery electric vehicles are expected to dominate. There is also evidence to show that there is growing demand in the tourism industry for electric bicycles, enabling city visitors to move around dense urban areas at their own pace and without contributing to the congestion on mass transport infrastructures. However, it is the potential for electric vehicles to supplant more traditional fossilfuel powered vehicles that this paper will focus on.
Battery Monitoring Sensors for EVs and HVs Ultra-Small and Reliable, Flexible Type FL NTC Temperature Sensors ISSUE 1 | FIRST QUARTER 2020 | TRANSPORTATION 11
While they are intended to look and behave in a similar way to internal combustion engine (ICE) vehicles, EVs and HEVs represent a massive change in terms of the infrastructure needed to support them and the manufacturing processes used to make them. While disruptors like Tesla and Google are leading the charge, they are considered Technology Companies; it will be the incumbent automotive manufacturers who will really define the EV/HEV market. This will require support from within its existing supply chain, as well as significant commitment from its target markets. Governmental policies around the world are key to the continued adoption of EV and HEV technology, part of which involves putting in place the charging infrastructure on both public and private property to support the shift from ICE to EV. We can expect public funding to initiate this process, but it will eventually fall to the private sector to maintain the momentum in order for the EV industry to become self-sustaining. The availability of charging stations in general, whether private or public, is not likely to match the number of EVs on the roads; as the market grows not all owners will have the opportunity to install a charging station at home, and not all EV owners will have access to a charging station at their place of work. This disparity will further drive the development of batteries that offer higher energy density, to provide longer time between charges, and solutions that can support faster charging for shorter time spent recharging. The IEA is also running the EV30@30 Campaign, which aims to see EVs representing at least 30% of all new car sales by 2030. This echoes the fact that countries and governments around the world are making bold statements about their plans to phase out ICE and usher in EV/HEV with relatively short timescales, suggesting the IEA’s goal is achievable. The IEA also coordinates the Electric Vehicles Initiative (EVI), which was launched in 2010 by the Clean Energy Ministerial, comprising energy ministers from the world’s leading economies
including the UK, the USA, Canada, Chile, China, Finland, France, Germany, Norway, Portugal and Sweden. The EVI’s mandate is to help the worldwide adoption of electric vehicles. From an infrastructure point of view, the public sector (and ultimately the private sector) is investing in installing charging points in numbers and locations commensurate with the uptake of electric vehicles. The high voltage and currents involved is creating new demand for solutions suited to this application area, such as high-voltage DC contactors that can safely switch the high power required to deliver rapid charging. This would include the Kilovac high voltage contactor and relay range from TE Connectivity, for example,
Cost Now $130/kWh (cell) $280/kwh (pack) 2035 $50/kWh (cell) $100/kWh (pack) Energy Density Now: 700Wh/ (cell) 250Wh/kg (cell) 2035: 1400Wh/l (cell) 500Wh/kg (cell) Power Density Now: 3kW/kg (pack)
A major part of the change necessary will involve battery technology and its management, both within the car and throughout the infrastructure of charging points that will need to be put in place. The opportunity here is expected to be significant, at least according to research carried out by the University of Warwick, with the support of the Innovate UK Knowledge Transfer Network and the UK Chemistry Growth Partnership. The research carried out by Warwick University indicates eight areas where improvement is required, including power density, energy density and safety (Figure 2).
2035: 12kW/kg (pack)
The Faraday Battery Challenge is a UK government program intended to support R&D into automotive battery technology, with the aim of making the UK a critical part of the global supply chain for rechargeable and recyclable battery technology suitable for the automotive, aerospace and rail sectors. With a budget of £246 million, it intends to close the productivity gap by addressing the eight areas of concern highlighted above, stating that the European market for batteries will be worth £50 billion by 2025.
Now: -20° to + 60°
Safety 2035: Eliminate thermal runaway at pack level to reduce pack complexity 1st Life Now: 8 years (pack) 2035: 15 years (pack) Temperature
2035: -40° to + 80° Predictability 2035: Full predictive models for performance and aging of battery Recyclability Now: 10-50% (pack) 2035: 95% (pack)
Figure 2: Battery technology targets
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THE CHEMISTRY OF PHYSICS The chemical reaction that takes place during the movement of charge carriers in a secondary (rechargeable) battery generates heat, this is an inescapable part of the physics involved. Managing that heat is crucially important and it is a task that falls to the Battery Thermal Management Systems, or BTMS. At a high level, this is a closed system that uses temperature sensors to detect the thermal condition of the battery, which is then interpreted by a processing element to determine if the battery is operating within its allowable temperature window and in a way that is commensurate with the operating conditions. The loop is closed by the Electronic Control Units (ECUs) that will either allow or inhibit that operating condition to continue.
Batteries based on today’s technology vary in capacity and cost, depending on the size and type of vehicle, as well as the profile of the target market. Typically, batteries range from 20kWh to 100kWh and, in general, the size of the battery has a direct impact on its cost, as well as the cost and complexity of the BTMS. As well as the proportional cost and overall durability of the battery, charge time is a crucial aspect of owning an EV. Most current or potential owners will probably agree that battery charge time influences their decision to move away from an ICE powertrain. It is largely agreed that current battery technology can support fast charging (approximately 80% charge in 60 minutes or less) without degrading the battery, however in order to make owning an EV more like owning an ICE vehicle there is a great deal of motivation throughout the industry to bring charge times down, to something more like refuelling at a petrol station.
Supporting ultra-fast charging by modifying the battery’s structure would probably mean the energy density of batteries based on existing technology would decrease. In addition, the cost would go up, while lifetime would go down; all unfavorable consequences that could significantly impact consumer adoption. In addition to recharging, it is clearly crucial to the overall user experience that the battery is capable of delivering its charge reliably over its entire lifetime. Many factors impact a battery’s functionality; the electrochemical composition most prevalent in EVs and HEVs today is Lithium Ion (Li-Ion), which comes in many variations, depending on the application. Thermal management is critical with the use of any Li-Ion based rechargeable battery, so the balance that needs to be achieved, using today’s technology, is to deliver fast and safe charging and discharging.
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THERMAL MANAGEMENT One of the main conditions that must be avoided when using Li-Ion technology is thermal runaway. It would be simpler if Li-Ion could be kept cool at all times, but in fact the chemical process required to deposit electrons onto the battery’s anode and to discharge the battery relies on the temperature remaining within an operating window. If the battery’s temperature is too low it will impede the chemical reaction that takes place during charge and discharge. However, the chemical reaction will actually result in an increased temperature, which must also stay within specified limits. In short, a high temperature will increase the power output, but a high-power output will also result in higher heat dissipation. The potential for this loop to escalate is referred to as thermal runaway and will result in catastrophic failure if left unchecked.
The Temperature Probe that Does More in Transportation
Battery cooling solutions are not dissimilar to the way coolants are pumped around a conventional ICE to keep its parts within their specified operating temperature. A coolant can be passed over or around the Li-Ion cells. Recent innovations include examples of where cells are housed in a sealed enclosure and completely immersed in a coolant. This modular approach lends itself to using temperature sensing solutions designed for larger assemblies, like the Bus-Bar Integrated Temperature Sensor from Amphenol Advanced Sensors (Figure 3), which has been designed specifically for EV/HEV/ PHEV battery packs in passenger and commercial vehicles. As it has been designed to attach to the battery pack’s busbar there is no welding required, resulting in a more compact solution. The sensor itself gives a fast response time (T63) of less than 5.5 seconds between 25°C and 85°C in water. Figure 3: The Bus-Bar Integrated Temperature Sensor from Amphenol Advanced Sensors
Honeywell LTP Series Passive Probes • Thermistor Based Probes Using Common Transportation Connectors • Enhanced Response Time Over a Wide Operating Temperature Range • High-Reliability in Harsh Environments
1.800.CALL.TTI ttiinc.com
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Irrespective of how the coolant is dispersed and circulated, its purpose is to conduct heat away from the battery cells, and as with an ICE vehicle this requires the coolant’s temperature to be closely monitored.
Figure 4: The JS8741 in a typical application
Figure 5: The A-1984 CTS provide in-line temperature measurement of a coolant fluid.
Figure 6: The WTF083B001 is provided in an IP67 rated enclosure
The role of the BMTS is to control the battery coolant temperature and, by extension, the battery’s own temperature such that it remains within the operational window; not too hot, not too cold. It must do this under all conditions; during slow or fast charge and slow/fast discharge. For vehicles that employ a cooling system distributed using metal pipes, a sensor like the JS8741 integrated pipe clip surface temperature sensor from Amphenol provides a simple yet effective solution. The sensor attaches to a metal pipe (Figure 4) using spring-loaded clips, creating a direct thermal path to provide high sensitivity in a compact design rated to IP57.
Figure 7 shows another example of an in-line flow-through fluid temperature sensor from Amphenol, in this case featuring an SAE J-1231 interface and available in three standard hose sizes, ranging in weight from 8g to 26g. The temperature-depended resistor design sees the internal resistance varying from 332.776kΩ at -40°C to 338.2Ω at +120°C.
VDC
10kΩ
Vout
Sensor
The sensor is formed of a temperaturedependent resistive element and a load resistor, forming a potential divider (Figure 8). It is rated for an operating temperature of -40°C to +120°C and is certified to AEC-Q200 Rev (D) – Pending. Along with the spring-loaded clip the sensor features an integrated connector with locking mechanism. The A-1984 Coolant Temperature Sensor (CTS) from Amphenol is an example of a sensor that is designed to be positioned in-line with the coolant, forming part of the pipework (Figure 5). It features an SAE J-2044 compliant quick-connect interface (3/8in), which is rated to operate at a pressure of up to 5 bar.
Figure 8: Equivalent circuit diagram for the JS8741
Other examples of a CTS from Amphenol include the WTF083B001 (Figure 6), which offers an IP67 rating in a compact design that includes an integrated connector.
Figure 7: Flow-through temperature sensors like this are used to control coolant temperatures in battery management systems
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FLEXIBLE TEMPERATURE SENSING SOLUTIONS
R1
R3
+5V RS
NTC
In some cases, the use of a fully enclosed sensor may need to be augmented by additional sensors distributed around the cooling system, to detect the temperature in areas as opposed to fluids, for example. In this case it may be appropriate to use a simple device like a Negative or Positive Temperature Coefficient (NTC/PTC) device. These discrete components are easily mounted on a PCB or flying lead and can be used in various configurations. For example, Figure 9 shows how a temperaturedependent device can form part of a classic Wheatstone bridge circuit; as the temperature changes the circuit becomes imbalanced, causing more current to flow through the ammeter.
CONCLUSION The thermal management of batteries in EVs and HEVs is critical in so many ways. It directly influences the longevity of the battery, it enables the rate of charge and, just as importantly for the driver, it controls the rate of discharge. The faster a battery can discharge safely without entering thermal runaway, the more instantaneous energy can be transferred to the drive motor; all of these features impact the user experience and as a result the propensity of consumers to adopt EV/HEV technology. The Battery Thermal Management System is fundamental to the performance of EV/HEV technology and, in turn, the BTMS is directly dependent on the performance, stability and reliability of the sensors it employs to accurately detect the temperature of the battery and battery coolant, at all times during charge and discharge.
R
A
R2
RT
Figure 9: A classic Wheatstone bridge featuring a temperature-dependent resistive device such as a Negative- or Positive-Temperature Coefficient thermistor.
Figure 10 shows how an NTC can be easily interfaced to a microcontroller. In this case it forms part of potential divider network, with additional passive components providing hysteresis. These types of thermistors are used extensively in the automotive industry, to measure the temperature inside LED lighting or a dashboard, for example.
C
C
ÎźC
-
Figure 10: An NTC as part of a potential divider network can be easily interfaced to a microcontroller
They are also used in ICE vehicles, EVs and HEVs to measure the battery temperature. Examples of devices used in these applications include the S861, S863, S867 and S869 Series of mini-sensors from TDK, which are supplied with bendable wires already attached to the device’s legs, formed of PTFE-insulated leads manufactured from silver-plated nickel wire.
The solutions presented in this Whitepaper are applicable to EVs and HEVs, as well as batteries found in ICEs, but they have further applications in a range of sectors and industries. Temperature sensors are a fundamental part of system engineering and enable a wide range of modern applications. The specific requirements found in battery management for EVs and HEVs is perfectly addressed through advanced sensors such as those presented in this paper. As the automotive industry continues to transition to a more sustainable powertrain we can expect to see significant developments in the electrochemical profile of rechargeable batteries. While Li-Ion is expected to dominate for at least another decade, the industry in general fully expects new solutions to emerge and take its place. However, the need for accurate and responsive temperature management in battery systems is unlikely to disappear.
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DEALING WITH EMC FILTERING
3
In Today’s Electric and Hybrid Vehicles
By Joseph Pulomena, TDK Electronics Inc, www.tdk-electronics.tdk.com
Automobiles have changed significantly over the past 40 years, from mechanical systems to computerized systems. As a result, there is an increased need for electromagnetic compatibility (EMC) filters in today’s electric and hybrid vehicles, also called e-vehicles.
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THE HISTORY
40 years ago in the mid-1970s, there were few, if any, computers or electronics in vehicles aside from the car radio. Prior to this time, engines had simple, mechanical designs and circuitry was too large to be practical for automobiles. However, the gas crisis in the late 1970s led automotive manufacturers to include solid state circuitry to control ignition timing, particularly as smaller engines
became the norm. About 30 years ago in the 1980s, microchips were used as part of the creation of fuel injection and for other emissions system controls. As the 1990s came, on-board computing became the norm and these systems began to control more and more functions of vehicles. Around this time, most automobiles became too complex for the average car owner to fix.
Since the early 2000s and throughout the past decade, most automotive manufacturers began to include GPS, entertainment systems, advanced climate control and more as standard features. As a result, electronics and the on-board computer have become an essential performancedetermining part of the vehicle.
HYBRID AND ELECTRICAL VEHICLES Today’s automotive manufacturers are creating dozens of electric and hybrid vehicles. The difference between yesterday’s combustion vehicles with basic electronics and simple onboard computers, and today’s fully computerized electric vehicles is an important one: Computers now control every aspect of an electrical vehicle. Without on-board computing systems, the vehicle won’t operate. With good on-board computing systems the vehicle’s passengers are safe. They provide not only for the safety, comfort, and convenience of passengers, but they also power the electrical drive systems, high-voltage batteries, inverters, and at least one electric motor. ISSUE 1 | FIRST QUARTER 2020 | TRANSPORTATION 18
EMI/EMC FILTERING
Discrete Semiconductors Optoelectronics Capacitors
As a result, there are potentially hundreds of things that can go wrong with e-vehicles and their computing systems. Electromagnetic interference (EMI) and the physical damage it can cause is one of the biggest. EMC components and filters help maintain the correct operation of the automotive communication networks and all the different equipment in common electromagnetic environments. EMC requirements are regulated by international standards such as CISPR 25 or the EU Directive ECE-R10. As a result, the biggest priority when developing e-vehicles is to ensure that the individual systems, crammed into very restricted spaces, do not cause mutual interference. Because of the unique design of electric vehicles, design engineers must use electronic components that are able to withstand vibration, impact, and wide temperature ranges while reducing electromagnetic interference, voltage spikes and ground currents. It is critical for design engineers to ensure that no interference affects systems outside the vehicle.
Relays
Resistors
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Inductors
Switches
Charging Couplers
Connection Systems Thermal Management Power Supplies Circuit Protection
Built Tough Inductors qualified to AEC-Q200 for automotive applications. Laser welded terminals allow for more robust performance.
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SHIELDED CABLES AND EMC Batteries and inverters are one of the first places to look for EMC problems. Inverters operate with pulse-width-modulation control of the motor. The sharp edges of these pulses can cause EMC issues for both the input and output sides of the inverters. This most often manifests as both conducted and radiated emissions which can be minimized through a complete encapsulation or shielding. Without a combustible engine, and with space constraints due to batteries and computing systems, designers must distribute weight and drive components throughout the vehicle. Most often the battery is situated in the back of the vehicle while the inverter is in the front. Motors are typically installed as close to the wheels as possible – either on the axles or in many cases directly on the wheels. As a result, the connection of the inverter and battery has to be made by a long shielded cable. This poses great EMC risk for three main reasons: • High shield currents can be created which contribute to emissions in the high-frequency range. • Voltage spikes caused in longer cables can be large enough to damage the inverter and battery. • There is a possibility of interference being coupled into the lowvoltage system of the vehicle due to the length of cables. In addition, the connection of the cable shielding to the battery shielding can cause issues. The impedance of the connection from the cable shielding to the battery shielding must be tremendously low in order to provide the shielding required. This is further exasperated by the vibrations, impacts and temperatures that all vehicles experience. Also, oxidation and corrosion may occur as the system ages, which should also be taken into account. These can weaken the shielding connection which causes impedance to rise over time.
EMC IMPROVEMENT WITH FILTERS The best solution for design engineers to use in dealing with these EMC issues is to design the system with highvoltage DC filters. As a company, this is something that we realized and why we were the first to develop a family of 2-line high-voltage DC EMC filters for electric vehicles. DC filters used in hybrid and electric vehicles should be designed for a maximum voltage of 600 V DC, which correlates to the standard voltages of high voltage batteries.
Next, the EMC filters must offer a very low DC resistance to avoid significant losses. As a result, they should filter drive systems with power ratings in excess of 100 kW, and their current capabilities should cover the range of up to around 150 A DC or 350 A DC. By doing this, the conducted interference could be reduced by up to 70 dB, or a factor of 3,000 – even when using an unshielded cable. In fact, by using EMC filters engineers can eliminate the need for shielded cables to save on weight, weight distribution and space. Of course, this EMC performance should be tested and confirmed in a test setup with the EMC filter in place.
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CONCLUSION The use of such 2-line high-voltage DC EMC filters in electric vehicles enables a considerable reduction in the number of conventional EMC measures in the individual system components. Moreover, by using such filters, as we’ve discussed, engineers can get back much-needed space and weight for tomorrow’s even more advanced on-board computing systems. For more specific product information regarding EPCOS components, please contact Joseph Pulomena, Director of Product Marketing; Magnetics, TDK Electronics Inc., at joseph.pulomena@ tdk-electronics.tdk.com or 732-906-4300
THANKS FOR JOINING US TTI developed SoluTTIons as an electronically delivered magazine, dedicated to showcasing new ideas and innovations from across the electronics industry. Each issue, we'll focus on a specific market such as Transportation or Industrial Applications, wherever new concepts and interesting applications of technology take us. We're working with writers and engineers around the world to bring these insights to your screen on a regular basis and hope you find it helpful. If you know of a colleague who might benefit from reading SoluTTIons, we encourage you to pass along this link ttiinc. com/solutions so they can subscribe and have this type of specific engineering content delivered to their desktop. Thanks again for your time. The Electronics Components Specialists at TTI
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