Achim Groß, Field Application Engineer Automotive, Arrow Electronics
New vehicle models with electric motors are automobile manufacturers’ lighthouse projects, even more so against the background of current arguments about combustion engines or, more specifically, diesel engines.
In close alignment with policy makers, manufacturers are offering premiums to tempt buyers. Various countries aim to stop licensing vehicles with combustion engines by 2025. Urban driving bans for vehicles with diesel engines threaten individual mobility and it appears to be just a matter of time before electric cars are our only rational alternative.
The fact remains, on the other hand, that the necessary infrastructure to charge considerable numbers of electric cars cannot be created even in the medium term, except possibly in metropolitan areas. This is where we will also benefit from zero emission capabilities and where the relatively small range of such vehicles will be less of an issue. The combustion engine will, however, retain the advantage outside metropolitan areas and on longer trips.
The WKM view
WKM, a respected scientific society comprising academic specialists in automotive and engine technology, makes the following three assertions on this topic. First, that the combustion engine will remain the driver of mobility, commercial transport and mobile machinery. This role will be augmented by electric drives, but not substituted. Further development of drive systems, whatever the technology, is a prerequisite to successful climate policies and a prosperous society. Prohibitions may achieve the opposite.
Secondly, due to the low contribution of harmful emissions by combustion engines in future, the topic will cease to be an argument against diesel or petrol engines. Present day technologies already ensure that the limits to harmful emissions can be complied with without exception. Weak points recognised with hindsight will become irrelevant in future. Intensive research can demonstrate that environmentally fully neutral combustion engines are possible.
Thirdly, the paramount advantage of combustion engines is the efficient and flexible use of fuels that have high energy densities and excellent storage and distribution potential. These fundamental attributes ensured that combustion engines could constantly reinvent themselves and can, viewed holistically, boast CO2 emissions that are lower than those of alternative technologies. The flexibility to also use non-fossil and thus CO2 neutral fuels is a further guarantee of long-term and sustainable future use of this technology.
Average allowed CO2 emissions in the EU since 2015 are 130 g/km for passenger cars and 175 g/km for light utility vehicles. In the endeavour to meet these goals with traditional combustion engines, various measures have been taken to limit harmful emissions by such engines. These include: exhaust gas recirculation; SCR catalytic converter; controlled coolant flow; high-pressure fuel injection; multiple ignition; variable valve train and cylinder switch-off; and exhaust gas turbocharger.
Attempts have furthermore been made to minimise the electrical power the vehicle needs and thereby the mechanical power drawn by the generator. Examples of this are: control of motor and pump power; servo-motor steering; start/stop systems; LED exterior lights; and charging the battery only by regenerative braking.
Vehicles using these techniques are also referred to as micro-hybrids. Most of the measures are based on intelligent control of motors, flaps and valves. A typical controller design for these applications is shown in Figure 1.
Communication between the microcontroller and the in-vehicle network (IVN) will be via the CAN or LIN communication interface (or in exceptional cases maybe also Flexray, SENT, PSI5, or PWM). Physical linking is via a transceiver.
For small LIN nodes the microcontroller may only be an 8-bit component; CAN nodes typically have 32-bit controllers with AUTOSAR software. The power supply for smaller electronic controllers is via Ldo; switching regulators are used for higher power requirements. Encapsulated metal composite types (MCI) are used as inductors; the capacitor will often be an affordable aluminium electrolytic or hybrid type, as required.
The power supply and interface wiring must be protected against overvoltage. A wide range of suitable TVS diodes is available for this. Filter components such as common mode chokes (CMC) for the CAN bus are also available. The power supply may also be integrated into the transceiver and any other functions such as watchdog and HV I/Os may also be included in this module. This would then be called a System Basis Chip (SBC).
When the microcontroller is also integrated, it will be called an embedded MCU or a System in Package (SIP). These are also available with integrated drivers, such as 3-phase motor support bridges. Only the MOSFETs and sensors (e.g. angle sensor or hall switches) are then still required to control a motor.
Figure 2 shows examples of the wide range of components for automotive applications that are available from a wide variety of manufacturers.
The EU CO2 target for 2020 of 95 g/km for passenger cars and 147 g/km for light utility vehicles is not within reach with these measures alone. CO2 emissions could be reduced by about 15 per cent through energy recovery when braking or coasting without decoupling and then using this energy again for acceleration. These features are applied in mild hybrid vehicles.
Using a larger 12 V battery and a motor/generator in the drive chain will not be possible due to the high power and associated high currents. A combination of high voltage electric drives with a combustion engine is not an option due to the cost and the required protection from high voltages.
48 V vehicle power supplies are an alternative here to allow relatively inexpensive implementation of the necessary functions and turn the vehicle into a mild hybrid. This voltage will also be suitable for the supply of other electrical loads that require considerable energy, such as radiator fans, air-conditioning compressors, supplementary heating, water pump and servomotor for steering. The electric turbocharger, active suspension, heated windows, interior heating and seat belt tighteners can also benefit from[ this voltage source.
The block diagram for a 48 V controller as described above will not initially differ much from a 12 V controller as shown in Figure 1. However, the range of components that can be directly supplied from the 48 V battery is very limited currently; SiPs are not available for this voltage range, meaning they must be supplied either via a voltage regulator or replaced entirely by discreet components.
Although just a few types of automotive voltage regulators and motor drivers are currently available on the market, the manufacturers do have some suitable components on their roadmaps. In these cases, solution providers such as Arrow can assist users to find the best possible solution and to obtain first samples of such modules during the project phase, sometimes even long before the type is shown on the manufacturers’ websites.
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Figure 2: Manufacturers of automotive controller components Source: Arrow Electronics
The withstand voltage transceivers (primarily CAN) require in their specific application must also be considered. Here, not only withstand to the supply voltage is important but also the maximum voltages on the CAN lines.
The 48 V MOSFET range is relatively extensive. Manufacturers use current trench technologies for this voltage range. Apart from the motor drivers, the market has very few alternative controllers to offer. New components are currently under development.
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Figure 3: MOSFETs for 48 V on-board voltage; Source: Infineon
Implementations of 48 V vehicle power supplies with motor/generator contain additional components including:
· DC/DC converter 12 V / 48 V with reverse battery protection,
· Battery isolator and management for 48 V Li-Ion (BMS),
· Motor controller and generator rectifier for ca. 10 kW (DC/AC),
· Circuit breaker and motor controller for the different loads.
Battery management will, among other things, demand very accurate measurement of individual cell voltages; special modules are used here. External components will be required for cell balancing to either convert excess load to heat (passive balancing) or to top up a cell that needs it (active balancing).
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Figure 4: Components of a 48 V vehicle power supply
All other functions are implemented mainly via MOSFETs in single or multi-phase bridge configurations controlled using relevant gate drivers.
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Figure 5: Lockstep microcontroller for ASIL D applications, Source: Infineon
Individual functions in 48 V vehicle power supplies must often satisfy functional safety requirements defined in ISO 26262 according to levels ASIL A-D. Special microcontrollers are used in critical ASIL C or D applications, possibly combined with fail-safe SBCs or fail-safe DC/DC converters as needed.
This additional vehicle power supply will adapt parts of vehicles with conventional combustion engine to the demands of the future. Small cars and electric vehicles will not need this power supply.
The service life of these vehicles on the market will depend on statutory regulations in force after 2020. The CO2 value is just one variable here; the measuring cycle will be decisive.