FEATURE POWER ELECTRONICS The importance of battery power conversion
Axel Stangl, product sales manager power at Rutronik, and Steve Roberts, CTO at Recom explore the key requirements that are associated with power supply and conversion and examine some of the key factors to consider when specifying converters
B
attery voltage converters are the unsung heroes of today’s e-mobility
revolution. These vital components are key to powering an evergrowing number of automotive electronics, particularly in electric vehicles (EVs). Automotive electronics all share one key requirement: battery voltage always needs to be converted to a stable lower voltage, whether its source is a 12V lead-acid battery or a 400V lithium-ion battery. EVs also require current transformers to
enable battery charging from a domestic power supply or charging station. Various upwards and downwards three-phase AC/DC converters are also needed within subsystems and charging points for high- power fast-charging stations. This is where bidirectional AC/DC converters come in, allowing energy from the batteries to be returned for off-grid AC supply or to the grid for load control.
HOW TO COMPLY WITH THE LATEST STANDARDS? All types of vehicles, including EVs, require 12V batteries. The main reason for this is that many safety systems, from airbags through to belt tensioners and automatic braking systems, are only certified for 12V power supply. As the voltage of a 12V lead-acid battery can vary significantly from starting conditions in a cold environment to high overvoltages during load shedding, the LV124 (also known as VW80000) standard has been brought in to define the values for systems with a 12V nominal voltage. To comply with this standard, as well as
strict EMC emission limits (typically CISPR25), all current converters require additional filtering and reverse polarity protection. Depending on the classification of the converters, an overvoltage limiter may also be necessary, which reduces all high overvoltages and causes only a minimal voltage drop during normal operation. Current converters for critical
applications such as engine control and safety systems are often embedded in the host electronics and manufactured from components certified as compliant with the corresponding stress tests and
34 DECEMBER/JANUARY 2021 | ELECTRONICS
THE LATEST POWER CONVERSION SOLUTIONS TO LOOK OUT FOR Some of the latest converters come in the shape of isolated DC/DC converters for general automotive applications. They feature a filtered 5V DC power supply that provides an isolated 5V and 1W output with full and permanent short- circuit protection. The insulation rating of the SMT converter is 5kV DC/1 s (2.8kV AC/1 min) with >4mm creepage distance. A typical application is the generation of an isolated 5V for the CAN bus data system used in most vehicles. Another primary application is the power supply of current sensors on the high-voltage side in battery-management systems. Here the sensor circuit needs a local 5V power supply, which must be isolated from the system ground around the 400V battery voltage due to its offset. These isolated power supplies also
enable the use of a modular battery where each cell can be independently monitored and controlled. In this way, the battery voltage is not compromised if a single-cell, multiple-cell or cluster failure occur. This means that many locally isolated 5V supplies are required in one unit, isolated from both the low-voltage supply and from each other.
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automotive specifications. The companies supplying these components must comply with the IATF 16949:2016 standard and may also establish a Production Part Approval Procedure (PPAP) to ensure the release and control of components and assembly procedures before, during and after manufacture.
It is also important to remember that
some of the latest DC/DC converters do not have their own AEC-Q category for stress testing. Consequently, their design has to be verified according to AEC-Q200 for service life, shock and vibrations, board flex capability, ESD, terminal strength and temperature change (1000 cycles). The AEC-Q104 tests are also applicable for board level reliability, low- temperature storage, drop test and temperature steps. The design of the DC/DC converters
should also be tested according to ISO 16750 and certified for safety approval according to IEC60950-1. With a basic external filter, the EMC complies with CISPR25 Level 3 and EN55032. Some of the latest models offer impressive reliability in the region of 1000 hours at the maximum operating temperature of 105°C. Another important solution that is
currently available on the market are 10kW bidirectional AC/DC converters. They use a three-phase current input/output and have a short-circuit proof output of 20V and 500A. They are designed for controlled charging and discharging for battery conditioning so that battery packs can be fully charged, discharged and recharged to reach full capacity. During the discharge process, the energy is not lost, but fed back into the supply. Some of the latest converters come with digital interface for controlling and monitoring the charging and discharging cycles.
Rutronik
www.rutronik.com
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