Need electricity? Recom turns its attention to battery management systems in the automotive area

03/05/2020 Know-How

From very small to very big: The (automotive) industry requires power supplies in many different designs and of particular quality. Recom covers almost all high-end areas. An overview.

Automotive electronics comprises various systems ranging from entertainment and communication electronics, to driver assistance systems and traction control in conventional, electric and hybrid vehicles. A common element of all vehicle electronics is the conversion of a battery voltage, whether from a 12V lead-acid battery or a 400V lithium-ion battery, to a stable lower voltage for powering the electronics. An electric vehicle (EV) also has a current transformer on board for charging the battery from a domestic power supply or a charging station while on the road. In EV/HEV ecology, there are also various upwards and downwards converters within subsystems and charging points for high-power fast-charging stations for fast charging using three-phase AC/DC converters. Bidirectional AC/DC converters are increasingly used, allowing energy from the batteries to be returned for off-grid AC supply or to the grid for load control, or for the efficient conditioning of high-voltage battery packs for maximum performance at high voltages.

Power supply characteristics in the automotive area

12V batteries are still required in all types of vehicles, including electric cars, as many safety systems (airbags, belt tensioners, automatic braking systems, etc.) are only certified for a 12V supply. The voltage of a 12V lead-acid battery can vary over a wide range, from starting conditions in a cold environment to high overvoltages during load shedding. The LV124 (also known as VW80000) standard defines the values for systems with a 12-V nominal voltage, and the LV148 standard for systems with 48V, as present in hybrid vehicles (HEVs) (Image 1). These are the voltage levels that can exist from high power sources, but there are also fast low-energy transients at higher voltages, positive and negative, which can be present as per the ISO 7637-2 and ISO 16750-2 standards for power supply lines.

In addition to various failure situations and slowly changing voltages, the LV standards also specify AC voltages superimposed on the nominal values with up to 6-V peak-to-peak amplitude and frequencies from 15Hz to 200kHz.

Additional filtering and protection

In order to comply with the LV standards and strict EMC emission limits in the automotive area (typically CISPR25), all current transformers intended for connection to the vehicle electrical system require additional filtering and reverse polarity protection compared with conventional commercial or industrial components (Image 2). 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 transformers for critical applications such as engine control and safety systems are often discrete, embedded in the host electronics and manufactured from components certified as compliant with the corresponding stress tests and automotive specifications. Important standards are issued by the Automotive Electronics Council AEC-Q: AEC-Q101 for semiconductors, AEC-Q200 for passive components and AEC-Q400 for multichip modules with different operating temperature classifications for the respective automotive environment, from high temperatures in the engine compartment to the relatively benign environment of the vehicle interior. The companies supplying these components have been certified according to IATF 16949:2016 for the automotive sector, thereby proving that their quality meets the required standards. The supplier 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.

Product example for the automotive industry

The RAQ-0505S (Image 3) is an isolated DC/DC converter for general automotive applications where a filtered 5V DC power supply is already available to provide 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 for the component 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 in EVs (Image 4). 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. Such isolated power supplies also enable use of a modular battery where each cell can be independently monitored and controlled so that the battery voltage is not compromised in the event of a single-cell, multiple-cell or cluster failure. This means that many locally isolated 5V supplies are required in one unit, isolated from both the low voltage supply and from each other.

The RAQ-0505S operates from -40°C to +105°C without derating, is manufactured in Recom's IATF 16949:2016-certified factory in Taiwan and has PPAP documentation. DC/DC converters do not have their own AEC-Q category for stress testing, so the design of the component has been 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 is also tested according to ISO 16750 and certified for safety approval according to IEC 60950-1. With a basic external filter, the EMC complies with CISPR25 Level 3 and EN 55032. Reliability is an impressive 1000h at the maximum operating temperature of 105°C according to MIL-HDBK 217F.

DC/DC converters in production applications

Other Recom products undergo similar environmental, accelerated service-life (HALT) and production tests for the RAQ part and are manufactured in the same automotive approved facility, making these high-quality modular DC/DC converters suitable for use in a wide range of manufacturing, industrial automation, automotive test and measurement and non-critical automotive applications. CAN bus isolators used in robot manufacturing are a popular application for the RKE series, RB components are built into circuits for automotive leakage current detectors, and RP and RKE components are found in on-board chargers, to name just a few examples.

DC/DC converters with a wide input voltage range such as the REC15E-Z for 6-36V or 18-75V are suitable for automotive supplies with 12V and 48V rated voltages. Interphase AC/DC converters have established themselves in automotive charging circuits as auxiliary power supplies for access-negotiation circuits.

Bidirectional AC/DC applications

Power Control Systems, now part of the Recom Group, recently introduced a 10kW bidirectional AC/DC converter (Image 5). The initial version uses a three-phase current input/output and has a short-circuit proof output of 20V and 500A. With the bidirectional current flow, the model is used in 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. The product has a digital interface for controlling and monitoring the charging and discharging cycles.

Modular converters save development time

Modular current transformers from qualified manufacturers can be a cost-effective solution for automotive applications with competitive unit prices and savings in development and certification time. Together with the newly-acquired Power Control Systems, the Recom Group offers products from 1W to 10kW with a growing portfolio of AEC-Q-verified components.

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