AUTOMOTIVE JOURNAL
Q2 + 2021

ni.com/automotive“High-performance modular instruments allow us to do test-bench-based
development of future vehicular fail-operational low-voltage power systems.
Through communication with selected measurement and control components,
the system under test can be stressed electrically with an automated validation
test process. Highly dynamic and accurate measurements are immediatelyevaluated. Results from these physical tests help us to significantly improve
our models deployed in our digital twin.”
Martin Baumann
Simulation Electrical Power Supply, BMW

Challenge

SolutionVehicle electrification and automation greatly impact safetyrelevant and functional power system requirements becauseinterferences to those can cause fatalities. Critical situations
should be discovered in the early concept phase throughsimulation. Countermeasures such as harness redesign,
component modifications, and anti-interference solutions
can be derived. Virtual designs reduce development time andpreserve financial resources, but they also require a close
measurement feedback loop to validate the models against thereal physical systems and system-inherent retroactive effects.

The BMW Group designed and developed a digital twin for
low-voltage vehicular power systems. With a newly definedvalidation approach and the development of a system-level
physical and digital twin, highly dynamic processes can be
simulated and emulated to fully stress the low-voltage powersystem and therefore identify weaknesses quickly, which
reduces development time and costs.

CUSTOMER STORY

Designing and Developinga Digital Twin for Low-Voltage
Vehicular Power Systems
Digital Twin Methodology
A digital twin is a virtual replica of the physical twin, which
represents a physical asset (object, system, device, process,product, service, and so on). This includes modeling and simulating
its functionality and behaviors. A tight connection between thedigital and physical twins is required to make sure that the virtual
replica can mimic the physical effects as closely as possible.
Real-time data and sensor measurements play a critical rolein establishing and evolving the digital twin because data andmeasurements are key to compare and fine-tune the modelingand simulation aspects of the digital twin.

Solution Requirements
BMW’s ultimate goal is to shift the development of the low-voltage
power system toward a virtual approach, thus making it a digital
twin. Therefore, accurate models are needed for those components
connected to the power system influencing its behavior.
Safety-relevant components ranging across multiple Automotive
Safety Integrity Levels (ASILs) include brakes, steering, windshieldwipers, headlights, central electronic control units (ECUs), and sensors
for object recognition purposes (advanced driver assistance systems,
or ADAS). High-power components such as power electronic driven
machines, audio boosters, fans, and amplifiers impact the powersystem’s voltage stability. Hence, precise models are needed forthe power supply and wiring harness. As a first step, BMW improved
these models by characterizing the physical components on acomponent-level test bench. Then they recorded electrical behaviors
through road testing and replaying those phenomena back in the lab.
Finally, BMW developed a system-level test bench as a physical twin
within the lab (see FIGURE 01) to validate the results of the digitaltwin against reality. By injecting the recorded electrical waveforms
from road testing into the power system of the physical and digital
twins, BMW can further optimize the simulation. The physical twin also
includes simulation and emulation technology to mimic real driving,startup, and malfunction behavior by injecting interferences.

Before BMW implemented this multistage model characterizationand validation process including the previously mentioned
system-level validation test bench, virtual development had
successfully provided valid results for long-term processes such asdriving cycles. Initial improvement steps were taken by implementing
a first test bench for a low-voltage vehicular power system using
adequate loads1 but no highly dynamic effects and interferences.
With further developments on functional safety, particularly focusing
on highly automated vehicles (HAVs) ranging up to fully automatedvehicles (FAVs), fail-safe functionalities and fail-operational
functionalities have become more crucial. At the same time, thesesafety features and the already existing non-safety-critical devices
and subsystems (for example, HVAC) are all connected to the sameenergy (voltage) source. This can lead to a severe impact on safetyrelevant components as well as comfort systems. With the newlydefined validation approach and the development of a system-level
physical and digital twin, these highly dynamic processes can besimulated and emulated to fully stress the low-voltage power systemand therefore identify weaknesses quickly, which prompts designingand implementing appropriate countermeasures.

Approach
The previously mentioned requirements can be met witha high-performance modular instrument that is capable ofhigh-accuracy measurements and process elaboration at highspeeds. A modular design supports customizable test applications.
NI’s real-time PXI system meets these requirements. The instrument
acts as the central test system and main connection to guarantee
a seamless integration of all necessary measurement and control
capabilities needed to fully orchestrate (time, trigger, sync) the wholesystem-level validation test bench.
The PXI hardware is controlled with engineering software products
including LabVIEW and VeriStand. Besides that, the measurement
system architecture allows for preserving existing investments inthird-party tools and equipment through full integration into thewhole setup (for example, Vector CANoe for Restbus Simulation).
This software-connected PXI-based test system has become
an all-in-one solution to address communication bus simulation,measurements, and control of third-party devices, such as
electronic loads, sources, and in-house-developed prototypes, aswell as logical interfaces to the safety environment including safetyswitches, relays, circuit breakers, and so on (see FIGURE 02). The
established measurement setup enables the development of highly
automated test sequences, which leads to never-before-achieved
repeatability within the whole validation workflow.
The predecessor of the current system was developed as a joint
project between the Technical University of Munich and BMW,1 so
BMW has had a lot of positive experiences with high-performance
modular instruments, which can be reused. Modular instruments
also address demanding requirements such as high-frequency
measurements (>3 MS/s), communication with third-party products,
test automation capabilities, and automatic report generation ofresults. Additionally, the software toolchain is comprehensive, allowing
for straightforward test solutions for both experts and students.
Furthermore, the modular and scalable design of the PXI systemenables expansion and adjustments of measurement and control
capabilities at any point in time, so the setup is optimized to meet
future challenges and requirements easily and cost-effectively.
Simple yet powerful details like standardized connection concepts
such as the SCB-68 Terminal Block and SH96 connectors andcables allow for straightforward system upgrades to enhance theperformance when necessary.
The models used are either acquired directly from the component
suppliers or developed by BMW itself. Simulation tools andprogramming languages used include the MathWorks MATLAB®
and Simulink® software, Plexim PLECS, Python, Modelica Dymola,and others. Homegrown models are typically generated throughsystem identification methods and/or designed by acquiring
current and power profiles from each component to perform aproper device characterization.2 This, again, includes measuring
back high-dynamic current pulses and fault-injection behavior.3

Signals used to stress test the system range from 0 kHz to 150 kHz.
The acquired profiles are then imported into the simulation as
lookup tables to further fine-tune and improve the existing models.

Results and Benefits
This new approach to validate the low-voltage power system,
including both physical and virtual testing techniques, has enabled
BMW to design completely new models by leveraging a new model
development methodology. It is now possible to find new defects
earlier in the overall design and development process, which
reduces development time and cost because engineers can fast
track to an initial higher quality prototype. The data and insights
generated can be shared with suppliers and internal stakeholders
at BMW to further improve their models. Some of the models used
are running 95% faster now,4 while interferences to the powersystem in the range of 10 kHz to 100 kHz have been reduced by
75% due to stability countermeasures made to the previously
mentioned physical-to-digital design flow.5 Moreover, the newand improved models already achieve a less than 5% deviationcompared with the real-world component in the up to 150 kHz
frequency range. Because of this, BMW feels confident it is on
track to achieve 20% faster development cycles, leading to shorter
times to market through digital design, as predicted by research
initiatives such as the PANDA project.6

Outlook
A complete system simulation model still needs to be validatedbecause only parts of the system have been fully validated. System
optimization concepts will be physically implemented and comparedwith the simulation results. Furthermore, time-overlapping pulse
injections will be implemented in the future to fully understand anddiagnose cross interference. Last but not least, a Network Analyzer
will be integrated to acquire online transfer functions and execute
impedance measurements.

1

M. WINTER, A. RENNER, J. TAUBE, AND H.-G. HERZOG, “GENERATORPRÜFSTAND MIT GEKOPPELTER GENERATOREMULATION ZUR VERWENDUNG AN EINEM BORDNETZPRÜFSTAND,” 2016.

2

M. BAUMANN, T. BREM, S. SCHWIMMBECK, C. WEISSINGER, AND H.-G. HERZOG, “IMPEDANCE-BASED MODELING OF AN AUTOMOTIVE ELECTRIC POWER STEERING,” 2020.

3

M. BAUMANN, C. WEISSINGER, AND H.-G. HERZOG, “AUTOMOTIVE POWER SYSTEM MODEL VALIDATION USING IMPULSE RESPONSE ANALYSIS,” 2020.

4

M. BAUMANN, B. HAJ ALI, C. WEISSINGER, AND H.-G. HERZOG, “EFFICIENT SMALL-SIGNAL ALGORITHM FOR HIGH DYNAMIC PHASE-SHIFTED FULL-BRIDGE CONVERTERS,” 2020.

5

M. BAUMANN, A. SHOAR ABOUZARI, C. WEISSINGER, B. GUSTAVSEN, AND H.-G. HERZOG, “PASSIVE FILTER DESIGN ALGORITHM FOR TRANSIENT STABILIZATION OF AUTOMOTIVE POWER SYSTEMS,” 2021.

6A. BOUSCAYROL AND W. VAN DORP, “EUROPEAN UNION’S HORIZON 2020 RESEARCH AND INNOVATION PROGRAMME: PANDA.”

Company:
BMW AG
Stationary Host PC
Oscilloscope

MUNICH, GERMANY
Network Analyzer

Power Protection

ElectronicLoads

Industry:
Power
SupplyAUTOMOTIVE, RESEARCH

Application Area:
MULTIDOMAIN VALIDATIONAuthors:
MARTIN BAUMANN, M.SC.
BMW AGMUNICH, GERMANYNI SystemDevice under TestBackup
Restbus Simulation

Supercapacitor

DANIEL RIEDELBAUCH, DIPL.-ING. (FH)NI GERMANY GMBHMUNICH, GERMANYMICHAEL HAMMERL, B.SC.
BMW AG

FIGURE 01
System-Level Validation Test BenchMUNICH, GERMANY
DR.-ING. CHRISTOPH WEISSINGER
BMW AGMUNICH, GERMANY
SCB-68Terminal Block

SHC-68

Network Analyzer

Ethernet

Ethernet

GPIB
GPIB

NI System

Logic/
DigitalTCP/IP

LaptopStationary
Monitoring TCP/ Host PC

Ethernet

OscilloscopePower Supply withProtection Technology
Electronic Loads

Supercapacitor
Backup for
Restbus Simulation

IPSerialBus Interface

FIGURE 02
System-Level Validation Test Bench: Measurement and Control Architecture

Analog/Digital/BNC
Analog/BNC

PROF. DR.-ING. HANS-GEORG HERZOGTECHNICAL UNIVERSITY OF MUNICH,ENERGY CONVERSION TECHNOLOGYMUNICH, GERMANY

Analog/BNC

AnalogNI PRODUCTS USED:Analog
Analog

System under Test/
Device under Test
+Prototyped Hardware
Bus Communication(CAN, LIN, FlexRay)

PXI System
FPGA-based Multifunction I/O
VeriStand
LabVIEW