Accelerating Vehicle Power System Simulation

March 1, 2008
One of the key trends in the automotive market these days is to make vehicles safer, more reliable and more comfortable via emerging applications like

One of the key trends in the automotive market these days is to make vehicles safer, more reliable and more comfortable via emerging applications like telematics (e.g., vehicle-tracking, satellite navigation, mobile communications, and television) and mechatronics (e.g., anti-lock braking systems, spin assist and airbag deployment). As automakers work hard to introduce new advances in these areas, the amount of in-vehicle electronics and, in turn, electronic components, has and will continue to rise. Likewise, the number of electronic control units (ECUs) required to control the new electronic components will increase. In contemporary automotive electronic systems, for example, it is common to have anywhere from six to 12 control ECUs. These ECUs, as well as the electronic components they control, function in an extremely harsh electrical environment. They are constantly subject to power system voltage transients and dropouts caused by high-current motors, solenoids and other components on the power system. In this mission-critical environment, any malfunction is simply not tolerated as it could severely erode the consumer's confidence in his or her vehicle, not to mention jeopardizing vehicle driver/passenger safety.

Successful operation of automotive electronics, therefore, depends on adequate power transient immunity, making thorough ECU and electronic component testing absolutely critical. A variety of test standards such as ISO-7637 and ISO-16750 document transient waveform profiles and can help automotive R&D engineers with power system transient testing, but those waveforms are difficult to create and therefore require expensive, specialized equipment. A new category of instrument has emerged — the DC power analyzer — which now offers automotive R&D engineers a flexible, cost-effective alternative. It allows the engineer to test the electrical components being used in a vehicle by simulating various power conditions. This ensures that the components will continue to work properly, regardless of the different power conditions from the vehicle's charging system such as the abrupt loading of the power system during starter crank, which causes voltage dips powering the electrical components.


Simulating the vehicle charging system is a crucial task for any automotive R&D engineer, but the process can be challenging. Consider the example of a voltage dip waveform (Figure 1). To ensure proper electrical component operation, the engineer must thoroughly test the components through a variety of charging scenarios similar to that of the voltage dip shown in Figure 1. These scenarios replicate cranking profiles, power disturbances or decay reflected on the vehicle's power system.

Simulating the various power waveforms is traditionally done using test systems that are custom in nature. These solutions are generally created by the engineers themselves and involve the use of specialized equipment, such as a power supply with fast response, a high-speed function generator, an industrial computer interface, and application software that has been specifically developed for recreating the necessary power waveforms. Often times, this specialized equipment must be ordered from outside vendors. And, because the test systems are custom-made for specific tests, they do not allow for much flexibility in terms of changing test settings. Furthermore, to actually test the electrical components, the engineer is forced to go to a local test station since the number of customized systems is low due to the high cost.

While these custom test systems are expensive, inflexible and require a lot of time and energy, not simulating the power waveforms is an option deemed too risky, often leading to problems that may not be found until vehicle production. Prime examples of the types of problems that can occur include a radio that goes mute after cranking the starter motor, or vehicle-integrated cell phones that temporarily cease to function. Today's automakers can hardly afford the risk and expense associated with finding these types of problems during production.


Thanks to a new category of instrument that provides the flexibility and functionality needed to recreate some of the automotive power waveforms (e.g., slow decreasing/increasing of operating voltage, quick charges, cranking profiles and voltage dips) to power the electrical components in a vehicle, R&D engineers now can test their ECUs with many of the troublesome transients at the comfort of their lab bench. This saves both time and expense by giving the engineer the opportunity to fix ECU problems before traveling to the remote and expensive qualification lab. The DC power analyzer integrates multiple instrument functions such as an arbitrary waveform generator, multiple DC power supplies, digital multimeter (DMM), oscilloscope, and data logger into a single box. It is capable of producing several different voltage waveforms and features a configurable slew rate along with an intuitive front panel. With these capabilities, the DC power analyzer provides a cost-effective, easy, and highly productive way of sourcing, measuring and analyzing DC voltage and current in electrical components. This is accomplished in minutes — not hours — without having to write a single line of code.

To better understand how a DC power analyzer can be used to quickly and easily simulate transients in vehicle charging systems, consider the following example that uses the N6705A DC power analyzer with its programmable slew rates — as fast as 5 V in 160 µs, depending on the module (Figure 2). The solution's built-in arbitrary waveform controls allow the engineer to create nine different waveforms: sine, step, pulse, ramp, trapezoid, staircase, exponential, user-defined voltage and user-defined current waveforms. The waveforms are all configurable from the instruments front panel, thereby eliminating the need for the engineer to write any code.

To begin, the signal from Figure 1 is replicated using the N6705A DC power analyzer by creating a four-step user-defined voltage waveform (Figure 3a). The voltage waveform is described via the following parameters:

  • begins at 14 V;
  • drops to 9 V for 10 seconds;
  • dips down to 4.5 V for a brief 100 milliseconds;
  • rises to 9 V for 1 second; and
  • finally, it returns to 14 V after the dip.

Once the waveform is created, it can be viewed in scope view (Figure 3b). Notice that in this example, the DC power analyzer is able to measure and display both voltage and current data at the device under test (DUT) in an oscilloscope-like display. It also allows users to save user-defined waveform setups and scope data either to an internal memory or external USB memory device.


Use of the DC power analyzer to simulate transients in vehicle charging systems can provide significant benefits to the automotive R&D engineer. To begin with, because the solution boasts functionality similar to that of multiple discrete solutions, it offers a much quicker time to measurements at a lower cost. The time consuming, cumbersome and complex process of setting up and programming these multiple discrete solutions (e.g., current probes and shunts) is completely eliminated. In fact, the DC power analyzer's design makes it ideal for use in design validation, where ease of setup and ease of use are paramount.

Another key benefit that results from eliminating the need for multiple instruments, concerns developing and debugging the programs that control those instruments. Traditionally, when executing complex tasks requiring the simultaneous connection to and physical interaction with multiple test instruments, the risk of error increases. R&D engineers may choose to automate tests that are too complex to do manually. But while automating tasks reduces human error, writing and debugging programs adds more work to already overloaded R&D engineers. The DC power analyzer eliminates the need to develop and debug programs altogether. All the functions and measurements are available at the front panel and there is no longer a need for a PC, drivers and software. As a result, the R&D engineer can realize a significant reduction in the effort associated with setup.

As an added benefit, the DC power analyzer allows the user to playback captured waveforms by importing the data from a “.CVS” file into a user-defined waveform — a feature crucial to ensuring accurate testing for power system transients. Ideally, testing of an ECU would occur in the vehicle itself, under all operating conditions. Since this is not practical, the next best thing is to capture or record the voltage transients as they occur in the vehicle and then play them back later in the development lab to test the ECU. To capture the transients, the engineer simply connects an oscilloscope to the power system where the ECU will be located and then exercises conditions known for generating transients, such as engine cranking, compressor activation and cold temperature operation. Note that the N6705A scope referenced in the above example cannot be used to capture this waveform because it can only measure the power that it sources (e.g., the power that comes out of it). Any resulting power system transients are captured as shown in Figure 4 and the information is then downloaded to the DC power analyzer for replication using the built-in arbitrary waveform capability.


Simulating vehicle charging system power waveforms for R&D testing of electrical components is a critical, and yet costly and difficult task. Use of a new category of measurement instrument — the DC power analyzer — can greatly simplify this task by providing functionality similar to that of multiple instruments in a convenient benchtop solution. Along with arbitrary waveform control, slew rate control and flexibility, this capability provides today's automotive R&D engineers with a quick, efficient and cost-effective means of gaining insight into potential problems in vehicle charging systems.


Al Lesko is an applications engineer with Agilent Technologies' System Products Division. Lesko began his career at Hewlett-Packard/Agilent in 1980, where he worked as a manufacturing engineer on various instrumentation products. In 1989, Lesko joined the Ford Motor Company to work on anti-lock brake systems as an R&D design engineer. In 1993, he returned to H-P/Agilent to work on various automotive-related systems. He was the lead hardware architect on the TS-5400 SII VXI-based automotive test system and in 2006 became an applications engineer for Agilent Technologies' System Products Division.

Sponsored Recommendations


To join the conversation, and become an exclusive member of Electronic Design, create an account today!