Electric Vehicle Power Electronics Push Test Equipment Performance Limits

Power Electronics in New Vehicle Systems

Automotive electronics are changing in dramatic ways. While it is true that “traditional” internal combustion engine vehicles still dominate the market, the automotive world is racing into a disruptive future. The market demand for reduction in the use of fossil fuels is driving the inexorable move toward EVs. The complexity of testing the whole spectrum of electronic devices and systems within this new breed of vehicles is placing higher demands on test equipment used in the design and manufacturing. Where once this technology area was centered on electronic ignition systems, navigation systems, adaptive cruise control systems, lighting and infotainment, the rapid emergence of electric vehicles (EVs) and hybrids (HEVs) is now concerned with higher power, high-energy power conversion systems and drive trains. It is not only the battery and drive train electronics, but also the power conversion systems required to interface these systems with myriad low-voltage systems. These demands are driving innovation in test equipment manufacturers to produce programmable power sources and programmable electronic loads that can accommodate the needs for higher power, faster response, the capability of simulating complex operating scenarios and doing all of this with higher efficiency.  

Vehicle testing standards

The automotive industry on a global basis has perhaps the widest array of testing standards for electronic components and systems – and rightfully so. As with medical devices, reliable operation of automotive electronic systems has life safety implications. These standards spell out the test conditions that must be met to comply. It is beyond the scope of this article to explore this topic in detail. Suffice it to say that programmable power sources and loads must be adaptable to an extraordinary array of standards.

To illustrate the point, the well-publicized LV123, utilized by German auto manufacturers, will be briefly described. LV123 is an organized listing of test requirements for all German automotive OEMs. The systematic approach and transparent definition of test parameters enable the exchanging of qualification results among participants, and comparability of product qualifications between OEMs.

LV123 covers high-voltage (HV) systems in a methodical manner. When HV components are operational, and there is no power demand, its level B1. When the HV components are fully operational, and operate as intended, it's at B2. When it gets to B3, the HV components are still operational, shall not assume any undefined states and shall not cause any malfunctions in other HV components. (Figure 1)

Automotive Testing Utilizing Arbitrary Waveforms

Many of the tests prescribed in LV123 (and, for that matter, in every other comparable standard) require extensive use of arbitrary waveforms to replicate the conditions. Arbitrary waveform generation has long been a standard feature of programmable power sources and programmable electronic loads. The latest automotive specifications are extending performance requirements with respect to voltage and current levels and voltage dynamics. Figure 2 presents an example LV123 test profile where the input voltage to the device under test is varied from LV123 Condition B1 (no power demand – input voltage nominal) to Condition B2 (up to maximum operating voltage – intended operation).  This test sequence is repeated 3 times.  The image on the left is the prescribed sequence, the image on the right is its programmed counterpart – in this case using the Elektro-Automatik PSB 10000 Programmable Power Source / Load.

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Figure 1a & Figure 1b. Typical LV123 test profile and arbitrary waveform generator simulation

Note that this waveform only prescribes the voltage points in the test profile and slew rates between the various levels. But this test also requires the DUT to be without load during Condition B1 and then at normal load during the multiple Condition B2 segments. Depending on the LV123 “HV” category - as defined in Table 1 (between 220VDC for HV_1 to 800 VDC for HV_3) and the nominal power level of the device under test, current required could be 10s or even 100s of Amperes.

Plug-in hybrid (PHEV) and battery electric (BEV) vehicles, for example, have battery voltage standardized at approx. 450 V with a trend towards higher voltages, as this supports faster charging times and enables lighter cabling within the vehicle. Peak charging currents could reach 600A!

High Performance Bidirectional Supplies Provide the Best Solution

Utilization of the latest generation of bidirectional, regenerative programmable power sources and loads provides a highly efficient means for conducting these tests. An example of such a bidirectional power solution is the Elektro-Automatik PSB 10000, a 4U 30 KW power supply and load in one (Figure 3). It has an AC input range from 360 V to 528 V, for operation on 400 V and 480 V grids.

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Figure 2: The PSB10000 is an example of the new generation of programmable bidirectional, regenerative power sources

Electronic loads typically dissipate the power transferred to them as heat, but it can add up, especially in test applications where multiple systems are tested in parallel.  Because of the need to remove the heat from the electronic loads, they are often large, with significant forced-air or water circulation to cool them. This normally leads to an increase in test system cost, size, and HVAC requirements, to control and remove the heat from the facility.

Regenerative programmable source / sink solutions, utilizing an integrated DC-AC inverter stage (Figure 4), can seamlessly move from sourcing current to sinking current without external circuits, or synchronized programming of a separate power supply and electronic load. Such integration enables a testing regimen that is not only accurate and effective, but also energy-efficient and cost-effective.

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Figure 3: An integrated DC/AC inverter stage is capable of returning up to 95% of the load power to the source

Conclusion

Design and production testing of electric vehicle power electronics is adding new performance requirements and enabling the development of innovative test systems. Advanced arbitrary waveform generation capabilities are essential in meeting the newest automotive electronics testing requirements. While arbitrary waveform generation has been a common feature, new testing requirements demand higher slew rate capabilities at wider voltage ranges than most other applications.

It’s ironic that utilizing traditional programmable load technology to test these “green” innovations can expend so much energy. Testing of many EV / HEV systems – battery charging, electric motor control – require extraordinary levels of voltage and current. Innovative regenerative systems effectively resolve this and become part of the total green solution.

EA Elektro-Automatik, Inc.