Testing Gear Emerges for EV Charging Applications

Article By : Maurizio Di Paolo Emilio

Electric vehicle test systems are certifying the reliability of complex EV powertrains along with related charging interfaces and supply gear.

Power-management and battery technologies are advancing via more efficient and flexible designs aimed at the growing electric-vehicle sector. Related test and measurement systems must therefore meet more stringent technical requirements.

With that in mind, Keysight Technologies recently launched its SL1200A Series Scienlab Regenerative 3-Phase AC Emulator for EV and supply equipment (EVSE) charging and grid applications. The system is composed of hardware, software, and support services.

Keysight executives stressed the importance of EV test systems for certifying the reliability of increasingly complex EV powertrains. Among the focuses are charging interfaces and EV supply equipment along with grid-edge power converters.

The portable and high-power versions of the SL1200A Series are aimed at users’ growing EV test and measurement requirements. The aim is simulating real-world charging scenarios along with the ability to meet global EV charging standards.

Keysight executives highlighted the importance of test systems capable of certifying the reliability of EV powertrains.

EV charging is expected to generate significant demand on power grids. At the same time, energy storage opportunities are emerging through vehicle-to-grid (V2G) power applications. Renewable energy sources will propel that transition, leading to increased grid complexity. That creates testing challenges when rolling out charging applications.

Performance, design metrics

Key performance metrics in EV design focus on battery and propulsion systems. Design parameters include power level, conversion efficiency, and operating temperature in the vehicle powertrain, along with thermal energy dissipation capacity and system packaging.

EV systems must be adapted for high-voltage measurements(1,000 V and higher) to ensure safe, reliable operation. Real-world driving conditions present the largest challenges for system testers. Harsh environments range from –30°C to 60°C.

“At the component level, wide-bandgap semiconductors are used in the different power converters inside the EV, as well as in EVSE” and grid-tied inverters, said Kevin Cavell of Keysight’s Automotive and Energy Solutions business unit.

“Double-pulse test equipment is needed here. WBG [wide-bandgap] modeling and circuit simulation is also a valuable tool.”

Battery testing starts with cell grading. “High-volume manufacturing is needed to supply the large quantities of cells for EVs,” said Julian Tomczyk, a Keysight marketing specialist. “This manufacturing equipment is needed to take the cells through their initial charge/discharge [or battery formation] and then grade the cells based on quality. While most grading can be done in a few minutes, measuring self-discharge during cell aging is a lengthy test that requires many days, creating large work-in-process inventories stored during aging.”

Keysight says its tool cuts inventory costs by reducing self-discharge measurement time from days to hours, thereby reducing aging while speeding cell grading.

Once cells are fabricated, aged, and graded, they are assembled to create a battery. Depending on voltage and power requirements, an individual battery could include thousands of cells. “Battery management systems are put in place to monitor the health of each cell in the battery,” Tomczyk said. “Test and measurement equipment is needed at this phase as well to test the [management system] and the entire battery pack.”

A variable-frequency drive (VFD) converts DC power from the battery into variable-frequency AC used to drive the motors. Large power supplies capable of hundreds of kilowatts of power are needed to emulate the DC side; a machine emulator is necessary to reproduce the motor to surround the device under test. The instruments can run the VFD through many scenarios while measuring input and output power to calculate power-conversion efficiency.

Wide-bandgap devices

Using WBG semiconductors yields potential efficiencies of more than 95%, greatly extending range, Keysight claims.

Power converters are a key component for leveraging renewable energy for transportation and industrial applications.

To facilitate needed advances in power converter design, new WBG semiconductor technologies based on silicon carbide and gallium nitride are options.

Compared with silicon and gallium arsenide semiconductors, the wider bandgap of SiC and GaN devices translates into a greater breakdown voltage and the possibility of operating at high temperatures while reducing radiation susceptibility without losing electrical characteristics. As temperatures increase, thermal energy of the electrons in the valence band also increases until they reach the necessary energy (at a certain temperature) to jump to the conduction band. In the case of silicon, this temperature is about 150°C. Those values are much higher for WBG devices.

WBG semiconductors provide performance increases as high as 100× that of conventional designs, along with higher voltage and thermal operation. Those attributes translate into improved efficiency and reduced size and cost.

“However, the resulting high-performance power converters are proving difficult to design due to many new challenges when characterizing WBG semiconductors,” said Cavell.

With commercial systems in short supply, homegrown test systems are sometimes used to characterize WBG semiconductors. Tomczyk noted, however, that “it is difficult to produce repeatable and reliable measurement results with one-off, homegrown testers,” and “unreliable results create additional obstacles for power-converter designers when correlating their measurements with the semiconductor’s datasheets.

SiC device cross-section
SiC device cross-section (Source: System Plus Consulting)

Keysight programmed its PD1500A dynamic power device analyzer as a platform for reliable characterization of WBG semiconductors. The company said its analyzer was developed in collaboration with chip manufacturers along with EV and power-management designers.

Electrification of powertrains changes testing requirements by requiring more than just combustion process analysis.

Electric and hybrid vehicles may have multiple motors, inverters, and battery packs. Hence, all energy sources and loads must be considered.

The challenges facing EV manufacturers and their suppliers vary by specialty, whether it be powertrains, autonomous driving, or in-vehicle networks.

“An engineer focused on cell and battery test would address the battery, since it is the fuel required to drive the powertrain,” said Cavell. “An engineer focused on power conversion would address the power converter [and] variable-frequency drive. Each is critical to the proper, efficient, long-range operation of the EV. And each presents its own unique test challenges.”

Charging specs, evolving grid

Meanwhile, EV charging standards continue to proliferate. Keysight notes several specs such as the American and European Combined Charging Standard, the Chinese GB/T spec, the Japanese CHAdeMO framework, and, soon, the new Asian standard dubbed ChaoJi.

The regional standards cover EV-EVSE communications, physical plug design, power flow, and test scenarios. “Each region has many conformance standards that are dependent on the type of charging: AC, DC, high-power DC,” said Cavell.

EV and equipment manufacturers targeting the global market need to test regional standards in order to address diverse requirements. Hence, Keysight promotes an automated test framework addressing different charging standards, including power flow and communications.

EV adoption is also reshaping grid infrastructure, said Tomczyk. “Within the automotive industry, the electrification of vehicles is expected to create significant demand on the grid for charging while also expanding the opportunity for energy storage through vehicle-to-grid power applications,” he said. “As the energy mix intensifies, so does the challenge of managing the way we produce, distribute, and consume electricity.”

SL1200A Series Scienlab Regenerative 3 Phase AC Emulator
SL1200A Series Scienlab Regenerative 3 Phase AC Emulator (Source: Keysight Technologies)

Smart inverters with grid support have emerged as a key enabler for overcoming such challenges. Hence, inverter manufacturers are required to adhere to a specific set of grid compliance and interconnection specs requiring extensive testing.

For example, grid emulation equipment testing is mandatory. Distributed energy resources are moving to higher output voltages to reduce losses, moving to as high as 1,000 VAC.

“The goal of higher voltages combined with the requirement to provide grid support functions such as high-voltage ride-through creates the need to test to even higher than the 1,000-VAC limit,” Tomczyk said.

According to Keysight, “To achieve the high voltages needed to test new inverter [and] control designs, inverter engineers often must either connect multiple power supplies in series or use an external transformer. This leads to costly, complex test setups with an inability to easily expand, along with reduced performance.”

The vendor’s automated testing approach can therefore be configured to regional charging standards and accommodates different physical plugs. Testers must select the appropriate test standard, and the automation software takes it from there.

With the rise of bidirectional power flows, including V2G and EVs themselves becoming energy-storage systems, standards organizations must specify required tests and testing configurations. Hence, V2G implementations “will add even more complexity, and there will be grid codes and interoperability standards that will need to be tested,” said Cavell.

Vehicle electrification and the transformation of the grid infrastructure is reshaping test and measurement requirements. Instruments must adapt to the presence of high-voltage signals and must withstand harsh environmental conditions. On the software side, the synchronous acquisition of electrical and mechanical data, along with the plethora of standards, requires a fundamental rethinking for optimizing EV test and measurement.

This article was originally published on EE Times.

Maurizio Di Paolo Emilio holds a Ph.D. in Physics and is a telecommunication engineer and journalist. He has worked on various international projects in the field of gravitational wave research. He collaborates with research institutions to design data acquisition and control systems for space applications. He is the author of several books published by Springer, as well as numerous scientific and technical publications on electronics design.

 

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