A good idea is never lost, as Thomas Edison said. At the turn of the 20th century, nearly 30 percent of all cars manufactured in the US were electric-powered, but by the 1920s they had effectively disappeared, thanks to cheap gas and mass production of conventional cars. But fast-forward 100 years and electric cars are back with a vengeance, in response to rising fuel prices and Government-mandated emissions controls. Article by Joel Conover, Senior Director of Industry Solutions & Digital Marketing at Keysight Technologies.
The number of pure electric and plug-in hybrid cars on the world’s roads passed the three-million mark in 2017, and will accelerate to over five million by the end of 2018, according to analyst EV-Volumes. This rapid growth in production volumes is being matched by equally rapid advances in powertrains, power electronics and battery technologies.
These advances also highlight the increasingly critical role played by a previously unsung vehicle component:the DC:DC converter. Irrespective of whether a car is a pure EV or a hybrid, DC/DC voltage conversion is at the heart of its power electronics systems. It manages the energy exchange between the vehicle’s high-voltage (HV) bus which serves the main HV battery, electric traction which drives the motors and generators, and the traditional 12V power bus, from which most of the car’s electrical systems (in-car entertainment, navigation, heating, lights and more) are powered.
The converter is fundamental to the overall efficiency and performance of electric vehicle (EV) and hybrid vehicles, for several reasons:
- The flow of power between the HV and 12V buses is bi-directional and can change in milliseconds according to the demands of the vehicle’s systems and driver input (for example, when transitioning from acceleration to regeneration), so large loads have to be converted seamlessly and safely for smooth, predictable vehicle operation.
- Because of the high electrical loads they carry, most DC:DC converters are water-cooled, which adds weight and costs when installed in the vehicle. There is strong pressure to simplify this, to minimise cooling requirements, cut weight, and improve efficiency.
- The converter must be robust enough to continue to operate efficiently across a wide range of environmental and driving conditions.
Given the pace of development of vehicles, and the constant pressure to keep costs down across the test and development lifecycle for converters, efficient simulation, design, validation, and manufacturing test of the converters is essential. But this, in turn, presents its own challenges.
Converter Testing Challenges
The design and test obstacles result from many factors:
- Bi-directional test: Testing bi-directional power flow demands equipment that can both source and sink power to the converter. But conventional test methods using external circuits and multiple instruments typically doesn’t allow for smooth signal transitions between sourcing and sinking power, and give inaccurate simulations of operating conditions. It also leads to excess heat build-up in the test environment.
- New power semiconductor technology: Designers are starting to use Wide Bandgap (WBG) devices. While these offer better power efficiency and the ability to handle higher voltages and temperatures than conventional silicon devices, their use complicates the simulation and design of DC:DC converters. Users need to evaluate each device to determine if the WBG devices will work in their designs.
- Reliability and safety concerns: Using new semiconductors means extra validation and reliability testing is needed to ensure converters will last in harsh operating conditions. Also, given the power levels used with converters, testers need to be careful when testing them. This requires special safety mechanisms in manufacturing, including redundant systems that do not expose the tester to high voltages if a failure occurs.
- Maximising efficiency: Because of the various operational and environmental influences on efficiency, it’s difficult for testers to simulate all of these to evaluate the real-world, whole system operation of the converter. Also, measuring small percentage changes in efficiency demands instruments with high dynamic range.
Converting Challenges Into Solutions
To address these design and test issues, Keysight has developed and introduced new, innovative approaches that help manufacturers accelerate their programmes. For example, high-frequency enabled simulators can accurately simulate the behaviour of new WBG semiconductors, helping to improve the efficiency of DC:DC converter designs.
New, fully integrated source/sink solutions* enable more accurate simulation and testing of DC:DC converters’ transitions in power flow direction during acceleration and regeneration. These test solutions also feature the ability to return clean power to the test lab’s AC mains, reducing regenerative heat and dramatically cutting the need for costly HVAC equipment in the test system environment.
* Solutions include the EV1003A Power Converter Test Solution for HEV/EV and HEMS. This solution is the only commercial-off-the-shelf (COTS) regenerative power system with highly integrated safety features that protect your devices under test and your people. The regenerative capabilities enable the energy consumed to be put back onto the grid cleanly, saving costs from energy consumption and cooling, while not interfering with the grid.
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