High-voltage battery simulator and test systems critical for EV and HEV development

Systems essential for conducting research and development, performance and durability testingon electrical vehicles and hybrid/electric vehicles.

With durability testing, engineers are simulating what the device will actually see in the real world (or typically much worse). The system doesn’t have to be as fast, or include extra voltage/current/dynamic range, because at that point the performance is pretty well known. Durability testing systems have to be extremely stable and robust, since engineers will be running durability tests 24/7, for days, weeks, or months without interruption. The system can be set up to run unattended, and even send a text or call a beeper if there are any problems.

Better understanding of real world conditions

The battery’s dynamic response to real world conditions is often very different than its response under simple laboratory cycling. In the past, batteries were subject to step testing, in which they were charged, discharged, and then cycled at two or three different loads. Nowadays, this simple battery cycling just doesn’t tell the complete story – you also need to know the battery’s mileage or range, and you need to know how it will operate in the vehicle in a particular environment. Modern testing systems now have to be able to test batteries by simulating actual road load conditions.

The vehicle environment is continuously changing, and therefore the battery needs to be tested for a variety of vehicle running conditions, for example driving up a hill, down a hill, starting, and stopping etc. The trick here is to create a good cycle that accurately represents what the battery would experience in the vehicle during real world conditions.

This can be done in two different ways. The first is to use a mathematic simulation of charge and discharge dynamics, and performing drive cycles developed by EPA, the European Union, or customer-specific requests. The second method is to instrument the vehicle and drive it over an actual road course, while monitoring key required parameters, such as throttle position, vehicle speed, voltage, and current. The resulting profile is then loaded into the test system and played back, assuring that the battery sees exactly what it would have if it were in a vehicle. One additional benefit is that the test can be conducted on the battery without the need for any of the vehicle driveline components or a dynamometer system.

Taking it to the next level

The high voltage battery test system is a very powerful and efficient tool, but it really comes into its own when coupled with a high performance AC motoring dynamometer. The resulting test system is then capable of testing the entire vehicle drivetrain to a high degree of accuracy and in a very power efficient manner.

With a standard system that requires 100 kilowatts of power, about 110-120 kW would have to be pulled from the AC mains because of energy losses to heat. In addition, you would also need approximately 100 kW of electricity to cool the water used for the dynamometer. This would cost approximately two times as much as the operating power of the system. With this new system most of the absorbed power is recaptured and reused. Total cost to operate at the same 100 kW level may draw only 10-15 kW to run the entire system, including cooling. In addition, control is easier, as switching from driving to loading happens automatically and seamlessly. The result is a significant reduction in the total operating cost by using a much more energy efficient “Green Technology” to perform full system testing.

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