With inverters playing such an important role in hybrid and electric vehicle powertrain systems—converting the battery’s dc power into ac power for the electric motor, maintaining the correct charge, and adjusting regenerative braking power—ensuring their accurate performance prior to a vehicle entering production is a crucial part of the development process.
D&V Electronics Ltd. of Toronto, Canada, recently introduced the EPT-350 series of inverter/motor testers for the HEV-EV market. It designed and manufactured six testers for Delphi for use in the endurance testing of inverters for the next generation of hybrid and electric vehicles.
“Delphi has developed an inverter for a hybrid application, and the engineers finished their development on it and now they want to prove the durability,” said Tom Stilo, Engineering Manager, D&V Electronics. “Delphi’s customer installed a system in one of their vehicles and they drove it around the test loop and made some recordings during that drive. It was a 1-h drive around a very specific course they use for their testing. We took that recording and now we play it back through the tester over and over again for days and weeks and months. That’s used to verify the durability of the inverter.”
This test platform, to be on display at the SAE 2011 World Congress April 12-14 in Detroit, is believed to be the first built for the testing of inverters for a dual-mode hybrid vehicle, and according to Delphi, these testers will provide the longest and most severe drive schedules currently used in the industry.
The design incorporates dual back-to-back motors with an auxiliary motor concept, allowing the stations to function independently of one another, with one motor in motoring mode and the other in regenerative mode. The system was also mechanically designed to allow different motor/generator sizes to be interchanged in the system.
“While you’re driving, the inverter will control what each motor is doing,” Stilo said. “There are times when one is motoring, one is generating, or both are motoring, and all that is controlled by the inverter as the vehicle is moving. We just take the recording and play it back exactly the way it is in the vehicle.”
“Then," said Gary Tse, Sales Engineer, D&V Electronics, "we measure the requirements of what happens with the motors, with the inverter, the drive, and it shows out in software, spreadsheets—whatever data the customer would like to view it in.”
With the EPT-350, Delphi is capable of running dual 65-kW motors and a single 3-kW oil pump. The tester is designed to electrically load an HEV inverter/converter with dual three-phase motor output control and provide regenerative braking back into the product, as is typical in a HEV.
The tester features a unique oil and water/glycol cooling system, supplying oil for the motors under test and water/glycol for the dynamometer motors.
“We can actually supply custom cooling systems for the application,” Stilo said. “In this case, the inverter required a water/glycol mixture and the motors required automatic transmission fluid. We have a system that will control the temperature of the fluid to keep each of those devices cool.”
The system also features a built-in battery simulator with power recuperation.
“When we run the test, we’re not just emulating the mechanical power on the motors, but all the electrical as well,” Stilo said. “With the dc voltage that goes into the inverter, we reproduce the voltage that the battery would be providing. It’s a battery simulator, so when it goes into regen it’ll absorb the energy just the way a battery would.”
The six testers were built under a tight production schedule—two months from start of assembly to shipment. At time of publication, the testers were undergoing final commissioning at Delphi’s facility in Kokomo, IN.