A consortium led by Prodrive has successfully run a silicon carbide-based multiport DC-DC converter in an electric car.
Prodrive said the converter controls power flow between multiple energy sources and has been able to achieve a class leading efficiency of 98.7 percent, while increasing power density and reducing the size and weight of the converter when compared to silicon-based systems.
The DC-DC converter acts as a hub that transfers energy between key components of the vehicle’s high voltage electrical system, explained Prodrive. It has four ports: two connect to the traction motor and high voltage battery; a third connects to a secondary energy source, which in this test car is a super capacitor bank; and the fourth powers the vehicle’s 12V systems. The converter is able to match the voltages of these components and transfer energy between them in response to CAN commands from an external supervisory controller.
The test vehicle on which Prodrive and its partners installed this converter is a Tata Vista EV demonstrator vehicle, developed by the Tata Motors European Technical Centre in Warwick. Prodrive said this vehicle has a 220 volts battery and 37 kilowatt electric motor. The vehicle also has two 200 kilojoule super capacitor banks, which operate at 75-150 volts.
“In normal driving, the converter boosts the battery voltage to around 400 volts to optimize motor performance and can supplement the battery supply with additional energy from the super-cap banks when the driving situation demands it,” said Mark Willows, Prodrive electrical systems and control specialist. “During re-generation, the converter transfers energy from the motor to the battery or super-capacitor banks as requested by the supervisory controller. Energy can also be transferred directly between the battery and super capacitor ports. The system can be configured to support other energy sources, such as fuel cells or could supply multiple traction motors.”
A key aspect of the converter is the use of silicon carbide devices, explained the consortium. These operate at a much higher frequency than equivalent silicon components – at 75 kHz in the test vehicles – with a significant reduction in switching losses. This has resulted in a significant reduction in the size of the magnetic components and has enabled the converter to achieve a class leading efficiency of 98.7 percent, a gravimetric power density of 10.5 kilowatt per kilogram and a volumetric power density of 20 kilowatt per liter.
Prodrive stated the use of silicon carbide power modules could also allow much higher temperature operation than conventional silicon modules. This provides the potential to integrate the power electronics and IC engine cooling systems in hybrid applications. The consortium is now working on a follow up project which increases the converter operating voltage to 750 volts, further increases power density and demonstrates operation at increased coolant temperatures.
“For this project we have developed a rolling test bed based on a light commercial vehicle chassis, which has a 75 kilowatt traction motor. The energy storage consists of a 320 volts Li-ion battery and two super capacitor banks, all of which were built by Prodrive specifically for this project,” said Willows.
The consortium of British companies is backed by the Technology Strategy Board and led by Prodrive, working in conjunction with The University of Manchester, Tata Motors European Technical Centre, IST Power Products, Raytheon Systems and SCISYS.