Electric Vehicles started to become more and more accepted. However they must get much more energy efficient. Therefore a large part of this kind of developments could be realized in Formula E.
In recent years, EVs (Electric Vehicles) and HEVs (Hybrid Electric Vehicles) started to become more and more accepted as the soon-to-be replacement for traditional gasoline powered vehicles. However, electric vehicles must get much more energy efficient to achieve the same range as traditional cars and thus people’s acceptance. A lot needs to be invested in the development of the required electronic components.
For gasoline powered cars, a large part of this kind of developments was realized in Formula 1. Technology, regarding for example fuel efficiency, developed for and tested in race cars, was later used in normal street cars. The still rather new Formula E is expected to have the same effect on e-mobility.
ROHM and Venturi for Formula E
In Formula E, all teams use the same car. Own developments are only allowed for certain parts of the drive system. But these small differences have a lot of potential for trendsetting technologies. ROHM Semiconductor is working on some of these technologies and became official technology partner of the Venturi Formula E team.
Just recently, the team announced two personal details for the coming fifth season. First, the former DTM race car driver and Formula 1 test driver Susie Wolff joint Venturi as team principal. And second, the former Formula 1 driver and vice world champion Felipe Massa will drive for Venturi. He will visit the ROHM booth (C3.511/512) at electronica for autographs and pictures on 13th of November (details will be announced in the run up to electronica).
Improved inverter with SiC
The personal changes are one part of Venturi’s strategy for the fifth season. Another part is the technology provided by ROHM. The company uses Silicon Carbide (SiC) to improve the performance of the main inverter, one of the core parts of a Formula E race car or many other electric vehicles. Figure 1 shows two traction inverters. The left hand inverter is rated at 200kW and utilizes power modules with Si IGBTs and Si Fast Recovery Diodes (FRDs). This inverter is working in the field since 2013. The right hand inverter was newly developed utilizing full SiC modules and is rated for 220kW.
Table 1 shows a specification comparison of both inverters. The new inverter utilizes a variable switching frequency which can be varied depending on the motor operating point from 16kHz to 24kHz. Even in the lower rotor shaft speed range, the inverter utilizes 16kHz switching frequency to avoid the risk of resonance between the DC link capacitor and input cables. While the available maximum output power is 20kW higher the SiC MOSFET based inverter has lower volume and less weight than the Si IGBT based one. The weight is reduced by ca. 6kg and the volume is shrunk by 30% as well. These factors lead to a high power density of 22kW/L, which is 57% higher than the conventional IGBT based solution.
Power for the fifth season
Of course, weight is always an issue in a race car. Reduced size means more flexibility in the optimal positioning of the different devices. But the most important advantage of the new inverter is the higher efficiency. The reduced inverter losses equate to more power at the wheels of the car. In addition, lower losses lead to reduced chip temperature with the same cooling system.
These improvements contribute to increasing the driving distance, which will be needed, because in the fifth season of Formula E every driver will only have one car instead of two cars as before. To make this possible the battery capacity will go up to 54kWh. Apart from that, it’s all about efficiency as a matter of course. Better efficiency leads to less losses and can be used to bring down the dimensions of the cooling parts. The testing of the new car has already begun and ROHM hopes that its SiC power modules will contribute to Venturi’s success.
Table 1. Comparison of inverter parameters.
|Inverter||Si-IGBT based||SiC-MOSFET based|
|Output Power||200 kW||220 kW|
|Inverter Efficiency (Maximum Efficiency)||98,0 %||99,1 %|
|Inverter Efficiency (Maximum Power Operation)||96,9 %||98,2 %|
|Maximum Switching Frequency||16 kHz||24 kHz|
|Weight||15,0 kg||9,1 kg|
|Volume||14,3 L||10,0 L|
|Power Density||14 kW/L||22 kW/L|