Electrically assisted turbo charger for fuel cell vehicles

Starting point 

The fuel cell is an interesting alternative to batteries as the energy supply for electric vehicles. The high energy density offers a considerable higher range, filling up is faster than recharging and it requires fewer resources.

Task definition 

Development of the control electronics for an electrically assisted turbo charger while taking the mechatronic overall system into consideration. Due to the limited space available and the mechanical limitations due to the speed the turbo charger must be very compact and light. Furthermore, the automotive use demands a robust and cost-optimised system.

A reduction in the turbo charger reaction time is essential for faster response times of the fuel cell vehicle while accelerating, because energy production can only begin when the turbo charger has built up the fuel cell air supply. Until now a battery has delivered the energy required to bridge the run up time.

Implementation 

First of all the ARADEX engineers built a prototype consisting of control cabinet, controller and industrial inverter. Using this system solutions were worked out for all eventualities on this system. 

Once the framework was determined the development of a modified end stage was begun. In order to keep the firmware development progress seamless from the prototype to the first test product, the ARADEX development engineers used the logic board of an industrial inverter.

Using the findings of the first test product a modified logic board was developed in the second stage of the project. This second test product already fulfilled the automobile requirements for component selection and temperature stability. A small series was produced with this sample and tested in various testing benches and vehicles for stability and durability.

Results

The system reached speeds of 90 000 to 120 000 rpm in the last stage of completion and peak powers of 20 kW (capacity rating 16 kW). In order to save costs the system control was without sensors. Leaving out the sensors also reduces the error rate. 

The high speeds (approx. 2 000 Hz electric) and the small size mean that the motors are very sensitive to harmonics. For this reason the ARADEX developers integrated an LC filter into the inverter. Effects such as phase distortion caused by the LC filter are compensated by the intelligent firmware in the inverter. 

System reaction times: from idle running speed (25 000 rpm) to end speed (90 000 rpm) in 1.1 s. The fast ramp-up time means that the battery required for bridging this time can be considerably smaller.