Another turbocharger development of recent years is that by Japanese engine maker Mitsubishi. The company’s hybrid MET83MAG turbocharger generator was given an initial reference in 2011 on the bulk carrier Shin Koho. The hybrid unit has been designed to meet the vessel’s entire at-sea electrical power needs by utilising the exhaust gas from the main engine not only for driving the turbocharger compressor but also for power generation. At 9,500rpm the power output of the hybrid unit is 754kW.
The system generates AC power which is converted to DC current using an insulated gate bipolar transistor and an inverter. The system can also be run in reverse using other sources of power making the generator serve as a motor that boosts the turbocharger when engine speed is low. Making use of the same technology but incorporating the variable turbine concept is the MET66MAGVTI developed in co-operation with Mitsui Zosen and Kobe Diesel. The turbocharger has gained references on a series of car carriers owned by NYK.
In 2017, Rolls-Royce acquired the exclusive rights of use for a new patented technology for electrically-assisted turbocharging from G+L innotec that is suited to engines over 450kW. The electrically-assisted charging system comprises an electric drive combined with a traditional turbocharger developed and manufactured by MTU. As a result, the turbocharger can be accelerated electrically and the charge pressure built up earlier. In operating conditions, in which the energy required for a faster charge pressure of the turbine would normally not be sufficient, it is also possible to build up with the aid of the electric drive.
The system is similar in principal to the Mitsubishi system but makes use of a permanent magnet installed upstream of the compressor wheel and electrical winding is integrated into the casing of the compressor. With this arrangement, the air drawn in by the compressor is not obstructed and at the same time the electrical components are cooled by the air. The special feature of this arrangement is the large gap between the magnet and winding. This so-called media gap motor requires specially designed power electronics. This ensures that there is no aerodynamic impact on the charger and that existing chargers can be adapted easily to enable them to make use of this technology.