The fundamental points of your developmental research
Because we have a very broad research area I will split the main research directions according to the application field:
Drive systems for electric and hybrid vehicles
For hybrid vehicles and especially electric vehicles the autonomy is an important parameter due to the rather slow battery charging. It is therefore important to consider the whole vehicle including its mass and aerodynamic performance, which together with the efficiency of the drive system components and the battery capacity influences the autonomy. A full vehicle model, which uses simplified analytical models for the different vehicle components and is able to apply different drive cycles to the vehicle, is used to investigate the autonomy and performance.
Furthermore, it is possible for automotive electrical drive systems to use distributed motors like in-wheel motors which free a lot of space in the vehicle interior and allow revolutionary interior configurations. For this kind of machine which has a disk like shape, permanent magnet motors in outer rotor and transversal flux configuration are investigated using finite element method.
Central drive synchronous motors with permanent magnet and electrical rotor excitation are also at the moment investigated with the goal of obtaining a higher power density.
Direct drive systems
If the mechanical gearbox is omitted, the force generated by the machine is transferred directly to the mechanical load of the motor or the actuator. This way the efficiency is increased and no maintenance is necessary for the gearbox. Some successfully closed projects in this area are: a spherical positioning system for an infrared telescope installed on an airplane, direct drive PM traction motor for high speed trains and linear actuators and motors used for tractive effort boosting for railway locomotives. An active project is concerning direct drive wind generators for power up to 5 MW. For this power range the removal of the gearbox is interesting because the gearbox is expensive and requires intensive maintenance. A low maintenance wind generator is especially for offshore wind turbines interesting, where the maintenance is difficult and expensive.
High-speed bearingless magnetically levitated motor (60000 rpm)
Electrical generators for renewable energies
Along with the direct drive wind generators mentioned earlier, the high speed wind generators represent at the moment the backbone of the wind energy production. Thus analytical and numerical models for the induction generators and doubly fed induction generators are investigated.
Of further interest are also small modular hydro generators in Straight-Flow technology. These modular generators can be used to harvest the energy potential of existing dams without important investment in infrastructure.
Hydro generators that use the tidal energy are another interesting research area. These generators can be installed in the shallow waters in the coast regions that have a significant tidal stream. The generator functions similar to wind generators, but is driven by the flowing water. In this case the construction needs to ensure safe functioning in a very hostile environment as the turbine is submerged in sea water.
High-speed motors can be used to reduce the mass and volume of the drive system. Interesting applications are compressors, and high-speed cutting. In this area we have experience in the bearing less motors, integrated levitated motors for mechatronic pump systems and digital levitation control systems with and without position sensors.
Influence of the inverter switching on electrical machines
The fast switching of the IGBT inverters causes dangerous high voltage peaks and damaging capacitive bearing currents. After rigorous measuring of the bearing currents for different motor sizes, the bearing currents mechanism is now theoretically investigated, using numerical and analytical investigation. Measurements are performed on different mitigation techniques and the influence that the chemical composition of the bearing lubricant has on the bearing currents is investigated.
The invertor switching also induces additional harmonics in the stator current spectrum and for this reason the hysteresis losses and eddy current losses increase. In order to investigate these additional losses, analytical models and time intensive numerical transient FEM calculation are developed.
High performance industry drive systems and special machines
For the modern high performance industry motors the highest torque density combined with an excellent efficiency is expected. For servomotors a low torque ripple combined with a high dynamic response is expected. In these research directions investigations are done in designing of high density PM motors with water cooling and tooth coil concentrated winding, in calculation of the additional losses in induction machines for more exact efficiency calculation, increase of the efficiency of the induction machines and control methods for highly saturated PM tooth coil synchronous motors which compensate the motor non-linearity.
Special machines like self-starting line operated synchronous motors, variable impedance induction motors optimized for high starting torque and good efficiency at rated speed are also investigated.