Modular power electronics integration for improved performance in C-GEN generation systems

Abstract

‘C-GEN’ machines derive the name from the rotor, which consists of steel ‘C’ core modules, which are built around a highly modular design and specifically designed for renewable energy generation. The C-GEN machine can be easily scaled in power, dismantled in parts for maintenance, and even carry on operation with defective modules. Such high degree of modularity on the machine side has yet to be matched with modular power electronics conversion and control on the electrical side. In this thesis, the modular power electronics topology is integrated in the C-GEN machine, which aims to improve the performance of the generation system in a wide range of rotational speed, especially at partial load operation. According to the mechanical structure and electrical specification of a 16kW C-GEN machine, simulation models which include the C-GEN machine model and modular power electronics model are built. On the basis of the C-GEN machine model, four modular power electronics options are proposed, and these options are mainly assessed in terms of power losses in rectifiers and fault tolerance. A novel circuit named ‘electric gear’ is proposed to adjust the modulation index of the rectifiers in the low speed region. The electric gear is able to transmit the rectifiers’ connection between parallel and series quickly, thus the DC voltage seen by the rectifier is changed, and the modulation index of the rectifier is therefore varied. Utilising the outcomes from the studies above, the modular power electronics technology is applied in a practical wave generation project. The simulation results of this project indicate that this modular power electronics topology can maintain the modulation index larger than 0.5 as long as the generator runs more than 15% of its rated speed and reduce the power loss in rectifiers by up to 70%. As a benefit brought by the improvement of the modulation index, the power quality is enhanced as well: the current THD is less than 5% in a wide rotational speed range of the generator. Finally, the functionality and operation of the modular power electronics technology and electric gear are demonstrated in the realistic system via the hardware experiment.