Harmonics in rotating transformer exciting systems for turbine generators

Since the expansion of renewables in Germany, a fast start-up of turbine generators increases in importance to compensate load peaks and reactive power. Therefore, the machines need an excitation field at standstill. Conventional brushless excitation systems consist of two different synchronous machines, which are not able to provide currents to the rotating part of the generator without rotational speed. With tiny modifications the excitation system can be implemented with an induction machine without changing rotating components, such as the rectifier wheel. This paper deals with the analytic calculation and simulation of resulting harmonics and their optimization.