Influence of rectifier and DC/DC converter on a hybrid excitation synchronous generator robust control for wind applications

The purpose of this paper is to study the influence of harmonics generated by a rectifier and a DC/DC converter on a robust and low-cost structure generator connected to an isolated load for wind applications. The machine used to convert mechanical power into electric power is a hybrid excitation synchronous generator (HESG). In this machine, the excitation flux is created by both permanent magnets and excitation coils, so the output voltage can be controlled by the DC excitation field. For isolated loads, it is then possible to use very reliable wind generator architecture, composed only by a HESG, a rectifier and a DC/DC converter to control the excitation flux. However, HESM are non-linear machines so, regarding their control, conventional controllers are not always sufficient to ensure a good stability and high performance. An H_∞ controller is then used and designed assuming first harmonic hypothesis in order to control the wind generator in all the regions of the shaft output power versus wind speed curve. The effect of harmonics on the system robustness is then analyzed.