Capacitor-assisted excitation of permanent-magnet generators

Voltage regulation can restrict the useful capacity of permanent-magnet gen erators. Wind power applications are acutely affected because of the cubic variation of power with speed. The solution adopted for a new form of modul ar permanent-magnet wind turbine generator was to employ a capacitor connec ted across the generator AC terminals providing additional excitation due t o the capacitive current flowing in the stator coils. The resulting circuit displays unusual characteristics and its analysis must take account of non linearities introduced by rectifier loading, magnetic saturation and salien cy of the permanent-magnet excitation system. The paper describes the circu it configuration adopted and its analysis by methods ranging from a lineari sed first approximation to a complete numerical simulation. The theoretical studies are supported by experimental results. Part of the analysis is arr anged to assist the designer in the selection of capacitance.