Analysis of Brushless Wound Rotor Synchronous Generator with Unity Power Factor Rectifier for Series Offshore DC Wind Power Collection

Abstract

Due to various advantages offshore wind farms are getting higher attention from industrial and research perspectives. The DC power collection topologies are preferred as they reduce both system and transmission cost in case of offshore power transmission. Offshore wind turbines are expected to be lighter, smaller and prone to lesser maintenance. Permanent magnet synchronous generator (PMSG), though most popular choice, they are getting more and more expensive due to the availability of raw earth permanent magnets (PM). Thus a wound rotor synchronous generator (WRSG), with brushless excitation is a probable alternative to PMSG. For front-end converters three-phase-diode bridge rectifiers are suitable for high power ratings but they are not controllable. It requires additional auxiliary circuitry or to be followed by a DC-DC converter, in order to be used for DC power collection. With these regards, this study is carried out for the scenario of series connected DC power collection of wind turbines with brushless excited WRSG. For the front-end converter, an auxiliary circuit based three phase diode bridge unity-power-factor rectifier is selected. The brushless excitation ensures the generator terminal voltage regulation. The rectifier controls DC link voltage, improves the power factor and reduces the generator output current total harmonic distortion (THD). The control of converter is done based on hysteresis current control. To verify its efficacy, the proposed system is simulated under various dynamic wind speed scenarios.