A Converter with Flexible Multi-pulse Thyristor Rectifier as Front End for Wind Power Systems

A novel converter is proposed for wind turbines to free the converter's power range from insulated gate bipolar transistors(IGBTs).A flexible phase-controlled thyristor rectifier and a 3-level inverter are used as generator and grid interface separately.The rectifier is composed of two 3-phase thyristor rectifiers.The two parts can operate in either parallel mode or series mode.By using an auxiliary circuit with two diodes and a switch,the mode can be changed dynamically during the operation.The switching of topology during operation is to boost voltage under low wind speed and to extend the capacity in high speed.A novel peak current predictive controller substitutes the traditional proportional-integral(PI),and a seamless switching transition during topology changing is realised.The 3-level inverter improves the DC-link voltage linearly when the output reaches the rated level,thus a constant displacement power factor(DPF) is achieved.Simulations and experiments verify the improved dynamic response and the seamless transition during topology switching.