Periodic pulsation mitigation and operation speed extension in wind-driven squirrel-cage induction generators through voltage injection

Abstract Wind-driven squirrel-cage induction generators (SCIGs) can connect directly to the power grid and serve as generators. However, their limited slip ratio restricts their ability to adapt to variable and random wind speed fluctuations. In this study, a combined series and shunt power inverter (SSPI) is introduced to extend the operating range of the SCIG. The SSPI consists of two power inverters that are connected back-to-back through a shared DC link. The series inverter plays a pivotal role by injecting voltage at multiple frequencies. One is fundamental voltage that aligns its phase with the fundamental current of the stator, which supplies additional electrical power to the DC link. The other is harmonic voltage, which effectively mitigates disturbances caused by periodic pulsations, such as wind shear and tower shadow. The shunt inverter regulates the DC-link voltage and restores any surplus power gained from the series inverter to the power grid. The proposed approach allows the SCIG to integrate electrical power into the grid across a broad range of wind speeds without requiring a full-scale converter. The method also effectively addresses periodic pulsations in rotor speed, grid power, and DC-link voltage.