Two frequency-bandwidths real-time sensitive inverter-current-feedback control for LCL-type DG systems connected to weak grid

For LCL-type distributed generation (DG) systems connected to weak grid, a novel two frequency-bandwidths real-time sensitive inverter-current-feedback (TFBRTS-ICF) control method is proposed to enhance the system reliability and robustness, which mainly includes the synchronous reference frame quasi-proportional-integral (SRFQPI) control, un-attenuated inverter-current-feedback active damping (UICFAD) control, and high-sensitivity real-time PWM algorithm. The SRFQPI control can compensate reactive power, and regulate the instantaneous current without steady-state error regardless of the fundamental frequency fluctuation. The UICFAD control can suppress the LCL-resonance peak well without requiring additional sensors. The proposed PWM algorithm can solve the robust problem of the UICFAD controller against grid-impedance variation through removing the computation delay. Meanwhile, the proposed PWM algorithm can achieve a full range of duty-ratio between 0∼1 and offer half of switching period for the inverter-current sampling and the duty-ratio calculating, which is easy to implement using a digital microcontroller. Experimental results confirm the theoretical expectations and the effectiveness of the proposed method.