Thiran-All-Pass-Filter-Based Repetitive Control for Wide-Variable-Frequency Inverter

The wide-variable-frequency (WVF) inverter is characterized by relatively high fundamental and harmonic frequencies. The repetitive control (RC) is beneficial for achieving harmonic suppression and reference tracking. However, the ratio of the sampling frequency to the fundamental frequency may be a fraction, which greatly challenges the digital implementation of RC. To address this, an enhanced RC for WVF is proposed, which includes, i) employing a Thiran all-pass filter to approximate the fractional delay, ii) implementing the internal mode gain using the elaborated damped zero-phase-shift filter. It is found that the proposed RC is capable of providing high gain at selected harmonic frequencies and ensure system stability in the application of the WVF inverter. Finally, a 600VA prototype is built in the laboratory, and experimental results demonstrate that the WVF inverter with the proposed RC features good steady-state performance and low total harmonic distortion.