Fractional‐order repetitive control of programmable AC power sources

Abstract

Programmable AC power sources that provide variable-frequency and variable-amplitude output voltages are widely used in automatic testing equipment and bench top applications. Under various load conditions, a high-performance programmable AC power source not only can generate very clean sinusoidal output voltages, but also to accurately synthesise specified harmonic distorted wave-shapes. Digital repetitive control (RC) can achieve zero steady-state error tracking of any periodic signal with known integer period, but usually fails to provide precise tracking of variable-frequency periodical waveform with fractional period. In this study, a frequency adaptive fractional-order RC (FORC) strategy at fixed sampling rate is proposed to track or eliminate any periodic signals with variable frequency, where a Lagrange interpolation-based fractional delay filter is used to approximate the factional delay items in RC. The proposed FORC that offers fast on-line tuning of the fractional delay and the fast update of the coefficients, provide a simple but high-performance real-time control approach to dealing with variable-frequency variable-magnitude periodic signals. A case study of FORC-based programmable AC power source is conducted. Experimental results are provided to show the effectiveness of the proposed FORC strategy. It can be widely used in extensive applications.