Analysis and synthesis of fractional order repetitive control for power converters

Repetitive control is widely employed in power converters due to its zero-error compensation of periodic signals. However, conventional repetitive control is sensitive to frequency variations of the periodic signals. For example, in grid-connected applications, conventional repetitive controlled power converters will produce higher harmonics distortion under grid frequency variations. Based on finite impulse response (FIR) fractional delay filters, fractional order repetitive control (FORC) scheme provides fast on-line computation and frequency adaptability to compensate for harmonics in grid-connected applications at fixed sampling time. In this paper the analysis and synthesis of the proposed FORC are comprehensively investigated. A stability criterion for FORC systems is derived. As a case study, experimental tests on a standalone single-phase PWM inverter, supplying a non-linear rectifier load, are provided to evaluate the effectiveness of the proposed FORC.