Constant Delay-Line Repetitive Control Analysis for Variable Frequency Operation

The proposed paper deals with the complete analysis which is the basis of the common tuning procedure of variable sampling Repetitive Controllers for adjustable output frequency applications. The described approach can be applied without limitations to grid-tied inverters (narrow frequency variations), as well as to AC waveform generators (wide frequency variations). The operation of the proposed approach is to keep the Repetitive Control main delay line at a constant size, resulting in a very suitable implementation on FPGA-based control platforms. The effects of the desynchronization between the PWM modulator and the Control Loop will be accurately described, and the inherent delays will be expressed in closed form. Additional effects, like beating frequencies, are illustrated as well and described by closed-form expressions. Experimental verification is carried out to prove the effectiveness of the presented analysis.