Virtual variable sampling repetitive control of single-phase DC/AC PWM converters

Repetitive control (RC) presents an attractive solution to achieve low steady-state tracking error and total harmonic distortion (THD) for periodic signals. For conventional RC (CRC), it requires that the ratio of reference signal period to the fixed sampling period to be an integer. Therefore, the reference signal with variable frequency or a fractional period ratio will lead to severe performance degradation. Although existing hardware variable sampling rate methods enable CRC to be frequency adaptive, the variable sampling frequency will also influence the overall system stability, and they need that the CPU has variable sampling frequency ability. In this paper, a flexible and easy-to-implement method, virtual variable sampling (VVS), is proposed to enable RC to be frequency adaptive. The proposed VVS method, which creates a virtual delay unit to approximate each variable sampling delay, achieves a flexible variable sampling as similar as hardware-based variable sampling, but it does not influence overall system sampling frequency and stability. Experimental results of a single phase DC/AC converter system are presented to show the effectiveness of the proposed VVS-RC.