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 for periodic signals. For the conventional RC (CRC), it requires the ratio of the reference signal period to the fixed sampling period to be an integer. Therefore, the reference signal with a variable frequency or a fractional period ratio will lead to severe performance degradation. Although existing hardware variable sampling (VS) rate methods enable the CRC to be frequency adaptive, the VS frequency will also influence the overall system stability, and they need that the CPU has the VS frequency ability. In this paper, a flexible and easy-to-implement method, virtual VS (VVS), is proposed to enable the RC to be frequency adaptive. The proposed VVS method that creates a virtual delay unit to approximate each VS delay achieves a flexible VS as similar to the hardware-based VS but it does not influence the overall system sampling frequency and stability. Experimental results of a single-phase dc/ac converter system are presented to demonstrate the effectiveness of the proposed VVS-RC.