A simple digital sinusoidal reference generator for grid-synchronized power electronics applications

This paper presents a simple method to generate low distorted sinusoidal references improving the power quality or the accuracy of power measurement in grid-synchronized applications. The proposed control strategy uses a half cycle detector, combining a square-wave discrete PLL with some functions embedded in a low-cost digital device. Using the proposed method it is possible to dedicate the digital device to perform the more difficult and complex numerical functions. The discrete PLL generates a low frequency (LF) signal with the same frequency and phase of the grid and a signal whose frequency is an integer number of times higher than the grid frequency (HF). Then, despite of the possible frequency variations, a constant number of samples-per-period is imposed in the control algorithms reducing deviations and errors. A descriptive study of the control loops provides the understanding to define the required controller parameters. The method is experimentally evaluated in a Sine-wave Pulse Width Modulated (SPWM) inverter, a grid-tied inverter and a monitoring system for a two-stage photovoltaic microinverter showing its simplicity and high applicability.