Offset error compensation algorithm for grid voltage measurement of grid-connected single-phase inverters based on SRF-PLL

Abstract

This paper proposes a method for compensating the offset error in the grid voltage measurement process of grid-connected single-phase inverters. In general, the offset error in the grid voltage sampling process results in a fundamental frequency component in the synchronous reference frame phase locked loop (SRF-PLL). As a result, the dq-axis currents and phase current based on the synchronous reference frame PI current regulator include the unwanted DC component, as well as first- and second-order harmonic ripples when compared with the grid frequency due to the distorted grid angle. Therefore, in this paper, the influences of the offset error are mathematically analyzed based on the SRF-PLL. In particular, the d-axis integrator output of the SRF-PLL with a PI controller is selected to detect the offset error. Then it is compensated using a simple proportional-integral controller. Moreover, the root mean square function is easily applied to obtain the offset error. The usefulness of the proposed algorithm is verified through simulation and experimental results.