A simulation study on tracking and restructuring AC signals based on enhanced SOGI-PLL

This paper presents an enhanced phase-locked loop (PLL) based on the second-order generalized integrator (SOGI) for tracking and restructuring alternating current (AC) signals with unknown amplitude, DC offsets, frequency, phase angle and phase sequence. According to the second-order generalized integrator configured as a quadrature signal generator (SOGI-QSG), amplitudes, DC offsets and the phase error are deduced. The phase error is used to estimate the frequency and phase by the PI regulator and integrator. The phase sequence is determined by the sign function. The proposed algorithm for tracking and reconstruction of single-phase and three-phase AC signals are both proposed. Compared to the existing dual second-order generalized integrator phase-locked loop (DSOGI-PLL), the effectiveness of the proposed algorithm has been validated through simulations.

I. Introduction

The power generation system is relatively sensitive to harmonic interferences, frequency variations, electrical load variations and unbalanced generating voltage with single-phase or three-phase DC offsets [1]. So, many phase-locked loop (PLL) algorithms are proposed to accurately measure the phase, DC offsets, amp litudes, and frequency of the AC signals in real-time. The single-phase PLL based on construction of virtual two-phase from a delay method is one PLL algorithm for single-phase grid voltage, but this algorithm is limited by periodic delay and slow dynamic response [2]. The single-phase PLL algorithm based on Park inverse transformation is limited by filter design difficulty, and slow response under voltage unbalance [3]–[4]. For three-phase AC signals, the phase of positive-sequence voltage components contains 2-order harmonic waves in a single synchronous reference frame SPLL (SSRF-SPLL) when the three-phase voltage imbalance occurs [5]. The SSRF-SPLL based on symmetrical component method is not very frequency-flexible [6]–[7].