A Novel Phase Locked Loop for Grid-Connected Converters under Non-Ideal Grid Conditions

Abstract

Grid synchronization is one of the key techniques for the grid-connected power converters used in distributed power generation systems. In order to achieve fast and accurate grid synchronization, a new phase locked loop (PLL) is proposed on the basis of the complex filter matrixes (CFM) orthogonal signal generator (OSG) crossing-decoupling method. By combining first-order complex filters with relation matrixes of positive and negative sequence voltage components, the OSG is designed to extract specific frequency orthogonal signals. Then, the OSG mathematical model is built in the frequency-domain and time-domain to analyze the spectral characteristics. Moreover, a crossing-decoupling method is suggested to decouple the fundamental voltage. From the eigenvalue analysis point of view, the stability and dynamic performance of the new PLL method is evaluated. Meanwhile, the digital implementation method is also provided. Finally, the effectiveness of the proposed method is verified by experiments under unbalanced and distorted grid voltage conditions.

A Novel Control Scheme for T-Type Three-Level SSG Converters Using Adaptive PR Controller with a Variable Frequency Resonant PLL

“…th and 99 th harmonics [27]. A traditional PI regulator cannot eliminate this deviation which varies periodically and sinusoidally.…”

“…As a result, the frequency and phase are difficult to obtain by a traditional PLL or position encoder. When the detected voltage is distorted by low-order harmonics or switching frequency harmonics, the precise frequency and phase are hard to obtain by a general digital PLL (DPLL) which is called a traditional PLL [27]. In some references, an enhanced PLL is proposed to lock the frequency in a polluted utility grid [27]- [30].…”

“…When the detected voltage is distorted by low-order harmonics or switching frequency harmonics, the precise frequency and phase are hard to obtain by a general digital PLL (DPLL) which is called a traditional PLL [27]. In some references, an enhanced PLL is proposed to lock the frequency in a polluted utility grid [27]- [30]. The authors of [28] propose a grid synchronization PLL based on an adaptive low-pass notch filter, which is a modified version of a PLL based on the fast Fourier transform, which is robust to harmonics and imbalances of the grid voltage.…”

A Quantitative Evaluation and Comparison of Harmonic Elimination Algorithms Based on Moving Average Filter and Delayed Signal Cancellation in Phase Synchronization Applications

“…A diagram of the closed-loop phase synchronization scheme in the d-q frame [8] is obtained, and shown in Fig. 1.…”

“…Therefore, the security and stability of grid-connected converters cannot be ensured [2]- [4]. Consequently, performing accurate phase synchronization under distorted grid conditions has become a major concern in both industrial applications and in the research field [5]- [8].…”