Performance Evaluations of Four MAF-Based PLL Algorithms for Grid-Synchronization of Three-Phase Grid-Connected PWM Inverters and DGs

Abstract

The moving average filter (MAF) is widely utilized to improve the disturbance rejection capability of phase-locked loops (PLLs). This is of vital significance for the grid-integration and stable operation of power electronic converters to electric power systems. However, the open-loop bandwidth is drastically reduced after incorporating a MAF into the PLL structure, which makes the dynamic response sluggish. To overcome this shortcoming, some new techniques have recently been proposed to improve the transient response of MAF-based PLLs. In this paper, a comprehensive performance comparison of advanced MAFbased PLL algorithms is presented. This comparison includes HPLL, MPLC-PLL, QT1-PLL, and DMAF-PLL. Various disturbances, such as grid voltage sag, voltage flicker, harmonics distortion, phase-angle and frequency jumps, DC offsets and noise, are considered to experimentally test the dynamic performances of these PLL algorithms. Finally, an improved positive sequence extraction method for a HPLL under the frequency jumps scenario is presented to compensate for the steady-state error caused by non-frequency adaptive DSC, and a satisfactory performance has been achieved.

A Non-Adaptive Single-Phase PLL Based on Discrete Half-Band Filtering to Suppress Severe Frequency Disturbances

“…Although those techniques are effective, they require the incorporation of more processing elements, and sometimes, the usage of additional MAFs. It is also noteworthy that anti-aliasing considerations and additional filtering are commonly overlooked in design tasks; however, they are ultimately required for implementation, as confirmed throughout the literature where MAFs are implemented [5,6,8,10,15,21,22].…”

“…revealing that k d enhances the close-loop speed but enables high frequencies to affect the system through ∆φ(s) as discussed in [6]. Accordingly, k d is commonly omitted-as done in this work.…”

“…To overcome the problems derived from rounded sampling, different proposals have been tested, as mentioned in [8], mainly involving some discrete interpolation [6,18]. Although those techniques are effective, they require the incorporation of more processing elements, and sometimes, the usage of additional MAFs.…”

“…Recent proposals have focused on positive sequence extraction, disturbances filtering, harmonics elimination, and others [4]. The performance of different proposals has been documented exhaustively [4][5][6][7][8], showing that no single PLL solves every challenge. However, a clear trend toward discrete filtering, being led by the moving average filter (MAF) approach, can be identified from the references listed above.…”

“…Discrete implementation of SRF-PLLs is now dominated by MAFs, regarded as ideal low-pass filters (LPF) as they notch their cut-off frequencies and their harmonics [9]. Nevertheless, the MAF interacts with non-harmonic frequencies, just as a first-order LPF [6], making frequency disturbances particularly harmful for the PLL performance. This problem has been faced by adding a loop to adapt the MAF's cut-off frequency; yet, non-harmonic components cannot be rejected, and sudden frequency variations would compromise the additional loop's performance and stability [10].…”