Moving Average Filter Based Phase-Locked Loops: Performance Analysis and Design Guidelines

Abstract

The phase locked-loops (PLLs) are probably the most widely used synchronization technique in grid-connected applications. The main challenge associated with the PLLs is how to precisely and fast estimate the phase and frequency when the grid voltage is unbalanced and/or distorted. To overcome this challenge, incorporating moving average filter(s) (MAF) into the PLL structure has been proposed in some recent literature. A MAF is a linear-phase finite impulse response filter which can act as an ideal low-pass filter, if certain conditions hold. The main aim of this paper is to present the control design guidelines for a typical MAF-based PLL. The paper starts with the general description of MAFs. The main challenge associated with using the MAFs is then explained, and its possible solutions are discussed. The paper then proceeds with a brief overview of the different MAF-based PLLs. In each case, the PLL block diagram description is shown, the advantages and limitations are briefly discussed, and the tuning approach (if available) is evaluated. The paper then presents two systematic methods to design the control parameters of a typical MAF-based PLL: one for the case of using a proportional-integral (PI) type loopfilter (LF) in the PLL, and the other for the case of using a proportional-integral-derivative (PID) type LF. Finally, the paper compares the performance of a well-tuned MAF-based PLL when using the PI-type LF with the results of using the PID-type LF, which provides useful insights into their capabilities and limitations.

An Improved Frequency Measurement Method from the Digital PLL Structure for Single-Phase Grid-Connected PV Applications

“…Usually, PLL is used to detect voltage information [21,22]. The conventional PLL controller uses phase information to calculate the frequency of PV inverter output voltage after every line cycle, and has shown a relatively low accuracy [23][24][25][26][27][28]. This paper presents a novel frequency measurement method, with high accuracy, from the digital PLL control structure for single-phase grid-connected PV applications.…”

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

“…Therefore, a smaller window length results in a faster dynamic response of the MAF-based PLL algorithms. As shown in (2), the application of a MAF in the z-domain is computationally efficient with simple delay blocks [26], as shown in Fig. 1.…”

“…From the aforementioned analysis, the delay factor N can be set as a constant to remove the fixed frequency signal or as frequency adaptive according to the equation N=round (mπ/ω 0 T s ), in which the MAF is used to remove the odd-order harmonic for m=1, and to remove the dc offset for m=2. The detailed discrete-time realization was discussed in [26].…”

“…The MAF technique is the most popular and widely used technique (it can be used in the natural abc coordinates, the αβ coordinates and the dq coordinates) owing to its simple digital realization, low computational burden, and effectiveness under grid disturbance conditions [26].…”

“…In [26], a detailed analysis and design guideline of a MAF-PLL and its frequency adaptive implementation were presented, in which a performance comparison of the welltuned MAF-based PLL with a PI controller and the PID controller was presented. It was shown that the PID-type MAF-PLL has a higher bandwidth, which means a faster dynamic response while decreasing the noise immunity and disturbance rejection capability.…”