Modified non-adaptive bandpass filter based phase locked loop

Abstract

In this Letter, a demodulation based pre‐filtering technique is proposed for fast detection of the single‐phase grid variables. The estimation of grid voltage parameters is achieved through a Type‐I synchronous reference frame phase‐locked loop (PLL). The modified bandpass filter in the pre‐filtering stage ensure a better rejection of the DC‐offset and harmonics. Thus, the grid variables are estimated rapidly with the help of a simple proportional controller. Consequently, in‐loop filtering burden and the effort required to tune the PLL is minimal. However, steady errors are witnessed in the fundamental amplitude and the phase information which are mitigated by a curve fitting technique. Importantly, the proposed PLL scheme has improved the dynamic performance under off‐nominal frequency conditions with immunity against grid disturbances. The robustness of the proposed algorithm is experimentally verified vis‐à‐vis existing literature.

Enhanced Single-Phase Phase Locked Loop Based on Complex-Coefficient Filter

“…9(b) shows the relative frequency error in the estimated frequency for different changes in grid frequency. The IEC standard 61000-4-7 allows 0.03% tolerance on the estimated frequency [26]. The error in frequency estimation from ECCF is well below the permitted limit and finer than ETD.…”

Development of Frequency-Fixed All-Pass Filter-Based Single-Phase Phase-Locked Loop

“…As each OSG has different characteristics to generate an orthogonal signal set, each warrants a distinct frequency fixed configuration and requires separate design and analysis. Such frequency-fixed (FF) OSG filter has been applied to TD-PLL [6], [18], [19], SOGI-PLL [17], [20]- [22], CCF-PLL [11], [23], DFT-PLL [8], [24], and HT-PLL [25]. In contrast, only a few works are reported for frequency-fixed APF-PLL (FFAPF) but are found inadequate in meeting one or the other performance criteria.…”