Phase-locked loops (PLL) are widely used in the synchronization of grid interfaced power converters. One solution is based on orthogonal signal generation (OSG), which requires the grid frequency information for their appropriate operation. This article developed a new solution to achieve the PLL function for single-phase grid interconnection but eradicate additional frequency feedback loops in the traditional architecture of all-pass filter PLL (APF-PLL). Four new topologies are developed along with their small-signal modeling and dynamic analysis. A thorough comparison among them on their dynamic response, steady-state accuracy, implementation, and disturbance rejection capability is carried out. Finally, the best approach of frequency-fixed (FF) APF-PLL is experimentally evaluated with frequency adaptive APF-PLL and FF PLLs belonging to time delay (TD) and second-order generalized integrator (SOGI) families.

Removing the isolation transformer in grid-connected photovoltaic (PV) inverters is desirable to increase efficiency and reduce the size, weight, and cost of these systems. However, it may also allow leakage current through the stray capacitance between the PV array and ground, causing a safety risk. Both efficiency and leakage current depend upon both inverter topology and modulation strategy. In this work three single-phase inverter topologies, i.e. the H-bridge, HERIC, and H5 inverters, are compared with respect to efficiency and leakage current to determine their suitability as transformerless PV inverter systems. Experimental results are presented for the most promising case, i.e. the HERIC inverter with standard sinusoidal pulse-width modulation.

Complex coefficient filters (CCF) are widely utilized for the phase-locked loop (PLL) in three-phase power systems, while its usage is largely sparse in the single-phase domain. Single-phase CCF-PLLs so far reported in the literature do not yield satisfactory performances at off-nominal frequency conditions, which is a crucial PLL attribute. Whether they are a suitable filtering technique of choice for single-phase PLL is yet to be formally documented in a methodological way. In this regard, this paper derives an enhanced version of the single-phase CCF-PLL (ECCF-PLL), which is able to provide accurate estimation of grid parameters in dynamically changing grid frequency environment. The proposed ECCF-PLL is then numerically and experimentally compared with few other single-phase PLLs to gauge its efficacy and suitability. The test shows the advantage of harmonic robustness from ECCF-PLL, which is specifically useful in a weak grid.

Phase‐locked loop (PLL) is commonly utilised for AC power systems to detect phase and frequency. With the increasing use of small‐scale distributed power generation, the technique becomes widely available for grid interconnection of renewable power source into single‐phase AC distribution network. Through comprehensive analysis and design, this study proposed a new approach that includes dual independent control loops to enhance the transfer delay‐based PLL capability in terms of speed and accuracy. The effectiveness and advantages of the proposed PLL structure are demonstrated by numerical simulation and verified by experimental test.