The increasing number of electronic power inverters connected to the electricity grid means that their synchronization with the electricity grid is becoming increasingly important. Typically, a phase locked loop (PLL) is an essential part of power inverters for achieving synchronization with the utility grid. Throughout the phase angle of the grid voltage, a reference signal is generated to synchronize the operating condition of the renewable energy production systems with the utility grid. This paper presents quantified analyses and comparisons of the main PLL techniques based on different structures for single-phase systems, and a comparative study of the enhancement for conventional phase-locked loop using four different methods, including, PLL with notch filter, PLL with notch filter based on fuzzy logic, PLL with a secondorder generalized integrator filter (SOGI-PLL), PLL with a second-order generalized integrator filter (SOGI-PLL) based on fuzzy logic. A comparison among these four studied improvements was conducted under normal operation condition. On the other hand, the performance of these filters was tested under three abnormal scenarios; Amplitude variations, amplitude and frequency variations, frequency and a phase jump variations. In addition, simulation results with PSIM software are developed to verify the performance and effectiveness of the strategy of each proposed method. Finally, experimental tests are used to extract the results and discuss the validity of the proposed quarter algorithms using the STM32F407 microcontroller board with phase angle and frequency estimation, which are visualized using a digital oscilloscope.
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