Improved phase detection technique for grid synchronization of DG systems during grid abnormalities

Operation of actively controlled grid connected inverter system largely depends on information about the phase of the grid voltage, and the control system must be capable of tracking the grid voltage phase angle. Many different methods can be used for synchronizing to the grid, ranging from simple methods based on detection of zero-crossings of grid voltage to more advanced numerical processing of the grid voltage measurement. However, accurate phase detection is decisive during grid abnormal conditions such as: line notching, voltage unbalance, voltage dips, frequency variations etc. This paper presents an Auto adjustable synchronous reference frame (ASRF) phase locked loop (PLL) for phase detection during unbalanced condition of the grid. The performance of the studied PLL is compared with conventional SRF PLL and the results are discussed. The complete model is studied in MATLAB-Simulink environment.