Single-phase PLL structure using modified p-q theory for utility connected systems

Phase-Locked Loop (PLL) systems have been used in several equipment used in power conditioning applications such as, uninterruptible power supply systems (UPS), active power filters, PWM rectifiers, etc., in which phase angle information of utility voltage is necessary. This work presents a description of the phase detection method applied to a single-phase PLL structure for utility connected systems. The proposed single-phase PLL system is based on the modified single-phase instantaneous reactive power theory (p-q theory). A fictitious two-phase system is obtained introducing a lag of 90° in the measured single-phase voltage. Therefore, a new two-phase system can be studied in αβ coordinates using the three-phase instantaneous reactive power theory. The analysis is performed using a two-phase stationary reference frame model which uses the instantaneous active power as the reference signal of PLL. To validate the theoretical analysis, a model of the PLL system is presented. Mathematical analysis of the PLL system is performed and its dynamic response is discussed. Both simulation and experimental results are presented to validate the theoretical analyses.