PLL Structures for Utility Connected Systems under Distorted Utility Conditions

This work presents a phase detecting method applied to three-phase PLL (phase locked loop) systems for utility connected devices under distorted utility voltage conditions. PLL systems have been used in several equipment applications such as, UPS systems, active power filters, PWM rectifiers, etc, in which phase angle information of utility voltage is necessary. The presented three-phase PLL system is based on instantaneous power theory. The analysis is performed considering a three-phase stationary reference frame model, which use the instantaneous active power as the PLL references. The proposed PLL system uses the method of symmetrical coordinates to detect the positive sequence component of the voltages in an unbalance there-phase system. To validate the theoretical analysis, the model of the PLL system is presented and its dynamic response is discussed considering distorted utility voltage conditions. Mathematical analysis of the PLL system is made and a design procedure to determine the controller gains is presented. Both simulations and experimental results are presented to validate the theoretical analyses