Youngjong Ko, Kiwoo Park, Kyo-Beum Lee, and Frede Blaabjerg, "A New PLL System using Full Order Observer and PLL System Modeling in a Single Phase Grid-Connected Inverter," in Proc. ICPE (ECCE-Asia) Conf., May/Jun. 2011, pp. 803–808. > Paper

  In a grid connected power conversion system, the phase angle information of a grid voltage is very essential for supplying power to

  the grid since it is used for active and reactive power control. A Phase Locked Loop (PLL) system is used and should be robust

  because often the actual grid voltages are usually distorted by unexpected harmonics. However, conventional PLL systems have

  steady state errors when distorted voltages are used as a PLL input. Furthermore, using this distorted phase angle in the power

  control could reduce the output power quality. In this paper, the grid voltages are separated into fundamental and harmonic

  components and a virtual phase voltage is generated from the fundamental component using a Full Order Observer (FOO). Two

  virtual voltages are used as an input for the PLL system so the phase angle errors can be reduced and the output power quality can

  be improved. The dynamic characteristics of the PLL system are designed using the modeling method to improve the dynamic

  response and stability of the whole system. The performance of the proposed method has been verified by a comparative analysis

  to the conventional PLL system. It is concluded the proposed method works well.