Sun-Min Kim, “전차원 상태 관측기와 PLL 시스템 모델링을 통한 계통연계형 전력변환 장치의 성능개선,” 아주대학교 공학석사 학위 논문, 2011. > 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.