Impact of PLL on Harmonic Stability of Renewable Dominated Power System: Modeling and Analysis

Abstract

For reliable operation of power system, the system should be stable not only in the fundamental domain but also in harmonic domain. Power electronic converters of renewable generators inject harmonics into the power systems. So, at higher renewable penetration levels, study of power system stability in harmonic domain i.e. harmonic stability is required. The Phase Locked Loop(PLL) is used for grid synchronization of renewable generators. PLL affects the dynamic behavior of power electronic converters in harmonic domain also. This paper analyzes the impact of PLL on the harmonic stability of renewable dominated power systems. A small signal state space model is developed for PLL in harmonic domain to analyze the behavior of PLL. The obtained state space model is a periodic Linear Time Varying (PLTV) system, making the state space model of the whole power systems also a PLTV system. As the obtained state matrix is periodic in nature, the concept of time varying eigen-values is employed to analyze the harmonic stability. The standard IEEE-39 bus system is modified to enable high renewable penetration level and the modified system is used to carryout the harmonic stability analysis. Impact of PLL parameters on harmonic stability is analyzed using the modified IEEE 39 Bus system. The impact of renewable penetration level on harmonic stability for given PLL parameters is also analyzed. It is observed that the PLL parameters and renewable penetration level have impact on the harmonic stability of power system.