Damping sensitivity analysis and optimized battery controller for small-signal stability enhancement in wind penetrated networks

Abstract

Alarming greenhouse gaseous emissions is one of the key factors for meeting future energy demand from sustainable eco-friendly resources like wind and solar. These resources use power electronic converters for the interconnection with the grid resulting in their zero/low inertia response. This can lead to non-deterministic damping of low-frequency oscillations in the power system. Moreover, this may impose Small-Signal Stability (SSS) challenges for the secure operation & control of power systems. A two-stage method is proposed in this paper to enhance the damping of multiple critical modes in large interconnected networks with high penetration of wind turbine generators (WTGs). Damping Ratio Sensitivity Index (DRSI) at a candidate location is the summation of sensitivities of damping ratios (DRs) of critical electromechanical modes (EMs) against inertia. But, the sensitivities of DRs of various EMs w.r.t inertia at a specific candidate location can be equal and opposite. This can lead to their mutual cancellation and hence DRSI may not be sufficient to identify the impact of WTGs in networks with multiple critical EMs. Thus, stage-1 of the proposed method introduces an improved Weighted Damping Sensitivity Ratio (WDSR) for identifying the locations for integrating WTGs with beneficial impacts on SSS. It assigns weight to the sensitivity factors of DRs and hence annihilates the problem with their amalgamation which exists in the case of DRSI. The modified WDSR performs the sequential computation of DR sensitivity analysis. This ensures that the variations in the DR sensitivities of critical modes against inertia due to WTG integration are not ignored. A multiband Optimized Battery Damping Controller (OBDC) is proposed in stage-2 for improving the damping of critical inter-area (IA) modes in networks with high WTG penetration. The location of the battery energy storage system (BESS) is determined based on a stability index. The proposed multiband controller is implemented using a single BESS and is optimally tuned for the most vulnerable operating scenarios identified for the critical modes. The performance of the proposed two-stage method is evaluated using the modified IEEE 68 bus system for a wide range of operating conditions and it is observed that damping of all the critical modes has improved to more than 5% in each operating scenario.