Impact of distributed generation with storage on electric grid stability

Penetration of distributed generation (DG) has significantly increased over the last few decades. Several states in USA have set their own target to meet significant percentage of DG penetration over the years. These requirements will have impacts on grid reliability and operational requirements given inherent intermittency for some of the DG. Energy storage integrated with DG has been proposed as a solution by several researchers to provide greater levels of flexibility and reliability. Energy storage will have impact on electric grid in several other ways including stability. This work addresses the impact of DG with storage on transient stability of the electric grid system. DG based on wind energy and biomass have been modeled based on synchronous and induction generators. Wind based DG has been modeled as both the fixed and variable speed wind energy farms. Battery and ultra-capacitor have been modeled as storage with suitable power electronics interface. MATLAB/ Simulink and PSS/E have been used as a tool for this study. Transient stability of the test systems has been assessed for different types and locations of faults as well as for different penetration levels of the DGs, with and without the energy storage devices. Transient stability have been analyzed in terms of generator rotor speed deviation, rotor angle and terminal voltage of the DGs. Results indicate that the presence of DGs and storage devices enhances the transient stability of the system in most of the cases. This work also identifies the lack of dynamic model for storage in most of the commercial available tools.