Improving Small-Signal Stability of Power Systems with Significant Converter-Interfaced Generation

This work presents a hierarchical control strategy to improve the stability of electrical networks with significant converter-interfaced generation (CIG). Due to the lack of inertia of CIG systems, these networks can undergo a high rate of change of frequency, compromising the frequency stability. In a first level control, a local controller based on the virtual synchronous generator (VSG) concept is used to emulate inertia and provide short-term frequency regulation. However, the inclusion of significant VSG units can have a negative impact on the damping of inter-area oscillations. Therefore, in a second level control, a centralized controller is proposed to damp these low-frequency electromechanical oscillations affected by VSGs. Several practical issues such as the identification of a system model for the control design, the compensation of communication delays, and the discrete-time implementation of the controller are particularly analyzed. The introduced supplementary controls allow increasing the penetration of renewable energy sources without jeopardizing the frequency and small-signal stability. Eigenvalue analysis and nonlinear hybrid simulations combining DIgSILENT and Python are performed to validate the proposed control strategy.