Small-Signal Stability Analysis of High Inertia Energy Storage Synchronous Condensers with the Impact of Different Reactive Power Control

The high inertia energy storage synchronous condenser (HIESS) has emerged as a promising equipment in power electronic dominated power system due to its inherent capabilities of fast voltage regulation and frequency support. However, the control dynamics of HIESS are extremely sensitive to voltage disturbances, which makes HIESS easily affected by its various reactive power control (RPC) and become unstable under weak grid conditions. This paper first establishes a small-signal model of HIESS considering various RPC behavior and the dynamics of the phase-locked loop (PLL), simultaneously. Furthermore, the compact HIESS model has been developed which uses the single-input single-output (SISO) form to intuitively present the interaction between PLL and RPC under weak grid conditions. On this basis, the SISO system stability criteria can be used to assess the system stability performance intuitively. In this manner, the effects of different RPC methods, grid strength, reactive power reference, and PLL bandwidth on system stability performance are analyzed in detail. It reveals that the HIESS is more unstable when outputting capacitive reactive power under weak grid conditions. The high PLL bandwidth and type of CRPC can stabilize the system. Simulation results validate the correctness of the stability analysis.