A Study of Voltage Oscillations caused by Constant Power Devices

Conventional power system stability assessments have primarily focused on voltage stability, frequency stability, and synchronous stability, based on grid configurations dominated by synchronous generators. However, the increasing integration of inverter-based resources has introduced new stability challenges, particularly resonance phenomena and converter dynamics. While previous studies have examined inverter-induced instability using control-theoretic approaches and numerical simulations, the time-domain behavior of constant power devices—commonly used to model inverter characteristics—under near-critical system conditions remains insufficiently understood. This study employs the Y-method, developed by the Central Research Institute of Electric Power Industry (CRIEPI), to perform dynamic simulations on a simplified single-generator, single-load system. The load is modeled as a constant power device using both static load and simplified inverter representations. Under conditions approaching the system's stability margin, voltage oscillations were observed. To clarify the underlying mechanism, the temporal evolution of the operating point was mapped onto the P-V curve, enabling a detailed causal analysis. The findings provide new insights into the dynamic response of inverter-modeled loads and contribute to a deeper understanding of voltage instability phenomena in future power systems with high inverter penetration.