Voltage and frequency stability assessment of medium-voltage distribution systems under high penetration of solar PV: A Case Study of EDTL RAEOA Timor-Leste

Abstract

To reduce dependence on diesel-based power generation and associated carbon emissions, the Government of Timor-Leste has initiated the development of a 15 MWp on-grid solar photovoltaic (PV) power plant within the EDTL RAEOA operational area. While this initiative supports the national clean energy transition and rising electricity demand, high PV penetration poses voltage and frequency stability challenges, particularly in medium-voltage distribution networks of small island power systems. This study presents the first comprehensive assessment of voltage and frequency stability resulting from the integration of a 15 MWp on-grid PV system into the real 20 kV EDTL RAEOA distribution network. The analysis is conducted under both steady-state and dynamic operating conditions using a case-study-based simulation approach. System performance before and after PV integration is evaluated to quantify changes in power quality and stability. The results indicate a substantial improvement in voltage profiles following PV integration. The minimum voltage level increases from 92.36% under pre-integration conditions at Bus 151 to 96.99% at Bus 212 after PV connection, demonstrating effective voltage recovery within the distribution network. Frequency response remains within acceptable limits under dynamic disturbances, indicating that high PV penetration does not adversely affect frequency stability. By simultaneously evaluating voltage and frequency stability at the medium-voltage level, this study provides a more comprehensive stability assessment than most existing PV integration studies, which often focus on a single domain or higher-voltage systems. The findings confirm the technical feasibility of large-scale PV integration in weak and isolated distribution networks and offer practical insights for renewable energy deployment in small island power systems such as Timor-Leste.