Open Access

ARTICLE

A Double-Time-Scale Dynamic Reactive Power Optimization Method for the AC/DC Hybrid Power Grid Incorporating UPFC

Wei Yin^1,*, Jun Wang¹, Ming Tong¹, Zhijun Chen¹, Ke Zhang¹, Meiqing Huang², Ran Gu², Keman Lin²
1 State Grid Suzhou Power Supply Company, Suzhou, China
2 College of Electrical and Power Engineering, Hohai University, Nanjing, China
* Corresponding Author: Wei Yin. Email:
(This article belongs to the Special Issue: Operation and Control of Grid-connected New Energy and Emerging Loads)

Energy Engineering https://doi.org/10.32604/ee.2026.075066

Received 24 October 2025; Accepted 29 January 2026; Published online 28 February 2026

Abstract

With the high penetration of renewable energy and the rapid development of AC/DC (Alternating Current/Direct Current) hybrid power grid, the power grid is confronted with challenges such as frequent voltage fluctuations and insufficient dynamic reactive power reserves. Full utilization of unified power flow controller (UPFC) in dynamic voltage regulation is of great significance for mitigating voltage excursions of the power grid. This paper proposes a double-time-scale dynamic reactive power optimization method for the AC/DC hybrid power grid with UPFC. A control framework for reactive power optimization of slow-time-scale and fast-time-scale is constructed incorporating the LCC-HVDC and UPFC. In this method, the slow-time-scale aims to improve the voltage profiles and reduce the system cost by setting the voltage regulation weight coefficients based on trajectory sensitivity to preserve reactive power regulation capability. The fast-time-scale adopts an adaptive feedback control mechanism. When slow-time-scale optimization is insufficient to keep the voltage within a safe range, it adjusts the real-time reactive power output of the UPFC, and damps rapid voltage swings accordingly. By implementing the additional fast-time-scale control method, the frequent variations of both the Photovoltaic (PV) and load are managed for the reactive power compensation. Case studies on a modified IEEE-30 bus system demonstrate that compared with the conventional control method, the proposed method reduces the maximum voltage deviation by 3.17% compared to the baseline, while ensuring the economic efficiency.

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Keywords

AC/DC hybrid power grid; UPFC; double-time-scale; dynamic reactive power optimization; trajectory sensitivity

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