Analysis of Voltage and Frequency Characteristics of Small Hydropower Islanded Grid Considering Governor and Excitation Regulation Characteristics

doi:10.3969/j.issn.1008-0198.2026.05.003

Abstract

Abstract: Existing studies mostly treat voltage and frequency as decoupled independent variables, neglecting the voltage-frequency coupling effect caused by constant-impedance loads and frequency-dependent synchronous reactance. This paper establishes a coupled voltage-frequency steady-state analytical model considering governor droop characteristics and excitation saturation constraints, derives simultaneous voltage-frequency equations for the islanded grid, and reveals the impact mechanism of excitation saturation on steady-state operating points. A simulation model of a 10 kV neutral ungrounded distribution network incorporating small hydroelectric generating units is established, and the correctness of the coupled model has been verified under load levels ranging from 50% to 150%. Simulation results show that the excitation system rapidly saturates at its ceiling after islanding, fully exposing the voltage-frequency coupling effect. The voltage-dependent characteristic of constant-impedance loads cannot compensate for the power deficit exceeding unit capacity under heavy-load operating conditions.

Key words: small hydropower, islanded grid, voltage-frequency coupling, governor, excitation regulation, steady-state analytical model

CLC Number:

TM712

TAN Liming, OUYANG Fan, LI Zhenwen, LIU Yonggang, XIAO Fan, OUYANG Zongshuai. Analysis of Voltage and Frequency Characteristics of Small Hydropower Islanded Grid Considering Governor and Excitation Regulation Characteristics[J]. Hunan Electric Power, 2026, 46(5): 16-23.

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