EMT and RMS Modeling of Thyristor Rectifiers for Stability Analysis of Converter-Based Systems

TL;DR

This paper introduces a new nonlinear EMT model in the dq domain for thyristor rectifiers, enabling accurate small-signal stability analysis of converter-based power systems with complex dynamics.

Contribution

It presents a novel nonlinear state-space EMT model in polar coordinates that captures key dynamic phenomena and facilitates stability analysis of thyristor rectifiers in power systems.

Findings

Model accurately captures PLL, commutation, and switching delays.

Model verified against detailed switching simulations.

Enables small-signal stability analysis of complex power systems.

Abstract

Thyristor rectifiers are a well-established and cost-effective solution for controlled high-power rectification, commonly used for hydrogen electrolysis and HVDC transmission. However, small-signal modeling and analysis of thyristor rectifiers remain challenging due to their line-commutated operation and nonlinear switching dynamics. This paper first revisits conventional RMS-based modeling of thyristor rectifiers and subsequently proposes a novel nonlinear state-space EMT model in the dq domain that can be linearized for small-signal analysis. The proposed model accurately captures all the relevant dynamic phenomena, including PLL dynamics, the commutation process, and switching delays. It is derived in polar coordinates, offering novel insights into the impact of the PLL and commutation angle on the thyristor rectifier dynamics. We verify the RMS and EMT models against a detailed switching model and demonstrate their applicability through small-signal stability analysis of a modified IEEE 39-bus test system that incorporates thyristor rectifier-interfaced hydrogen electrolyzers, synchronous generators, and grid-forming converters.