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

Ognjen Stanojev, Pol Jane Soneira, Gösta Stomberg, Mario Schweizer

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.

EMT and RMS Modeling of Thyristor Rectifiers for Stability Analysis of Converter-Based 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.
Paper Structure (22 sections, 37 equations, 13 figures, 2 tables)

This paper contains 22 sections, 37 equations, 13 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Modeling and Stability Analysis Preliminaries
  3. RMS and EMT Power System Modeling
  4. Small-Signal Stability Analysis
  5. Thyristor Rectifier RMS Modeling
  6. RMS Model Assumptions and Limitations
  7. EMT Modeling of Thyristor Rectifiers
  8. DC Voltage Dynamics
  9. Dynamics of the Commutation Process
  10. Input Current Dynamics
  11. PLL Dynamics
  12. Switching Delay Modeling
  13. EMT Model Summary
  14. Model Validation
  15. Time Domain Validation
  16. ...and 7 more sections

Figures (13)

  • Figure 1: Configuration of a six-pulse thyristor rectifier supplied from a three-phase voltage source and feeding a constant current load.
  • Figure 2: Control block diagram of the output DC voltage calculation.
  • Figure 3: Control block diagram of the commutation angle calculation.
  • Figure 4: Control block diagram of the input current model.
  • Figure 5: Circuit representation of the thyristor rectifier EMT model.
  • ...and 8 more figures