Electromagnetic Transient Models of Bridge Thyristor Converters for Multirate Simulation of Large Power Systems

In large power system simulations with positive-sequence root-mean-square (RMS) dynamic programs, bridge thyristor converters of conventional HVDC transmissions are usually represented by equations describing steady-state operation. The use of electromagnetic transient (EMT) bridge converter models reflecting commutations of the thyristor valves can enhance the accuracy of RMS simulations of large power systems with HVDC transmissions. The development of efficient EMT models suitable for multirate simulation with commercial RMS dynamic programs is a challenging task. The paper focuses on EMT models of the single-bridge (Graetz) converter and multi-bridge converters. The thyristor valve is represented by a variable resistor in parallel with a resistor-capacitor branch (the R-RC representation). R-RC bridge models are presented for line-commutated and capacitor-commutated converters. The paper discusses numerical solution of the differential and algebraic equations of the R-RC bridge models and their interface with the main RMS dynamic program.