Extended-frequency dynamic phasor modelling of LCC-HVDC systems for electromagnetic transient simulations

Abstract

A new model for line-commutated converter (LCC) HVDC systems based upon the concept of extended-frequency dynamic phasors is developed in an electromagnetic transient (EMT)-based simulation platform. The proposed model is capable of representing LCC-HVDC converters during normal as well as abnormal operating modes, such as system imbalances and commutation failure, by automatically adjusting its parameters based upon converter terminal quantity measurements. The model offers a high level of accuracy with reduced computational burden as a suitable replacement for conventional switch-based models of LCC in EMT simulation platforms. The proposed model is then extended to real-time EMT simulations. The performance of the proposed model is first evaluated against detailed EMT simulations of a simple LCC system. The evaluation is then extended to simulation of large electric networks such as CIGRE HVDC benchmark and IEEE 12-bus systems with an embedded LCC-HVDC link. Simulation results confirm that the proposed dynamic phasor-based model retains EMT-grade accuracy even at large simulations time steps. Significant acceleration ratios reaching up to an order of magnitude are observed in the simulations using the proposed model compared with conventional EMT models. A real-time EMT variant of the model is then implemented in RTDS real-time simulator. The performance of the dynamic phasor-based model is investigated against existing real-time LCC models with large and small time steps in a hardware-in-loop simulation scenario. The results confirm that the proposed dynamic phasor model retains the same level of accuracy as existing small time-step real-time models while using significantly larger time-steps, thus relieving the burden of real-time computations.