A Harmonic Phasor Domain Cosimulation Method and New Insight for Harmonic Analysis of Large-Scale VSC-MMC Based AC/DC Grids

Recently, frequency coupling oscillation events, such as harmonic oscillations, subsynchronous and supersynchronous oscillations, driven by multiple converters with different switching frequencies have brought new challenges of ac/dc grid modeling, despite the traditional one of improving the accuracy and efficiency. There is an urgent requirement of practical engineering projects to produce a modeling method that can produce instantaneous and harmonic phasor waveforms simultaneously, dedicated to harmonic interaction analysis of large-scale ac/dc grids. To realize the above-mentioned targets, the harmonic phasor domain (HPD) modeling of power electronic based dc grids is proposed. The HPD modeling is then combined and coordinated with electromagnetic transient (EMT) based ac-grid models based on the proposed HPD transmission line model (HPD-TLM). The overall HPD cosimulation is realized by the EMT-based ac-grid models, HPD-based dc-grid models, and HPD-TLM, which is governed by the decoupled and coordinated time sequences. The performance (efficiency and accuracy of instantaneous and harmonic phasor waveforms) for the HPD cosimulations is validated on practical large-scale voltage source converter modular multilevel converter based ac/dc grids in China.