Authors: Yin Chen; Lie Xu; Agustí Egea-Àlvarez; Benjamin Marshall; Md Habibur Rahman; Adeuyi Daniel Oluwole
This article develops a small-signal impedance model of modular multilevel converters (MMCs) using the harmonic state-space (HSS) method and studies the stability in a multiple converter scenario. In order to simplify analysis of the coupling characteristics between different frequencies in MMCs, the proposed model is developed in the positive–negative–zero (PN0) sequence frame, where the zero-sequence current in a three-phase three-wire system is directly set to zero without introducing a complicated method. A simple 2 × 2 admittance matrix in the PN0-frame is extracted from the MMC small-signal model for ease of system stability analysis. Using the developed impedance model, the multi-infeed interaction factor (MIIF) measure is adopted to analyze the most significant interactions for multi-infeed converter systems to be prioritized. Different outer-loop controllers are adopted and compared in the analysis to illustrate the effect of different control modes on converter impedance and system stability. Analytical studies and time-domain simulation results are provided to validate the proposed model and stability analysis.
Published in: IEEE Journal of Emerging and Selected Topics in Power Electronics ( Volume: 9, Issue: 6, Dec. 2021)
Supported by the HVDC Centre as part of project: Stability assessment and mitigation HVDC converter interactions
To view the paper please select one of the following links
https://ieeexplore.ieee.org/document/9224850
https://pureportal.strath.ac.uk/files/112563148/Chen_etal_IEEE_JESTPE_2020_MMC_impedance_modelling_and_interaction_of_converters.pdf
Authors: Deyang Guo; M. H. Rahman; G. P. Adam; Lie Xu; Abdullah Emhemed; Graeme Burt; Yash Audichya
This paper presents a detailed study of DC grid operation using a range of user-defined offline and real-time HVDC converter models which were rigorously validated against offline and real-time benchmarks. Provided that these models are destined for use in real-time hardware in the loop simulation and a wide range of offline system studies, this paper assesses their suitability for studying complex DC grids that consist of multiple voltage source converters which differ in their control range and fault ride-through capabilities. Detailed quantitative studies show that the offline and real-time DC grid models produce well matched results and provide efficient approaches to investigate DC grid operation during normal condition and AC and DC faults.
Published in: 15th IET International Conference on AC and DC Power Transmission (ACDC 2019)
Supported by the HVDC Centre as part of project: Developing Open-Source Converter Models
To view the paper please select one of the following links
https://ieeexplore.ieee.org/document/8690252
https://strathprints.strath.ac.uk/65998/
Authors: Guo, Deyang; Rahman, M.H.; Adam, G.P.; Xu, Lie; Emhemed, Abdullah; Burt, Graeme and Audichya, Yash
This paper presents a detailed comparison of different modelling methods of the half-bridge modular multilevel converter (HB-MMC), namely, switching function, Thevenin equivalent and averaged, considering both MMC implementations (large and reduced number of cells). The theoretical basis that underpins each modelling method are discussed. Offline PSCAD simulations are used to validate user-defined switching function and averaged MMC models against the Thevenin equivalent model provided in PSCAD library for accuracy, considering steady-state and dc fault conditions. Furthermore, the RTDS based real-time simulation results of the user-defined HB-MMC switching function model are validated against the above mentioned offline models, considering steady-state and dc short circuit fault operations. Simulation speed and efficiency of different offline HB-MMC models being studied in this paper are compared. From comprehensive corroboration of different HB-MMC models presented in this paper, it has been found that the averaged, switching function and Thevenin equivalent models produce practically identical results during steady-state and dc faults. In detailed offline and real-time simulation studies where fundamental and harmonic dynamics are of interest, switching function model is found to be faster and computational efficient compared to the Thevenin equivalent model.
Published in: 14th IET International Conference on AC and DC Power Transmission (ACDC 2018). IET, CHN, pp. 1-8.
Supported by the HVDC Centre as part of project: Developing Open-Source Converter Models
To view the paper please select the following link:
https://strathprints.strath.ac.uk/63527/
