Abstract
In a modular multilevel converter (MMC) system, the grid asymmetry on AC side will cause problems like non-sinusoidal 3-phase current on AC side of MMC converter, fluctuation of active and reactive power, and large fluctuation of double frequency current and voltage on DC side. In order to solve these problems, a differential-based positive and negative sequence separation is proposed, which has limited delay and high precision after grid asymmetry occurring. Then the fluctuation form on AC-side power is analyzed according to the instantaneous power theory. Secondly, in conjunction with the control objectives of suppressed negative sequence current and instantaneous active power, theoretical analysis on the bridge arm circulating current is carried out, which obtains the expression of given current in the inner loop under the corresponding control objectives. Finally, MMC simulation model is established based on PSCAD/EMTDC, then the simulation verification for two control objectives under asymmetric grid is carried out respectively.
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Acknowledgements
This work is supported by National Key R&D Program of China (No. 2018YFB0904700), Science and Technology Program of State Grid Corporation of China (No 524608170147).
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Wu, T., Wang, X., Ma, W., Li, X., Chen, D., Zhong, J. (2020). Control Scheme of Modular Multilevel Converter Under Unbalanced Grid Voltage. In: Xue, Y., Zheng, Y., Rahman, S. (eds) Proceedings of PURPLE MOUNTAIN FORUM 2019-International Forum on Smart Grid Protection and Control. PMF PMF 2019 2021. Lecture Notes in Electrical Engineering, vol 584. Springer, Singapore. https://doi.org/10.1007/978-981-13-9779-0_39
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DOI: https://doi.org/10.1007/978-981-13-9779-0_39
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