Abstract
Positive and negative sequence based current control strategy is developed for the modular multilevel converter (MMC), which complies with the grid code requirements during the balanced and unbalanced faults at the point of common coupling of AC grids. This research proposes an efficient and simplified current limiting technique to keep the inverter individual phase current at a predefined threshold during faults. In this work, the current controller of the MMC converter is designed based on stationary reference frame while positive sequence synchronous reference frame is used to design the current limiter. The proposed work considers the complete dynamics of permanent magnet synchronous generator (PMSG) and doubly fed induction generator (DFIG) based wind energy. The MMC aggregate model is developed and simulated in Matlab/Simulink. The MMC model is also developed using real-time digital simulation (RTDS). A comparative performance analysis between the proposed and the conventional current limiter is provided where the proposed sequence-based current controller with the current limiter shows promising performance under severe disturbances. Besides grid compliance, the results with the proposed control scheme demonstrate the improvement of low voltage ride-through capability without any violation of converter current and HVDC link voltage limits.
Highlights
Renewable energy is getting more attention for the climate change, increasing electricity demand, fossil fuel depletion, and cheaper and improved technology
The controller parameters are designed based on the analysis provided in [49], [50], [55]
A sequence-based current control strategy with a fast current limiting technique for the modular multilevel converter (MMC) in line with positive and negative sequence grid code requirements has been developed in this work
Summary
Renewable energy is getting more attention for the climate change, increasing electricity demand, fossil fuel depletion, and cheaper and improved technology. Series connected resistor based bridge type fault current limiter has been discussed for a two-level VSC-HVDC system to mitigate different kinds of faults in [20] This approach keeps a large number of semiconductor switches turned on at normal operating conditions, resulting in continuous conduction loss. The performance of the proposed current controller with the current limiter has been assessed in line with converter current and HVDC link voltage limit and positive and negative sequence grid code requirements during the severe balanced and unbalanced disturbance at the point of common coupling of AC grids. Provides the mathematical modeling and controller design for The rotor flux position uses to transform the stator phase the converters used in PMSG and DFIG based wind energy current to d-q current and provide the angle for modulating integration.
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