Positive-Negative Sequence Current Controller for LVRT Improvement of Wind Farms Integrated MMC-HVDC Network

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.

Real-Time Optimization-Based Reference Calculation Integrated Control for MMCs Considering Converter Limitations

“…Unbalanced scenarios are analyzed in [23], whereby the control strategy consisted in disabling the positive active and reactive current components to maximize the negative part. Reference [24] considered both positive and negative components during the fault. Still, the prioritization proposed by [24] makes the MMC to exceed its AC grid current limits during transients.…”

Detailed and Average Models of a Grid-Connected MMC-Controlled Permanent Magnet Wind Turbine Generator

“…The implementation of an MMC in a wind power generator, however, has not been extensively reported. The majority of reports have investigated the stability of grid-connected wind farms using MMC-based High Voltage Direct Current (HVDC) transmission systems [6][7][8][9][10], but only a few papers have discussed the topology concept of the implementation of MMC-controlled wind turbine generators. The performance and topology of MMCs for 2 MW 0.69 kV and 10 MW 10 kV has been discussed in [11]; however, the study only discusses the grid side converter and concentrates mainly on loss distribution between submodules.…”

LVRT Enhancement of a Grid-tied PMSG-based Wind Farm using Static VAR Compensator

“…The conventional back-to-back converter control strategy of Rotor Side Converter (RSC) was introduced for Maximum Power Point Tracking (MPPT) [15] and Grid Side Converter (GSC) was implemented to regulate the DC link voltage resulting from the grid fault occurrence [7,8,16]. When an LVRT occurs, the DC link voltage can be increased because MSC does not sense the grid fault and GSC fails to control the DC link voltage [5,6,17,18] which results in the tripping of the wind farm. The use of a non-linear, SVC controller is rapidly growing because of its robustness with respect to external disturbances.…”

“…The prime issue of controllers using traditional back-to-back converters is blathering. To reduce blathering, various LVRT methods have been introduced [1][2][3][4][5][17][18][19]. The most attractive LVRT method is the SVC because of shunt connection and longer life cycle [2].…”

“…The most attractive LVRT method is the SVC because of shunt connection and longer life cycle [2]. Moreover, many authors have proposed different control techniques to enhance the LVRT capability of wind farms [18]. The SVC controller is robust and cost-effective and can be implemented in wind farms.…”