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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.

Modular multilevel converter (MMC) based HVDC system for renewable energy integration has attracted the researcher’s interest nowadays. This paper proposes a control strategy for MMC based multiterminal HVDC system for grid integration of squirrel cage induction generator (SCIG) based wind energy systems. Unlike the average model, this work models the MMC using the aggregate model and develops multiterminal HVDC transmission network in MATLAB/Simulink. It further develops the MMC multiterminal HVDC transmission network in real time digital simulator (RTDS). Instead of simplified current source, the proposed network considers the complete dynamics of SCIG based wind source from generation to integration. It employs field-oriented control for optimum wind energy tracking and forms isolated AC grids using feed forward controller. The proposed MMC controller performance has been tested under severe balanced and unbalanced disturbances. The results from aggregate model based MMC network in MATLAB/Simulink and those of the experimental MMC network in RTDS are in full agreement. The results confirm optimum wind energy tracking, fulfill grid code requirements, and improve low voltage ride through capability.

Phasor measurement units (PMUs) are becoming popular and populating the power system grids rapidly due to their wide range of benefits and applications. This research paper proposes a comprehensive, effective, and revised formulation of the optimal PMU placement (OPP) problem with a view to minimizing the required number of PMU and ensuring the maximum number of measurement redundancy subjected to the full observability of the distribution grids. The proposed formulation also incorporates the presence of passive measurements/zero injection buses (ZIB) and the channel availability of the installed PMU. Additionally, the formulation is extended to various contingency cases i.e., the single line outage and single PMU loss cases. This paper solves the proposed OPP formulation employing a heuristic technique called backtracking search algorithm (BSA) and tests its effectiveness through different IEEE standard distribution feeders. Additionally, this study compares the obtained results with the mixed integer linear programming (MILP)-based approach and the referenced works. The obtained results demonstrate the superiority of the proposed formulation and solution methodology compared to other methodologies.

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