Hani Saad

Detailed and Averaged Models for a 401-Level MMC–HVDC System

Voltage-source-converter (VSC) technologies present a bright opportunity in a variety of fields within the power system industry. New modular multilevel converters (MMCs) are expected to supersede two- and three-level VSC-based technologies for HVDC applications due to their recognized advantages in terms of scalability, performance, and efficiency. The computational burden introduced by detailed modeling of MMC-HVDC systems in electromagnetic-transients (EMT)-type programs complicates the study of transients especially when these systems are integrated into a large network. This paper presents a novel average-value model (AVM) for efficient and accurate representation of a detailed MMC-HVDC system. It also develops a detailed 401-level MMC-HVDC model for validating the AVM and studies the performance of both models when integrated into a large 400-kV transmission system in Europe. The results show that the AVM is significantly more efficient while maintaining its accuracy for the dynamic response of the overall system.

Modular Multilevel Converter Models for Electromagnetic Transients

Modular multilevel converters (MMCs) may contain numerous insulated-gate bipolar transistors. The modeling of such converters for electromagnetic transient-type (EMT-type) simulations is complex. Detailed models used in MMC-HVDC simulations may require very large computing times. Simplified and averaged models have been proposed in the past to overcome this problem. In this paper, existing averaged and simplified models are improved in order to increase their range of applications. The models are compared and analyzed for different transient events on an MMC-HVDC system.

Real-Time Simulation of MMCs Using CPU and FPGA

Modular multilevel converter (MMC) structures are composed of several hundreds to thousands of half-bridge converters. Such large numbers of power switches and electrical nodes introduce important numerical challenges for the computation of electromagnetic transients. The problem becomes particularly more complex for the real-time simulations. This paper presents a feasibility study on the real-time simulation of the MMC models. CPU-based and field-programmable gate array-based implementations are proposed and evaluated for the MMCs having up to 401 levels. The study also provides guidelines for the real-time simulation platform requirements to simulate these MMC models.

MMC Capacitor Voltage Decoupling and Balancing Controls

A modular multilevel converter control system, based on converter energy storage, is proposed in this paper for two different control modes: active power and dc voltage. The proposed control system decouples the submodule (SM) capacitor voltages from the dc bus voltage. One of the practical applications is the management of active redundant SMs. A practical HVDC system with 401-level MMCs, including 10% redundancy in MMC SMs, is used for validating and demonstrating the advantages of the proposed control system. This paper also presents a novel capacitor voltage balancing control based on

Dynamic performance of average-value models for multi-terminal VSC-HVDC systems

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Full-Bridge MMC Converter Optimal Design to HVDC Operational Requirements

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Detailed and averaged models for a 401-level MMC-HVDC system

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Offshore Wind Farm Modeling Accuracy and Efficiency in MMC-Based Multiterminal HVDC Connection

functions. It is used to drastically reduce the number of switchings for each SM and enhances computational efficiency.

On the modeling of MMC for use in large scale dynamic simulations

Voltage Source Converter (VSC) HVDC technologies present a bright opportunity in a variety of fields within the power system industry due to their recognized advantages in comparison to conventional line-commutated HVDC systems. Computational burden introduced by detailed modeling of VSC-HVDC systems in EMT-type programs complicates the study of transient events. Detailed modeling includes the representation of semiconductor switches and causes significant deterioration in computational speed. This paper presents the concept of average-value modeling applied to two- and three-level VSC-HVDC systems. The modeling approach is validated for a multi-terminal VSC-based HVDC system used to integrate off-shore wind generation. Dynamic performance simulation results using average-value models are compared against detailed model results. Some results are also presented for MMC converters.

Short-circuit current contribution of converter interfaced wind turbines and the impact on system protection

Summary form only given. Design and operation of FB (full bridge) MMC that meets HVDC specifications are studied in this paper. Three new design parameters: the over-modulation index (kMMC), the DC modulation index (Mdc), the minimal DC voltage (Vminpu) are introduced to specify the operation of a FB MMC. Power increase and semiconductor count increase with the increase of kMMC is analyzed to understand benefits of over-modulation. The required number of submodules and the number of more-costly FB submodules for specified rated dc voltage, Vminpu and kMMC are calculated. The relationship of the submodule inserting logic and dynamics of an arm is analyzed. The submodule voltage balancing is studied and the constraints on the required number of FB submodules are deduced. The capability of over-modulation and the operation under low DC voltage with optimal submodule count are verified using EMTP simulation.