Jean Mahseredjian

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.

Dynamic Averaged and Simplified Models for MMC-Based HVDC Transmission Systems

Voltage-source converter (VSC) technologies are rapidly evolving and increasing the range of applications in a variety of fields within the power industry. Existing two- and three-level VSC technologies are being superseded by the new modular multilevel converter (MMC) technology for HVDC applications. The computational burden caused by detailed modeling of MMC-HVDC systems in electromagnetic transient-type (EMT-type) programs complicates the simulation of transients when such systems are integrated into large networks. This paper develops and compares different types of models for efficient and accurate representation of MMC-HVDC systems. The results show that the use of a specific type of model will depend on the conducted analysis and required accuracy.

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.

A Combined State-Space Nodal Method for the Simulation of Power System Transients

This paper presents a new solution method that combines state-space and nodal analysis for the simulation of electrical systems. The presented flexible clustering of state-space described electrical subsystems into a nodal method offers several advantages for the efficient solution of switched networks, nonlinear functions and for interfacing with nodal model equations. This paper extends the concept of discrete companion branch equivalent of the nodal approach to state-space described systems and enables natural coupling between them. The presented solution method is simultaneous and allows to benefit from the advantages of two different modeling approaches normally exclusive from one another.

Simulation Tools for Electromagnetic Transients in Power Systems: Overview and Challenges

This paper presents an overview on available tools and methods for the simulation of electromagnetic transients in power systems. Both off-line and real-time simulation tools are presented and discussed. The first objective is to give the reader an overview on the modeling and simulation capabilities in currently available state-of-the-art tools. The second objective is to provide perspectives on research topics and needed enhancements.

Creating an Electromagnetic Transients Program in MATLAB: MatEMTP

The traditional method for developing electric network analysis computer programs is based on coding using a conventional computer language: FORTRAN, C or Pascal. The programming language of the EMTP (Electromagnetic Transients Program) is FORTRAN-77. Such a program has a closed architecture and uses a large number of code lines to satisfy requirements ranging from low level data manipulation to the actual solution mathematics which eventually become diluted and almost impossible to visualize. This paper proposes a new design idea suitable for EMTP re-development in a high level programming context. It presents the creation of the transient analysis numerical simulator MatEMTP in the computational engine frame of MATLAB. This new approach to software engineering can afford a dramatic coding simplification for sophisticated algorithmic structures.

Dynamic Average Modeling of Front-End Diode Rectifier Loads Considering Discontinuous Conduction Mode and Unbalanced Operation

Electric power distribution systems of many commercial and industrial sites often employ variable frequency drives and other loads that internally utilize dc. Such loads are often based on front-end line-commutated rectifiers. The detailed switch-level models of such rectifier systems can be readily implemented using a number of widely available digital programs and transient simulation tools, including the Electromagnetic Transient (EMT)-based programs and Matlab/Simulink. To improve the simulation efficiency for the system-level transient studies with a large number of such subsystems, the so-called dynamic average models have been utilized. This paper presents the average-value modeling methodologies for the conventional three-phase (six-pulse) front-end rectifier loads. We demonstrate the system operation and the dynamic performance of the developed average models in discontinuous and continuous modes, as well as under balanced and unbalanced operation.

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

Utilizing DFIG-Based Wind Farms for Damping Subsynchronous Resonance in Nearby Turbine-Generators

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