Vector control of a modular multilevel matrix converter operating over the full output-frequency range

The Modular Multilevel Matrix Converter ( M 3 C ) is an ac-to-ac converter topology suitable for the control of high-power variable-speed drives. The control of this converter is complex, particularly when the two ac system frequencies are similar or identical because large voltage oscillations can be produced in the floating capacitors within the M 3 C . This paper proposes a new Vector Control System based on nested controllers to regulate the M 3 C over the full-range of frequencies. The proposed control scheme is especially useful to mitigate or eliminate the oscillations that arise when the frequencies are similar. An extensive discussion of the model and control of the M 3 C is presented in this work. The effectiveness of the proposed Vector Control System is demonstrated through simulation studies and experimental validation tests conducted with a 27-cell-5kW M 3 C prototype

An Overview of Modelling Techniques and Control Strategies for Modular Multilevel Matrix Converters

The Modular Multilevel Matrix Converter is a relatively new power converter topology appropriate for high-power Alternating Current (AC) to AC purposes. Several publications in the literature have highlighted the converter capabilities such as modularity, control flexibility, the possibility to include redundancy, and power quality. Nevertheless, the topology and control of this converter are relatively complex to design and implement, considering that the converter has a large number of cells and floating capacitors. Therefore multilayer nested control systems are required to maintain the capacitor voltage of each cell regulated within an acceptable range. There are no other review papers where the modelling, control systems and applications of the Modular Multilevel Matrix Converter are discussed. Hence, this paper aims to facilitate further research by presenting the technology related to the Modular Multilevel Matrix Converter, focusing on a comprehensive revision of the modelling and control strategies.Agencia Nacional de Investigacion y Desarrollo (ANID) of Chile Fondecyt 11191163 Fondecyt 1180879 Fondecyt 11190852 Fondef ID19I10370 University of Costa Rica 322-B9242 University of Santiago Dicyt 091813D

An Overview of Applications of the Modular Multilevel Matrix Converter

The modular multilevel matrix converter is a relatively new power converter topology suitable for high-power alternating current (AC)-to-AC applications. Several publications in the literature have highlighted the converter capabilities, such as full modularity, fault-redundancy, control flexibility and input/output power quality. However, the topology and control of this converter are relatively complex to realise, considering that the converter has a large number of power-cells and floating capacitors. To the best of the authors’ knowledge, there are no review papers where the applications of the modular multilevel matrix converter are discussed. Hence, this paper aims to provide a comprehensive review of the state-of-the-art of the modular multilevel matrix converter, focusing on implementation issues and applications. Guidelines to dimensioning the key components of this converter are described and compared to other modular multilevel topologies, highlighting the versatility and controllability of the converter in high-power applications. Additionally, the most popular applications for the modular multilevel matrix converter, such as wind turbines, grid connection and motor drives, are discussed based on analyses of simulation and experimental results. Finally, future trends and new opportunities for the use of the modular multilevel matrix converter in high-power AC-to-AC applications are identified.Agencia Nacional de Investigación y Desarrollo/[Fondecyt 11191163]/ANID/ChileAgencia Nacional de Investigación y Desarrollo/[Fondecyt 1180879]/ANID/ChileAgencia Nacional de Investigación y Desarrollo/[Fondecyt 11190852]/ANID/ChileAgencia Nacional de Investigación y Desarrollo/[ANID Basal FB0008]/ANID/ChileAgencia Nacional de Investigación y Desarrollo/[Fondef ID19I10370]/ANID/ChileUniversidad de Santiago/[Dicyt 091813DD]//ChileUCR::Vicerrectoría de Docencia::Ingeniería::Facultad de Ingeniería::Escuela de Ingeniería Eléctric

An optimal full frequency control strategy for the modular multilevel matrix converter based on predictive control

The modular multilevel matrix converter (M3C) is a promising topology for high-voltage high-power applications. Recent researches have proved its significant advantages for adjustable-speed motor drives compared with the back-to-back modular multilevel converter (MMC). However, the branch energy balancing in the M3C presents great challenge especially at critical-frequency points where the output frequency is close to zero or grid-side frequency. Generally, this balancing control depends on the appropriate injection of inner circulating currents and the common-mode voltage (CMV) whereas their values are hard to determine and optimize. In this paper, an optimization based predictive control method is proposed to calculate the required circulating currents and the CMV. The proposed method features a broad-frequency range balancing of capacitor-voltages and no reactive power in the grid side. For operation at critical-frequency points, there is no increase on branch voltage stresses and limited increase on branch current stresses. A downscaled M3C system with 27 cells is designed and experiment results with the R-L load and induction motor load are presented to verify the proposed control method

Inherent SM Voltage Balance for Multilevel Circulant Modulation in Modular Multilevel DC--DC Converters

The modularity of a modular multilevel dc converter (MMDC) makes it attractive for medium-voltage distribution systems. Inherent balance of submodule (SM) capacitor voltages is considered as an ideal property, which avoids a complex sorting process based on many measurements thereby reducing costs and enhancing reliability. This article extends the inherent balance concept previously shown for square-wave modulation to a multilevel version for MMDCs. A switching duty matrix dU is introduced: it is a circulant matrix of preset multilevel switching patterns with multiple stages and multiple durations. Inherent voltage balance is ensured with a full-rank dU . Circulant matrix theory shows that this is equivalent to a simplified common factor criterion. A nonfull rank dU causes clusters of SM voltage rather than a single common value, with the clusters indicated by the kernel of the matrix. A generalized coprime criterion is developed into several deductions that serve as practical guidance for design of multilevel circulant modulation. The theoretical development is verified through full-scale simulations and downscaled experiments. The effectiveness of the proposed circulant modulation in achieving SM voltage balance in an MMDC is demonstrated

Optimal circulant modulation for submodule voltage ripple minimization with inherent balancing capability in modular multilevel dc-dc converters

The modularity of the modular multilevel dc-dc converters (MMDCs) makes it as a competitive candidate in medium voltage applications but brings the submodule (SM) voltage balancing issue. This paper proposes an optimal circulant modulation method for minimizing the SM voltage ripples with inherent balancing capability proven at the same time, which allows smaller SM capacitors and avoids the high-frequency communication for SM voltage balancing. Firstly, the optimal switching pattern is strictly derived providing a general method to theoretically minimize the SM capacitor voltage ripple. Then the switching matrix of the optimal circulant modulation is formulated by introducing the generalized-circulant matrix. It verifies the circularity and full-rank feature of the optimal switching matrix, which promises the uniformity of SM actions and the inherent balancing of SM voltages. Finally, full-scale simulations and down-scaled experiments are both provided with the isolated LLC -based MMDC model and prototype. The results show that the proposed optimal circulant modulation can reduce the SM capacitor voltage ripple by 37% compared with the existed method, and it also promises the inherent SM voltage balancing and the SM uniformity

Analysis of optimized multilevel matrix converter for DFIG based wind energy conversion system

Wind power generation is an increasing trend worldwide. Multilevel converters in this regard are playing an essential role in high power system applications due to various features. In this paper, multi-objective optimization based multilevel matrix converter (MOMMC) is proposed for wind energy conversion system. The assessment of feasibility through the discussion of two objectives: reliability and cost have been considered in this study. Initially, the model of the two objectives is assessed against redundancy configuration and power loss. Then a multi-objective function is defined for achieving low cost and high reliability. The optimal topology for the matrix multi-level converter is determined using the membership function, and the solution is selected from the Pareto-optimal set. The reliability and cost analysis of the proposed MOMMC is performed. Simulation is carried out for the proposed multi-objective optimization based multilevel matrix converter using the PSIM software. To establish the validity of the proposed method, two different cases: 1) fixed and 2) variable speed of 9 MW doubly-fed induction generator-based wind energy system are considered. The results show the superiority of the proposed method over the others.

An integrated converter and machine control system for MMC-based high power drives

The Modular Multilevel Converter (MMC) is a promising topology for high power drive applications. However, large voltage fluctuations are produced in the floating capacitors when the machine is operating with high stator currents at low rotational speed. To compensate these oscillations, relatively large mitigation currents are required to keep the capacitor voltages within an acceptable range. In this paper, a new integrated control scheme is discussed to regulate the voltage fluctuations. The strategy is based on closed-loop vector-control of the voltage fluctuations, maintaining them inside a pre-defined threshold. The proposed control system is also augmented using flux weakening operation of the machine at low rotational speeds. An experimental prototype composed of eighteen power cells, feeding a vector-controlled induction machine in the whole speed range, is used to validate the effectiveness and feasibility of the proposed control strategies

State Space Modelling and Control of the Modular Multilevel Converter

In der vorliegenden Arbeit wird ein neuer Ansatz zur Modellierung von Systemen basierend auf dem Modularen Multilevel Umrichter (MMC) vorgestellt. Mit Hilfe dieses Ansatzes ist es möglich, neue, effiziente Regelungsalgorithmen für das System zu entwerfen. In Zukunft wird es für netzeinspeisende Umrichter immer wichtiger, nicht nur stabil, sondern auch netzverträglich operieren zu können. Ausgehend von analytischen Differentialgleichungen wird ein Zustandsraummodell des MMC abgeleitet und eine Methode zur Entkopplung des Systems abgeleitet. Mathematische Werkzeuge erlauben eine systematische Analyse der auftretenden Steuer- und Ausgangsgrößen. Eine einfache Matrixdiagonalisierung erlaubt eine allgemeine Transformationsregel für MMC-basierte System zu formulieren. Daraus resultieren einfache Möglichkeiten, Leistungsterme zu identifizieren, die die Zweigenergien des Systems im erlaubten Betriebsbereich halten können. Zusätzlich werden Freiheitsgrade der Kreisströme und der Nullspannung formuliert. Wie für MMC-basierte Topologien erwartet, können sie zur Reduzierung der Energiepulsationen der Zweige eingesetzt werden. Mit der vorgestellten Modellbeschreibung ist es möglich, neue Optimierungsverfahren unter Einbeziehung aller Freiheitsgrade durchzuführen, die eine Reduzierung der Energiepulsationen ermöglichen

Modular Multilevel Converters with Module-Level Energy Storage for Medium Voltage Applications

This dissertation is on Modular Multilevel Converter (MMC) converter design and analysis and its integration with energy storage at the low voltage module-level. The developed converter concept and topology can be used in various applications especially for the support of intermittent renewable energy resources. The general converter structure is analyzed and extended to include integrated energy storage suitable but not limited to medium voltage applications. The behavior of the idealized structure is analyzed to obtain equations that govern general converter behavior and identify possible control loops. Detail mathematical switching model is developed for the MMC converter with generalized module structure. The switching model is averaged to obtain a large signal model and then reduced to obtain lower order models suitable for sizing and optimization. Open and compensated closed loop current control is proposed and extended to include feedback loops needed for full control of integrated energy storage. General sizing procedure with the optimization aspects is then proposed and used on the example system to obtain the converter structure parameters. The example system models are then used to fine tune the control and structure parameters and investigate the converter behavior