| EPE 2022 - DS3a: Modular Multilevel Converters | ||
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 | A detailed View on the Trapezoidal Operation for MMC Type Braking Chopper in Medium Voltage Application
By Patrick HOFSTETTER | |
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Abstract: A detailed view on the trapezoidal operation of the modular multilevel converter (MMC) type brakingchopper is given. The in_uence of different limitations on the possible operational range is derived andan optimization algorithm is suggested. Finally, the analysis is veri_ed on an exemplary medium voltageapplication and validated by simulation.
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| | A novel parameter for the evaluation of protective circuits for IGBT explosion protection in submodules of MMC
By Christoph JUNGHANS | |
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Abstract: Faults in high-power converters can cause sudden release of the energy stored in the charged intermediate circuit capacitor, destroying power semiconductors and causing secondary damage, such as the release of debris, the deformation of busbars and the emission of interference fields. This paper examines the effectiveness of certain protective circuits for the electrical explosion protection of IGBT modules in submodules of Modular Multilevel Converters (MMC) for HVDC applications and introduces a new parameter for the characterization of IGBT explosions. The protective circuits are arranged within the intermediate circuit of the submodule and are intended to reduce the surge current in the event of a fault and accordingly to dissipate or divert the energy of the storage capacitor and thus relieve the IGBT modules. The examinations indicate, that the connection of RL-combination and bypass thyristor can be recommended as protective circuit for IGBT explosion protection and surge current reduction used in MMC submodules with low switching frequencies. The newly introduced Explosion Integral XI improves the evaluation of electrical explosion protection measures. The parameter takes into account the thermal and magnetic mechanisms that cause the explosion of IGBT modules.
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| | Analysis of balancing algorithms for Quasi-Two/Three-Level Single Phase Operation of a Flying Capacitor Converter
By Stefan Christoph MERSCHE | |
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Abstract: Today's standard medium voltage converters are operated with low switching frequencies and containbulky passive components. One concept to change this is the Quasi-Two-Level operation (Q2O) ofmultilevel converters with fast switching semiconductors to minimize passive components. The FlyingCapacitor Converter (FCC) with SiC semiconductors and operated with Q2O is thus a converter withminimized passive components. In this paper, a comparison of balancing algorithms for Quasi-Two-Level operation of a FCC is presented. The differences between the various methods are demonstrated by simulation and measurement results. Furthermore, a modulation principle with balancing for Quasi-Three-Level operation of a FCC is introduced. With the FCC, it is easy to upgrade from the Q2O to Quasi-Three-Level operation (Q3O) to take full advantage of a three-level output voltage.
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| | Design and Modulation Optimization of an MMC Based Braking Chopper
By Viktor HOFMANN | |
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Abstract: This paper investigates MMC based braking chopper configurations with a centralized resistor. It analyzes, optimizes and compares different cell configurations and modulation methods. A detailed description of the limiting factors and boundary conditions as well as the available degrees of freedom are provided and the theoretical derivations are validated by simulation.
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| | Experimental Evaluation of Battery Impedance and Submodule Loss Distribution for Battery Integrated Modular Multilevel Converters
By Arvind BALACHANDRAN | |
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Abstract: Greenhouse gas emissions and the increase in average global temperature are growing concerns now more so than ever. Therefore it is of importance to increase the use of alternative energy sources, especially in the automotive industry. Battery electric vehicles (BEV) have gained popularity over the past several years. However, the performance of a BEV is limited by the battery pack, in particular, the weakest cell in the pack. Therefore, improved cell controllability and high efficiency are seen as important directions for research and development and one direction where it can be achieved is through using battery-integrated modular multilevel converters (BI-MMC). The battery current in BI-MMCs contains additional harmonics and the frequency dependent losses of these harmonics are determined by the resonance between the battery and the DC-link capacitor bank. The paper presents an experimental validation of previously published theoretical results for both harmonic allocations and loss distribution at the switching frequency within the BI-MMC submodule. Furthermore, a methodology for measuring the battery impedance using the full-load converter switching currents is presented.
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| | Extended Balancing and Dimensioning of Capacitors in MMC Double Submodules
By Ali SHARAF ADDIN | |
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Abstract: The Double-Zero Submodule in Double Connection (DZDCSM) is one of the most promising submodule topologies for future Modular Multilevel Converter (MMC) applications. Internal paralleling of semiconductors and capacitors in the DZDCSM during the time spans of high load currents results in low losses and reduced energy pulsation. Furthermore, full controllability of the capacitors enables their critical balancing in a passive and lossless manner. This paper presents an analytical investigation of the internal balancing process as well as the energy pulsation reduction in the full operating range of the MMC utilizing the DZDCSM. A simulation, applying the nearest level modulation and a basic sorting algorithm, verifies the general energy pulsation reduction in comparison to a conventional Full-Bridge Submodule (FBSM).
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| | Full-Bridge Modular Multilevel Converters for the Four-Quadrant Supply of High Power Magnets in Particle Accelerators
By Manuel COLMENERO MORATALLA | |
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Abstract: Many particle accelerators require to supply chains of magnets with high quality, high value, cycling currents. To do this, the power converters need to provide high output voltages, reaching in some casestens of kV. For such application, Modular Multilevel Converters based on Full-bridge Submodules (FB-MMC) could be used given their capacity to store energy, their inherent reliability and their good har-monic performance. This paper studies how this converter topology could be used for this application,proposing a method to recover and store the energy of the magnet using the converter submodules.
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| | GaN-Based Modular Multilevel Converter for Low-Voltage Grid Enables High Efficiency
By Philip KIEHNLE | |
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Abstract: Gallium Nitride (GaN) semiconductors with low inductance packages enable low switching losses andhigh efficiency. In this paper we present a compact arm PCB design with low loop inductance, allowingfor fast and efficient switching. The PCB includes four full-bridge cells for a 7 kW Modular MultilevelConverter (MMC) for low-voltage grid applications.
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| | Modular Battery-Integrated Power Electronics - Modelling, Advantages, and Challenges
By Nima TASHAKOR | |
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Abstract: Modular battery-integrated converters (dynamically reconfigurable modular batteries) are expanding intoemerging applications. Although widely popular, we are yet to fully exploit their potential. This paperprovides a critical discussion of the more neglected aspects with particular focus on electro mobility applications. It also provides insight on the challenges and/or concerns.
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| | Multi Busbar Sub-module Modular Multilevel STATCOM with Partially Rated Energy Storage Configured in Sub-stacks
By Chuantong HAO | |
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Abstract: This paper presents a modular multilevel STATCOM with partially rated energy storage configured insub-stacks based on full bridge multi busbar Sub-module (SM). The soft-paralleling mechanism anddoubled paths increase the current limit. The lower level controller of the proposed topology is detailed introduced and the performances are compared with a conventional single-busbar full bridge STATCOM controlled by classic SM sorting based low level controller. When providing reactive power compensation, power losses is reduced by 14.9\%, and the maximum SM voltage deviation is reduced by 35.2\%, while active power capability is further improved from power factor = 0.5 to power factor = 0.7 with the proposed control framework of the MBSM STATCOM.
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| | Multi-Objective Optimization of Modular Multilevel Converter Systems
By Nikolaus PATZELT | |
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Abstract: This paper investigates a multi-objective optimization method for modular multilevel converter systems. The method is applied to the AC-AC MMC topology, which connects the three-phase utility grid to the single-phase railway grid. The presented paper aims at a joint optimization of all system components providing a set of pareto-optimal system designs. The optimization space encompasses core system design parameters, such as the number of cells in a branch, the sizing of cell capacitor and branch inductance, but also the switching frequency and other parameters. The objectives studied in this paper are the overall system cost and losses. The considered constraints comprise limitations on system components as well as the power capability of the converter, compliance with grid codes and system efficiency. The obtained optimized design improved the total system cost by 7 \% compared to a manually derived benchmark design. It has been verified by offline and real-time simulations.
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| | Multilevel battery converter with cascaded H-bridges on cell level -battery management system or a renewed attempt for Power Electronic Building Blocks_
By Max ROTHENBURGER | |
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Abstract: The combination of battery management system and power electronics, using multi-level topologies ingeneral and cascaded H-bridges in particular, offers advantages over the state of the art. Theirevaluation must consider possible effects on battery life. Experimental studies of battery cells showthat these effects are small compared to typical loads.
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| | On chain-link based multi-port converters able to connect HVDC and MVDC to AC transmission network
By Daniele FALCHI | |
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Abstract: Multi-port converters may offer an attractive solution to contribute in achieving a more compact, flexible and efficient network. Recently, in literature, a few converter topologies have been proposed to interconnect high-power and high-voltage systems. Most of converter topologies are based on chain-link or modular concept, which is considered a very beneficial way to scale different ranges of voltages and current keeping a high level of reliability, feasibility and power quality. The aim of this paper is to provide, first, a qualitative description of a few selected multi-port converter configurations (non-isolated and fully isolated arrangements) able to interconnect HVDC, MVDC to HVAC systems. And, second, to present a qualitative comparison among cost and footprint of each topology. Also, the paper introduces some practical implications to take into account abnormal conditions e.g fault and port disconnections for such converters.
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| | Open-Delta SBC: a New Converter Topology with Low Number of Sub-Modules for MV applications
By Damiano LANZAROTTO | |
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Abstract: Medium voltage direct current (MVDC) technology has been experiencing a great boom of interest in recent years. This paper aims at giving a contribution to this field by proposing a new converter topology for MVDC applications. This topology is characterized by a low number of sub-modules (SMs) which is strongly related to the converter footprint and complexity. The new topology sizing is compared to the modular multilevel converter (MMC) for the same requirements to highlight advantages and disadvantages of the proposed solution.
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| | Overview and Evaluation of Energy Balancing Techniques for MMCs with Various Input and Output Frequencies
By Gyanendra Kumar SAH | |
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Abstract: This work provides an overview of all possible arm energy regulation techniques for the Modular Multilevel Converter (MMC). This research aims to identify all degrees of freedom (manipulated inputs) and possible combinations to regulate the arm energies of the MMC. Further, it offers a new generalized analytical toolchain to compare and evaluate the stability and performance of these balancing techniques. This toolchain includes normal operation, failure operation, and different three-phase and single-phase frequency conditions such as equal and unequal frequency applications (AC/AC, DC/AC). The common-mode voltage plays an essential role in regulating arm energies of the MMC for equal frequency operation. The proposed toolchain can also help to validate dimensioning of the converter analytically. Any existing energy balancing technique for MMC could be linked directly or indirectly to all derived energy balancing methods.
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| | Single-Arm MMC-based Converter for Transformerless Rail Interties
By Simon BECK | |
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Abstract: MMC-based converters are suitable to efficiently intertie the 50Hz three-phase grid with the 16.7Hz single-phase railway grid without a 16.7Hz transformer. In this paper, a new single-arm MMC-based converter topology with a multi-winding 50 Hz transformer is presented and simulated. The findings are compared to the direct and indirect MMC variants. The comparison shows a substantial reduction of the required number of modules, switches and installed semiconductor power with the proposed topology, while the system reliability is improved at the same time.
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| | Steady-State Analysis and Comparison of SSFB, SDFB and DSFB MMC-based STATCOM
By Mohamed Moez BELHAOUANE | |
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Abstract: This work focuses on the steady-state analysis of three types of MMC based STATCOM. For a given STATCOM rating, Double-Star Full Bridge, Single-Star Full Bridge and Single-Delta Full Bridge have been compared in terms of design and losses. In this approach, the number of submodules is chosen according to the voltage and current ratings of semiconductor devices while the submodule capacitor value is obtained by following an energy storage criterion to maintain the submodule voltages within an acceptable voltage range.
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| | Sub-Modules Switching Algorithms for Dual Active Bridge Modular Multilevel Converters to Optimize Capacitor Voltage Deviation versus Power Efficiency
By Peizhou XIA | |
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Abstract: This article firstly presents a detailed analysis and improvement for the dual active bridge employingMMC cells (MMC-DAB converter). The presence of MMC cells can effectively address the concernthat medium or high voltage level is beyond voltage rating of semi-conductor devices in conventionalDAB converter. However, the introduction of MMC cells results in significant losses originated fromresonance between line inductor and sub-module capacitor. Besides, the non-negligible switching loss is another factor of efficiency drop. In order to solve the additional losses and improve the overall conversion efficiency, this article proposes three innovative switching algorithms, where manipulating cell states to stop current oscillation and enable zero voltage switching (ZVS). Simulated results for a medium voltage level MMC-DAB converter is provided to verify the efficiency gain under optimal switching algorithms. Moreover, a 2-level MMC-DAB converter is implemented and the experimental result shows the proficiency of the converter.
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| | Ultra Low Loss - MMC Submodules favorable for SiC-FET enabling High Functional Safety
By Christopher DAHMEN | |
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Abstract: Further progress of Modular Multilevel Converters (MMC) is mainly related to advanced submodule topologies (SM), semiconductors (SiC) and improved control concepts. Fully electronic failure management for external failures (i.e. DC-short circuit) and protection against internal failures of the converter are key issues. A new submodule for MMC is presented, which meets these requirements. In addition, a novel SiC-JFET super-cascode is investigated, suitable for these and other applications.
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| | Utilizing the Reactive Current Control Capability of an MMC-Fed AC/DCConverter for Volt-Second Balancing in Medium Frequency Transformers
By Kaveh POURESMAEIL | |
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Abstract: The non-ideal behavior of power switches and/or circuit asymmetries in transformer-isolated convert- ers can result in nonzero average voltage across the transformer terminals, which, in turn, can saturate the transformer. In this paper, a volt-second balancing scheme is developed for a Modular-Multilevel- Converter (MMC)-fed AC/DC converter to avoid transformer saturation.
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| | Voltage Estimation for Diode-Clamped MMCs Based on a Simplified Neural Network
By Nima TASHAKOR | |
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Abstract: The modular multilevel converter (MMC) is a popular solution in high-voltage dc application and has significant potential in others. Generally, the MMC's stable operation is at the expense of numerous sensors, communication burdens, and complicated balancing strategies that can suppress its expansion in to cost driven applications. Hence, the introduction of a sensorless voltage balancing strategy with a simple controller is an attractive objective. A diode-clamped MMC offers a simple and yet effective solution by providing a balancing path between two modules through a diode. However, to compensate the lack of bidirectional energy transfer, modifying modulation technique is necessary. The level-adjusted phase-shifted carrier (LA-PSC) modulation introduces a small circulating current that ensures a correct balancing direction. Although the open-loop implementation of LA-PSC might be necessary for cost reduction in some applications, protection and control considerations may still necessitate careful monitoring of the modules' voltages. This paper proposes a voltage estimation strategy based on a simple neural network that does not require any measurement of the modules' voltages. Provided analysis as well as the simulation results confirm that the estimator can track the voltages with above 99\% accuracy during balanced and imbalanced conditions.
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| | Zero-Sequence Voltage Reduces DC-Link Capacitor Demand in Cascaded H-Bridge Converters for Large-Scale Electrolyzers by 40\%
By Roland UNRUH | |
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Abstract: Cascaded H-bridge Converters (CHBs) are a promising solution in converting power from a three-phase medium voltage of 6.6kV...30kV to a lower DC-voltage in the range of 100V...1kV to provide pure DC power to applications such as electrolyzers for hydrogen generation, data centers with a DC power distribution and DC microgrids. CHBs can be interpreted as modular multilevel converters with an isolated DC-DC output stage per module, require a large DC-link capacitor for each module to handle the second harmonic voltage ripple caused by the fluctuating input power within a fundamental grid period. Without a zero-sequence voltage injection, star-connected CHBs are operated with approximately sinusoidal arm voltages and currents. The floating star point potential enables to utilize different zero-sequence voltage injection techniques such as a third-harmonic injection with 1/6 of the grid voltage amplitude or a Min-Max voltage injection. Both well-known methods have the advantage to reduce the peak arm voltage and thereby the number of required modules by 13.4\% (to v3/2). This paper proves analytically that the third-harmonic injection with1/6 of the grid voltage amplitude reduces the second harmonic voltage ripple by only 15.1\% compared to no-voltage injection for unity power factor operation and balanced grid voltages. Then it is shown, that the Min-Max injection has the often overlooked advantage of reducing the second harmonic voltage ripple by even 18.8\% . By applying the here proposed zero-sequence voltageinjection in saturation modulation, the second harmonic voltage ripple of the DC-link capacitors is reduced by even 24.3\%, while still requiring the same number of modules as the Min-Max injection. For a realistic number of reserve modules, the overall energy ripple in the DC-link capacitors is reduced by 40\%.
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