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The following paper presents new fault tolerant converter topology for switched reluctance machines, that features multilevel output along with its advantages. The principle of operation in normal as well as in the fault conditions are described. Previously proposed modulation strategy including DC bus voltage balancing scheme is applied and tested in measurements. Low cost, discrete implementation...
A novel battery energy storage system (BESS) based on an enhanced modular multilevel converter (M2C) with the ability to switch its modules in parallel is being presented. Compared to a full-bridge M2C equipped with batteries as energy storage elements on its submodules, the losses are reduced by 20%. The raise in efficiency is thoroughly explained as well as its reliability. Its high efficiency,...
This paper analyzes the design and construction of a SiC-based Dual Active Bridge (DAB) converter for its use in a three-stage Power Electronic Transformer (PET) based on a Modular Multilevel Converter (MMC). The galvanic isolation between primary and secondary of the PET provided by the DAB High Frequency Transformer (HFT) is 24 kV. Challenges for the HFT design are discussed. A 5 kW DAB prototype...
Medium voltage grids are a suitable selection for the connection of high power applications. However, for certain applications, such as PV energy conversion systems or fast charging stations for PEVs, the DC voltages are limited to be below 1000 V, making difficult their connection to such grids without the use of a step-up transformer. Multilevel converters allow the grid connection of such DC loads,...
This paper describes a transformerless STATCOM (Static synchronous compensator) based on the MMCC-SDBC (modular multilevel cascade converter — single-delta bridge-cells) for independent control of positive- and negative-sequence reactive powers. A three-phase 200-V 6-kVA experimental system is designed, constructed and tested to verify the effectiveness of the topology and the control method including...
The AC/AC single-phase/single-phase Modular Multilevel Converter (MMC) presents very interesting features for the realization of a Medium Frequency Power Electronic Transformer for traction applications, in AC-fed or multisystem railway rolling stock, like locomotives, Electric Multiple Units (EMU), high-speed units, and so on. Aiming to maximize the output frequency of the converter, i.e. the operating...
This paper presents two predictive control methods with reduced number of calculations for five-level AC/DC rectifier. The first method is the simpler and required to calculate the value of cost function for only three converter voltage vectors. The second method is using two steps prediction horizon and required to calculate cost function for seven vectors in first step and for three vectors for...
The multilevel converters have advantages of low voltage stresses of the switches and possible reduction of size of the passive components. Input-series output-series (ISOS) configuration of the converter enable the utilization of low voltage rating switches in converters with high input voltage and high output voltage in applications that requires galvanic isolation. While multilevel topology offers...
The increasing number of renewable energy sources and their integration into the medium voltage grid leads to an increasing interest in multilevel structures for the interfacing power electronic converters. A feasible topology for MV applications is the Stacked Multicell Converter (SMC) offering a modular structure and several voltage levels. A robust control, current limiting strategies under grid...
Fault-tolerant multilevel inverters outperform known fault-tolerant 2-level inverters regarding efficiency and power density. The most promising fault-tolerant multilevel inverters for system voltages below 2 kV are the flying capacitor and the active neutral point clamped type. They differ regarding required voltage overrating of semiconductors, tolerance for open and short-on failure types and maximum...
An improved modulation algorithm is proposed for three-phase face-to-face topology. The algorithm could make the face-to-face dc transformer use 1: 1 ac transformer or omit ac transformer in a wide variable ratio range to reducing the volume of the system. The simulation in MATLAB/Simulink validates the proposed algorithm.
This paper presents a comparison between two DC-voltage balancing strategies for cascaded star-connected multilevel STATCOM: zero-sequence voltage, and negative-sequence current control. Different levels of unbalance and grid strengths are considered. The impact of the control strategies on the convert ratings in terms of voltage and current requirements are compared and the operating range of the...
The Advanced-ANPC converter is designed to withstand almost every possible short-circuit failure of the semiconductors in comparison to state-of-the-art (A)NPC converters. The idea behind this concept is an additional short-circuit inductor to improve the robustness against faults. The presented investigations within this paper examine all the possible short-circuit situations and their effects for...
The impact of capacitor voltage changes during the modulation period is examined in order to improve the arm voltage of a modular multilevel converter. Different methods are used to predict and compensate for the capacitor voltage change and the resulting arm voltage error, whereby two of the improvements provide a possibility to easily upgrade existing modulation algorithms. Simulation and measurement...
Recently, modular multilevel conterters (MMC) are also considered for medium voltage (MV) applications, where the number of modules and the switching frequency are relatively low compared to high voltage (HV) applications. In this context, standard modulation methods can cause relatively large output voltage errors. This effect is amplified even more, if the value of the module capacitances is decreased...
This paper presents the verification of a concept of operation and the in-depth analysis of the bidirectional multilevel switched capacitor converter with high voltage ratio and strongly limited stresses of switches. These features as well as efficiency and effective voltage ratio are investigated analytically by simulations and experiments presenting many original results.
A modular-multilevel (MMC) DC/DC converter is proposed in this paper, which can be deployed to inter-connect DC grid of different voltage levels, especially in the new energy sources such as wind power and solar power grid connection. Its key features include: 1) step-up and step-down operation. 2) bidirectional power flowing. 3) bi-directional fault blocking similar to a DC breaker. The operation...
In this paper a comparative loss analysis between a cascaded H-bridge (CHB) low-capacitance static compensator (LC-StatCom) with symmetrical I-V characteristics and a conventional CHB StatCom is presented. Effect of the capacitor voltage ripples on switching and conduction losses are determined through theoretical analysis. Simulation-based analyses on a 350-VA three-cell CHB LC-StatCom system are...
A multi-terminnal hybrid UHVDC is planned by China Southern Power Grid. The UHVDC system consists of one LCC-based sending end and two VSC-based receiving ends, rated at ±800kV. In this paper, steady-state control strategy is designed to coordinate LCC and VSCs at both sides. Smooth start-up, shutdown and reduced DC voltage operation are achieved.
This paper describes three modern predictive control methods of three-level AC/DC rectifier. Additionally, it presents a comparison of the methods both in static and dynamic states. Simulation and experimental results confirm that all presented control algorithms ensure a good control quality (low THD) in static states and excellent dynamic properties.
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