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This paper is about the design for the control of a cascaded hybrid converter for railway applications. It shows, how to control the converter with considerations of special aspects for the use in rail vehicles. It considers several aspects of reducing THD of the current and reduction of switching losses.
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...
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.
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...
The proposed control method for dual converters combines two approaches as space vector PWM (SVPWM) and finite control set model predictive control (FCS-MPC). The SVPWM is used for suitable output voltage vectors preselection and the FCS-MPC enables using a mathematical model of the system and a proposed cost function to reduce power losses and to redistribute power losses among transistors. The suitable...
In order to achieve high-quality, high-dynamic power amplification a method is proposed to split and process the current ripple independently from the main bulk current. As a consequence, low-power switching circuits with reduced stress, so-called basic crossover correction cells, can be effectively applied. Comparisons are presented to validate the proposals.
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...
The paper discusses an issue of the voltage balancing in the intermediate DC circuit of a three-level converter system for a smart grid application. A combination of two methods of the voltage balancing is presented in the paper. The voltages of DC-link capacitors, depending on the operating mode, are controlled by the three-level grid connected AC/DC converter or by the two level DC/DC converter...
This paper compares several multilevel topologies (3L-NPC, 3L-TNPC, 5L-ANPC and 5L-SMC converters) as an alternative to the 2L converter for low voltage applications, using low voltage IGBT modules. The comparative evaluations are made considering figures of merit such as the total losses and their power loss distribution, the amount of devices of each converter, the maximum output power, the harmonic...
The accurate control of the line current, robust and dynamic behaviour even under distorted grids and the behaviour on other faults are important requirements for grid connected inverter systems. This paper presents a sensorless grid voltage determination system in combination with an direct current control method optimized for multilevel inverters.
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...
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...
Modular Multilevel Converter (MMC) has served as a promising Voltage Source Converter (VSC) for High Voltage Direct Current (HVDC) applications. In this paper, a new MMC Submodule (SM) topology called Modified Switched Capacitor Sub-Module (MSCSM) is proposed. The MSCSM is able to block the DC fault using the power electronics semiconductor diodes due to its intelligent configuration without the need...
In modern traction drives the transformer causes a high amount of the overall losses. A transformer with lower losses however increases the THD of the output current and the amplitude of the fault current. Two converters will be presented which make the utilization of an enhanced transformer possible.
Supplying 25 kV, 50 Hz railway systems is a challenging task due to the load characteristics of those systems. Hence, several approaches are developed to improve their grid integration with the static frequency converter based substations. However, this supply system can be further refined by the application of a dc grid. Hence, this paper presents and discusses one possible approach to enhance the...
In the frame of a collaboration project within Swiss Competence Centre for Energy Research, a Multi Terminal DC pilot has been implemented. For the interaction with the medium voltage AC grid, a Modular Multilevel Converter has been designed for its features in low harmonic content, scalability, and flexibility. The control of converters in the MTDC network implements a non-dead band voltage control...
This paper presents a new modulation concept for three-to-single-phase direct AC/AC modular multi-level converter-based railway interties. The concept minimizes the inherent harmonic coupling between the two grid sides and is therefore particularly suited to operation at very low cell numbers and switching frequencies. Moreover, it facilitates the use of specific modulation methods, such as optimized...
The performance of a Modular Multilevel Converter (MMC) is presented in this paper, comparing Silicon (Si) and Gallium Nitride (GaN) semiconductors. Moreover, the benefits of high-frequency operation in a MMC topology are analysed along with a power loss distribution evaluation, highlighting the main advantages and drawbacks of different semiconductor technologies.
A Multilevel Cascaded H-Bridge (MLCHB) converter was designed and implemented for the application of an Ironless Axial Flux Permanent Magnet (IAFPM) motor drive. This paper provides an analysis of the IAFPM motor and the performance of the converter's ripple current regulation capabilities. Lastly a comparison between the simulation and the experimental results is presented.
A comprehensive energy balancing concept for the Modular Multilevel Converter (MMC) under unbalanced grid conditions was proposed. Grid supporting converters need to be able to fed unbalanced grid currents; grid failures lead to unbalanced grid voltages. Both unbalanced grid conditions generate energy unbalance inside the MMC. In order to handle these critical operating points, an analytical description...
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