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In this paper the design and measurement results of a grid analysis and grid impedance measurement system are presented. The system is provided to measüre the freqüency dependent grid impedance in different PoCs to detect resonances and improve the power quality especially of grids with high amount of DERs. Moreover Active Filtering (AF) and reactive power feed-in are possible. It comprises also measurement...
This paper addresses the modular multilevel converter applied as a static synchronous compensator. The main objective of this work is to compare the converter performance considering two different submodule capacitor voltage balancing strategies: nearest level control and phase-shifted pulse width modulation, during positive and negative sequence current injection. Results of a 15 MVA MMC STATCOM...
In this paper the effects of the circulating currents on the modular multilevel converter, for HVDC applications, are presented. The first part is a review of an analytical study of the converter, aimed to minimize the capacitors rms current. In the second part the effects on the converter efficiency and on the safe operating area (SOA) margins are studied.
The paper deals with loss issues in an experimental 3.3 kV drive system consisting of back-to-back three-level NPC converter integrated with an induction machine. This integration significantly reduces the size and weight of the whole drive system. It also allows for a better understanding of loss generation and verifying the effect of operational conditions on such losses e.g. the effect of the converter...
The impact of converter based generation systems on transmission and distribution grids is steadily increasing. Therefore, new control efforts regarding fault ride-through, fault current injection and voltage support are necessary. These grid services lead to high stress on the converter which has to be protected thoroughly in any operation mode. Especially conditions, where the grid voltages become...
Modular multilevel topologies are possible candidates for medium-voltage wind turbines because of their scalability and possible redundancy. This paper concentrates on their design and investigates the influence of generator-to-grid voltage ratio, generator nominal frequency, module-capacitance minimising control approaches, third harmonic injection and fault ride-through capability requirement on...
Electromobility is expected to successfully compete with conventional propulsion technology in the near future and thus creates new challenges for the automotive industry. Major issues with state of the art electric vehicles (EVs) include limited range due to insufficient energy density and heavy weight of existing battery storage systems, unsatisfactory charging duration as well as comparatively...
Multi-level flying-capacitor converters are a promising topology for low-power applications. Conventional buck, 3- and 4-level converters have been modeled as a geometric program and optimized for loss and volume. Results show that 3- and 4-level converters are both smaller and more efficient over a wide range of design parameters.
This paper presents a modular multilevel Chain-link converter with reduced energy storage requirement by utilizing an active filter storage method at the converter cell level. The active filter circuit and control are analyzed in detail. A comparison with the conventional cell proves the effectiveness of the reactive energy storage reduction.
The most stressful operation point for the inverter of an electric vehicle drive is at low speed. In this operation point, one power semiconductor is mainly stressed because of a high loss concentration. The possibilities of distributing the losses among the power semiconductors through a new modulation is studied for the three-level NPC and the T-Type inverter. The effect of the proposed modulation...
This paper proposes a systematic procedure in order to make an optimal comparison/selection of modulation techniques and output LCR filter components for adjustable speed drives. Useful indicators are identified, which may help the designer to a global solution, optimizing the modulation-filter selection. The procedure is applied into the design of a real 6.6 kV equipment.
This paper analyses new model-predictive modulation strategies applied to hybrid Silicon Silicon-Carbide cascaded H-bridge (CHB) converters. The analysis identifies a suitable ratio of Silicon to Silicon-Carbide cells and the appropriate modulation strategy applied to this topology concept. The evaluation is based on semiconductor losses and harmonic performance.
The trend in wind turbines has shown an ongoing power rating growth, reaching sizes up to 10 MW. Multilevel converters have therefore become a favourable solution for Multi-MW Wind Energy Conversion Systems (WECSs), due to high efficiency, reliability, controllability and the ability to reach high power/voltage ratings. Moreover, stringent grid codes to regulate the connection of WECSs to the electrical...
With the aim to solve the unbalanced thermal behavior in the modular multilevel converter, introduced by mismatch in the submodule parameters, a thermal balancing control strategy is proposed here. The proposed solution ensures a balanced junction temperature for the power devices, while the balance between the capacitor voltages is maintained.
The average switching frequency of the Modular Multilevel Converter (MMC) is a characteristic system parameter, which affects the losses of the converter system. Several investigations were done to reduce the switching frequency by applying different modulation strategies. Up to now the switching frequency is always an indirect and random outcome of the modulator and it is not directly controlled...
In this paper, branch energy balancing as part of a generalised control concept for modular multilevel converter topologies is investigated. A way to derive an optimal branch energy balancing regarding current stress is introduced. Afterwards, this generalised approach is applied to the Modular Multilevel Converter as an example topology. The approach is tested via simulation and verified with a low-voltage...
In this paper, a comparison of the energy storage requirements is performed for the modular multilevel converter (MMC) with half-bridge and full-bridge submodules as well as for the alternate arm converter (AAC). Concerning the AAC, the operational mode with overlap period is taken into account and an analytical relation between the overlap angle and the modulation index is presented. This ensures...
The modular multilevel converter (MMC) has become a very attractive solution for interfacing high voltages hybrid networks. The MMC enables scalability to different power levels, full controllability provided by IGBTs and can achieve very high efficiencies by using a low switching frequency method as the nearest level modulation (NLM). However, in order to limit failures of the power modules, the...
Development and research for power converters is focused on high power density, high modularity, low costs as well as high reliability and efficiency. The use of multilevel converters, like Neutral Point Clamped (NPC) Converters, in high power applications in the range of 1.5 MW up to 6MW can be favorable because of the filter size reduction and therefore reduction of weight and total volume of the...
A control structure for the modular multilevel converter motor drive with integrated energy storage system (ESS) is described. The control approach uses the ESS to limit the cell capacitor voltages and to avoid circulating currents in the converter at low output frequencies.
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