Power direction control of medium frequency isolation DC/DC converter for modular double cascade converter

Strom

et al. 2015

IET Power Electronics

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The modular double-cascade converter (MDC) is a new multilevel AC/AC converter topology, which has a modular structure. The proposed topology can be used in medium-voltage motor and generator drives, and in interfacing of grids of different voltages and frequencies. MDC is formed with two sets of cascaded H-bridges where the isolation of the power modules is carried out with medium-frequency multiwinding transformers. Although the transformers have a transformation ratio of one, the presented topology can be used to transform the voltage level by using different connections for the input and output H-bridges. The number of steps of input and output voltages can be varied by connecting the modular units of MDC in series or in parallel. The functionality of the topology is verified by simulations of a seven-level version for a 3.3 kV, 1.1 MW application and experimental results are shown for a 400 V, 76 kW three-level inverter. In particular, an inherent submodule energy sharing capability through the transformer is analysed and assessed by simulations and experimental tests.

Section: Experimental Device and Resultsmentioning

confidence: 79%

Section: Modular Double‐cascade Convertermentioning

confidence: 99%

Modular double‐cascade converter for high‐power medium‐voltage drives

Strom

et al. 2015

IET Power Electronics

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“…In normal MDC operation the six winding voltages are synchronous rectangular waves whose amplitudes are determined by the highest DC link voltage. Submodules whose DC link voltages are lower than the winding voltages will receive energy through the transformer [4], [6], [7].…”

Section: System Descriptionmentioning

confidence: 99%

“…8. The nominal values of the system were selected in accordance with the parameters of the prototype system [6]. The parameters are listed in Table I.…”

Section: Simulationsmentioning

confidence: 99%

Flux and winding current balancing control for a medium-frequency six-winding transformer

IECON 2014 - 40th Annual Conference of the IEEE Industrial Electronics Society

Hannonen

et al. 2014

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Solid state transformers normally include a transformer whose operating frequency is well above the usual grid frequencies. These transformers are supplied by power electronic inverters such as an H-bridge. The average value of transformer supply voltage can drift to a non-zero value which may lead to saturation of the magnetic core. This paper presents an active control method to prevent saturation of a multi-winding mediumfrequency transformer. The control method comprises two control loops: the first balances the flux of the transformer and the other balances the currents in different windings. Simulation results which show the feasibility of the proposed control method are shown.

“…In the publications on the MDC, the grid is interfaced with diode bridges (Sankala et al, 2012(Sankala et al, , 2013(Sankala et al, , 2014a(Sankala et al, , 2015Korhonen et al, 2013a). In these publications, the focus is mainly on the medium-frequency transformer link, and the diode bridges are selected because higher DC link voltage fluctuations occur and reveal characteristics that would not be visible when an active front end is used.…”

Section: Grid Interfacementioning

confidence: 99%

Modular double-cascade converter

2012 Twenty-Seventh Annual IEEE Applied Power Electronics Conference and Exposition (APEC)

Strom

et al. 2012

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Medium-voltage motor drives extend the power rating of AC motor drives in industrial applications. Multilevel converters are gaining an ever-stronger foothold in this field. This doctoral dissertation introduces a new topology to the family of modular multilevel converters: the modular double-cascade converter.The modularity of the converter is enabled by the application of multiwinding mediumfrequency isolation transformers. Owing to the innovative transformer link, the converter presents many advantageous properties at a concept level: modularity, high input and output power quality, small footprint, and wide variety of applications, among others. Further, the research demonstrates that the transformer link also plays a key role in the disadvantages of the topology.An extensive simulation study on the new converter is performed. The focus of the simulation study is on the development of control algorithms and the feasibility of the topology. In particular, the circuit and control concepts used in the grid interface, the coupling configurations of the load inverter, and the transformer link operation are thoroughly investigated. Experimental results provide proof-of-concept results on the operation principle of the converter. This work concludes a research collaboration project on multilevel converters between LUT and Vacon Plc. The project was active from 2009 until 2014.