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Your search keyword '"Xiaotian Zhang"' showing total 3 results
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3 results on '"Xiaotian Zhang"'

1. A Compact Modular Multilevel DC–DC Converter for High Step-Ratio MV and HV Use

Author

Thomas Luth, Xin Xiang, Timothy C. Green, Michael M. C. Merlin, Xiaotian Zhang, and Engineering & Physical Science Research Council (EPSRC)

Subjects
Technology, Computer science, 02 engineering and technology, TRANSFORMER, DC/DC CONVERTER, Inductor, Topology, 09 Engineering, law.invention, Engineering, DESIGN, law, 0202 electrical engineering, electronic engineering, information engineering, Inductors, modular multilevel converter (MMC), POWER-CONVERSION, Transformer, compact volume, Instruments & Instrumentation, Network topology, ACTIVE-BRIDGE CONVERTER, OFFSHORE WIND FARMS, Electrical engineering, Modular multilevel converter, Power (physics), Offshore wind power, Capacitor, DC-DC power converters, dc grids, Electrical & Electronic Engineering, Compact volume, 020209 energy, Capacitors, HVDC transmission, high step-ratio, FREQUENCY, CONNECTION, Automation & Control Systems, Electrical and Electronic Engineering, 08 Information And Computing Sciences, Science & Technology, business.industry, 020208 electrical & electronic engineering, Engineering, Electrical & Electronic, Modular design, Control and Systems Engineering, Voltage control, OPERATION, Inverter, business, SYSTEM, Voltage
Abstract

In multi-terminal dc networks or future dc grids, there is an important role for high step-ratio dc-dc conversion to interface a high voltage network to lower voltage infeeds or offtakes. The efficiency and controllability of dc-dc conversion will be expected to be similar to modular multi-level ac-dc converters. This paper presents a modular multilevel dc-dc converter with a high step-ratio for medium voltage and high voltage applications. Its topology on high-voltage side is derived from the half-bridge single-phase inverter with stacks of sub-modules replacing each of the switch positions. A near-square-wave current operation is proposed which achieves near-constant instantaneous power for single-phase conversion, leading to reduced stack capacitor and filter volume and also increased the power device utilization. A controller for energy balancing and current tracking is designed. The soft-switching operation on the low-voltage side is demonstrated. The high step-ratio is accomplished by combination of inherent half-bridge ratio, sub-module stack modulation and transformer turns-ratio, which also offers flexibility to satisfy wide-range conversion requirement. The theoretical analysis of this converter is verified by simulation of a full-scale 40MW, 200 kV converter with 146 sub-modules and also through experimental testing of a down-scaled prototype at 4.5 kW, 1.5 kV with 18 sub-modules.

Published
2018

2. A New Resonant Modular Multilevel Step-Down DC–DC Converter with Inherent-Balancing.

Author

Xiaotian Zhang, Green, Timothy C., and Junyent-Ferre, Adria

Subjects
*RESONANT power convertors, *DC-to-DC converters, *HIGH voltages, *ELECTRIC transformers, *POWER electronics, *ELECTRIC power conversion
Abstract

Modular multilevel converters (MMCs) have become increasingly interesting in dc-dc applications, as there is a growing demand for dc-dc converters in high-voltage applications. Power electronics transformers can be used for high step-down ratio dc-dc power conversion, with high power rating and efficiency achieved. However, this arrangement requires a large number of high isolation voltage transformers and a complicated balancing control scheme. To provide a simple solution with inherent voltage balancing, this paper presents a new resonant MMC topology for dc-dc conversion. The proposed converter achieves high-voltage step-down ratio depending on the number of submodules. The converter also exhibits simplicity and scalability with no necessary requirement of high-voltage isolation transformers. By using phase-shift control, a much higher converter operating frequency is achieved compared to the switching frequency. Resonant conversion is achieved between the series inductor and submodule capacitors. The operation principle and theoretical analysis are presented in this paper, which have been verified by experimental results based on a bench-scale prototype. [ABSTRACT FROM AUTHOR]

Published
2015
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3. Analysis of Boost PFC Converters Operating in the Discontinuous Conduction Mode.

Author

Xiaotian Zhang and Spencer, J. W.

Subjects
*CONVERTERS (Electronics), *DISCONTINUOUS functions, *ELECTRIC conductivity, *ASYNCHRONOUS circuits, *SWITCHING theory
Abstract

As power factor correction (PFC) converters for low-power applications usually operate in the discontinuous conduction mode (DCM), operating in continuous conduction mode (CCM) will produce input current distortion. This distortion can be observed in a few switching cycles of one line cycle. Asynchronous switching maps are derived to obtain the time-domain waveforms of input current and output voltage. It can be seen that the cause of the distortion is the change in the current conduction mode. A model for PFC converters operating in DCM with fixed switching frequency and duty-ratio is developed, which can predict the converter operation mode under practical circumstances. Analysis of the output voltage and power limitations is provided based on the proposed model. Simulation and experimental results are presented to verify the proposed method. [ABSTRACT FROM AUTHOR]

Published
2011
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