Triangular/trapezoidal current mode for high step ratio modular multilevel dc-dc converter
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Date
2022
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Abstract
Recent developments in dc powered technologies have increased interest in highly efficient dc-dc converters, especially at high voltage and high-step voltage ratios. Modular multilevel converters (MMCs) are an attractive alternative approach to this demand because they can manage medium and high dc voltages while using standard semiconductor devices with high efficiency if they employ soft-switching techniques. However, the latest soft-switching techniques proposed to MMCs require resonant circuits, limiting their operation. This thesis proposes a new zero-current switching modulation technique for a high-step-ratio MMC dc-dc converter without resonant circuits. The proposed modulation generates trapezoidal or triangular current as result of a rms current minimization problem. The proposal enables the soft-switching operation of the converter over a wide output voltage and power range, using a simple control scheme to regulate the output voltage and the voltage balance among the floating cell capacitors. The effectiveness of the proposed control strategy is validated through simulations and experimental results. Simulation results are obtained for a 1MW, 10kV to 1kV converter model developed in PLECS software. Additionally, a 1 kVA downscale prototype has been designed and constructed during this Ph.D. Simulation and experimental results for steady-state, bidirectional power-flow, and input voltage and load disturbances have confirmed the successful operation of the triangular/trapezoidal current mode. In all the experiments, the proposed control systems ensure proper capacitor voltage balancing, proving that the converter has satisfactory dynamic response and cell voltage balance over a wide output voltage and power range.
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Tesis (Doctor in Engineering Sciences)--Pontificia Universidad Católica de Chile, 2022
Tesis (Doctor of Philosophy in Electrical and Electronic Engineering)--University of Nottingham, 2022
Tesis (Doctor of Philosophy in Electrical and Electronic Engineering)--University of Nottingham, 2022