The Modular Multilevel Converter for High Step-Up Ratio DC–DC Conversion

Abstract

Abstract-High step-up ratio dc-dc converters with megawatt ratings are of interest in wind turbine interfaces and HVDC systems. This paper presents a modular multilevel dc-dc converter based on the standard boost converter topology but with the normal single switches replaced by a number of capacitor clamped sub-modules. The converter is operated in resonant mode with resonance between sub-module capacitors and the arm inductor. A phase-shifted switching arrangement is applied such that there is a constant number, N of sub-modules supporting the high voltage at a time. In this operation mode, the step-up ratio is dependent on the number of sub-modules and the inductor charging ratio. The converter exhibits scalability without using transformer and is capable of bidirectional power flow. An application example of a wind turbine interface with a 10 : 1 conversion ratio is demonstrated in simulation. The experimental verification of the concept using a lab-scale prototype is provided.

An Input-Parallel-Output-Series Switched-Capacitor Three-level Boost Converter with a Three-Loop Control Strategy

“…Additionally, the average current across the switch S 2 is bigger than S 1 because the current across the diode D 2 added on the current of S 2 . These results prove correctness of the theoretically derived results shown in (28). On the whole, the simulation results basically verify the effectiveness of the IPOS-SC-TLB converter and the proposed three-loop control strategy.…”

Energy Storage Characteristic Analysis of Voltage Sags Compensation for UPQC Based on MMC for Medium Voltage Distribution System

“…In Equation (15), C is the SM capacitor, N is the number of submodules, U SMN is the rated voltage of the submodule, and U SM is the voltage of the submodule when the DC side voltage is discharged to 24 kV. ∆t = W S = W 3 × 10 6 = 74 ms (16) Considering that the series side sag compensation system requires energy from the capacitor energy storage case, in the case of the 3 MVA series side output, the theoretical calculation for the duration of the compensation system for 60% voltage sag is 74 ms; considering the loss of switches and other components, which would slightly decrease the duration, an approximate estimate is 60 ms.…”

“…MMC technology has obvious advantages in its application in the field of high voltage and large capacity represented by flexible DC transmission. It has been a breakthrough in the field of HVDC [14,15], and there has been a gradual shift to DC/DC converters [16,17], high-voltage DC power systems of high-power variable frequency drive [18], flexible AC transmission systems [19,20], and the development of large-scale photovoltaic grid-connected energy storage areas [21,22], These technologies have made many valuable contributions in scientific research as well as some engineering applications, showing good application prospects. The development of MMC technology enables the application of UPQC in the field of high voltage and large capacity [23].…”

Design of a Modular, High Step-Up Ratio DC–DC Converter for HVDC Applications Integrating Offshore Wind Power

“…By using the modular structure, the voltage stress on switching devices is decreased. The topologies in [14], [16], [17], [20], [23] are all bi-directional power conversion while the power flow is typically uni-directional for wind power systems. As a result, this paper develops a DC-DC converter for unidirectional power flow to transfer wind power from the wind farm to the HVDC terminal.…”