Modified Nearest Level Modulation for Full-Bridge Based HVDC MMC in Real-Time Hardware-in-Loop Setup

Jahangeer Badar Soomro,Jongsuk Ro,Irfan Sami,F Akhter,Syed Sabir Hussain Bukhari,Saddaqat Ali

doi:10.1109/access.2021.3105690

Jahangeer Badar Soomro, Jongsuk Ro + Show 4 more

Open Access

https://doi.org/10.1109/access.2021.3105690

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Abstract

Modular Multilevel Converter (MMC) is an emerging converter topology for medium and high voltage applications. Nearest level Modulation (NLM) is the conventional control topology used to control the MMC that produces the N+1 AC output waveform. In previous research work, the Modified NLM has been already proposed, producing a 2N+1 and 4N+1 output waveform while utilizing a half-bridge (HB) submodule (SM) topology. However, half-bridge-based MMC has a similar behavior as two-level Voltage Source Converter (VSC) and cannot block DC fault current in case of DC-side short circuit fault. So, in recent years, full-bridge-based MMC topology is preferably used by manufacturers as it has DC fault blocking capabilities. This paper presents the Modified NLM for Full bridge (FB) SM topology to take the critical benefits of FB SM topology and improve power quality. The proposed method is simpler to implement and produces a 4N+1 AC output waveform. The THD of the output voltage and current reduces to half compared to the conventional NLM method. The proposed method is verified using LabVIEW Multisim co-simulation and as well as real-time simulation.

Highlights

Modular Multilevel Converter (MMC) is a promising converter topology used nowadays, especially in the applications of High Voltage Direct Current (HVDC) Transmission systems and in multi-terminal DC (MTDC) grids due to its various advantages over conventional converters [1]
To increase the number of levels, the power quality of the output voltage and current Modified nearest level modulation (NLM) methods are presented in various research articles
The Modified NLC is implemented in FPGA-based controller Compact Reconfigurable input/output (CRIO), and the circuit is implemented in NI PXI for real-time results verification

Summary

INTRODUCTION

Modular Multilevel Converter (MMC) is a promising converter topology used nowadays, especially in the applications of High Voltage Direct Current (HVDC) Transmission systems and in multi-terminal DC (MTDC) grids due to its various advantages over conventional converters [1]. The conventional NLM method generates N+1 AC output levels (N is the number of SMs in the upper/lower arm) [14]. To increase the number of levels, the power quality of the output voltage and current Modified NLM methods are presented in various research articles. The authors in [15] proposed modified NLM for Half Bridge (HB) MMC to produce 4N+1 level output AC waveform. The authors in [17] proposed the binary, trinary, and modified MMC-based topology to improve power quality and reduce circuit complexity. In various other articles [21]–[25], the authors presented the Modified NLM method to improve the power quality and reduce the circuit complexity. The proposed modified NLC produces a 4N+1 AC output waveform which improves the power quality of the voltage and currents. The Modified NLC is implemented in FPGA-based controller Compact Reconfigurable input/output (CRIO), and the circuit is implemented in NI PXI for real-time results verification

WORKING PRINCIPLE OF MMC

PROPOSED MODIFIED NLC

Findings

CONCLUSION