A pinboard by
Mahmoud Fawzi

Assistant Professor, Port Said University


operating MMC HVDC networks to transfer power under DC faults

Modular multi-level converters (MMC) are considered a promising topology for HV applications like HVDC transmission systems. Such systems must be designed to provide high reliability against different types of faults. MMCs using Half-Bridge (HF) cells are well known for lacking the capability to block short circuits in the DC link. On the contrary, Full-Bridge (FB) can block the short circuit current in the DC link, they also enable the implementation of fault ride-through (FRT) functionalities, as the cells can generate bipolar voltages in this case. This paper presents a DC short circuit fault ride-through strategy for HVDC transmission system using an MMC topology with FB cells (FBMMC).


Circulating current mitigating scheme in MMC based HVDC system with H∞ repetitive controllers

Abstract: The Modular Multi-level Converter (MMC) topology is one of the most important switch mode converter topology and provides indispensable potential applications in the power systems industry, specifically, for High Voltage Direct Current (HVDC) transmission systems. Recent applications of MMC in HVDC transmission systems has posed problems such as circulating currents in the converter legs, which threatens the safe operation and also deteriorates the system’s performance. The circulating currents occur mainly due to the fluctuations in the capacitor voltages in the Sub Modules (SMs) of the MMC. Hence, in order to nullify the SM’s unbalanced voltage, this article aims to use a new counting sort based technique in conjunction with Carrier Phase Disposition Pulse Width Modulation Technique (CPD PWM). The increased harmonic content in the output voltage and current waveforms may be attributed to the unpredictable dynamics of capacitors. To address this, the article also proposes a cascaded voltage and current H∞ repetitive control scheme under normal and fault conditions. This entire scheme has been applied for back to back connected HVDC systems for mitigating the Total Harmonic Distortion (THD) in current and voltage respectively. Further, stability analysis for the proposed controllers has been performed to prove its robust operation and finally all the results have been explored.

Pub.: 05 Sep '16, Pinned: 17 Aug '17