PROJECT TITLE :

Virtual Capacitor Control: Mitigation of DC Voltage Fluctuations in MMC-based HVDC Systems - 2017

ABSTRACT:

The modular multilevel converters (MMCs) have emerged as the foremost suitable converter technology for HVDC applications. Besides the recognized advantages over typical voltage supply converters, one among the remarkable options of the MMC is its ability to store energy in the distributed submodule capacitors. This important feature will be used to mitigate the fluctuations of the DC voltage, which is inherently volatile against power disturbances compared to the frequency of standard AC systems. This paper proposes a unique management strategy, known as virtual capacitor management, that permits the use of the energy storage capability of the MMC to attenuate voltage fluctuations of HVDC systems. With the proposed control, the MMC behaves as if there have been a physical capacitor whose size is adjustable and will be even bigger than the physical capacitor embedded within the converter. This management permits the system operator to optionally change this virtual capacitor of every MMC station and, so, it provides a further degree of freedom to the HVDC system operation. The EMT simulations of a 401-level MMC-based mostly HVDC link system show the effectiveness of the proposed management to boost dc voltage transient dynamics.