PROJECT TITLE :

Thermal Analysis and Balancing for Modular Multilevel Converters in HVDC Applications - 2017

ABSTRACT:

The modular multilevel converter (MMC) has become a terribly attractive solution for interfacing high voltages in hybrid networks. The MMC enables scalability to completely different power levels, full controllability provided by insulated-gate bipolar transistors, and will achieve terribly high efficiencies by using a low-switching-frequency method as the nearest level modulation. However, the nearest level modulation needs a capacitor voltage-balancing algorithm, that can end in unbalanced loading for the power semiconductors in the different submodules. Particularly at low-power-factor operation, that might occur within the case of low-voltage ride through and of reactive power injection, the standard algorithm isn't any a lot of effective. This paper provides thermal stress analysis of the MMC in operation and proposes a thermal balancing approach, that is embedded within the capacitor voltage-balancing algorithm. The purpose of the thermal balancing is to realize similar stress distribution among the different submodules to enhance the lifetime. The junction temperatures in the different submodules are studied for HVDC applications, and this paper proves experimentally that the thermal balance within the submodules is considerably improved.