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Thermal regulation and balancing in modular multilevel converters

Goncalves, Jorge 2018. Thermal regulation and balancing in modular multilevel converters. PhD Thesis, Cardiff University.
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Modular multilevel converters (MMCs) are envisaged as the key power electronic converter topology to enable a multi-terminal pan-European high voltage direct current (HVDC) Supergrid for the interconnection of offshore wind farms and exchange of energy between different countries. A key feature of MMCs in the large number of semiconductor devices employed in each converter station, distributed over a stack of series-connected sub-modules (SMs). These semiconductors possess strict thermal limits, which can constrain the operating range on the converter by limiting its capability of providing enhanced functionalities to the AC grid such as short-term power overloads. Furthermore, due to different loading conditions and ageing, significant temperature differences can exist between SMs which can lead to a very different lifetime expectancies for the semiconductor modules. This thesis proposes active thermal control methodologies to act of two distinct converter levels. Firstly, two novel dynamic rating strategies are proposed to define the converter current injection limit as a response to the maximum semiconductor temperature feedback. This enables the exploitation of the semiconductors thermal headroom to provide short-term power overloads, which can be used for the improvement of the frequency support of a power-distressed AC grid. Secondly, a SM-level temperature regulation and balancing algorithm is proposed, aiming at the equalisation of the maximum semiconductor die temperature in all the SMs of an MMC arm. The proposed methods are validated in a detailed and combined electro-thermal simulation model with 3 and 10 SMs per arm developed in MATLAB®/Simulink® using PLECS® Blockset. An experimental platform has been designed and utilised to verify the effectiveness of the dynamic rating strategies and the SM temperature regulation and balancing strategy.

Item Type: Thesis (PhD)
Status: Unpublished
Schools: Engineering
Uncontrolled Keywords: Power Electronics; Electrical Engineering; Semiconductors Temperature Control; HVDC; MMC; Thermal Management.
Date of First Compliant Deposit: 1 March 2018
Last Modified: 03 Sep 2021 15:19

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