Submodule Temperature Regulation and Balancing in Modular Multilevel Converters

In modular multilevel converters (MMCs), tem5 perature control of semiconductor devices in the submod6 ules (SMs) is a key factor for the safe and reliable opera7 tion. Under normal operation, significant temperature differ8 ences can exist between SMs due to, for example, aging of 9 semiconductor modules and module parameter mismatch. 10 This paper presents a method for achieving SM thermal bal11 ancing by controlling the capacitor voltage of each SM in an 12 arm, while maintaining the sum of the SM capacitor voltages 13 at a constant value in order to regulate the dc-link voltage. 14 The proposed temperature balancing strategy is validated 15 using an experimental MMC setup with three SMs, where an 16 increase in the thermal resistance to ambient of one or more 17 SM semiconductors is created by restricting coolant flow to 18 simulate a partial failure in the cooling system. Increases 19 in the thermal resistance by 21% and 42%, corresponding 20 to temperature increases of 5 and 10 ◦C, respectively, are 21 managed by three SMs, using a capacitor voltage margin of 22 60%. 23