Modulation and control of a new alternate arm multilevel converter for high-voltage direct current system with direct current fault ride-through capability

A new alternate arm multilevel converter composed of direction switch (DS) and cascaded H-bridge (CHB) with direct current (DC) fault blocking capability is presented. First, the topology and operation principles of the converter are introduced. Second, an overlap square modulation scheme for the DS is proposed to keep energy balance, then the nearest level modulation (NLM) is applied to the CHB, and a new capacitor voltages balancing strategy of sub-module in CHB is proposed. Third, blocking mode and multiple static synchronous compensator modes of the converter under DC fault condition are analyzed. Finally, the effectiveness of the modulation strategies and DC fault ride-through capability for the new alternate arm multilevel converter-based voltage direct current system is verified by PSCAD (R)/EMTDC (Manitoba HVDC Research Centre, Manitoba, Canada) simulations. Copyright (C) 2013 John Wiley & Sons, Ltd.