Modulation and Control for a New Hybrid Cascaded Multilevel Converter With DC Blocking Capability

• Published in: IEEE transactions on power delivery Vol. 27; no. 4; pp. 2227 - 2237
• Main Authors: Xue, Yinglin, Xu, Zheng, Tu, Qingrui
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.10.2012; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Applied sciences; Asymmetrical square-wave modulation (ASWM); capacitor voltage-balancing control; Capacitors; Carriers; Circuit faults; Connection and protection apparatus; Converters; Convertors; dc fault; Decision support systems; Direct current; Electrical engineering. Electrical power engineering; Electrical machines; Electronics; Energy flow; Exact sciences and technology; hybrid cascaded multilevel converter (HCMC); Modulation; Multilevel; Other multijunction devices. Power transistors. Thyristors; Overcurrent; phase-shifted carrier (PSC); Power electronics, power supplies; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Strategy; Switches; Voltage control; Performance evaluation; Very low frequency; Power converter; Stacking; Power system stability; Asymmetrical square-wave modulation (ASWM); capacitor voltage-balancing control; phase-shifted carrier (PSC); Spread spectrum; Selector switch; Multilevel system; Direct sequence; Short circuit currents; Phase shift; Insulated gate bipolar transistor; dc fault; Finite state machine; Voltage regulation; Power electronics; Switching; Voltage source converter; Diversity combining; hybrid cascaded multilevel converter (HCMC); Pulse duration modulation; Capacitor; Cascade connection; Square wave; Overcurrent protection
• ISSN: 0885-8977; 1937-4208
• DOI: 10.1109/TPWRD.2012.2207743

The hybrid cascaded multilevel converter is a newly introduced voltage-source converter with dc blocking capability. It has two key parts, that is, the director switch (DS) made of insulated-gate bipolar transistors in series and the wave-shaping circuit (WSC) containing stacks of full-bridge submodules (FSMs). This paper focuses on the modulation schemes of the DSs and the WSCs. First, to reduce switching losses of the DSs, a novel asymmetrical square-wave modulation at a very low frequency is proposed, and the energy flow of the WSC under this modulation is analyzed. Second, modified phase-shifted carrier-based pulsewidth modulation (PSC-PWM) is presented to determine the number of FSMs to be inserted or bypassed; and the specified FSMs to be fired are selected according to the capacitor voltage-balancing strategy. Third, the capability to limit the short-circuit current during the dc fault is investigated, and fast ac overcurrent protection is designed. The effectiveness of the modulation and control strategies is verified by PSCAD/EMTDC simulations.