Multimodular UPFC operated by phase-shifted triangle carrier SPWM strategy

The acronym UPFC covers L. Ggugyi´s unified power flow controller and Akagi and Fujita´s unified power flow conditioner. The paper describes one method of meeting high MVA specifications by using multiple modules of 2-level, 3-phase power converter modules controlled by the phase-shifted triangle carrier technique of the sinusoidal pulse width modulation (SPWM) strategy. Two conceptual designs are presented: (1) the GTO-SPWM-UPFC at the lowest switching rate, f_c/f_m=3, to minimize GTO switching loss. The design is based on applying the fundamentals of SPWM theory to overcome unbalances arising from sideband harmonic interferences; and (2) the IGBT-SPWM-UPFC, at f_c/f_m=12 or higher, which SPWM theory assures that direct paralleling of the modules is free of current unbalance. A laboratory UPFC based on 6 modules of 3-phase, 5 kVA size, IGBT power converters operating at the baseline condition of dual unity displacement factor at the sending-end and the receiving end, has been implemented