Modelling approach for multi‐carrier‐based pulse‐width modulation techniques utilised in asymmetrical cascaded H‐bridge inverters

Abstract

The increasing use of medium-voltage drives and high-power equipment requires a detailed study on the switching method and topology of multi-level inverters. Asymmetric cascaded H-bridge topologies that have unequal input dc voltages with different devices in various parts of the cascaded H-bridge inverter (CHB) are representative of significant improvements in medium-voltage industrial drives. Various modulation strategies are used in multi-level power conversion applications. In the multi-carrier switching method for asymmetric CHB, the number of switches is less than carriers and is usually used in the offline switching method. These methods of switching are not applicable to online systems. In this study, equations for combining different pulse-width modulation (PWM) to use the controllability advantage of the multi-carrier method are introduced in asymmetric topologies. Then, the dual Fourier series equations are applied to model each inverter switching relation of the asymmetric cascaded blocks. To model each inverter switching relation of the asymmetric blocks using sinusoidal PWM, the dual Fourier series equations were applied. The presented analytical modelling switching method was validated using simulation and experimental case studies.

Seven‐level power conversion system for solar power generation system

“…Conventionally, each HI in a CHT multilevel power converter requires an independent DC voltage [5][6][7][8][9][10][11]. In the applications of SPGS, the CHT multilevel power converter can be divided into two structures, as shown in Fig.…”

“…Common types of multilevel power converter are cascaded Hbridge type (CHT) [5][6][7][8][9][10][11], flying-capacitor type (FCT) [12,13] and diode-clamped type (DCT) [14,15]. A DCT multilevel power converter uses several series capacitors in the DC bus to create different voltage levels and several clamped diodes are connected between the power electronic arm and these voltage levels.…”

“…However, the voltages in the capacitors for an FCT multilevel power converter should be carefully regulated by redundant switching states of power electronic arms [13]. A CHT multilevel power converter has several H-bridge inverters (HIs) that are connected in series [5][6][7][8][9][10][11]. Asymmetric voltages can be used for HIs in CHT multilevel power converter to increase the number of levels in the AC output voltage [10,11], but this is difficult to implement in DCT and FCT multilevel power converters.…”

“…Besides, several independent voltage sources are required for these HIs. The ratio of DC bus voltages for two HIs is 1:2 for generating a seven-level voltage and 1:3 for outputting a nine-level voltage [10,11]. Since each topology has its advantages and drawbacks, a hybrid multilevel converter has been developed [16][17][18].…”

Improved post‐fault operation strategy for a cascaded H‐bridge based STATCOM

“…STATCOM is a parallel‐connected device, which exchanges reactive power with the grid to improve voltage profile and voltage stability of the grid [1–4]. On the other hand, cascaded H‐bridge (CHB) converter is known as one of the most interesting topologies in FACTs, especially in STATCOM application [5–8]. Less number of power components, modular configuration and no necessity to isolated power sources in dc side of full‐bridge (FB) submodules make CHB (also known as the modular multilevel cascaded converter with bridge cells) an ideal candidate for reactive power compensation [8].…”