Abstract
Multiplicity of the triangular carrier signals is a criterion for the extension of sinusoidal pulse-width modulation, SPWM, to a number of output voltage levels per phase-leg in cascaded H-bridge (CHB) multilevel inverter (MLI). Considering medium and high voltage applications where appreciable number of output voltage levels from CHB MLI is needed, commensurate high number of carrier signals in either classical level- or phase-shifted SPWM scheme for this inverter is inevitable. High-quality output waveforms from CHB MLI system demands precise synchronization of these multi-carrier signals. Sampling issues, memory constraints and computational delays pose difficulties in achieving this synchronization for real-time digital implementation. This study presents a PWM template for CHB MLI. The developed control concept generates adequate modulation templates for CHB inverter wherein a sinusoidal modulating waveform is modified to fit in a single triangular carrier signal range. These templates can be used on CHB inverter of any level with no further control modification. Nearly even distribution of switching pulses, equal sharing of the overall real power among the constituting power switches and enhanced output voltage quality were achieved with the proposed modulation. For a 3-phase, 7-level CHB, simulation and experimental results, for an R-L load, were presented.
Highlights
In recent time, the field of power electronics has witnessed appreciable boost in the areas of power-conditioning circuit topologies and their corresponding control/modulation strategies
Inverters/dc-ac converters are among the cardinal power electronics devices deployed in various key areas such as high-voltage direct-current (HVDC) transmission, [1], [2], Flexible AC Transmission Systems (FACTS), [3], [4], renewable energy grid integration, [5]–[8], railway and vehicle traction, [9]–[11], energy storage systems, [12], marine propulsion, [13], solar water pumping system, [14], grinding and rolling mills, [15], compressors and extruders, [16], The associate editor coordinating the review of this manuscript and approving it for publication was Meng Huang
Therein, it was demonstrated that in-phase disposition (IPD) SPWM strategy could be deployed in the syntheses of multi output voltage levels in CHB multilevel inverter (MLI) using only one triangular carrier signal irrespective of the number cascaded H-bridge units
Summary
The field of power electronics has witnessed appreciable boost in the areas of power-conditioning circuit topologies and their corresponding control/modulation strategies. Therein, it was demonstrated that in-phase disposition (IPD) SPWM strategy could be deployed in the syntheses of multi output voltage levels in CHB MLI using only one triangular carrier signal irrespective of the number cascaded H-bridge units. Such representation still retains the contiguous bands occupied by these multi triangular carriers in the traditional level-shifted SPWM; since these bands are among the crucial prerequisites for proper stacking of the synthesized waveforms from each of the series H-bridges This modulation approach is based on the creation of multilevel waveform template, MWT, from which the power switches in all the H-bridge units are controlled. In the subsections that follow, explanations on the MWT creation, for phase a, are given following the block diagram shown in figure 2
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