DC-Voltage-Ratio Control Strategy for Multilevel Cascaded Converters Fed With a Single DC Source

Abstract

Recently, a multilevel cascaded converter fed with a single dc source has been presented. An analysis of the steady state working limits of this type of converter is presented in this paper. Limits of the maximum output voltage and the minimum and maximum loading conditions for a stable operation of the converter are addressed. In this paper, a way to achieve any dc voltage ratio (inside the stable operation area of the converter) between the H-bridges of the single dc source cascaded H-bridge converter is presented. The proposed dc voltage ratio control is based on a time domain modulation strategy that avoids the use of the inappropriate states to achieve the dc voltage ratio control. The proposed technique is a feed-forward modulation technique which takes into account the actual dc voltage of each H-bridge of the converter leading to output waveforms with low distortion. In this way, the dc voltage of the floating H-bridge can be controlled whilst the output voltage has low distortion independently of the desired dc voltage ratio. Experimental results from a twocell cascaded converter are presented in order to validate the proposed dc voltage ratio control strategy and the introduced concepts.

New Three-Phase Multilevel Inverter with Shared Power Switches

“…In a search for more innovative designs, recent studies have introduced modifications to the existing topologies [10]- [12]. Other studies have introduced combinations of various low and high switching frequencies to develop hybrid control methods [13], [14].…”

Design of an FPGA Based Controller for Delta Modulated Single-Phase Matrix Converters

“…The matrix converter (MC) is an advanced circuit topology that offers many advantages such as the ability to regenerate energy back to the utility, sinusoidal input and output currents and a controllable input current displacement factor [4]. It has the potential for affording an "all silicon" solution for AC-AC conversion and for removing the need for the reactive energy storage components used in conventional rectifier-inverter based systems [5].…”

Dual Vector Control Strategy for a Three-Stage Hybrid Cascaded Multilevel Inverter

“…• Replacing the dc supply of the lower voltage stages with capacitors and controlling the inverter to receive zero average power from the capacitor-fed stages [21], [22].…”

“…The approach of combining high and low switching frequencies for various stages of a hybrid inverter has been considered recently [21], [26] where the two level stages have been operated in square wave mode, while the three-level inverter has been controlled by a carrier-comparison PWM strategy. In [38] a 9-level, 3-stage, asymmetrical cascaded MLI has been controlled with a hybrid strategy; the high power cells have been operated at the fundamental frequency while the low power stage is controlled by high frequency PWM.…”

“…In this case PWM control can be considered as in [21], [26], [38]. In other studies, when the dc souring is selected to have a maximum number of levels PWM control is unsuitable as the high voltage stage will be subjected to a high switching frequency as in [13].…”