A Three-Phase Symmetrical DC-Link Multilevel Inverter With Reduced Number of DC Sources

Abstract

This paper presents a novel three-phase DC-link multilevel inverter topology with reduced number of input DC power supplies. The proposed inverter consists of series-connected half-bridge modules to generate the multilevel waveform and a simple H-bridge module, acting as a polarity generator. The inverter output voltage is transferred to the load through a threephase transformer, which facilitates a galvanic isolation between the inverter and the load. The proposed topology features many advantages when compared with the conventional multilevel inverters proposed in the literatures. These features include scalability, simple control, reduced number of DC voltage sources and less devices count. A simple sinusoidal pulse-width modulation technique is employed to control the proposed inverter. The performance of the inverter is evaluated under different loading conditions and a comparison with some existing topologies is also presented. The feasibility and effectiveness of the proposed inverter are confirmed through simulation and experimental studies using a scaled down low-voltage laboratory prototype.

A Novel Concept for Three-Phase Cascaded Multilevel Inverter Topologies

“…A number of single phase MLI topologies along with different input voltage algorithms have been recently published [12][13][14][15][17][18][19][20][21][22][23]. The proposed three-phase inverter concept in this paper permits easy conversion of the existing single phase MLI into three-phase structures without tripling the number of semiconductor switches and dc-supplies as per the current conventional practice.…”

“…Several cascaded MLI topologies comprise two main parts; level generator and polarity generator as shown in Figure 1a can be found in the literature [12][13][14][15]. The level generator is a cascaded connection of a number of inverter cells that generates multilevel unipolar voltage while the polarity generator converts this unipolar voltage into bipolar voltage waveform [13].…”

“…The number of cascaded cells in the level generator may be increased and/or asymmetric input voltage sources can be used to enhance the number of levels in the output voltage waveform without any change to the polarity generator [12]. The level generator switches may work with high frequency, but the polarity generator switches always function at line voltage frequency [13].…”

“…Although several topologies have been proposed in the literature in order to reduce the device count and increase the number of levels in the output voltage of single phase CMLIs, the majority of these topologies have not been extended to three-phase structure yet. It is a common trend that the number of components of single phase topologies is tripled when they are extended to three-phase structures [13,14,[26][27][28].…”

Flexible cascaded multilevel inverter with multiple operation modes

“…Compared with traditional twolevel inverters, multilevel inverters are more suitable for PV systems due to their unique characteristics [3][4][5]. Multilevel inverters come with the benefits of reduced du/dt, reduced device voltage stress, improved output waveform quality and smaller filter inductance [6][7][8]. These benefits make it easier to meet the demands in photovoltaic applications.…”