Multilevel inverters (MLIs) have gained increasing interest for advanced energy-conversion systems due to their features of high-quality produced waveforms, modularity, transformerless operation, voltage, and current scalability, and fault-tolerant operation. However, these merits usually come with the cost of a high number of components. Over the past few years, proposing new MLIs with a lower component count has been one of the most active topics in power electronics. The first aim of this article is to update and summarize the recently developed multilevel topologies with a reduced component count, based on their advantages, disadvantages, construction, and specific applications. Within the framework, both single-phase and three-phase topologies with symmetrical and asymmetrical operations are taken into consideration via a detailed comparison in terms of the used component count and type. The second objective is to propose a comparative method with novel factors to take component ratings into account. The effectiveness of the proposed method is verified by a comparative study.

Voltage Source Multilevel Inverters With Reduced Device Count: Topological Review and Novel Comparative Factors

Z-Source Inverterの性能評価に関する検討

In this study, a fault-tolerant structure and its controlling method for a cascaded H-bridge multilevel inverter is introduced. When a fault occurs in one of the modules, the proposed circuit is able to isolate and eliminate the defective module from the whole system. The isolation and elimination is done by four relays in each module and a controlling circuit. This solution makes the system continue the normal operation by means of the remained healthy modules with decreased output voltage level. Therefore, the whole system failure will be prevented and higher reliability of the inverter will be guaranteed. Principles of operation and the controlling method are presented in this study. Reliability evaluation and comparison of the proposed fault-tolerant structure and the conventional one are considered. To ensure the correct performance of the proposed cascaded H-bridge multilevel inverter, a prototype has been synthesised in the laboratory. The obtained results affirm higher reliability and mean time to failure of the proposed circuit, so suitability of the proposed structure for sensitive industrial applications is confirmed.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-pel.2015.1025

Fault-tolerant structure for cascaded H-bridge multilevel inverter and reliability evaluation

Latterly, multilevel inverters have become more attractive for researchers due to low total harmonic distortion in the output voltage and low electromagnetic interference. This paper proposes a novel single-stage quasi-cascaded H-bridge five-level boost inverter (qCHB-FLBI). The proposed five-level inverter has the advantages over the CHB quasi-Z-source inverter in cutting down passive components. Consequently, size, cost, and weight of the proposed inverter are reduced. Additionally, the proposed qCHB-FLBI can work in the shoot-though state. A capacitor with low voltage rating is added to the proposed topology to remove an offset voltage of the output ac voltage when the input voltages of two modules are unbalanced. Besides, a simple PID controller is used to control the capacitor voltage of each module. This paper presents circuit analysis, the operating principles, and simulation results of the proposed qCHB-FLBI. A 1.2-kVA laboratory prototype was constructed based on a DSP TMS320F28335 to validate the operating principle of the proposed inverter.

Quasi Cascaded H-Bridge Five-Level Boost Inverter

In this letter, an enhanced step-up five-level inverter is proposed for photovoltaic systems. Compared with conventional five-level inverters, the proposed topology can realize the multilevel inversion with high step-up output voltage, simple structure, and reduced number of power switches. The operating principle of the proposed inverter has been analyzed and the output voltage expression has been derived. In addition, the comparison with existing topologies of single-phase five-level inverters is presented. Finally, experimental results validate the performance of the proposed topology.

An Enhanced Single-Phase Step-Up Five-Level Inverter

In this study, a structure of single-phase seven-level boost DC-link cascaded multilevel inverter (BDCLCMLI) is proposed. It consists of boost converter, DC-link module and H-bridge inverter. Compared with conventional CMLI and two level H-bridge inverter configurations, the proposed system results in reduction of voltage stress across the inverter switches, reduced power switches, DC source count and gate drive requirements. DC-link switching is achieved by multicarrier sinusoidal pulse-width modulation technique which results in improved quality of obtained output AC power. Reduction in DC source and switch count makes the system more cost effective. A simulation and prototype model of seven-level BDCLCMLI system is developed and its performance is analysed for various operating conditions.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-pel.2014.0746

Structure of boost DC-link cascaded multilevel inverter for uninterrupted power supply applications

Three-phase seven-level cascaded DC-link converter (CDCLC) is proposed for solar photovoltaic (PV) applications. The proposed configuration is integrated with stepped DC-link module (DCLM) and H-bridge inverter. In CDCLC configuration, the stepped DC-link voltage is attained through DCLMs with reduced inverter voltage stress. Compared with conventional two-level and three-level inverters, power spectral density in the multiples of switching frequency is significantly reduced. Elimination of inverter end filter components emphasises the advantage of CDCLC systems over conventional inverters. A reduction in DC sources, power switches, and gate driver units make the system more cost-effective over conventional cascaded multilevel inverter. To achieve the quality of power output in the proposed converter, carrier level shifted pulse width modulation (CLSPWM) schemes are developed for the DC-link converter switching. Simulated and experimental models of three-phase seven-level CDCLC configuration are developed and its performance is analysed for CLSPWM switching schemes.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/iet-rpg.2017.0360

Investigation on three-phase seven-level cascaded DC-link converter using carrier level shifted modulation schemes for solar PV system applications

This paper presents the experimentation of Cascaded Multilevel Inverter (CMLI) for Photo Voltaic (PV) generator feeding an isolated load. For the improvement of PV system utilization, boost chopper interfaced CMLI configuration is developed under Multicarrier Sinusoidal Pulse Width Modulation (MCSPWM) control schemes. Boost chopper interfaced CMLI configuration boost up the PV panel voltage and generates high quality of AC power for domestic and drive load applications. The entire systems of PV, boost chopper and CMLI are simulated using SIMULINK and the results are validated. Prototype hardware model of single phase boost chopper interfaced 7-Level CMLI configuration is developed and its output illustrations are validated

Experimentation of Boost Chopper Interfaced Cascaded Multilevel Inverter Topology for Photovoltaic Applications

This paper deals with the implementation of a single phase 15-level Sub-Multilevel Cascaded H-Bridge Inverter (SMCHBI) for variable speed industrial drive applications. It consists of sub-multilevel modules and H-bridge inverter configuration. Sub-multilevel switches synthesize stepped DC link voltage and current from the DC sources. H-bridge inverter switches renovate stepped DC link voltage and current into sinusoidal waveform. Compared with conventional Cascaded Multilevel Inverter (CMLI), the proposed system employs the reduced number of power switches, DC sources and gate driver requirements. The proposed system not only reduces the overall system cost but also reduces the voltage stress across the inverter switches. The proposed system does not required additional resonant soft switching circuits for Zero Voltage Switching (ZVS) of inverter. In the proposed method, variable frequency method is adopted for the speed control of industrial induction motor drives. A prototype model of 15-level SMCHB is developed and the performance of the systems is validated experimentally.

Structure of 15-Level Sub-Module Cascaded H-Bridge Inverter for Speed Control of AC Drive Applications

This paper presents the solar power based maximum boost Z-Source Inverter (ZSI) for Uninterruptible Power Supply (UPS) application. The concept of maximum boost Z-source can be applied to all dc-to-ac, ac-to-dc, ac-to-ac, and dc-to-dc power conversions. The maximum boost ZSI topology overcomes the limitations of conventional boost converter interfaced with Voltage Source Inverter (VSI). By this new topology, solar power is utilized properly with minimum controller circuit. The proposed system can maintain the desired output voltage through proper switching of maximum boost Z-source inverter. A prototype model of solar powered 400VA UPS system is designed and implemented. The entire system is simulated using SIMULINK and its performance is analyzed with experimental results.

R. Uthirasamy

Papers

Structure of boost DC-link cascaded multilevel inverter for uninterrupted power supply applications

Investigation on three-phase seven-level cascaded DC-link converter using carrier level shifted modulation schemes for solar PV system applications

Experimentation of Boost Chopper Interfaced Cascaded Multilevel Inverter Topology for Photovoltaic Applications

Structure of 15-Level Sub-Module Cascaded H-Bridge Inverter for Speed Control of AC Drive Applications

Design and realization of maximum boost Z-Source Inverter for solar power applications