Switched-capacitor Multilevel Inverters Research Articles

A Dual Source Switched-Capacitor Multilevel Inverter with Reduced Device Count

Implementing voltage boost multilevel inverter topologies for PV and fuel cell energy sources is highly advantageous. Switched-capacitor multilevel inverters (SCMLI) have a step-up feature with low device requirements and can remove the need for high gain dc-dc converters leading to reduced overall system bulk. This work proposes a dual input SCMLI to achieve an output of nineteen levels while using a low number of components and high boosting factor and self-balancing of capacitor voltages. A comprehensive analysis of the proposed structure is presented, focusing on component requirements, cost and dynamic performance. The efficiency and loss distribution during operation is also provided. The operation and real-time performance of the SCMLI have been verified by simulation. Experimental results further validate the simulation results.

A new generalized cross-connected switched capacitor multilevel inverter topology with high output voltage gain for single phase solar PV unit

Switched capacitor multilevel inverters are gaining much attention these days due to their merits like voltage boosting and voltage balancing characteristics. A Cross Connected Switched Capacitor Multilevel Inverter (C2SC-MLI) topology is proposed in this work. It can synthesize thirteen levels in the terminal voltage waveform and with a voltage boost ratio of 1:3. The topology is extendable by adding additional “n” modules in series. The number of levels (NLevel) and the voltage gain can be increased up to 4i+9 and 1:(i+2) respectively by connecting ‘i’ such ‘n’ modules. The topology also has inherent voltage balancing ability. To prove the advantage of proposed topology it is compared with recent switched capacitor multilevel inverter topologies and conventional multilevel inverter topologies in terms of number of power electronic components required, cost and voltage gain. The performance of proposed topology is validated using simulation in MATLAB and with an experimental prototype rated 0.1 kW fed by a solar PV emulator under steady state and dynamic loading conditions.

A new switched-capacitor multilevel inverter with soft start and quasi resonant charging capabilities

Switched-capacitor multilevel inverters (SCMLIs) are gaining widespread attention in recent decades due to their simple design, voltage boosting capability, and inherent capacitor voltage balancing feature. However, the advantages offered by SCMLIs come at the cost of employing a higher number of active and passive components and capacitor voltage balancing issues with an inrush current profile. This paper introduces a novel configuration of SCMLIs with a lower number of power components with inherent voltage boost. The basic 5-level topology consists of a single capacitor, an inductor, a diode, and seven active switching elements. To improve the transient response and the inrush current profile of the converter, a soft start and quasi-resonant charging capability has been explored and implemented. Considering the inherent capacitor voltage balancing of the proposed SCMLI, a new finite control set-model predictive control (FCS-MPC) method with a single objective and a less computational burden is also developed, which contributes to injecting a fully controlled current for the grid-connected applications. The proposed topology is compared with other existing five-level inverter topologies to show its superior capabilities/advantages. And finally, the performance of the proposed topology and its associated FCS-MPC mechanism are validated by the measurement results.

Switched Capacitor Based Cascaded Half-Bridge Multilevel Inverter With Voltage Boosting Feature

Cascaded multilevel inverter (CMI) topology is prevalent in many applications. However, the CMI requires many switches and isolated dc sources, which is the main drawback of this type of inverter. As a result, the volume, cost and complexity of the CMI topology are increased and the efficiency is deteriorated. This paper thus proposes a switched-capacitor-based multilevel inverter topology with half-bridge cells and only one dc source. Compared to the conventional CMI, the proposed inverter uses almost half the number of switches, while maintaining a boosting capability. Additionally, the main drawback of switched-capacitor multilevel inverters is the capacitor inrush current. This problem is also averted in the proposed topology by using a charging inductor or quasi-resonant capacitor charging with a front-end boost converter. Simulation results and lab-scale experimental verifications are provided to validate the feasibility and viability of the proposed inverter topology.

Switched Capacitor-Based 13L Inverter Topology for High-Frequency AC Power Distribution System

The power converters are taking responsibility to produce high-quality output voltage and current waveforms from the various PV sources. Recently, PV applications focus on high-frequency ac power distribution (HF-AC-PD). In particular, dc/ac switched capacitor multilevel inverters (SCMLIs) significantly reduce the power conversion stages and components, which result in high conversion efficiency. This article proposes a new SCMLI topology with a reduced number of switches and a self-balanced floating capacitor (FC) voltage. The proposed topology is configured as a single dc source and three dc sources. The proposed topology generates thirteen level output voltage waveforms, and the output voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{o}$ </tex-math></inline-formula> ) is two times higher than the input voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{in}$ </tex-math></inline-formula> ). The discharging time is less than the recently suggested topologies. Furthermore, the voltage stress on switches is reduced to 50% concerning the load voltage. Thus, a remarkable reduction in the bulky size of the FC is achieved. The simulation results are discussed for different fundamental frequencies of 360 Hz, 400 Hz, and 1 kHz and considering various loads. The proposed converter prototype is designed in the laboratory for 2 kW, and the results are presented. The results show a good agreement in terms of total harmonic distortions, power loss, and efficiency.

Analysis and implementation of a generalised switched‐capacitor multi‐level inverter having the lower total standing voltage

Most of the switched capacitor multi-level inverters (SC-MLIs) are designed with a single isolated voltage source and capacitors where voltage levels are obtained by the addition of these sources only. The common problems arise in SC-MLIs are an unequal number of conducting paths, higher voltage drop across capacitors, sum of total inverter DC link voltages across the highest voltage rated switches and higher total standing voltage (TSV). The motivation of this work is to design a hybrid generalized SC-MLI with reduced components aiming to maintain a constant voltage across the capacitors, to achieve higher voltage gain with minimum components used, minimum conducting paths, lower TSV, cost-effective and an efficient inverter. A generalised SC-MLI structure is also proposed, which can multiply the voltage across the capacitors in a binary asymmetrical manner. The design parameters of the proposed hybrid SC-MLI topology are compared with the recently developed SC-MLIs in terms of the number of switches, capacitors, TSV, conducting switches and industrial components cost to prove its superiority and effectiveness of the proposed inverter. The experimental prototype of a specimen 9-level and 17-level inverters are implemented using DS1103 and the corresponding results are presented.

A Novel Switched-Capacitor Multilevel Inverter Topology for Energy Storage and Smart Grid Applications

The recent advancement in the application of the internet of things in the smart grid has led to an industrial revolution in the power industry. The Industry 4.0 revolution has already set in, allowing computers to interact for an efficient and intelligent approach in solving smart grid issues. multilevel inverters (MLIs) are an integral part of the smart grid system for integrating the distributed generation sources and storage energy systems into the smart grid. It attracted attention in industrial applications as they can handle high power and high voltage with an inherent feature of superior output voltage waveform quality. Moreover, its variant, the switched-capacitor MLI (SCMLI), has the added benefit of lesser DC supply requirement. In this paper, a switched-capacitor multilevel inverter topology has been proposed, which can operate in symmetric and asymmetric mode. The proposed SCMLI generate thirteen and thirty-one level output voltages for symmetric and asymmetric selection of DC voltage sources, respectively. The proposed SCMLI has a smaller number of switching devices for a given output voltage level as compared to other recently proposed topologies. A thorough comparison is presented with the recently proposed topologies on several parameters, including cost function. To validate the proposed topology, symmetric and asymmetric cases were simulated using Matlab® 2018a and the results were verified using an experimental hardware setup.

A Novel Nine-Level Quadruple Boost Inverter With Inductive-Load Ability

A novel single-phase nine-level switched-capacitor inverter (9LSCI) is presented with quadruple boost ability and reduced components. The proposed topology with single dc source employs only eight switches to realize nine-level output, self-voltage balance of capacitors, quadruple boost and inductive-load ability, thus, the effective cost is cut down compared to other switched-capacitor multilevel inverters (SCMLIs). Different from other SCMLIs, the proposed 9LSCI has no need for back-end H-bridge, of which four switches need to withstand the peak voltage of output. Hence, total standing voltage can be reduced. The operation principles containing the self-voltage balance of capacitors are described in detail. The quantitative comparisons, modified cost function, as well as the loss evaluations are examined in depth. Finally, multicarrier phase disposition pulsewidth modulation method is adopted and a laboratory prototype is implemented with the rated output of 220 V–500 W. The experimental results also verify the feasibility of the proposed topology.

Family of Multiport Switched-Capacitor Multilevel Inverters for High-Frequency AC Power Distribution

This paper proposes a family of multiport switched-capacitor multilevel inverter (SCMLI) topologies for high-frequency ac power distribution. It employs asymmetric dc voltage sources with a common ground that makes it ideal to be employed in renewable energy farms and modern electric vehicles. The proposed family of step-up SCMLI attains higher number of output voltage steps with optimum component count in comparison to several existing topologies. The problem of capacitor voltage balancing is solved as the capacitors are inherently charged to a finite voltage every half cycle. In-depth study on two staircase modulation strategies, namely, selective harmonic elimination and minimum total harmonic distortion (THD) scheme is presented with study on the variation of switching angles and THD with modulation indices under both schemes. Working principle and analysis are presented for the proposed family of topologies. Simulation outcomes are validated with experimental results under both the aforementioned modulation schemes with equal and unequal output voltage waveform steps.

Symmetric/Asymmetric Hybrid Multilevel Inverters Integrating Switched-Capacitor Techniques

In conventional hybrid multilevel inverters (MLIs), the voltage balance controls of floating capacitors are usually realized by redundant switching states using high-frequency modulation. The switching frequency, as well as the switching loss, is hence increased, and the topologies are limited to low-frequency output occasions as a result. In switched-capacitor MLIs (SCMLIs), the capacitors are self-balanced, since they are charged to fixed voltage levels by the input source directly or indirectly. By integrating switched-capacitor techniques into conventional hybrid MLIs, a pair of symmetric/asymmetric hybrid MLIs is proposed in this paper with boost ability. Complicated balance controls are avoided for capacitor voltages, and thus the modulation gets simplified. Compared with SCMLIs, the backend H-bridges that withstand the accumulated voltage stress are removed. The peak inverse voltages of devices are decreased, and thus only low-voltage components are needed. Meanwhile, the component numbers are reduced greatly. All these advantages contribute to high efficiency and reduced costs. Consequently, the proposed hybrid MLIs are especially appropriate for synthesizing a staircase output directly from an input source of low voltage. Analyses and their operational principles are firstly presented for the proposed topologies. Comparisons are then carried out to illustrate their superiority. To evaluate the performance, simulation and experimental prototypes are implemented, whose results confirm the feasibility of the proposed hybrid MLIs.

A New Boost Switched-Capacitor Multilevel Converter With Reduced Circuit Devices

In this paper, a novel platform for the single phase switched-capacitor multilevel inverters (SCMLIs) is presented. It has several advantages over the classical topologies, such as an appropriate boosting property, higher efficiency, lower number of required dc voltage sources, and other accompanying components with less complexity and lower cost. The basic structure of the proposed converter is capable of making nine-level of the output voltage under different kinds of loading conditions. Hereby, by using the same two capacitors paralleled to a single dc source, a switched-capacitor (SC) cell is made that contributes to boosting the value of the input voltage. In this case, the balanced voltage of the capacitors can be precisely provided on the basis of the series-parallel technique and the redundant switching states. Afterward, to reach the higher number of output voltage levels, two suggested SC cells are connected to each other with a new extended configuration. Therefore, by the use of a reasonable number of required power electronic devices, and also by utilizing only two isolated dc voltage sources, which their magnitudes can be designed based on either symmetric or asymmetric types, a 17- and 49-level of the output voltage are obtained. Based on the proposed extended configuration, a new generalized version of SCMLIs is also derived. To confirm the precise performance of the proposed topologies, apart from the theoretical analysis and a complete comparison, several simulation and experimental results are also given.

Multi-Input Switched-Capacitor Multilevel Inverter for High-Frequency AC Power Distribution

This paper proposes a switched-capacitor multilevel inverter for high-frequency ac power distribution systems. The proposed topology produces a staircase waveform with higher number of output levels employing fewer components compared to several existing switched-capacitor multilevel inverters in the literature. This topology is beneficial where asymmetric dc voltage sources are available, e.g., in case of renewable energy farms based ac microgrids and modern electric vehicles. Utilizing the available dc sources as inputs for a single inverter solves the major problem of connecting several inverters in parallel. Additionally, the need to stack voltage sources, like batteries or supercapacitors, in series which demand charge equalization algorithms, are eliminated as the voltage sources employed share a common ground. The inverter inherently solves the problem of capacitor voltage balancing as each capacitor is charged to the value equal to one of the input voltage every cycle. State analysis, losses, and the selection of capacitance are examined. Simulation and experimental results at different distribution frequencies, power levels, and output harmonic content are provided to demonstrate the feasibility of the proposed multilevel inverter topology.

A New Cascaded Switched-Capacitor Multilevel Inverter Based on Improved Series–Parallel Conversion With Less Number of Components

The aim of this paper is to present a new structure for switched-capacitor multilevel inverters (SCMLIs) which can generate a great number of voltage levels with optimum number of components for both symmetric and asymmetric values of dc-voltage sources. The proposed topology consists of a new switched-capacitor dc/dc converter (SCC) that has boost ability and can charge capacitors as self-balancing by using the proposed binary asymmetrical algorithm and series–parallel conversion of power supply. The proposed SCC unit is used in new configuration as a submultilevel inverter (SMLI) and then, these proposed SMLIs are cascaded together and create a new cascaded multilevel inverter (MLI) topology that is able to increase the number of output voltage levels remarkably without using any full H-bridge cell and also can pass the reverse current for inductive loads. In this case, two half-bridge modules besides two additional switches are employed in each of SMLI units instead of using a full H-bridge cell that contribute to reduce the number of involved components in the current path, value of blocked voltage, the variety of isolated dc-voltage sources, and as a result, the overall cost by less number of switches in comparison with other presented topologies. The validity of the proposed SCMLI has been carried out by several simulation and experimental results.

Advanced DC\/AC Inverters: Applications in Renewable Energy (Luo, F.L. and Ye, H.; 2013) [Book News

This book presents advanced inversion technologies and provides design examples of inverters for renewable energy systems, including wind turbine and solar panel energy systems. The text systematically reviews cutting-edge inverter topologies and introduces new advanced topologies, originally developed by the authors, such as impedance source inverters (ZSI), quasi ZSI (qZSI), soft-switching inverters, and multilevel inverters up to 81 levels. Novel topologies include trinary hybrid multilevel inverters and four novel multilevel inverters: new series laddered multilevel converters, super-lift converter multilevel inverters, switched capacitor multilevel inverters, and switched inductor multilevel inverters. The authors also present modulation strategies and four methods to solve the problem of the accurate determination of the best switching angles to obtain lowest total harmonic distortion (THD) in advanced multilevel inverters. The analysis of the dc bus power injection is also presented, and methods to avoid regenerative power are also proposed. The text offers theoretical concepts, diagrams, summarizing tables, simulation and experimental results, and design examples for students, researchers, and engineers willing to learn from experts on how to design and implement inverters for renewable energy systems. Prof. Dr. Fang Lin Luo, Ph.D. (Cambridge U., U.K.), IEEE Senior Member, full professor at AnHui University, China,