Switched-capacitor Multilevel Inverters Research Articles

A single DC source, seven-level switched capacitor tripple boost inverter with fewer switches for renewable energy applications

This article presents a new SSTB-MLI with 3 times voltage boosting capability for medium voltage applications with optimal efficiency. Single DC source MLI topologies are more appropriate for many applications, including grid applications and renewable energy (RE) conversion systems than multiple DC source MLI topologies. The ability of switched-capacitor multi-level inverters (SCMLIs) to raise voltage has made them more and more popular in recent years. LS-PWM technique is used for the switching scheme. Two capacitors are employed in SSTB topology to operate alternatively in charging and discharging states at the carrier frequency of this LS-PWM algorithm for making the levels of output voltage. Comparing this innovative topology to those documented in the literature. It can also minimise the number of switches and capacitors needed, their voltage stresses, and switching loss. Since the suggested topology includes built-in capacitor voltage balancing, no additional voltage balancing circuit is required. Applications requiring industrial drives as well as grid-connected and R, RL loads can employ the suggested architecture. Based on less TSV (total standing voltage), MSV (Maximum standing voltage), the number of components used, optimum efficiency 98.43%, and other factors, a comparative analysis is done between the existing topology and the proposed topology. Experimental data and thorough simulation are used to verify the suggested switched capacitor multilevel topology.

RSO based selective harmonic elimination control for nine-level switched capacitor inverter

Abstract Renewable energy utilization has gained much attention in the recent time owing to the sharp increase in the power demand. Out of different renewable sources, photovoltaic (PV) energy utilization in different forms is one of key focus. Power converter such as multilevel inverters (MLIs) are proven as key components for PV systems as well as for other applications such as motor drives, electric vehicles, and charging stations. With the advancement of the design of MLIs, the switched-capacitor (SC) based MLIs have been widely deployed for their boosting capability which is a major requirement for PV systems. In this paper, a reduced switch single input step-up 9-level SC MLI is first proposed. Followed by this, a new Rat Swarm Optimization (RSO) based Selective Harmonic Elimination (SHE) control method is incorporated for switching operation. RSO has the ability to provide the solution with higher competency within less time and a less computationally complex approach. The operation of proposed structure is analyzed and its advantages are justified by comparison with exiting topologies. The effectiveness of RSO based SHE scheme is also verified by comparing it with other nature-inspired algorithms. The effectiveness and workability of the proposed system are examined using simulation and experimental tests.

A Switched-Capacitor Multilevel Inverter With Modified Pulsewidth Modulation and Active DC-Link Capacitor Voltage Balancing

Although switched-capacitor (SC) multilevel inverters (MLIs) offer self-voltage balancing of flying capacitors and voltage gain higher than unity, the advantages come at the cost of high current stress and power loss in the SC circuit and DC source. Moreover, the voltage balancing is often restricted to a limited range of modulation index. Another problem of MLIs with neutral-point clamped (NPC) front end is with DC-link capacitor voltage balancing under unbalanced load conditions, imploring sensor-based closed-loop control. This paper proposes a unity gain five-level active-NPC SC-MLI with inrush charging current attenuation and actively balanced DC-link capacitor voltages under all load conditions and over the entire range of modulation index and power factor. The modified pulse-width modulation results in most switches operating at a low switching frequency, minimizing switching losses in the SC circuit. The proposed MLI attains a maximum efficiency of 98.04% at an output power of 510 W. Experiments on a 2 kVA laboratory prototype validate the theoretical analysis. Results from transformerless grid-connected solar PV system show that the proposed MLI can inject power into the grid with a unity power factor under conditions of varying irradiance and provide the grid with reactive power as well.

ZVS and Inrush Charging Current Suppression Design for Switched-Capacitor Multilevel Inverters

ZVS and Inrush Charging Current Suppression Design for Switched-Capacitor Multilevel Inverters

A high boost switched capacitor multilevel inverter with reduced components

ABSTRACT Switched capacitor multilevel inverters (SCMLIs) became a popular DC-to-AC converter due to their unique features like self-capacitor voltage balancing and self-output voltage boosting abilities over conventional multilevel inverters in recent years. However, recently developed SCMLIs suffer from higher component counts, lower voltage boosting factors, higher total standing voltage, and the requirement of isolated DC sources for generating high-quality output voltage level waveform. These drawbacks make the inverter costly, complex, and bulky. To address these drawbacks of SCMLIs, a novel SCMLI is proposed in this paper. The proposed SCMLI can realise 17 output voltage levels with a higher boosting factor. In addition, the proposed SCMLI uses lower switches, driver circuits, capacitors, and diodes than similar SCMLIs. The proposed SCMLI also offers a cheaper cost function per output voltage level per boosting factor compared to others. A thorough description of the proposed inverter’s operating principle, voltage stress analysis, and capacitor selection procedure have been discussed. The proposed inverter’s cascaded form has been constructed and analysed for various DC source configurations. An extensive simulation study of 17-level SCMLI in MATLAB/Simulink platform and an experimental investigation on a 17-level laboratory prototype validate the proposed SCMLI’s merits and effectiveness.

Capacitor ripple reduction in T-type multilevel inverter operation for solar PV-application

Efficient and reliable power electronic converters are desired to integrate renewable energy sources into households or the grid. Multilevel inverters for their benefits are being explored for low-power applications. In this work, recently introduced 9-level T-Type switched-capacitor multilevel inverters are explored for 11-level operation, increasing their reliability in high-temperature conditions. The operation makes it capable of generating more voltage levels than the prior technology and diminishes capacitor inrush currents. Eventually, in 9-level operation, the undesired continuous high inrush current peaks are inevitable, which heat the capacitors due to electrolytic series resistance (ESR). This leads to early electrolyte evaporation and thus results in capacitance variation and an increase of ESR with time. In order to suppress the capacitor inrush currents, additional inductance of small value in the charging circuit is sought to mitigate these currents, but that leads to increased losses and increased switch ringing effect. In this work, the modulation of the inverter is performed to produce 11-levels at the inverter output. Inverter redundant states are so employed that the capacitors are always charged and discharged through the load. This results in reduction of inrush current peaks by approximately 20 times, thereby increasing the reliability and life of the inverter and making them more suitable for Solar PV applications in harsh weather conditions. This structure and modulation strategy also achieves lower switch voltage and current stresses. The improved topology and the modulation strategy are validated on the controller hardware-in-the-loop (CHIL) setup and PLECS environments. Further, the topologies are experimentally validated on a laboratory prototype.

A double boost 9‐level switched capacitor‐based multilevel inverter for photovoltaic applications

SummaryA self‐balancing 9‐level inverter is proposed in this paper. To generate a 9‐level voltage with a gain of two requires a single DC source, eight power switches, three capacitors, and two diodes. Without additional circuitry, the voltages of the capacitors in the proposed topology can achieve inherent balance. The peak‐inverse‐voltage (PIV) of six power switches equals or less than the source voltage, and the other two are twice. As power switches are complementary, the proposed topology requires fewer gate drivers. Furthermore, the self‐balancing capability of capacitors' voltage helps in simple control complexity. The description of topology, mode of operation, modulation strategy, and design of the capacitor of proposed topology are presented. The advantages of the proposed inverter are examined by comparing it with switched capacitor multilevel inverters (MLIs). Finally, a 9‐level prototype is built to verify the theoretical analysis and the practical efficacy of the proposed inverter.

Performance evaluation of seven level grid-tied PV inverter employs seven switches with the triple gain

Abstract In this paper, a novel switched capacitor converter has been proposed to generate 7-levels using seven semiconductor switches (7S7L) to get triple gain in the output voltage which is supplied by a single dc source. A PWM technique, phase disposition pulse width modulation (PD-PWM) has been designed to achieve a suitable switching operation for the 7S7L inverter. In addition, the capacitor voltage is balanced and the suggested inverter uses a charging inductor to decrease the capacitor inrush current, which is a shortcoming in the switched-capacitor multilevel inverters. Moreover, the 7S7L inverter is used to interface the solar panels with the utility grid using a synchronous reference frame-based controller. To check the efficiency, taking actual data, power loss calculation has been discussed for the 7S7L inverter. To illustrate the better performance of the proposed 7S7L inverter than the existing seven-level SC-MLI presented in the literature, a comparative study is also undertaken. To verify the feasibility and effectiveness of the proposed topology, a converter is simulated using Matlab/Simulink. To validate the simulation results, a real-time study is completed using the OPAL-RT 4510 real-time platform.

A Low Switch Count 13-Level Switched-Capacitor Inverter With Hexad Voltage-Boosting for Renewable Energy Integration

Switched-Capacitor multilevel inverters (SCMLI) are being explored for renewable power applications like solar-PV integration because of their benefits of low component count and low-cost factors. This work presents and explores a new multilevel inverter with a hexad voltage-boosting capability. It employs a single source and produces a 13-level waveform by utilizing only fourteen switches, two diodes, and four capacitors. The voltage across the capacitors is maintained at the desired magnitudes during the switching of the inverter by connecting the DC source and capacitors in parallel at several time locations in one operating cycle. The topology proposed in this work is compared with the recent 13-level topologies in terms of switches, diodes, capacitors, and cost factors (CF). A level-shifted PWM-based algorithm generates the circuit switches’ PWM pulses. The CF of the proposed SCMLI is found to be 2.461, which is the lowest among the compared hexad-boosted MLIs. Experimental validation is performed on a hardware prototype to validate various operational conditions of load change, modulation index change, and reference frequency change.

Performance evaluation of a 15-level inverter using two DC sources with lower standing voltage

ABSTRACT Most of the reduced switch multilevel inverters (MLIs), including switched capacitor MLIs (SC-MLIs), are designed with voltage sources/capacitors have obtained voltage levels with the addition of these sources only. This increases the number of voltage sources (capacitors) without full utilisation of these sources and has higher inverter total standing voltages, which leads the inverter inefficient (high conduction loss) and costly. The motivation of this work is to design a generalised reduced component MLI aiming for addition as well as subtraction of the voltage sources to obtain a voltage level, which results in the reduction of sources, enhance the voltage utilisation and lowering the inverter total standing voltage (TSV). The design parameters of the proposed MLI topology are compared with the recently developed MLIs in terms of the number of switches, capacitors and TSV to prove its superiority. The experimental prototype of the specimen 15-level and 27-level inverters is implemented using DS1103 and the corresponding results are presented.

An Active-Neutral-Point-Clamped Switched-Capacitor Multilevel Inverter With Quasi-Resonant Capacitor Charging

Switched-capacitor (SC) multilevel inverters (MLIs) offer various advantages over conventional series MLIs owing to the operation from a single dc source, self-balanced capacitor voltages, and inherent voltage gain. However, these advantages come at the cost of high current stress on the capacitors, associated semiconductors, and the dc source. This inrush current has limited the practical application of SC-MLIs to a fractional kilowatt rating. This article proposes a practical solution by introducing a unity gain nine-level active-neutral-point-clamped SC-MLI with an alleviated capacitor charging current. Switching loss in the SC circuit semiconductors is reduced by using a modified switching sequence that allows the charging current to flow with a minimum interruption till it is turned off at zero-current crossing. The structure also integrates protection against the detrimental effects of voltage transients across the charging inductor. The inverter exhibits a maximum efficiency of 98.03% at 583.91 W output power. Compared with similar SC-MLIs with hard-charging, the proposed inverter significantly reduces the losses and improves efficiency. Experimental results from a 2 kVA laboratory prototype validate the theoretical analysis and show the capacitor voltages stable under varying load impedance and modulation index.

Reduced Multisource Switched-Capacitor Multilevel Inverter Topologies

Multisource switched-capacitor multilevel inverters are proper topologies when multiple dc sources are available as renewable energy sources. However, these multilevel inverters have the main drawbacks of requiring a large number of power semiconductors and capacitors and a low boost factor to achieve a large number of voltage levels, which complicate control, reduce performance, and raise the cost. This article presents two configurations for multisource switched-capacitor multilevel inverters. First, a basic multisource switched-capacitor topology is proposed with a small number of capacitors and semiconductors that produce a zero voltage level and a large number of positive voltage levels. The input dc sources are operated in an asymmetric trinary algorithm, while the capacitors are charged/discharged in a binary algorithm using parallel/series modes (without the need for any circuit balancing). Based on the proposed basic topology, two multilevel inverter topologies are proposed, which create bipolar output voltage levels using two different circuits at the output. The first proposed topology uses a standard H-bridge inverter at the output of the basic topology, while the second topology uses an extra switched-capacitor (self-balancing) circuit. The comparison indicates that both the proposed topologies have advantages over most of the reported multisource switched-capacitor multilevel inverters, such as a small number of capacitors, a small number of power semiconductors, low voltage stress, and high boost factor. Furthermore, the proposed topologies decrease the low cost factor in comparison to other topologies. The capacitors' capacitance, power losses, and voltage ripple losses are all measured and evaluated in detail. Theoretical research is validated with the use of laboratory prototypes to validate the performance of the proposed topologies.

A Switched Capacitor-Based 13-Level Inverter With Reduced Switch Count

In this article, a 13-level switched capacitor multilevel inverters (SC-MLI) based single-phase inverter is proposed in which desired levels of output ac voltage are realized with reduced number of switch counts. The proposed inverter requires 12 switches, three diodes, one input dc source, and three capacitors. The requirement of less number of switches reduces the requirement of gate drivers, which enhances power density of converter. The second challenge in SC-MLI is to maintain self-voltage balancing across the capacitors. The self-voltage balancing capability becomes poor at low values of modulation index. The capacitors connected in proposed SC-MLI are capable to maintain the self-voltage balancing without requiring auxiliary circuits or complex control strategies. The operation of capacitors is self-balanced at all regions of modulation index values. The comparison of the proposed SC-MLI is carried out with state-of-art SC-MLIs discussed in the literature using the parameters like peak inverse voltage and total standing voltage. The switches connected in the proposed 13-level SC-MLI undergoes less voltage stress as compared to the SC-MLI configurations discussed in the literature. The proposed SC-MLI is highly competent to achieve good power quality and is capable to ensure voltage balancing of capacitors even at low values of modulation index. The validation of the proposed inverter topology is carried out using a laboratory prototype. The efficiency of the converter claimed using the simulation results is observed to be 96.2% while the efficiency evaluated using the experimental results is 94.1% at 500 W.

A Switched-Capacitor Multilevel Inverter Using Series-Parallel Conversion With Reduced Components

The switched-capacitor multilevel inverters (SCMLIs) are the popular type of multilevel inverter. This kind of inverter topology uses the on-off states of switches to control the charging and discharging of capacitors to achieve multilevel output. Most SCMLIs make use of an H-bridge structure to change the polarity of the output voltage, which cause the switches to withstand the peak of the output voltage. The H-bridge is replaced by two half-bridges on both sides of the proposed inverters, and the maximum voltage stress (MVS) on switches in half bridge is kept within 2Vdc, as well as in the extended structure. Therefore, the voltage stress of the switches is greatly reduced. In addition, the topology has a modular structure, which makes the expansion and modulation of the topology simple, while achieving a higher voltage gain. Moreover, with the growth of output levels, the MVS of the switches in the topology remains unchanged, which has good practical application scenarios. In this study, the correctness and feasibility of the topology have been verified by experiments.

Switched-Capacitor Multilevel Inverters: A Comprehensive Review

Multilevel inverters (MLIs) with switched-capacitor (SC) units have been a widely rehearsed research topic in power electronics since the last decade. Inductorless/transformerless operation with voltage-boosting feature and inherent capacitor self-voltage balancing performance with a reduced electromagnetic interference make the SC-MLI an attractive converter over the other available counterparts for various applications. There have been many developed SC-MLI structures recently put forward, where different basic switching techniques are used to generate multiple (discrete) output voltage levels. In general, the priority of the topological development is motivated by the number of output voltage levels, overall voltage gain, and full dc-link voltage utilization, while reducing the component counts and stress on devices for better efficiency and power density. To facilitate the direction of future research in SC-MLIs, this article presents a comprehensive review, critical analysis, and categorization of the existing topologies. Common fundamental units are generalized and summarized with their merits and demerits. Ultimately, major challenges and research directions are outlined leading to the future technology roadmap for more practical applications.

Efficient switched‐capacitor multilevel inverters for high‐power solar photovoltaic systems

Switched-capacitor multilevel inverters are suitable topologies for renewable and sustainable energy due to a low number of dc-link voltages. This article presents two extendable configurations for switched-capacitor multilevel inverters to be applied to solar photovoltaic systems. The first extendable configuration applies only to two DC supplies, and the number of levels is increased by connecting several capacitors in series, while the second extendable configuration uses a combination of DC sources and capacitors. The proposed inverters have a self-voltage balancing capability, and they reduce the voltage stress of switches, which leads to a reduction in the value of switching losses. The comparison indicates that both extendable topologies have advantages over most reported multilevel inverters, such as a low number of capacitors and semiconductors, low voltage stress, high boost factors, and a low-cost factor. An efficiency assessment is also presented, which shows the efficiency of the proposal is higher than recent topologies. The proposed inverter is tested and simulated for a high-power solar photovoltaic system that shows it possesses excellent performance with a high-quality output waveform. The functionality of the proposal is tested and evaluated by building a laboratory prototype.

A novel switched capacitor-based multilevel inverter structure for renewable energy conversion system

Switched capacitor multilevel inverters (SCMLIs) are one of the popular solutions to mitigate the different limitations of conventional multilevel inverters (MLIs). A large number of innovative SCMLIs have been reported in literature in recent years. However, the large requirement of power switches, capacitors and large voltage stress across the switching devices are the major limitations of SCMLIs. In this paper, a novel MLI structure using switched capacitor principle has been proposed. It does not require any H-bridge circuit which reduces the switch voltage stress of the structure. It has the ability to produce 13-level output voltage with a boosting factor of 2. Further, the cascaded arrangement of the proposed structure has been realised. The structure requires a lower number of components as compared to the other SCMLIs. The operating principle, capacitor selection procedure and power losses analysis of the proposed 13-level structure have been presented. Extensive simulation and experimental studies have been conducted to validate the effectiveness of the proposed structure.

An Asymmetric Switched-Capacitor Multicell Inverter With Low Number of DC Source and Voltage Stress for Renewable Energy Sources

Asymmetric multilevel inverters generate high-quality output voltage using the same number of components as symmetric multilevel inverters. The main drawback of these topologies is that they require many DC voltage sources, and the power switches must endure high voltage stress. In this paper, a switched-capacitor sub-module inverter topology is proposed to reduce the number of DC voltage sources and the voltage stress on the switches of asymmetric multilevel inverters. The proposed sub-module inverter can generate 15 voltage levels by using two DC power supplies and a capacitor. The voltage of the capacitor can be automatically charged at half of the input DC power supply without the need for any sensors. In addition, the capacitor charging operation does not produce an inrush current because it is charged by the direction of the output current; this is an advantage over switched capacitor multilevel inverters. A modular topology is also presented based on the proposed sub-module inverter to achieve high voltage levels while reducing the number of elements. A comprehensive comparison between the proposal and other multilevel inverter topologies is performed to validate the design of the proposed inverter. In addition, thermal and loss distribution simulations of the proposed sub-module inverter are performed. Finally, the performance, efficiency, and accuracy of the proposed inverter are confirmed through laboratory prototyping.

A Dual-Source Self-Balanced Switched-Capacitor Reduced Switch Multilevel Inverter With Extending Ability

Multilevel inverters (MLIs) with switched-capacitor (SC) combinations are widely recognized to improve the power quality and efficiency of the renewable energy and high-frequency power distribution systems. Self-balancing of SCs and voltage boosting ability are the salient features of the recently developed SC MLIs. This work presents a new SC MLI structure using a reduced number of switches and two dc sources. For increasing the voltage levels, the basic units of the proposed MLI can be extended without increasing the number of dc sources. By suitable charging-discharging patterns, the SCs are self-balanced and voltage boosting is achieved. Comparative analysis with prior-art MLIs demonstrates the merit of topological advancement. Further, extensive simulation and experimental results confirm the feasibility of the proposed MLI under different loading and dynamic operating conditions.

A New Hybrid Cascaded Switched-Capacitor Reduced Switch Multilevel Inverter for Renewable Sources and Domestic Loads

This multilevel inverter type summarizes an output voltage of medium voltage based on a series connection of power cells employing standard configurations of low-voltage components. The main problems of cascaded switched-capacitor multilevel inverters (CSCMLIs) are the harmful reverse flowing current of inductive loads, the large number of switches, and the surge current of the capacitors. As the number of switches increases, the reliability of the inverter decreases. To address these issues, a new CSCMLI is proposed using two modules containing asymmetric DC sources to generate 13 levels. The main novelty of the proposed configuration is the reduction of the number of switches while increasing the maximum output voltage. Despite the many similarities, the presented topology differs from similar topologies. Compared to similar structures, the direction of some switches is reversed, leading to a change in the direction of current flow. By incorporating the lowest number of semiconductors, it was demonstrated that the proposed inverter has the lowest cost function among similar inverters. The role of switched-capacitor inrush current in the selection of switch, diode, and DC source for inverter operation in medium and high voltage applications is presented. The inverter performance to supply the inductive loads is clarified. Comparison of the simulation and experimental results validates the effectiveness of the proposed inverter topology, showing promising potentials in photovoltaic, buildings, and domestic applications. A video demonstrating the experimental test, and all manufacturing data are attached.