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This paper proposes a new transformerless buck‐boost converter with an extended voltage conversion ratio. This converter has semi‐quadratic voltage gain, which provides more gain with lower duty cycles. This converter has a simple structure and easy implementation, which reduces the cost and increases efficiency. The proposed converter operates in continuous conduction mode and provides two operation modes by turning on and off the switches. The suggested converter has continuous input current and low input current ripple, which is important when utilizing renewable energy sources. The calculation of the proposed converter includes ideal and practical voltage gain, current calculations, voltage stresses of the switches and diodes, current stress of the switches, parameter design, efficiency, and a brief analysis of discontinuous conduction mode and boundary conditions. The proposed converter provides efficiency of about 93.1% in boost mode and 92.14% in buck mode at 50 W output power. The suggested converter varies the input voltage from 20 to 48 V in boost mode and changes the input voltage from 20 to 10.4 V in buck mode. Finally, a laboratory prototype has been built to prove and evaluate the simulation results and theoretical analysis of the proposed converter. [ABSTRACT FROM AUTHOR]

In this study, to solve total harmonic distortion (THD) and voltage stress on switches, challenges have been made by presenting a new multi‐level inverter (MLI). The proposed topology can operate with both symmetric and asymmetric sources. The proposed topology in symmetric and asymmetric mode with 18 switches can produce 17 and 49 voltage levels, respectively, with THD values of 4.14% and 1.45%, which passes the IEEE harmonic standard. The main advantage of the proposed topology is reducing the number of circuit devices, which reduces the price, volume, and complexity of the circuit by reducing the number of circuit devices. The proposed topology reduces the THD, the number of power electronics components, and voltage stress by increasing the output levels. The proposed topology is compared with other topologies and the advantage of the proposed topology is shown in terms of the number of switches and drivers. In addition, the proposed topology is compared in terms of the cost function. The power losses based on the thermal model of the proposed topology have been analysed and simulated. Simulation and experimental results are presented for different scenarios such as load type, load changes, and modulation index changes to validate the proposed topology. [ABSTRACT FROM AUTHOR]

Today, multilevel inverters are widely utilized in various applications. Reducing the number of components in the design of these converters is one of the crucial goals so that they have less volume and cost. This paper presents a single‐source structure for a multilevel switched‐capacitor inverter with voltage boost capability. The proposed structure can generate 25 sinusoidal‐like step voltage levels with a six times amplitude increase compared to the input. This converter uses only one direct current (DC) power source, 14 switches, and four capacitors. The nearest level control switching method has been used to control the converter, create voltage levels, and select the switching modes. A comprehensive comparison has been made with other recently presented structures to demonstrate the efficiency of the proposed structure. The advantages of the proposed structure include using only one DC voltage source, the ability to increase the output voltage six times compared to the input, the use of fewer power electronics components compared to the number of voltage levels, proper efficiency, self‐balancing of capacitors, and as a result, the lower cost. The performance accuracy of the proposed converter has been simulated in the MATLAB Simulink environment and then evaluated by a laboratory prototype. [ABSTRACT FROM AUTHOR]

Proton exchange membrane fuel cells (PEMFC) have been noticed by researchers due to their high efficiency, low pollution, and high‐power density in distributed generation systems. In this paper, an LCL‐type grid‐tied PEMFC fuel cell power conditioning system is evaluated in a harmonics‐polluted low‐voltage grid. The LCL‐filters can lead to resonance and instability despite their capability to attenuate harmonics. In this research, a transformer has been used to connect the fuel cell inverter to the grid. The grid‐side inductor of LCL‐filter is realized by the leakage inductance of the transformer. In addition, for more effective resonance damping and attenuation of current ripples caused by the grid voltage harmonics, a capacitor voltage comprehensive feedback control has been designed and investigated. The comprehensive feedback control of the capacitor voltage contains proportional, first and second‐order derivative terms. In the proposed control scheme, the capacitor‐current‐feedback is opposed by the capacitor voltage derivative term due to reverse loop gain, which leads to deleting both of these loop gains. As a result, there is no need to utilize a current sensor in this control method. Consequently, the proportional and second‐order derivative terms of the capacitor voltage attenuate the LCL‐filter resonance. A low‐pass filter is also considered in the second‐order derivative loop in the controllable frequency range to ensure system stability. The simulation results of the PEMFC power conditioning system in different conditions confirm the proper attenuation of LCL resonance of grid‐tied inverter, high‐quality current injection to the harmonics polluted grid, the suitable stability, and the appropriate dynamic response for the proposed system. Under the proposed control scheme, the fuel cell power conditioning system demonstrates satisfactory stability. Even when reducing the LCL filter values by 5%–20%, the system maintains its stability effectively. Moreover, the THD of the injected current into the grid, employing the proposed control strategy, has been successfully reduced to an impressive value of 1.97% in a weak and harmonical grid. [ABSTRACT FROM AUTHOR]

Summary: Multilevel inverters have many applications, such as the grid integration of photovoltaic cells, FACTSs devices, electric vehicles, variable speed drives, and smart grids. In this paper, a new bidirectional diode‐based unit is proposed for a symmetric single‐phase modular inverter topology that can achieve high output levels by using a small number of switching and circuit devices. The basic structure can generate nine‐level voltage with only nine IGBTs and two diodes. Another advantage of the proposed topology is the utilization of a half‐bridge module to change the voltage polarity and the low number of its voltage sources. Additionally, the proposed topology can be used as the cascaded structure with different approaches to select the value of voltage sources. The power losses are discussed for the proposed basic module. A comparison has been made with some recently presented topologies to compare the proposed multilevel inverter and demonstrate its superiority. The comparison is performed for the basic module and its generalized structure. In this paper, the pulse width modulation technique is utilized to achieve a voltage waveform with low harmonic content. The proposed basic structure has an efficiency of 58.98% in 5KW power. Finally, the operation of the proposed basic module is simulated, and the laboratory prototype results confirm the accuracy of the simulation results. [ABSTRACT FROM AUTHOR]

In this paper, a new transformerless buck–boost converter is proposed. This converter is based on combining two basic converters, including Cuk and traditional buck–boost converters, along with a voltage multiplier (VM) at the output side. The proposed semi‐quadratic buck–boost converter operates in continuous conduction mode (CCM) and provides two operation modes by turning the switches on and off. This converter has some merits such as a wide conversion ratio and continuous input current. The proposed converter consists of two switches with simultaneous operation resulting in simplicity in control. A modular configuration and a wide range of duty cycles are available through the proposed converter, which causes higher or lower output voltage and facilitates the converter maintenance. The calculations of the ideal and the real voltage gain, voltage stress of switches and diodes, efficiency, and design consideration of elements are given in this paper. Finally, a prototype is implemented, and experimental waveforms are obtained to prove and validate the simulation results as well as the theoretical analysis of the proposed converter. [ABSTRACT FROM AUTHOR]

Proton exchange membrane fuel cell (PEMFC), due to its high efficiency and good stability, is one of the most efficient and effective sources of alternative renewable energy. The LCL filters are utilized to attenuate the harmonics caused by inverter‐based distributed power generation systems (DPGS). In this paper, a systematic robust control design is presented for an LCL‐type grid‐tied PEMFC inverter. The proposed nested control includes the capacitor current feedback and the outer grid current loops, considering the computational delays. The proposed control results in more accurate and realistic modeling to transfer the power of PEMFC and inject a high‐quality current into a weak and harmonics‐polluted network. Also, by utilizing the proposed method, the computational delays that affect the damping capability are eliminated, and the performance of the control system is improved. In addition, designing a virtual series and parallel impedances strengthens the phase and amplitude of the inverter output impedance. As a result, the robust operation of the inverter for significant changes in network impedance is improved, and the system well attenuates the mains voltage harmonics. The simulation results in Matlab/Simulink environment confirm the performance of the control system and the suitable quality of the injected current of the PEMFC system into the weak and harmonic‐polluted network. [ABSTRACT FROM AUTHOR]

To meet the higher DC link voltage requirement in distributed energy resources (DERs) such as fuel cells (FCs), wind turbines (WTs), and photovoltaic (PV) systems, DC–DC converters are applied. A voltage‐lift (VL) circuit‐based transformer‐less active switched LC‐network (ASLC) converter with a high‐voltage gain is proposed in this paper. Compared to a similar reference converter, the voltage gain of the proposed converter increases efficiently by adding one extra capacitor and diode. The operation of the converter in continuous current mode (CCM) and discontinuous current mode (DCM), the analysis of the steady‐state condition, and comparative analysis with some similar converters are discussed. Moreover, the parasitic elements are assumed to calculate the DC‐voltage gain and the efficiency of the converter accurately. The performance of the proposed step‐up converter is simulated in the PSIM software. A prototype circuit rating of about 20/280 V, 200 W of converter model is designed, and its performance is validated. The experimental outcomes clarify the feasibility of the proposed converter. [ABSTRACT FROM AUTHOR]

Multi‐level inverters (MLIs) for medium or high power and voltage utilization have acceptable application in industry and are utilized commercially. The performance of MLIs is considerably preferable to traditional two‐level inverters due to their negligible harmonic content, small filter size, utilization of lower‐rated voltage devices, low electromagnetic interference (EMI), and so on. However, in the face of these many advantages, few disadvantages can be expressed such as more device count and a sophisticated control strategy. This paper presents an improved switched‐ladder topology to enhance the performance of multi‐level inverters by improving the above drawbacks. Compared to existing inverter topologies, the proposed extendable diode‐containing bidirectional structure requires fewer switches and driver circuits. The proposed topology is compared with other similar topologies, and its superiority is examined. Fundamental switching frequency modulation technique is utilized to obtain high‐quality output voltage waveforms with lower harmonic contents and reduced switching losses. This converter, despite the use of diodes, can supply the low power factor inductive‐resistive loads, bidirectionally. To demonstrate the performance of the proposed topology, in addition to simulation with the nearest level modulation technique, a prototype of the proposed structure has been implemented and tested. The results display the proper performance of the proposed topology in the real‐time environment. [ABSTRACT FROM AUTHOR]

Multilevel inverters (MLIs) have made great strides in utilizing renewable energy and industrial applications compared to conventional two‐level inverters in terms of output voltage quality, smaller size of the output filter, and higher efficiency. This paper describes a new diode containing bidirectional topology for single‐phase MLI. This structure is presented to reduce the count of switches, isolated voltage sources, and drivers that can increase the number of output levels modularly. This converter, despite the use of diodes, can feed bidirectionally the low power factor inductive–resistive loads. The proposed structure has been designed to achieve a higher output voltage levels relative to the number of switches, drivers, and direct current (DC) voltage sources. Three different algorithms have been proposed to determine the values of DC voltage sources. To confirm the superiority of the proposed structure, a detailed comparison has been carried out with other MLI topologies. Then the proposed topology is simulated in Matlab/Simulink environment using the nearest level modulation technique. Finally, experimental results are presented to confirm the performance of the designed structure in symmetric and asymmetric topologies. [ABSTRACT FROM AUTHOR]

Summary: In this paper, a bidirectional diode containing multilevel inverter is introduced to reduce the number of switching elements especially in the case of a high number of output voltage levels. In comparison with classic and recently introduced symmetrical topologies, which are trying to reduce the switch count, this topology has a lower number of semiconductor switches in the same number of output voltage levels. This makes the proposed inverter to be a suitable choice for medium voltage applications like renewable energy applications as well as medium voltage electric drives. Moreover, it can be used in a cascaded configuration for high voltage levels. To depict the performance of the proposed structure, a comprehensive comparison is made between this topology and classic and recently proposed symmetric topologies in terms of switch and gate driver count, power losses, and cost. The performance of the proposed symmetrical 11‐level converter is analyzed and simulated in MATLAB/Simulink for both PWM and selective harmonic elimination switching methods. Not only the results are desirable but also the experimental results of laboratory prototype validate the simulation results. [ABSTRACT FROM AUTHOR]

Inverters as one of the most important elements of power systems have been profoundly developed in recent decades and their performance has attracted researches in control and structure point of view. In this study, a novel structure based on the switch-diode-source cell is proposed for a multilevel converter that is capable of bidirectional feeding. The proposed structure is presented for symmetrical mode and the number of power electronic devices is decreased in comparison with similar works. Considering recent proposed symmetrical structures, the proposed structure has the superior condition in terms of semiconductor switches and drivers count as well as switching loss. Also, total blocked voltage (TBV) of the proposed converter is compared with conventional and novel symmetrical converters. Then, switch costs of the proposed converter are compared with the structure that its TBV is the lowest. The performance of the proposed symmetrical seven-level converter is analysed and simulated in MATLAB/Simulink for both PWM and selective harmonic elimination switching methods. Not only the results are desirable, but also the experimental results of laboratory prototype validate the simulation results. [ABSTRACT FROM AUTHOR]

This study proposes a multilevel inverter with optimised structure from switching device number point of view. Configuration of the presented multilevel inverter is modular and extendable. Three different methods are introduced to determine the magnitude of DC voltage sources. Characteristics of inverter topology based on suggested methods are given and compared with each other. Also, the proposed multilevel inverter is compared with some similar topologies in terms of controlled switches, driver circuits, DC voltage sources and total blocking voltage to verify its advantages and probable disadvantages where the results show the superiority of the proposed topology in the comparison items. Selective harmonic elimination pulse width modulation technique is applied to achieve output voltage with high quality. Finally, a laboratory prototype of the proposed multilevel inverter is implemented and then, the experimental and simulation results are derived to validate the inverter capability in generating staircase waveforms. [ABSTRACT FROM AUTHOR]

In this paper, the parallel operation of a three‐phase three‐wire inverter and a three‐phase four‐wire inverter in the presence of unbalanced and nonlinear loads is investigated. The proposed control method has two current internal and voltage external control loops. The current internal loop has a proportional‐resonant controller. The voltage external loop has two parts, including voltage controller and load current sharing. In the current sharing part, first, the output of the voltage controller is broken to a harmonic and is shared then between the inverters through the new strategy: (i) supply of harmonic components of load current by four‐leg inverter and sharing fundamental component of load current evenly between the inverters and (ii) supply of zero‐sequence load current by four‐leg inverter and sharing of the rest of components evenly between two inverters. The proposed system is capable of feeding balanced, unbalanced and nonlinear loads and provides the proper sinusoidal voltage at both ends of the loads by exact sharing of power between parallel inverters. The simulation results show the proper functioning of the proposed system. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

Summary Multilevel inverters are known as essential converters in renewable sources. First, in this paper, a new submodule is presented, and based on it, a new sub‐multilevel inverter is presented. The proposed sub‐multilevel inverter consists of several unidirectional and bidirectional switches and DC voltage sources. Then, the generalized topology, developed in two modular and cascaded modes, is presented to increase production levels. The proposed submodules are connected in series in the modular topology, increasing production levels. The proposed topology to produce the maximum output levels has the minimum number of IGBTs, drivers, DC voltage sources, etc. Mathematical analyses for conduction and switching losses are provided, and mathematical analyses for the number of devices and voltage across the switches are also presented. In addition to the mathematical analysis of losses, the simulation results are also presented. A general comparison of proposed topology components is presented to demonstrate their advantages. This comparison shows that the proposed topology has the minimum number of power electronic devices. In this paper, nearest level modulation is used to control the proposed topology. The simulation and experimental results of the proposed sub‐multilevel verify the performance of the proposed topology. [ABSTRACT FROM AUTHOR]