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The current trend is to go for more electric systems that rely extensively on power electronics such as EVs/HEVs and electric aircrafts, along with an increased use of renewable energy resources and variable speed motor drives. However, some field failure reports have revealed that power electronic converters represent the weakest point in these systems. A significant percentage of system failures are due to power electronic converter failures, which compromises systems reliability. This raises questions regarding the validity of relying on the current power electronic converter technology to run mission-critical/must-to-be-safe systems. Although power electronic converter technology has reached an advanced level in terms of efficiency, power density, and control, extra work should be done when it comes to reliability. Reliability engineering brings performing failure data analysis, accelerated life testing, lifetime prediction, and the implementation of efficient maintenance and reliability improvement schemes into an integrated process. This process is meant to enhance the reliability of a product throughout its life cycle. This paper provides an overview of the application of the key aspects of new approaches in reliability engineering for power electronic converters. The focus of this paper is on power switch bond-wire modules since they are the most vulnerable component in power electronic converters. This paper also proposes two general schemes for condition-based remaining useful lifetime (RUL) that are discussed in detail. [ABSTRACT FROM AUTHOR]

In this article, a new postfault control algorithm for cascaded H-bridge (CHB) multilevel inverter is proposed to increase the maximum available output voltage under semiconductor fault conditions. Once a semiconductor switch in an H-bridge power cell fails, instead of bypassing the faulty cell, it can be utilized to generate a voltage. However, one of the three levels (positive, negative, or zero) of the faulty cell output voltage is not available, reducing the available output voltage of the cell to half. In the proposed method, the faulty cells being utilized and combined with the neutral shift (NS) method to achieve a higher output voltage of the CHB in faulty conditions. The output voltage obtained by the proposed method is analyzed for different faulty conditions and compared with the conventional NS method. Experimental results are presented confirming the effectiveness of the proposed methods in increasing the maximum output voltage at different faulty conditions. [ABSTRACT FROM AUTHOR]

Demanding higher power, higher power quality, lower switching loss, and eliminating interface transformers in industrial applications caused significant attention toward multilevel converters. This paper presents current control of a seven-level topology for medium-voltage high-power applications. This topology has fewer active switches and components, and less control complexity in comparison to the other existing classic and advanced seven-level topologies. A comprehensive review has been done on seven-level topologies to demonstrate the advantages of this topology in this paper. A control method based on model predictive control (MPC) is developed to balance the flying capacitors of this topology at their desired values and control the output currents without the need of pulsewidth modulation blocks, and proportional-integral (PI) controllers, which is the advantage of MPC in power electronics applications. In order to evaluate the performance of the seven-level topology and the developed control method effectiveness, experimental results are shown for different conditions, which demonstrate the feasibility of the seven-level topology and the developed control technique. [ABSTRACT FROM AUTHOR]

This paper presents a new five-level T-type nested neutral point clamped (T-NNPC) converter. The proposed five-level T-NNPC topology is very attractive for medium-voltage applications as it can work in a wide range of voltages without the need of devices in series, and fewer components compared to the other five-level topologies. A model predictive control (MPC) strategy is also developed for the proposed converter to control the output currents at different output frequencies, and control flying capacitor voltages. A discrete-time model of the converter is developed and the control objectives that are the output currents and flying capacitor voltages are defined regarding switching states. A cost function is defined to minimize the deviation of the predicted values of the control objectives from their desired values. During each sampling time, the best switching state is selected and applied to the converter. The performance of the proposed five-level T-NNPC and the developed MPC strategy is studied in the MATLAB/Simulink environment, and the feasibility of the converter is evaluated experimentally. [ABSTRACT FROM AUTHOR]

In order to improve the conversion efficiency and mitigate the EMI problem of conventional hard-switching inverters, a new soft-switching DC-AC inverter with a compact structure and a low modulation complexity is proposed in this paper. In the proposed structure, resonant inductors are connected in series for the arm branches, and resonant capacitors are connected in parallel for the neutral point branches. With the help of resonant components, the proposed structure achieves zero-current switching on the arm branches and zero-voltage switching on the neutral point branches. When compared with state-of-art soft-switching topologies, the proposed topology does not need auxiliary switches. Moreover, the commutation algorithm to realize soft-switching can be easily implemented. In this paper, the principle of the resonant operation of the proposed soft-switching converter is presented and its performance is verified through simulation studies. The feasibility of the proposed inverter is evaluated experimentally with a 2.4-kW prototype. [ABSTRACT FROM AUTHOR]

Novel three-dimensional porous silk fibroin/graphene oxide (SF/GO) nanocomposite scaffolds with different graphene oxide (GO) concentrations were prepared by using the freeze-drying technique. The obtained SF/GO scaffolds were characterized by thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, Brunauer-Emmett-Teller isotherm and Fourier transform infrared spectroscopy techniques. The water absorption, compressive properties, porosity, degradation, biomineralization capability, cell attachment and cell viability of the composite scaffolds were studied as well. Cytocompatibility of the scaffolds was studied in vitro by employing the methylthiazoletetrazolium assay. The results showed that the presence of graphene oxide nanoparticles throughout the fibroin matrix led to an increase in water uptake and mechanical properties; at the same time, the porosity of the scaffolds was decreased. The cell adhesion results also indicated that human osteoblast cells (MG-63) could adhere to the surface of SF/GO nanocomposites and develop on them. These suggest that SF/GO nanocomposite scaffolds may be a good candidate for bone tissue engineering applications. [ABSTRACT FROM AUTHOR]

In this letter, a new control method based on the sinusoidal pulsewidth modulation scheme is proposed to control capacitor voltages of a T-type four-level nested neutral-point-clamped (NNPC) inverter. The T-type four-level NNPC inverter has a lower number of switches and components compared with other four-level classic and advanced inverters, which make this topology attractive for high-power medium-voltage applications. This topology has been proposed and studied with the assumption of constant dc sources instead of flying capacitors. In this letter, a simple single-phase modulator is developed to balance flying capacitor voltages. The performance and the feasibility of the proposed control technique are evaluated experimentally under a steady-state and transient conditions and for different modulation indexes and loads. The experimental results demonstrate the effectiveness of the developed control method to control the capacitors’ voltages. [ABSTRACT FROM AUTHOR]

The five-level nested neutral-point-clamped (5L-NNPC) converter is one of the most promising topologies for medium-voltage (2.3–7.2 kV) high-power applications such as medium-voltage drives, wind energy conversion systems, and grid-connected systems. The 5L-NNPC requires a fewer number of switching devices, freewheeling and clamping diodes, and flying capacitors compared to the existing five-level multilevel converters. In the 5L-NNPC topology, each flying capacitor voltage is regulated at one-fourth of the dc-bus voltage to obtain the five-level operation. Due to the lack of redundant switching states, it is difficult to control the flying capacitor voltages by using the pulse-width-modulation-based classical control methods. This paper proposes a model-predictive current control (MPCC) approach to control the flying capacitor voltages along with the output currents of the 5L-NNPC converter. The discrete-time model of 5L-NNPC is developed to implement the MPCC scheme. The simulation and experimental studies are conducted to verify the dynamic and steady-state performance of 5L-NNPC with the MPCC scheme. The performance of the proposed MPCC approach is compared with the conventional space-vector-modulation-based voltage-balancing approach. Furthermore, the flying capacitor voltage control capability of MPCC is verified at different load power factors. [ABSTRACT FROM AUTHOR]

This paper presents a novel seven-level (7L) voltage source converter for high-power medium-voltage applications. The proposed topology is an H-bridge connection o f two nested neutral-point clamped (NNPC) converters and is referred to as an HNNPC converter. This converter exhibits advantageous features, such as operating over a wide range o f output voltages, particularly for 10-15 kV applications, without the need to connect power semiconductors in series; high-quality output voltage; and fewer components relative to other classic seven-level topologies. A novel sinusoidal pulse width modulation technique is also developed for the proposed 7L-HNNPC converter to control flying capacitor voltages. One of the main features o f the control strategy is the independent application of control to each arm of the converter to significantly reduce the complexity of the controller. The performance of the proposed converter is studied under different operating conditions via MATLAB/Simulink simulation, and its feasibility is evaluated experimentally on a scaled-down prototype converter. [ABSTRACT FROM AUTHOR]

This paper proposes a new five-level voltage source inverter for medium-voltage high-power applications. The proposed inverter is based on the upgrade of a four-level nested neutral-point clamped converter. This inverter can operate over a wide range of voltages without the need for connecting power semiconductor in series, has high-quality output voltage and fewer components compared to other classic five-level topologies. The features and operation of the proposed converter are studied and a simple sinusoidal PWM scheme is developed to control and balance the flying capacitors to their desired values. The performance of the proposed converter is evaluated by simulation and experimental results. [ABSTRACT FROM PUBLISHER]

This paper proposes a model predictive control (MPC) strategy for a nested neutral point-clamped (NNPC) converter to control output currents and voltages of flying capacitors. The NNPC converter is a four-level converter topology for medium-voltage applications with interesting properties such as operating over a wide range of voltages (2.4–7.2 KV) without the need for connecting power semiconductor in series, high quality output voltage, less number of components compared to other classical four-level topologies. A discrete-time model of the converter is presented and all the control objectives are formulated in terms of the switching states. During each sampling interval, the predicted variables are assessed by the cost function and the best switching state which gives minimum value for the cost function is selected and applied to the converter gating terminals. The performances of the NNPC converter and predictive control scheme are verified through MATLAB/Simulink simulations and their feasibility is evaluated experimentally. [ABSTRACT FROM AUTHOR]

The contamination of the aquatic environment with antibiotics is among the major and developing problems worldwide. The present study investigates the potential of adsorbent magnetite-chitosan nanoparticles (Fe3O4/CS NPs) for removing trimethoprim (TMP) and sulfamethoxazole (SMX). For this purpose, Fe3O4/CS NPs were synthesized by the co-precipitation method, and the adsorbent characteristics were investigated using XRD, SEM, TEM, pHzpc, FTIR, and VSM. The effect of independent variables (pH, sonication time, adsorbent amount, and analyte concentration) on removal performance was modeled and evaluated by Box–Behnken design (BBD). The SEM image of the Fe3O4/CS adsorbent showed that the adsorbent had a rough and irregular surface. The size of Fe3O4/CS crystals was about 70 nm. XRD analysis confirmed the purity and absence of impurities in the adsorbent. TEM image analysis showed that the adsorbent had a porous structure, and the particle size was in the range of nanometers. In VSM, the saturation magnetization of Fe3O4/CS adsorbent was 25 emu g−1 and the magnet could easily separate the adsorbent from the solution. The results revealed that the optimum condition was achieved at a concentration of 22 mg L−1, a sonication time of 15 min, an adsorbent amount of 0.13 g/100 mL, and a pH of 6. Among different solvents (i.e., ethanol, acetone, nitric acid, and acetonitrile), significant desorption of TMP and SMX was achieved using ethanol. Also, results confirmed that Fe3O4/CS NPs can be used for up to six adsorption/desorption cycles. In addition, applying the Fe3O4/CS NPs on real water samples revealed that Fe3O4/CS NPs could remove TMP and SMX in the 91.23–95.95% range with RSD (n = 3) < 4. Overall, the Fe3O4/CS NPs exhibit great potential for removing TMP and SMX antibiotics from real water samples. [ABSTRACT FROM AUTHOR]

The contamination of the aquatic environment with antibiotics is among the major and developing problems worldwide. The present study investigates the potential of adsorbent magnetite-chitosan nanoparticles (Fe3O4/CS NPs) for removing trimethoprim (TMP) and sulfamethoxazole (SMX). For this purpose, Fe3O4/CS NPs were synthesized by the co-precipitation method, and the adsorbent characteristics were investigated using XRD, SEM, TEM, pHzpc, FTIR, and VSM. The effect of independent variables (pH, sonication time, adsorbent amount, and analyte concentration) on removal performance was modeled and evaluated by Box–Behnken design (BBD). The SEM image of the Fe3O4/CS adsorbent showed that the adsorbent had a rough and irregular surface. The size of Fe3O4/CS crystals was about 70 nm. XRD analysis confirmed the purity and absence of impurities in the adsorbent. TEM image analysis showed that the adsorbent had a porous structure, and the particle size was in the range of nanometers. In VSM, the saturation magnetization of Fe3O4/CS adsorbent was 25 emu g−1 and the magnet could easily separate the adsorbent from the solution. The results revealed that the optimum condition was achieved at a concentration of 22 mg L−1, a sonication time of 15 min, an adsorbent amount of 0.13 g/100 mL, and a pH of 6. Among different solvents (i.e., ethanol, acetone, nitric acid, and acetonitrile), significant desorption of TMP and SMX was achieved using ethanol. Also, results confirmed that Fe3O4/CS NPs can be used for up to six adsorption/desorption cycles. In addition, applying the Fe3O4/CS NPs on real water samples revealed that Fe3O4/CS NPs could remove TMP and SMX in the 91.23–95.95% range with RSD (n = 3) < 4. Overall, the Fe3O4/CS NPs exhibit great potential for removing TMP and SMX antibiotics from real water samples. [ABSTRACT FROM AUTHOR]

The nested neutral-point clamped (NNPC) converter is a four-level converter topology for medium-voltage applications with interesting properties such as operating over a wide range of voltages (2.4-7.2 KV) without the need for connecting the power semiconductor in series, high quality output voltage, and less number of components in compare to other classical four-level topologies. The control and balance of the flying capacitors (FCs) of the NNPCconverter can be done by different control techniques taking advantage of the large number of redundant switching states. This paper presents a simple single-phase modulator for the NNPC converter, which can be applied to each phase of a three-phase NNPC converter. The proposed simple technique can control and balance the FCs to their desired values. Performance of the proposed technique under different operating conditions is investigated in the MATLAB/Simulink environment. The feasibility of the proposed converter is evaluated experimentally. [ABSTRACT FROM AUTHOR]

A new interleaved three-phase PFC ac-dc single-stage multilevel is proposed in this paper. The proposed converter can operate with reduced input current ripple and peak switch currents due to its interleaved structure, a continuous output inductor current due to its three-level structure, and improved light-load efficiency as some of its switches can be turned ON softly. In the paper, the operation of the converter is explained, the steady-state characteristics of the new converter are determined, and its design is discussed. The feasibility of the new converter is confirmed with experimental results obtained from a prototype converter, and its efficiency is compared to that of another multilevel converter of similar type. [ABSTRACT FROM AUTHOR]

In this paper, a new voltage source converter for medium voltage applications is presented which can operate over a wide range of voltages (2.4-7.2 kV) without the need for connecting the power semiconductor in series. The operation of the proposed converter is studied and analyzed. In order to control the proposed converter, a space-vector modulation (SVM) strategy with redundant switching states has been proposed. SVM usually has redundant switching state anyways. What is the main point we are trying to get to? These redundant switching states help to control the output voltage and balance voltages of the flying capacitors in the proposed converter. The performance of the converter under different operating conditions is investigated in MATLAB/Simulink environment. The feasibility of the proposed converter is evaluated experimentally on a 5-kVA prototype. [ABSTRACT FROM AUTHOR]

A new zero-sequence circulating current (ZSCC) reduction method for multimodule voltage source inverters (MVSIs) consisting of P three-phase inverters that are connected in parallel is proposed in this paper. Four-switch inverter modules are used instead of the conventional six-switch modules to reduce the cost. In this paper, the effectiveness of the proposed ZSCC reduction method is studied using selective harmonic elimination pulse width modulation. The proposed ZSCC reduction method can remove about P times the number of harmonics using the same switching frequency as compared to more conventional methods, as explained later in this paper. The concepts discussed in the paper are confirmed with results obtained from an MVSI experimental prototype. [ABSTRACT FROM AUTHOR]

In this paper, a new integrated three-level ac-dc converter is presented. The proposed converter integrates the operation of the boost power factor correction and the three-level dc-dc converter. The converter is made to operate with two independent controllers-an input controller that performs power factor correction and regulates the dc bus and an output controller that regulates the output voltage. The input controller prevents the dc-bus voltage from becoming excessive while still allowing a single-stage converter topology to be used. The paper explains the operation of the new converter in detail and discusses its features and a procedure for its proper design. Experimental results obtained from a prototype are presented to confirm the feasibility of the new converter. [ABSTRACT FROM AUTHOR]

A modular voltage-source inverter (MVSI) uses individual three-phase modules in a shunt connection to allow lower power rated inverters to be implemented in higher power applications. It is standard practice to implement each module with the same pulsewidth-modulation (PWM) pattern. This paper proposes a new PWM approach for MVSIs for which each module is made to operate with a different PWM pattern. It is shown in this paper how more output voltage harmonics can be eliminated with the new approach than with the standard approach and how the new approach can be expanded to significantly reduce zero-sequence current that circulates among the inverter modules. The mathematical formulations needed to generate appropriate PWM patterns for the new PWM approach and experimental results obtained from a prototype MVSI are presented in this paper as well. [ABSTRACT FROM PUBLISHER]

Pulse-width modulated (PWM) full-bridge boost converters are used in applications where the output voltage is considerably higher than the input voltage. Zero-voltage-switching (ZVS) is typically implemented in these converters. A new ZVS-PWM full-bridge converter is proposed in this paper. The proposed converter does not have any of the disadvantages associated with other converters of this type, including a complicated auxiliary circuit, increased current stresses in the main power switches, and load-dependent ZVS operation. The operation of the proposed converter, its steady-state characteristics, and its design are explained and examined. The feasibility of the converter is confirmed with results obtained from an experimental prototype. [ABSTRACT FROM AUTHOR]

A new interleaved single-stage ac–dc converter is proposed in this paper to reduce line current harmonics while achieving power factor correction (PFC). The proposed rectifier can produce input currents that do not have deadband regions with high PFC, operate with a continuous output current, and minimize the input electromagnetic interference filter size. In this paper, the operation of the new converter is explained, its features and design are discussed in results, and its operation is confirmed with experimental results obtained from a prototype. [ABSTRACT FROM AUTHOR]

A new three-level ac–dc single-stage converter that can operate with standard phase-shift pulsewidth modulation is proposed in this letter. In this letter, the operation of the converter is explained, and its feasibility is confirmed with experimental results obtained from a prototype converter. Finally, the efficiency of the new converter is compared with that of a previously proposed converter of the same type, and it is shown that the new converter has better efficiency, particularly for light-load operation. [ABSTRACT FROM PUBLISHER]

A new three-level dc/dc converter is proposed in this paper. The outstanding features of this converter are that it operates with zero-voltage-switching (ZVS) from full-load to near no-load conditions with hardly any circulating freewheeling primary current due to its novel structure. Since the converter has little primary circulating current and its switches are exposed to only half of the input voltage, it has high efficiency even under light loads. In this paper, the new converter is introduced, its basic operating principles are explained, its modes of operation and its steady-state characteristics are discussed in detail as is its design, and experimental results obtained from a prototype converter that confirm its feasibility are presented. [ABSTRACT FROM AUTHOR]

A new three-phase single-stage rectifier is proposed in this paper. The outstanding features of the proposed rectifier are that it can produce input currents that do not have deadband regions and an output current that can be continuous when the converter is operating from maximum load to at least half of the load. In this paper, the operation of the new converter is explained, its features and design are discussed in results, and its operation is confirmed with experimental results obtained from a prototype. [ABSTRACT FROM PUBLISHER]

The diode-front-end cascaded H-bridge (CHB) inverters have prevailed in the nonregenerative industry drive domain for high-power medium-voltage applications. The regenerative version of the CHB drives is made possible by adding the extra active-front-end rectifier in each power cell, such as a three-phase PWM rectifier. However, due to the instantaneous power unbalance, the dc-link capacitors of the regenerative power cell need to be overdesigned to maintain a stable low ripple dc-link voltage. To reduce the dc-link capacitance, this article proposes a novel closed-loop voltage ripple controller for the regenerative CHB drive without adding extra sensors. In the proposed method, dc-link voltage ripple amplitude and phase angle are accurately detected with a high-performance adaptive filter. Moreover, a latent instability issue is discussed and is avoided in the proposed controller. The performance of the proposed control strategy is validated experimentally on a seven-level regenerative CHB drive. [ABSTRACT FROM AUTHOR]

This article proposes a new fault-tolerant technique to increase the maximum balanced line-to-line output voltage of the cascaded H-bridge (CHB) motor drives. The CHB converters have been widely used for medium-voltage motor drives due to their scalability and reliability features. A significant indicator of the reliability is the maximum balanced line-to-line voltage amplitude under fault conditions. This article adopts a nonsymmetrical selective harmonic elimination (SHE) formulation to further extend the output voltage range with a good harmonic profile under fault conditions. The dc current component can be regulated for the dynamic braking operation. Based on the nonsymmetrical SHE formulation, the fault-tolerant problem that achieves the maximum output voltage range and good harmonic profile is converted to an optimization problem, which can be solved by the proposed optimization framework. By properly selecting the output voltage waveforms, the entire converter voltage capability can be achieved under fault conditions with a good harmonic profile. The performance of the proposed method is evaluated experimentally on a seven-level CHB motor drive. [ABSTRACT FROM AUTHOR]

This article proposes a direct predictive current control approach to regulate the flying capacitor voltages along with the output currents in a new five-level voltage source inverter under a wide range of output frequencies and load power factors. Also, the proposed approach maintains the flying capacitor voltage ripples well below the desired limits (10%–15%) throughout the operating range. The sampled data model of a new five-level voltage source inverter is developed to predict the future behavior of the control variables such as output current, and flying capacitor voltage and its ripples. A three-objective cost function with reference and predicted control variables is formulated. The cost function is evaluated for all possible switching states, then an optimum switching state which gives the low cost value is selected. The optimum switching state is applied to the converter in one sampling interval. The feasibility of the proposed control method is verified on a new five-level voltage source inverter by using MATLAB/Simulink simulations and experimental studies on a scaled-down laboratory prototype with dSPACE Microlab Box. Furthermore, the performance of the proposed approach is analyzed in terms of voltage and current harmonic distortion, and flying capacitor voltage ripples at different current magnitudes, output frequencies, and load power factors. [ABSTRACT FROM AUTHOR]

In this article, a new seven-level voltage source converter topology is proposed for high-power medium-voltage applications. The proposed converter has less number of components in the circuit compared to the existing advanced seven-level topologies. All the switches have the same voltage rating. Space vector modulation technique is developed for the proposed topology to balance the flying capacitors voltage. The performance of the proposed converter is evaluated at both steady-state and transient conditions in MATLAB/Simulink. A scaled-down prototype is built to verify the feasibility and performance of the proposed converter at different operating conditions. [ABSTRACT FROM AUTHOR]

This article proposes a novel high-performance predictive control with long prediction horizons to improve the control performance of the multilevel inverters. The finite control set model predictive control (FCS-MPC) has obtained a lot of attention for power converters due to its advantages of high dynamic performance, multi objective capability, no need for PI regulators and PWM modulators. However, the MPC method requires a high number of computations especially for higher-level power converter topologies due to the existence of a huge amount of switching combinations and redundancies. Real-time searching for the optimal switching state among a large candidate pool at a high sampling rate is sometimes impossible with the standard commercial processors. This limitation also prevents real-time implementation of an MPC for multilevel converters with step prediction more than one. To solve the aforementioned issues, this paper presents a novel high-performance FCS-MPC scheme. The proposed FCS-MPC is reformulated mathematically MPC approach to an l 2 norm optimization problem, which can be solved on-line through matrix theory. Compared with the existing MPC optimization algorithms, the proposed MPC formulation has the advantage of a substantial reduction in computational burden, no need for the weighting factors or cost functions, and thus can operate at long horizon prediction length. The proposed method is verified experimentally on a seven-level CHB inverter prototype with a three-step prediction length to demonstrate the ability and performance of the proposed method for multilevel inverters. [ABSTRACT FROM AUTHOR]

The series connection of low-power modules is an alternative solution to realize a multilevel inverter. Unlike a cascade connection, the series connection approach significantly reduces the number of isolated dc sources, thereby the design complexity, cabling of the transformer, and overall system cost become low. In this article, the operation of the series-connected multilevel inverter is presented for a five-level operation, and it is realized by using two three-level half-bridge diode clamp converter modules per phase. Hence, each phase of the series-connected multilevel inverter requires a single isolated dc source. In the series-connected multilevel inverter, the net dc-bus voltage will be equally distributed between four dc-bus capacitors. Therefore, the converter generates a multilevel voltage waveform with uniform steps and ensures equal voltage stress on the semiconductor devices. To achieve these objectives, a space vector pulsewidth modulation scheme with an additional voltage balancing approach is employed. The feasibility of series-connected multilevel inverter is validated through simulations and a scaled-down laboratory prototype under steady-state and transient conditions. [ABSTRACT FROM AUTHOR]

Multilevel topologies gained considerable attention in medium-voltage high-power applications due to their advantages over classic two-level inverters, such as lower loss, higher power quality, and eliminating interface transformers. Moreover, vast research has been done in order to improve the control of the power converters to achieve more efficient and simple controllers. Model predictive control (MPC) is one of the control techniques that has been widely used in power electronics recently due to its advantages, such as fast dynamic response, no need for PI regulators and pulsewidth modulation blocks, and capability of nonlinearity inclusion. On the other hand, the high number of calculations especially for higher level topologies is the disadvantage of this approach. This article presents a new finite control set MPC (FCS-MPC) approach for a seven-level topology. This approach reduces the number of calculations significantly compared to conventional FCS-MPC. Applying the computational efficient FCS-MPC to control the output current and flying capacitors voltages’ of the seven-level topology reduces the number of calculations from 123 to 36, whereas the execution time is reduced six times. Moreover, simulation and experimental results have been shown to demonstrate the performance and feasibility of the developed control method applied to a seven-level topology. [ABSTRACT FROM AUTHOR]

This paper presents a novel fault-tolerant method for active–neutral-point-clamped (ANPC) inverter using a modified carrier-based pulsewidth modulation. At a fault event, the ANPC inverter is divided into subinverters, and the modulating signal is modified to two modulating signals. The modified modulating signals are used to control the subinverters and allow continuous operation of the three-level ANPC inverter during faulty conditions even up to four open-switch faults per phase. This technique provides the fault-tolerant capability of the ANPC inverter without the need to add any additional phase legs or complex control strategies. Furthermore, the proposed technique ensures the voltage balancing of the dc-link capacitors. The performance of the proposed fault-tolerant technique is verified through simulation studies in MATLAB/Simulink under different faulty conditions. The feasibility of the proposed technique is also verified experimentally. [ABSTRACT FROM AUTHOR]

Cascaded H-bridge (CHB) is a promising topology for medium-voltage high-power applications. CHB consists of low-power H-bridge modules in each phase, and these modules are connected in a cascade manner to achieve multilevel operation. However, CHB requires a phase-shifting transformer with multiple secondary windings to generate an isolated dc source for each module, and this requirement increases the overall system cost. In this paper, a series connection of low-power modules is employed to realize a new power converter called a series-connected multilevel converter. Each phase of the proposed topology requires a single isolated dc source. Hence, the required number of secondary windings is considerably reduced. This approach also minimizes the complexity and cost of the overall system. The operation of the proposed topology is presented by using three-level neutral point clamped modules in each phase. Model predictive control (MPC) is employed to control the dc-bus capacitor voltage and output currents of the proposed topology. A discrete-time mathematical model of the proposed topology is also developed to predict the future behavior of control variables. The performance of the proposed topology with MPC is verified through MATLAB simulations and a scaled-down laboratory prototype. [ABSTRACT FROM AUTHOR]

The five-level modular neutral-point-clamped (5L-MNPC) converter is realized by connecting two three-level neutral-point-clamped modules in series. For five-level operation, each dc-bus capacitor voltage of the modular neutral-point-clamped topology should be regulated at one-fourth of the net dc-bus voltage. In this letter, a simple voltage-balancing approach based on the carrier-based modulation scheme is proposed to achieve the above objectives. The proposed approach uses the redundancy switching states along with the current direction and the instantaneous value of the dc-bus capacitor voltage to achieve the voltage balancing in the 5L-MNPC topology. The dynamic performance of the 5L-MNPC topology with the proposed voltage-balancing approach is verified experimentally. [ABSTRACT FROM AUTHOR]

Compared with multilevel space vector modulation, level-shifted multicarrier sinusoidal pulsewidth modulation (SPWM) for nested neutral point-clamped (NNPC) inverters requires much less calculations and implementation efforts, but the existing conventional SPWM cannot suppress the severe flying-capacitor (FC) voltage ripples under low output-frequency conditions. In order to solve this problem, a multicarrier-based PWM strategy with complete voltage balance control (VBC) capacity is proposed in this paper. For NNPC inverters operating under low output-frequency conditions, two preprocessing steps, the zero-sequence injection and the modulation-signal rearrangement, are proposed before the comparisons between level-shifted carriers and modulating signals. These preprocessing steps make the average currents flowing through FCs zero, which is beneficial to greatly reduce the FC voltage ripples under low output-frequency conditions. Together with additional VBC, the proposed modulation can assure the FC voltages balanced under the entire output-frequency conditions. Principles and implementation processes of proposed modulation techniques and VBC methodsare elaborated in detail and compared with conventional modulation methods. Both simulation results from a 5-MVA system and experimental results based on a 5-kVA platform are presented to verify the effectiveness. [ABSTRACT FROM AUTHOR]

The recently-developed nested neutral-point clamped (NNPC) converter is a four-level converter for medium-voltage high-power applications. It has some merits such as operating over wide voltage ranges (2.4–7.2 kV) without switching devices in series and less diodes or capacitors when compared with classical four-level topologies. But it has severe voltage balancing problems under low output frequency conditions when conventional space vector modulation (SVM) or sinusoidal pulse width modulation (SPWM) is applied, which limits its wide applications. In order to solve this issue, a space virtual-vector modulation (SVVM) along with a voltage balance control (VBC) algorithm is proposed in this paper. It helps reduce the voltage ripples greatly and maintain them within an acceptable region under low output frequency conditions. Therefore, it guarantees even voltage stresses among switching devices and extends the NNPC converter's applications. Principles of the proposed SVVM and VBC algorithms are elaborated in detail, and the voltage balancing performance is investigated and compared with the cases where conventional SVM and SPWM with the same VBC are applied. The relationship curves between voltage ripples and flying capacitance, output power, and output frequency have been explored and compared for both conventional SVM and proposed SVVM. Simulation and experimental results are presented to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Solar photovoltaic (PV) power plant is an effective way to utilize the renewable energy sources. EMI is one of the major concerns in PV power plant. Typically, the multilevel inverters are used in high voltage PV power plant. However, the conventional multilevel inverters require more semiconductors, which complicate the circuit structure and control algorithm. In this paper, a novel five-level inverter is introduced for the high voltage PV power plant applications. The model of the inverter is analyzed. With the redundant switching states, a new modulation strategy is proposed to reduce the common-mode voltage and EMI. The proposed approach is able to eliminate the common-mode voltage; meanwhile it has the capability of balancing the capacitor voltages. The cosimulation tests with the Matlab/Simulink and S-function are carried out. The results verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

A capacitor voltage-balancing method for a nested neutral point clamped (NNPC) inverter is proposed in this paper. The NNPC inverter is a newly developed four-level voltage-source inverter for medium-voltage applications with properties such as operating over a wide range of voltages (2.4–7.2 kV) without the need for connecting power semiconductor in series and high-quality output voltage. The NNPC topology has two flying capacitors in each leg. In order to ensure that the inverter can operate normally and all switching devices share identical voltage stress, the voltage across each capacitor should be controlled and maintained at one-third of dc bus voltage. The proposed capacitor voltage-balancing method takes advantage of redundancy in phase switching states to control and balance flying capacitor voltages. Simple and effective logic tables are developed for the balancing control. The proposed method is easy to implement and needs very few computations. Moreover, the method is suitable for and easy to integrate with different pulse width modulation schemes. The effectiveness and feasibility of the proposed method is verified by simulation and experiment. [ABSTRACT FROM PUBLISHER]

This paper presents a finite control set model predictive strategy and its application to the load voltage control of two-level four-leg inverters. The proposed approach uses the novel discrete-time model of the inverter and output $LC$ filter in order to predict the variables to be controlled. These predictions are carried out for the 16 switching states of the inverter and are evaluated using a cost function. The switching state that forces the load voltages to be closest to their respective references is chosen and applied to the inverter. The behavior of the predictive controller has been investigated, and the changes to both inductive and capacitive filter parameters have been considered. In order to improve the reliability of the fourth leg as well as the overall inverter efficiency, a solution is proposed, which combines hardware and software reconfigurations. The feasibility of the proposed method is verified through simulation and experimental results considering single-/three-phase, balanced/unbalanced, and linear/nonlinear loads. [ABSTRACT FROM PUBLISHER]

The diode-front-end (DFE) cascaded H-bridge (CHB) inverter has prevailed in the nonregenerative industry drive domain for high power medium voltage applications due to its modularity, scalability, and fault-tolerant capability. The regenerative version of the CHB drives is made possible by adding the extra active-front-end (AFE) rectifier in each power cell, such as a three-phase Pulse width modulation (PWM) rectifier. However, AFE introduces the switching harmonics which requires to be attenuated by designing a grid interfaced filter to comply with the harmonic standard IEEE 519-2014. High-order filters like LCL filters are not preferred due to complex inherent resonances in a multiparallel AFE system. A large number of capacitive components in the system rouse multiple resonances, which decreases system reliability and modularity. This article proposes an active filtering strategy based on the optimal asymmetric carrier-shifting method for regenerative CHB drives with only L filters. The required filter size is reduced significantly while complying with IEEE 519-2014 standard and thus improves the overall size, cost, and efficiency. The proposed filtering strategy is validated experimentally using a seven-level regenerative CHB drive. [ABSTRACT FROM AUTHOR]

In this article, a new five-level voltage source inverter is proposed for high-power applications. The proposed inverter is competitive in performance, component count, and control complexity compared with the conventional multilevel inverters. Also, the proposed inverter has a simple structure as it does not have any dc-link neutral points, unlike hybrid converters. Furthermore, the proposed topology can be connected in a back-to-back due to the presence of a common dc-link. Also, there is no need of isolated dc source and a complex phase-shifting transformer. In addition, a simple voltage balancing approach based on a level-shifted carrier pulsewidth modulation scheme is proposed to control the flying capacitor voltages. The proposed approach will make use of the redundancy switching states to balance the flying capacitor voltages in the proposed inverter. The steady-state and transient performance of the proposed five-level voltage source inverter and voltage balancing approach is validated through MATLAB simulation studies at different power factors and modulation indices. The simulation studies are further evaluated experimentally by a scaled-down laboratory prototype. Furthermore, the feasibility of the proposed topology is analyzed under the performance indices of voltage and current harmonic distortion, flying capacitor voltage ripples, converter power losses, and converter efficiency. [ABSTRACT FROM AUTHOR]

[Display omitted] • A simple method has been utilized for synthesizing ZnO nanoparticles by use of Iranian green tea extraction without using any chemical reduction agents. • The average particle size was 40 nm. • The green synthesized nanoparticles have been used for sulfide removal from spent caustic which is an effluent in gas refinery. • The optimum amounts of the effective parameters have been obtained with a desirability of 1.000, corresponding to a nanoparticle loading of 0.37 wt%, an initial concentration of 777.5 ppm, a reaction time of 14.33 min, and a pH of 9.85. • Well-being regeneration could be performed due to its nontoxicity via Sulfur-Oxidizer bacteria. Clean and potable water is a basic human need for survival on Earth. Among the available water sources, wastewater has become increasingly valuable. However, certain types of wastewaters, such as spent caustic, are considered highly polluted and pose significant environmental hazards, making their proper treatment imperative. To address this issue, the present study focuses on developing a cost-effective and environmentally friendly solution using a ZnO nanocomposite synthesized with Iranian green tea as an adsorbent for sulfide adsorption from spent caustic wastewater. The synthesized nanoparticles were characterized using various analytical tools, including XRD, FTIR, FE-SEM, PSA, and EDX. The experiments were designed using Design Expert software to examine the impact of initial concentration, nanoparticle loading, initial pH, and time, leading to the determination of the optimum conditions. The optimized parameters for spent caustic recovery with spherical ZnO nanoparticles, obtained through the I-optimal method, were a nanoparticle loading of 0.37 wt%, an initial concentration of 777.5 ppm, a reaction time of 14.33 min, and a pH of 9.85, resulting in a remarkable 97% sulfide elimination. The adsorption isotherm and kinetics data indicated that the pseudo-second-order kinetics and Langmuir isotherm models were well-suited for sulfide elimination. Additionally, the ZnO nanoparticles exhibited the advantage of recyclability, maintaining up to 65% of their adsorption efficiency over five cycles. Consequently, the implementation of ZnO nanoparticles emerges as a promising and effective strategy for removing sulfide from spent caustic wastewater. [ABSTRACT FROM AUTHOR]

Four-level nested neutral-point clamped (NNPC) inverters experience severe voltage balancing problems under low output-frequency conditions when the conventional four-level space vector modulation (4L-SVM) technique is applied, which limits their wider application. In order to get a complete control of the flying-capacitor voltages, and to alleviate the calculation burden of conventional 4L-SVM, a simplified but effective 4L-SVM technique along with the voltage balance control (VBC) function is proposed in this paper. For low modulation indexes, zero and small vectors are selectively utilized and distributed to force the average charging and discharging time of flying capacitors to be equal to each other during every switching period, so that voltage ripples are greatly reduced to be within an acceptable level under low output-frequency conditions. For high modulation indexes, the simplification of conventional 4L-SVM for NNPC inverters into two-level SVM is proposed to reduce the computation complexity. Principles of the proposed 4L-SVM and VBC are elaborated in detail. The steady-state, transient-state, and VBC performances are investigated and compared with the case where the conventional 4L-SVM is applied. Simulation results of a 5 MVA inverter system and experimental results of a scaled-down 5 kVA inverter system are presented to validate the proposed method. [ABSTRACT FROM PUBLISHER]

Photovoltaic (PV) power plant is an attractive way of utilizing the solar energy. For high-power PV power plant, the multilevel inverter is of potential interest. In contrast to the neutral-point clamped (NPC) or flying capacitor (FC) multilevel inverter, the nested neutral point clamped (NNPC) four-level inverter has better features for solar photovoltaic power plant. In practical applications, the common mode voltage reduction of the NNPC four-level is one of the important issues. In order to solve the problem, a new modulation strategy is proposed to minimize the common mode voltage. Compared with the conventional solution, our proposal can reduce the common mode voltage to 1/18 of the DC bus voltage. Moreover, it has the capability to balance the capacitor voltages. Finally, we carried out time-domain simulations to test the performance of the NNPC four-level inverter. [ABSTRACT FROM AUTHOR]