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Microinverters operating into the single-phase grid from new energy source with low-voltage output face the challenges of efficiency bottleneck and twice-line-frequency variation. This paper proposed a multilevel inverter based on bridge modular switched-capacitor (BMSC) circuits with its superiority in conversion efficiency and power density. The topology is composed of dc–dc and dc–ac stages with independent control for each stage, aiming to improve system stability and simplify the control method. The BMSC dc–dc stage, which can be expanded to synthesize more levels, not only features multilevel voltage gain but also partially replaces the original bulk input capacitor and functions as an active energy buffer to enhance power-decoupling ability between dc and ac sides. In dc–ac stage, the control strategy of optimized unipolar frequency doubling sine-wave pulse width modulation is proposed to improve the quality of output waveform. Meanwhile, the multilevel voltage phase has been optimized to further reduce the power loss. Finally, a prototype has been built and tested. Associated with the simulation, the experimental results validate the practicability of these analyses. [ABSTRACT FROM PUBLISHER]

A new pulsewidth modulation (PWM) strategy which is an alternative approach of the discontinuous PWM (DPWM) for a three-level neutral-point-clamped (NPC) inverter is proposed in this paper. A three-level NPC inverter is completely mature and very well-established topology in high-power applications. However, the three-level NPC inverter has an inheritance problem of the neutral-point voltage unbalancing due to the split dc-link capacitors. This structure can cause large neutral-point voltage ripple. Furthermore, output currents of the three-level NPC inverter are distorted by the neutral-point voltage ripple. Therefore, the neutral-point voltage must be controlled. In this paper, a new DPWM method using two different offsets for the neutral-point ripple reduction is proposed and the effectiveness of the proposed DPWM method is verified by using the simulation and the experimental results. [ABSTRACT FROM PUBLISHER]

Multilevel inverters with dodecagonal (12-sided polygon) voltage space vector structure have advantages, such as complete elimination of fifth and seventh harmonics, reduction in electromagnetic interference, reduction in device voltage ratings, reduction of switching frequency, extension of linear modulation range, etc., making it a viable option for high-power medium-voltage drives. This paper proposes two power circuit topologies capable of generating multilevel dodecagonal voltage space vector structure with symmetric triangles (for the first time) with minimum number of dc-link power supplies and floating capacitor H-bridges. The first power topology is composed of two hybrid cascaded five-level inverters connected to either side of an open-end winding induction machine. Each inverter consists of a three-level neutral-point-clamped inverter, which is cascaded with an isolated H-bridge making it a five-level inverter. The second topology is for a normal induction motor. Both of these circuit topologies have inherent capacitor balancing for floating H-bridges for all modulation indexes, including transient operations. The proposed topologies do not require any precharging circuitry for startup. A simple pulsewidth modulation timing calculation method for space vector modulation is also presented in this paper. Due to the symmetric arrangement of congruent triangles within the voltage space vector structure, the timing computation requires only the sampled reference values and does not require any offline computation, lookup tables, or angle computation. Experimental results for steady-state operation and transient operation are also presented to validate the proposed concept. [ABSTRACT FROM PUBLISHER]

High-gain voltage conversion is a feature required for several applications, especially for power processing of low-voltage renewable sources in grid-connected systems. In this scope, the presented paper proposes a novel transformerless high gain step-up dc–dc converter based on an active switched-inductor and a passive switched-capacitor networks. The main advantages of the proposed converter are the high voltage gain (>10), the reduced voltage stresses across the switches and the reduced number of components when compared to topologies that provide the same voltage gain using similar principles. The detailed analysis of the proposed converter and a comparison considering other topologies previously published in the literature are also presented in this manuscript. In order to verify the proposed converter performance, a prototype has been built for a power of 200 W, input and output voltages of 20 and 260 V, respectively, and switching frequency of 50 kHz. Experimental results validate the effectiveness of the theoretical analysis proving the satisfactory converter performance, which peak efficiency is around 95.5%. [ABSTRACT FROM PUBLISHER]

This paper proposes the combination of a novel modified quasi-Z-source (MqZS) inverter with a single-phase symmetrical hybrid three-level inverter in order to boost the inverter three-level output voltage. The proposed single-phase MqZS hybrid three-level inverter provides a higher boost ability and reduces the number of inductors in the source impedance, compared with both the single-phase three-level neural-point clamped quasi-Z-source inverter and the single-phase quasi-Z-source cascaded multilevel inverter. Additionally, it can be extended to obtain the nine-level output voltage by cascading two three-level pulse width modulation switching cells with a separate MqZS and a dc source, which herein is called a single-phase MqZS cascaded hybrid five-level inverter (MqZS-CHI). A modified modulation technique based on an alternative phase opposition disposition scheme is suggested to effectively control the shoot-through state for boosting the dc-link voltage and balancing the two series capacitor voltages of the MqZS. The performances of both the proposed MqZS-CHI and the modulation techniques are verified through simulation and experimental results. [ABSTRACT FROM PUBLISHER]

This paper presents a nine-level active-neutral-point-clamped (ANPC) based multilevel inverter (MLI) topology for grid-connected applications requiring only ten switches. The envisaged structure comprises two parts, namely five-level ANPC unit, and a two-level converter leg whose midpoint is used as another ac terminal. An ad hoc switching state redundancy based modulation strategy is used to ensure that the voltage across the flying capacitor is tightly balanced and is implemented using a look-up table further simplifies the control complexity. The performance and effectiveness of the proposed topology with its control scheme are validated through simulations and experimental tests. Comparison with other MLIs is included to highlight the merits of the proposed topology. From the results, it will be shown that the proposed inverter requires the least part count as compared to other topologies with the same performance and output quality. [ABSTRACT FROM PUBLISHER]

Cascaded H-bridge (CHB) multilevel inverters (MLIs) have been widely used for power electronics systems. While high-voltage blocking across power switches is not a constraint for low voltage applications, the research trend has been oriented to the design of more compact module topologies as an alternative for CHB. Despite the generation of more voltage levels with reduced switch count, the existing module topologies in recent literature take no account of the freewheeling current path during dead-time, thus, inducing multistep jumps in voltage levels and giving rise to undesirable voltage spikes. Addressing this concern, this paper proposes two symmetrical compact-module topologies for cascaded MLI, where freewheeling current path during dead-time is provided for smooth transition between voltage levels to prevent voltage spikes. The proposed 7-level and 13-level compact-modules demonstrated low number of conducting switches for all voltage levels. Comprehensive analysis and comparison with the latest module topologies are conducted. To validate the operation of the proposed compact-module topologies, simulation and experimental results are presented. [ABSTRACT FROM PUBLISHER]

Direct current voltages unbalance of respective power cells is an inherent and critical problem in a cascaded multilevel converter, which is widely used in the solid-state transformer. In this paper, an n -dimension space vector pulse width modulation is presented to address this issue in a three-level H-bridge-based cascaded multilevel converter. This algorithm utilizes the redundant switching pairs of the inner cell and the redundant vectors of mutual cells to balance capacitors’ and cells’ voltages. Meanwhile, a smooth vector transition strategy is included in this algorithm to avoid the level-skip phenomenon. The calculation processes are analyzed in one-cell, two-cells, and three-cells modes, respectively. It is simple, calculable, and flexible to extend in n-cells mode. Finally, the voltage balancing capacity of the inner cell and mutual cells with smooth level transition are verified by simulations and experiments not only at startup but also with unbalanced loads. [ABSTRACT FROM PUBLISHER]

A nonisolated single-stage electronic lighting system with a high power factor for driving power light-emitting diodes (LEDs) is proposed in this paper. The presented topology is based on the integration of a bridgeless boost rectifier with a nonresonant half-bridge converter. Accurate steady-state analyses of the nonresonant- and resonant-based circuits are reported, serving as the basis for designing the lighting systems. The LEDs current is adjusted by means of frequency modulation, being the converter switches driven by complementary symmetrical signals. A small-signal analysis is detailed for the proposed nonresonant scheme, providing fundamental information regarding its dynamic behavior. Also, a step-by-step design procedure based on the performed mathematical analysis is elaborated, allowing the adequate design of the proposed lighting system. In order to confirm the validity and the feasibility of the proposed converter, experimental results for a 42-W, 127- \rmV{\rm{rms}}, 50-kHz, 94.2% peak efficiency prototype are presented. [ABSTRACT FROM PUBLISHER]

This paper presents an optimized topology of 3-$\phi$ , multilevel inverter (MLI) configuration for five or higher level operation with reduced switch count. The proposed solution consists of two basic units (BUs) of multilevel converter and a T-structured 3-level inverter (3-LI). Both BUs are equally shared by the three phases maintaining symmetry among the phases. Moreover, for a higher level operation of the proposed MLI, the modifications required are at two BUs only and not at three legs of the inverter. It further helps in reducing the requirement of extra components for higher level operation compared to the conventional solutions. Furthermore, the topology also has the benefits of reduced switching and conduction loss. An algorithm is also devised to generate the switching pulses for the BUs and the 3-LI, using a carrier-based space vector modulation technique. Presented topology is compared with other existing topologies to prove its advantage. All the details regarding the operating modes and pulse width modulation techniques employed for the proposed system are given and supported by the simulation and experimental results. [ABSTRACT FROM AUTHOR]

Adding the auxiliary switches to the conventional H-bridge inverter is an effective way to eliminate the leakage current for transformerless PV systems, such as H5, H6, etc. Inspired by the newly developed embedded-switch H6 topology, a novel embedded-switch inverter (ESI) is proposed in this paper for three-phase transformerless PV systems. First, the operation principle and characteristics of the proposed ESI are analyzed. Second, the common-mode model of the three-phase ESI is established, based on which the main factors that affect the leakage current are discussed. The finding reveals that the switching states with conventional modulation strategy result in high-frequency common-mode voltage, which is the source of leakage current. In order to solve the problem, a new modulation strategy is presented for ESI to eliminate the high-frequency leakage current. Finally, the time-domain simulation and the experimental tests are carried out. The results verify the effectiveness of the proposed solution. [ABSTRACT FROM AUTHOR]

This paper proposes an interleaved-stage ac–dc bidirectional power converter topology feasible to medium-voltage railway systems. It is based on an arrangement that uses input-series-output-parallel configuration with identical power modules. Each module consists of two interleaved legs employing coupled windings so that it is possible to connect a medium-frequency transformer. The topology conception is presented, followed by the adopted control and modulation technique. An estimation of semiconductor losses is also discussed, while a comparative analysis by means of simulation results validates the improved performance of the introduced approach if compared with similar solutions. The topology results are obtainedt through a medium-voltage high-power railway application, demonstrating the converter functionalities and performance under both steady-state and dynamic conditions. It is then possible to state that good performance in terms of efficiency is achieved even though the power stage presents higher component count if compared with the topology that presents the best result, thus making it suitable to high-power ac–dc machine drive applications. [ABSTRACT FROM AUTHOR]

In high-voltage output applications, the rectifier diodes in the conventional full-bridge converter have to bear the whole secondary voltage of a transformer. In this paper, a three-level rectifier structure with flying capacitors is proposed for the dc–dc converter. Compared with the conventional dc–dc converter, the converter with the proposed rectifier structure has the following advantages: low-voltage diodes could be used for high-voltage output applications; due to the secondary flying capacitors, there are no voltage spikes on the rectifier diodes even if no snubber circuits are attached; not only can the leading switches realize zero voltage switching (ZVS) as the same as the conventional converters, but also the lagging switches can realize zero current switching in discontinuous-conduction mode and ZVS in continuous-conduction mode; and the rectified voltage has no zero-state voltage, it has been raised to half of the input voltage, so the voltage fluctuation is lower than the conventional converter under the same modulation strategy, and the current ripple of the filter inductor can be reduced by half. The operation principle of the proposed rectifier structure is analyzed in details, and a prototype is fabricated to verify the features of the proposed converter. [ABSTRACT FROM PUBLISHER]

Wireless power transfer (WPT) has drawn more and more attention and has many applications, such as wireless electric vehicle charging systems, which require high power, high efficiency, and high power factor. In this paper, a single-stage WPT resonant converter with bridgeless boost power-factor-correction (PFC) rectifier is proposed to improve efficiency and power quality of line input, and reduce production cost and complexity for high-power WPT system. The bridgeless single-stage topology is creatively proposed to apply in WPT system, which is much more advantageous than conventional two-stage WPT converter with individual boost PFC stage. [ABSTRACT FROM PUBLISHER]

This paper proposes a family of novel flying capacitor transformerless inverters for single-phase photovoltaic (PV) systems. Each of the new topologies proposed is based on a flying capacitor principle and requires only four power switches and/or diodes, one capacitor, and a small filter at the output stage. A simple unipolar sinusoidal pulse width modulation technique is used to modulate the inverter to minimize the switching loss, output current ripple, and the filter requirements. In general, the main advantages of the new inverter topologies are: 1) the negative polarity of the PV is directly connected to the grid, and therefore, no leakage current; 2) reactive power compensation capability; and 3) the output ac voltage peak is equal to the input dc voltage (unlike neutral-point-clamped and derivative topologies, which requires twice the magnitude of the peak ac voltage). A complete description of the operating principle with modulation techniques, design guidelines, and comprehensive comparisons is presented to reveal the properties and limitations of each topology in detail. Finally, experimental results of 1-kVA prototypes are presented to prove the concept and theoretical analysis of the proposed inverter family for practical applications. [ABSTRACT FROM PUBLISHER]

This paper proposes a novel 49-level stacked inverter topology for drives. The 49 levels are achieved by stacking three 17-level inverters. Each of the 17-level inverter is developed by cascading a flying capacitor (FC) inverter with three capacitor-fed H-bridges. The device count can be reduced by making the FC and the three cascaded H-bridges common to the dc link in each phase using selector switches in between them. The selector switches need to operate at fundamental frequency only. Also, the devices need to block very low voltages. Hence, MOSFETs can be used. This topology requires three dc sources, each of V\text{dc} /6 only, which can be replaced with stacked batteries for electric vehicle applications. The reduction in the dc voltage requirement is achieved by using a normal symmetric six-phase induction motor with parallel connection of the opposite phase windings. All the floating capacitors in the topology can be balanced irrespective of any modulation index or load power factor. Due to the high number of voltage levels, nearest level control can be used instead of pulse width modulation, which reduces the switching losses. The $dv/dt$ during the inverter operation is also less. Detailed experimental results at different speeds of operation and during transients ensure that the novel topology can be a viable option for high-power adjustable speed drives. [ABSTRACT FROM PUBLISHER]

In this paper, a soft-switching topology is proposed for the bidirectional dc–dc converter. In order to achieve soft-switching conditions, the auxiliary circuits including a small inductor and two capacitors are introduced to the bidirectional dc–dc converter. By generating and keeping a recycle current in the auxiliary circuits, the proposed topology can provide soft-switching conditions for both switches of the bidirectional dc–dc converter in fixed frequency control application. Meanwhile, no auxiliary switches are introduced. Due to the existence of the auxiliary circuits, the proposed topology can also reduce the current ripple in the main inductor. Based on this soft-switching method, a family of bidirectional soft-switching dc–dc topologies is derived. These topologies have the similar structures and the same characteristics. The topology deduction, operating principles, and design guidelines are presented in detail. Finally, an experimental prototype is built to verify the analysis and characteristics of the proposed topologies. [ABSTRACT FROM PUBLISHER]

In this paper, a single-phase multilevel ac/ac converter with reduced number of power semiconductor devices is proposed. For the simple case of a three-level converter, only three bidirectional switches and two capacitors are required. The proposed converter provides a highly sinusoidal and regulated output voltage with a simple topology. The efficiency is high because in each state of operation only one semiconductor conducts. The converter can be easily extended to any desired levels in the output voltage to even more reduce the output total harmonics distortion. Another advantage of the proposed converter is that by increasing the voltage levels, the stress on the switches will decrease. The proper performance of the proposed converter is confirmed through extensive simulation and experimental tests. [ABSTRACT FROM PUBLISHER]

In this paper, an improved transformerless single-phase single-stage grid-tied flying inductor inverter is presented. The negative terminal of the photovoltaic (PV) array is grounded in the improved topology, which increases reliability and suppresses the leakage current. The proposed topology has buck–boost capability without increasing the number of required components and has a high efficiency. An improved control algorithm for proper operation of the proposed topology which decreases switching losses has been investigated. Moreover, a perturbation and observation maximum power point tracking (MPPT) algorithm has been adapted to the proposed inverter, which does not utilize proportional–integral (PI) controllers, for the purpose of the MPPT. Furthermore, a design procedure of the passive elements of the converter based on the corresponding operating has been demonstrated. Simulation in MATLAB Simulink plus an experimental prototype is developed to reconfirm the designed results. Finally, a comparison study has been investigated for better clarification of the advantages and disadvantages of the proposed inverter. [ABSTRACT FROM PUBLISHER]

This paper proposes a new bridge modular switched-capacitor-based ac–ac converter, which is intended to replace conventional transformers in commercial and residential applications, especially for microgrids. The main advantages of the proposed converter lie in high efficiency and power factor, bidirectional operation, and capacitor voltage self-balancing ability. Another distinct merit is its symmetric construction, with which the voltage ripple of charge/pump capacitors can be cancelled out, and the output voltage will be smooth with significant ripple reduction. It is also noteworthy that the symmetric construction ensures that the two symmetric parts can work independently under a simplified control strategy. In addition, the modular configuration contributes to convenient voltage extension. Compared with the reported flying-capacitor switched-capacitor ac–ac converter, the proposed converter requires fewer switches and capacitors per unit of voltage conversion, thus suffering lower voltage stress. To demonstrate the performance of the converter, a prototype with 600-W 220-Vrms high-side voltage, 55-Vrms low-side voltage, and a switching frequency of 100 kHz was designed and fabricated. The relevant experimental results are reported herein. The maximum and rated power efficiency obtained were 95.9% and 94.4%, respectively. [ABSTRACT FROM PUBLISHER]

A simple current-feed single-switch forward resonant converter with secondary diode-clamping is proposed for low-power high-density bus converter applications in this paper. The quasi-zero-voltage-switching turn-on and quasi-zero-current-switching (ZCS) turn-off for switch are both achieved. Due to the quasi-ZCS turn-off , the high voltage spike in traditional single forward converter with a reset winding is much reduced. A small diode connected to the output capacitor is utilized to clamp the voltage stress of the switches. The operating principle of the proposed converter is analyzed and a MHz 66 W 24 V-to-12 V prototype with all Si devices is built up. Experimental results show good soft-switching features, and the prototype achieves 95.3% peak efficiency with 270 W/in3 power density. [ABSTRACT FROM PUBLISHER]

In this paper, a new cascaded high step-up multilevel converter topology is designed, which is based on the series connection of several switched-capacitor submultilevel units. The voltage gain of proposed multilevel converter is related to the number of used switches-capacitor units. The main advantage of proposed topology is inherent voltage balancing of used capacitors. The proposed cascade topology is optimized to minimize the number of capacitors, power switches, and the value of voltage on switches for given levels. The proposed topology is compared with other high step-up multilevel converter topologies and conventional structures. The comparison results show that the presented structure requires the least number of switches and dc sources. Moreover, the voltage on the switches of proposed topology is low. In order to confirm the operation of proposed high step-up multilevel converter, both experimental and simulation works are provided. [ABSTRACT FROM PUBLISHER]

Photovoltaic (PV) microinverters dispense with the line frequency transformer, however at the cost of system grounding and ground leakage current problems. These have been erstwhile resolved by the topologies derived from buck, boost, buck–boost, Zeta, Watkins–Johnson, and Ćuk converters, or combinations of these. The Ćuk derived inverters, employing second-order input and output filters, offer the most efficient, lightweight, and economical solution in the class. This paper presents design and detailed operation of a Ćuk derived, common-ground PV microinverter in continuous conduction mode operation. The inverter is shown to be compatible with both linear and nonlinear loads, in stand-alone and grid-connected modes of operation. Optimal design rules of passive components are rigorously derived to ensure attenuation of input voltage ripples arising from the twin effects of switching and double-frequency output power oscillation. Additionally, the design rules also incorporate considerations of efficiency maximization and some aspects of easing control complexity. Inverter performance is experimentally validated with a 300 VA, 110 V, and 50/60 Hz laboratory prototype. [ABSTRACT FROM PUBLISHER]

This paper presents a modulation strategy for the modular multilevel converter (MMC) which provides the voltage balancing of the capacitors of different submodules comprising the converter. Not only is this modulation applicable to MMCs constructed with classic two level (2L) submodules, but it is also effective for arrangements with different submodule concepts, for instance, topologies like neutral point clamped (NPC), flying capacitors (FCs), neutral point piloted (NPP), etc. Therefore, firstly, the general modulation philosophy is explained applied to the two level (2L) submodule concept, and secondly, the extension to 3L-NPC and 3L-FC submodule topologies is analyzed. After that, the validation of the studied modulation strategy is carried out by means of successful simulation results, at different switching frequencies and number of submodules. The corresponding experimental results are shown in Part II of this paper after having implemented the aforementioned modulation strategy in a real test bench. In addition to this, a comparison based on thermal analysis and sizing of elements among the four studied submodule topologies is also included. [ABSTRACT FROM PUBLISHER]

This paper proposes a novel current link topology with a diode rectifier and magnetic energy recovery switch (MERS) using a current source inverter for offshore-wind-farm application. Despite the use of a diode rectifier, the proposed topology is capable of regulating individual turbine torque partially. Because offshore wind condition is more stable and has less turbulence intensity (typically 0.08) than that of onshore wind, the individual full-range controllability realized typically by pulse-controlled converters is not necessary. Instead of them, the proposed scheme, a diode rectifier with MERS, has only partial controllability of the individual generator torque which is estimated to be sufficient to achieve the maximum power point tracking operation for offshore-wind-farm application. The proposed topology is aiming to be applicable for offshore wind farms where maintenance reduction is conclusively a critical issue because of the inaccessibility. In this paper, experimental results represent the effectiveness of the topology. Moreover, a new control strategy for offshore wind farms with the proposed topology is also proposed. [ABSTRACT FROM PUBLISHER]

Many different topologies based on the multilevel converter approach have been presented in the last decades. In order to obtain improved output waveforms, several modulation techniques have been developed for such converters. Some of those modulation schemes can be directly applied to almost any multilevel converter, while others require significant adaptation in order to be implemented in certain specific converters. This paper presents the implementation of a phase-disposition level-shifted pulsewidth modulation to the recently introduced hybrid multicell converter (HMC). The HMC uses a flying capacitor module on each cell to generate a positive variable dc-link voltage. The variable dc link is inverted at fundamental switching frequency by an H-bridge to generate the cell output voltage. It is desirable to use PD-PWM for its well-known high-performance waveforms. In this paper, a state-machine decoder is developed to balance the floating capacitor voltages and to equalize the supplied power for the series-connected cells of the HMC when using a PD-PWM pattern. Experimental results obtained from a 10-kW prototype are presented, confirming the good-quality waveforms of the HMC modulated with PD-PWM and the adequate balance of all floating capacitors. [ABSTRACT FROM PUBLISHER]

Modular multilevel converter (MMC) is a newly emerging multilevel topology for high-voltage applications during recent years. In this paper, a new MMC is proposed, and the structure and operating principle are analyzed. Owing to the cascaded basic cells without multiwinding transformer, the voltage balancing of floating capacitors must be considered. However, the voltage fluctuation also exists, and theoretical analysis indicates that the amplitude is inversely proportional to the fundamental frequency. This paper has proposed a voltage-fluctuation-suppression method which can reduce the amplitude of the voltage fluctuation in low-frequency region. It can also be used in motor driving with pump/blowerlike load at low frequency and improve the start-up performance significantly. A low-power three-phase five-level prototype is designed and built up to demonstrate the validity of this method. [ABSTRACT FROM PUBLISHER]

This paper discusses the implementation of level-shifted and phase-shifted carrier-based modulation methods, in conjunction with a multiphase open-end winding drive topology. The considered drive is supplied using two five-phase two-level voltage source inverters (VSIs), with input provided from two isolated supplies of equal dc voltages. The topology is known to yield the same space-vector pattern as a corresponding three-level inverter in single-sided supply mode. It is shown in this paper that, with the application of a simple logic, the same phase voltage waveforms result as those obtainable with the appropriate carrier-based modulation scheme applied to the three-level VSI in single-sided supply mode. While the outcomes of the modulation techniques are the same, the open-end winding topology offers certain advantages, such as modularity and absence of capacitor voltage balancing requirements. The analysis is conducted for selected modulation methods using voltage and current waveforms, spectra Fast Fourier Transform (FFT), and total harmonic distortion as figures of merit. Theoretical considerations are verified by means of simulation and experimental results. [ABSTRACT FROM PUBLISHER]

In this paper, a new topology for Z-source inverter based on switched Z-source network is proposed. The proposed switched Z-source inverter can provide high voltage gain in low duty cycles. The continuous input current is one of the other advantages of the proposed inverter. The performance of the proposed inverter is investigated in different operating modes and the voltage and current equations of all elements and equations of critical inductance are calculated. Furthermore, the power losses and efficiency analyses are presented. The comprehensive comparison between the proposed inverter and the other conventional Z-source inverters shows its excellent performance. Finally, to prove the correct operation of the proposed topology, the experimental and simulation results using PSCAD/EMTDC software are presented. [ABSTRACT FROM PUBLISHER]

Electrolytic capacitors are the components that mainly impact the lifetime of ac/dc light-emitting diode (LED) drivers. Therefore, eliminating electrolytic capacitors from LED drivers is of vital importance. First, the basic derivation concept of a family of flyback-based three-port converters for electrolytic capacitor-less LED drivers is addressed in this paper, by manipulating the power flow among input port, output port, and storage capacitors. Together with the derivation of existing topologies, new topologies are also proposed. After evaluation, an integrated dual flyback converter (IDFC) is chosen, which requires less switching components and simpler control strategy. Following that, the operation principle and switching modes of the IDFC are elaborated, as well as the parameter design and implementation of control strategy. Finally, experiments on a laboratory prototype are carried out to verify the feasibility of the proposed topology. [ABSTRACT FROM PUBLISHER]

This paper presents a novel soft-switching galvanically isolated buck-boost dc–dc converter as a module-integrated converter for photovoltaic (PV) applications. It features three major operating modes: boost, normal, and buck mode. Their proper distribution over the input voltage range enables wide voltage regulation capabilities, i.e., close to those of nonisolated power optimizers. The proposed control algorithm requires only one buck-boost switching stage that performs voltage regulation by means of the switching stage reconfiguration with smooth transition between the modes. The design guidelines and the digital control system for PV applications are provided. The module-integrated converter was verified experimentally with a solar array simulator. The converter showed good maximum power point tracking performance and a peak efficiency of nearly 97%. [ABSTRACT FROM PUBLISHER]

A microconverter serves as a front-end dc–dc stage of a microinverter to convert the power from a photovoltaic module to a dc bus. These front-end microconverters require isolation, high-boost ratio, wide-input voltage regulation, and high efficiency. This paper introduces an isolated resonant converter with hybrid modes of operation to achieve wide-input regulation while still maintaining high efficiency. The proposed converter is designed as a series resonant converter with nominal-input voltage and operates under two additional modes: a boost converter with low-input voltage and a buck converter with high-input voltage. Unlike conventional resonant converters, this converter operates at discontinues conduction mode with a fixed frequency, simplifying the design and control. In addition, this converter can achieve zero-voltage switching (ZVS) and/or zero-current switching (ZCS) of the primary-side MOSFETs, ZVS and/or ZCS of the secondary-side MOSFETs, and ZCS of output diodes under all operating conditions. Experimental results using a 300-W prototype achieve a peak efficiency of 98.1% and a California Energy Commission efficiency of 97.6% including all auxiliary and control power at nominal-input voltage. [ABSTRACT FROM PUBLISHER]

In this paper, a new structure for high step-up dc–dc converters is proposed. In the proposed structure, it is possible to extend the topology by increasing the number of active–passive inductor cells. High voltage gain with lower duty cycle, low-current and -voltage stresses on switches, small inductors, and small size of filter are the main advantages of the proposed structure. The proposed converter is analyzed in different operating modes. In order to design the components’ values of the proposed converter, the equations of output voltage ripple are calculated in each operating mode and a design procedure is proposed based on the aforementioned equations. Moreover, the losses and efficiency of the converter are calculated. In order to validate the correctness of calculations and analyses, the experimental results are given. [ABSTRACT FROM PUBLISHER]

This paper presents a new active capacitor voltage balancing control method for the flying capacitor multicell (FCM) converters which is fully implemented using logic-form equations. The proposed active capacitor voltage balancing control technique, measures output current and flying capacitor (FC) voltages to generate the switching states in order to produce the required output voltage level and to balance FCs’ voltages at their reference values. Output voltage of the FCM converter controlled with proposed active capacitor voltage balancing method can be modulated with any pulse width modulation (PWM) technique such as the phase-shifted-carrier PWM or level-shifted-carrier PWM. An advantage of the proposed active capacitor voltage balancing control method is its simplicity as it does not require any complex computations and tedious optimization calculations. Simulation results and experimental measurements of a three-cell four-level and four-cell five-level FCM converters are presented to verify the performance of the proposed active capacitor voltage balancing control technique. [ABSTRACT FROM AUTHOR]

This paper proposes a novel active capacitor voltage balancing technique for stacked multicell (SM) converters. The proposed active capacitor voltage balancing control method detects the direction of the load current and measures the voltage of flying capacitors (FCs) to generate a proper switching state in order to form the required output voltage level and regulate the FC voltages at their desired reference levels. The proposed active capacitor voltage balancing control technique can modulate the output voltage through any of the pulse-width-modulation (PWM) techniques such as the phase-shifted carrier PWM or the level-shifted-carrier PWM. The foremost advantage of the proposed active control technique is that it does not demand any complex computations because it is not based on the optimization of the FC voltage-deviation cost functions. A thorough set of simulation results and experimental measurements for the five-level and seven-level SM converters are provided to validate the proposed active capacitor voltage balancing control method. [ABSTRACT FROM AUTHOR]

This paper proposes two nonisolated single-stage high power factor converters requiring low dc-link capacitance for power LEDs systems. Both converters result from the integration of the power factor correction and the LEDs driver stages, and require a relatively low dc-link capacitance value. A high power factor is demonstrated to be an inherent property of the proposed topologies and no input current control is necessary. The LEDs current is regulated by a symmetrical soft-switching half-bridge converter associated with a capacitive output filter. An accurate mathematical analysis valid for the two converters is detailed, yielding the elaboration of a step-by-step design procedure. In order to verify the analyses carried out, experimental results for two 90 W, 50 kHz, and 220 V converters are also presented. [ABSTRACT FROM PUBLISHER]

Low reliability is one of the major concerns of multilevel inverter due to the requirement of a large number of semiconductor devices as compared to two-level inverters. Thus, in this paper, a novel topology of multilevel inverter is proposed that can tolerate both open and short-circuit faults on its switches. The proposed topology also reduces dc sources and capacitors as compared to the conventional and recently proposed fault-tolerant topologies. Two types of solutions are provided in order to make the proposed topology fault tolerant; first provides a partial solution to fault, while the second provides a complete solution to fault. In addition, a novel switching strategy is proposed to reduce the amount of capacitor voltage ripples under normal and postfault conditions. Also, the proposed switching scheme offers an additional advantage of self-voltage balancing of its capacitor voltage both under normal as well as postfault conditions. To validate the proposed concepts, simulation and experimental analysis are carried out and different results are presented to show the viability of the proposed topology under normal operation, during fault and postfault conditions. [ABSTRACT FROM PUBLISHER]

In this paper, a new cascade switch-ladder multilevel inverter topology is presented which can generate a large number of output voltage levels. First, a fundamental switch-ladder multilevel inverter structure is described. Then, the structure of recommended cascade topology based on series connection of fundamental switch-ladder topologies is presented. To generate maximum number of levels with minimum number of switching elements, dc sources, and voltage on switches, the proposed cascade topology is optimized. Comparison results prove that the presented cascade topology requires fewer numbers of components. Also, the value of voltage rating on switches is less than other structures. Experimental results for two topologies are analyzed to verify the performance of the proposed topology. [ABSTRACT FROM PUBLISHER]

This paper presents a new multicell topology based on flying capacitor (FC) structure suitable for multilevel converters. The proposed topology employs the concept of phase-shifted carrier pulse width modulation (PWM) with modified modulating signals to generate appropriate PWM signals. The modulation strategy along with all possible switching states are explained. The implementation of the proposed PWM technique is shown by the help of illustrating waveforms. To show the advantages of the proposed structure, different performance criteria are compared with other FC multicell (FCM) structures. Simulation results are used to further evaluate the potential merits of the proposed topology. It is shown that the proposed structure is superior to other FCM-based structures from different standpoints. Specifically, it reduces the number of high-frequency switches, the number of FCs, and at the same time improves the quality of output voltage. A laboratory-type experimental setup is used to validate the modulation strategy and other theoretical findings. [ABSTRACT FROM AUTHOR]

This paper presents a nine-level inverter topology for an open-end induction motor drive requiring only eight switches per phase, using two three-level inverters with two isolated dc links in a 3:1 ratio. A space-vector-based formulation is used to determine pole voltages such that both inverters supply power to the load over the full modulation range, eliminating the possibility of dc bus overcharging. Proper selection of switching states ensures that all floating capacitor voltages are kept tightly balanced. A digital state machine is used to select sequences of switching states in order to eliminate deadtime-induced pole voltage transients, further improving the output-voltage quality. A level-shifted carrier-based pulse width modulation scheme is used. The steady-state and transient performance of this topology were verified and the experimental results are included. [ABSTRACT FROM AUTHOR]

A novel flying-capacitor-clamped five-level inverter based on bridge modular switched-capacitor topology is proposed in this paper. The inverter features the switched-capacitor circuit with dc–dc boosting conversion ability and the multilevel inverter circuit with flying-capacitor-clamped performance. With the special composite structure, the number of components is cut down compared to the topology of the conventional cascaded multilevel inverter. Meanwhile, part of switches can be operated under line voltage frequency, resulting in switching loss reduction. Hence, the potential of system efficiency and power density is released due to embed switched-capacitor circuit. More importantly, the optimized carrier-based phase disposition pulse width modulation method is employed as a control strategy. Under this control strategy, the capacitor voltage self-balance can be realized and quality of output waveforms can be improved significantly. After simulation, the prototype is built to validate the correctness and practicability of the analysis. [ABSTRACT FROM AUTHOR]

Cascaded converters are adopted in many power systems to manage sources and loads at different voltage levels simultaneously. DC bus capacitor is one of the key components in these converters due to its energy storage and fast response capabilities. However, the ripple current through the capacitor will influence its lifetime and the overall efficiency of the converter. Previous studies showed that the capacitor current of ac systems is optimized when the duty cycles are synchronized under in phase or antiphase condition. In this paper, the bus capacitor ripple current of cascaded two-stage converters for dc systems with different combinations of duty cycles is analyzed. It is found that the optimum capacitor current ripple varies depending on the values of individual duty cycles and the phase-shift angle between them. By properly adjusting the phase shift, the capacitor RMS current value can be reduced without affecting the converter normal operation or the need for extra sensing circuits, hence improving the energy conversion efficiency and prolonging the capacitor lifetime with relatively simple implementation. To illustrate, a case study of a two-stage dc/dc converter is carried out. A laboratory prototype converter confirmed a maximum efficiency improvement of 2.8% if the phase shift is adjusted properly when compared to the same converter with the worst case phase-shift angle. [ABSTRACT FROM AUTHOR]

This paper presents a multilevel step-up dc/dc converter for dc-grid-based offshore wind energy conversion applications. The main features of the proposed multilevel converter are as follows: 1) the voltage stress of the power devices can be reduced, making it suitable for high-voltage applications; 2) the boost inductor can be reduced significantly, leading to the outstanding dynamic performance; and 3) high-voltage gain can be obtained and thus is well-suited for high-gain applications. Theoretical analysis was carried out for a four-level step-up converter, based on which, the converter can be extended to any arbitrary number of levels. The proposed four-level converter was verified by a simulation and evaluated by comparing with a conventional multilevel dc/dc converter in terms of the component stress and power device count. The developed topology was implemented on a 2-kW prototype converter to evaluate its feasibility. [ABSTRACT FROM AUTHOR]

The five-phase coupled-inductor inverter is a newly proposed option for three-level five-phase inverter drives. This paper comprehensively analyzes the inverter including the coupled-inductor current, current stress on the dc-link capacitors, and a comparison of these performance aspects using three pulse width modulation (PWM) strategies. Mathematical derivations of the inverter currents and the associated current stress reveal that the current stress is not only influenced by the choice of modulation strategy, as in the neutral-point-clamped topology, but also by the value of coupled inductance; furthermore, the choice of the modulation strategy impacts the core loss of the coupled inductors. Three carrier-based PWM methods are considered: sinusoidal PWM (SPWM), and two methods with the common-mode voltage reduction (referred to as CMVR1 and CMVR2) for the five-phase coupled-inductor inverter. CMVR2 is shown to be the best solution if common-mode voltage reduction is required. The analysis demonstrates that SPWM performs better with respect to current stress and inverter losses, therefore is the preferable modulating strategy for the five-phase coupled-inductor inverter if common-mode voltage reduction is not required. The analysis is verified by simulations and experiments. [ABSTRACT FROM AUTHOR]

This paper proposes a novel high step-up nonisolated single switch dc–dc converter suitable for regulating dc bus in various microsources especially for photovoltaic (PV) sources. Quadratic boost and switched-capacitor technique are used as primary and secondary circuits, respectively. A coupled inductor is applied to make a connection between them, so a high dc voltage gain is achieved. High efficiency is yield where voltage stress on active switch is alleviated by clamped capacitor; consequently, smaller \rmR\rm{DS(ON)} for power switch is required. On the other hand, input current of the proposed converter is continued, hence stress on the input source is reduced. The operating principles and steady-state analyses are discussed in detail for both continuous and discontinuous conduction modes. Also, the boundary condition is computed. To verify the performance of the proposed converter and theoretical calculations, a 250-W prototype converter is implemented with an input voltage of 24 V and an output voltage of 400 V designed especially for PV sources in continuous conduction mode operation. Finally, simulation results are confirmed by experimental results; maximum efficiency is occurred at 150 W and full-load efficiency is 92.96%. [ABSTRACT FROM AUTHOR]

This paper proposes a new three-phase modular multilevel inverter (MMLI). The proposed inverter consists of repeated modular primary cells that are connected in series configuration. Therefore, the proposed topology can be extended to get more output voltage levels by adding additional cells without increasing voltage stresses across power switches. Both sinusoidal pulsewidth modulation (SPWM) and staircase modulation are successfully applied to the proposed inverter. The proposed inverter features many advantages such as reduced number of semiconductor power switches, driver circuits, dc-voltage sources, simplified control algorithm, and reduced voltage stresses across the switches independent of output voltage level. Furthermore, the performance of the proposed inverter is studied under both open-loop and closed-loop operations for highly inductive load. Beside the obtained simulation results, a laboratory prototype has been carried out and tested to verify the control techniques and performances of the topology. Simulation and experimental results are compared together to highlight the similarity and consistence of them. [ABSTRACT FROM AUTHOR]

The reduced capability of multilevel converters with more than one intermediate node to balance the dc-link capacitors voltage, as well as the lack of standard modulation methods to improve their balancing performance, makes these converter topologies unattractive for real power applications. This is especially true when the load demands active power. One of these topologies is the five-level multipoint clamped (5L-MPC) converter. The back-to-back (B2B) configuration of two 5L-MPC converters and the use of a space vector modulation (SVM) that exploits the voltage balancing capability of the redundant switching vectors extend the operation conditions range in which a proper voltage balance can be achieved. However, if practical modulation restrictions are considered (limitation of voltage steps, dead times, switching losses, etc.), the voltage balance cannot be achieved for all operation conditions. In this paper, an SVM which takes into account practical restrictions is proposed. In order to guarantee the voltage balance at any operation condition, the grid-side rectifier exchanges reactive power with the grid-side LCL filter. Thus, the voltage balance of the dc-link is guaranteed while a unity grid-side power factor is achieved. The proposed modulation scheme and the voltage balancing strategy are experimentally validated in a 6.6 kV 1.5 MW 5L-MPC B2B converter. [ABSTRACT FROM AUTHOR]

This paper presents a closed-loop space vector modulation (SVM)-based sliding mode controller (SMC) for a three-level grid-connected neutral point clamped (3L-NPC) inverter. The nonlinear SMC based on Gao's reaching law has been designed to control the grid current and inject desired amount of active and reactive power into the network. Due to using single dc source at the NPC inverter dc bus, neutral point voltage is controlled through redundant switching states and instantaneous dc voltage feedback integrated into SVM technique. Meanwhile, there is no external voltage controller involved, thus no associated fine tuning issues are existed. The performance of the proposed hybrid controller to inject a desired active/reactive power to the grid is investigated through external perturbations such as change in the line current amplitude/phase shift, ac voltage fluctuation, as well as dc voltage variation. Full converter state-space model was developed and simulated. Experimental results are provided to verify the fast dynamic performance, low content of line current THD%, and good voltage balancing of dc bus capacitors of the NPC inverter. [ABSTRACT FROM AUTHOR]

A new cascade topology for multilevel converter is introduced in this paper which comprises series connection of several submultilevel units. To determine the magnitudes of the dc sources, two new methods are described. The proposed topology is optimized to generate any levels with minimum number of components and peak voltage on switches. The presented topology can be used in high-voltage applications due to using the switches with low voltage rating. To indicate the merits of the proposed structure, comparison studies are provided with other topologies in terms of the number of elements and peak voltage on switches. The comparison results prove that the presented cascade multilevel converter requires fewer components. Moreover, it is shown that the total peak voltage on switches in the proposed topology is less than other structures. Experimental work is presented to demonstrate the performance of the presented multilevel converter. [ABSTRACT FROM PUBLISHER]

Multiterminal converters eliminate using several single-input-single-output converters and simplify their topologies and reduce their cost. In this paper, a new family of multi-input converters based on three switches leg is introduced. Inputs of the proposed converters are similar and they are topologically interchangeable and have boost or buck operation modes. The proposed converter has one output that operates as an inverter. Here, all operating modes of the proposed converters and their effects on each other are investigated, in details. Also, an appropriate switching technique for the converters is given. A detailed comparison between conventional and proposed two-input converters is also presented. A two-input, one-output prototype converter has been implemented to validate the given analyses and to verify the proposed converter's performance. The experimental results are in good agreement with the theoretical and simulated analyses. [ABSTRACT FROM AUTHOR]