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Enhancement of dc bus voltage utilization for a five-level inverter with single dc source and capacitor-fed H-bridge (CHB) units is investigated in this paper. A carrier-based modulation technique is used for boosting the dc bus utilization, which is established by providing detailed mathematical analysis. The five-level inverter used here is realized by cascading a CHB unit to each phase of a three-level neutral point clamped inverter. The increase in dc bus voltage utilization owes to the pole voltage redundancies offered by CHB units. The floating capacitors of H-bridge units are balanced within a quarter fundamental cycle using the switching state redundancies of pole voltage levels. The aforementioned modulation technique allows the inverter to enhance the dc bus utilization from 0.577 $\text{V}_{\text{dc}}$ to 0.63 $\text{V}_{\text{dc}}$ under unity power factor. This enhancement is obtained in the linear modulation range without increasing the dc bus voltage, and thus, the inverter can operate without the presence of low-order harmonics in its phase voltages. The strength of this paper lies in its detailed mathematical analysis for finding out the limiting modulation index and power factor condition in the light of floating capacitor voltage balancing issue. Simulation as well as experimental verification of the modulation scheme is carried out on an induction motor drive under various operating conditions. It is shown that this carrier-based modulation technique is suitable for any single source inverter topology with one CHB unit per phase. [ABSTRACT FROM AUTHOR]

This paper proposes a novel method for instantaneous balancing of neutral-point (NP) voltages with stacked multilevel inverters (MLIs) for variable-speed drives. The stacked MLI uses series-connected dc sources and NPs (connecting points of dc sources) to obtain the desired levels. The balancing of NP voltages are obtained by using a low-voltage-capacitor-fed cascaded H-bridge (CHB) per phase of a symmetrical six-phase induction machine (IM), which ensures zero current drawn from NPs (at any given instant). Since no current is drawn from NPs, the single dc-link operation with stacked capacitors is also possible. The scheme is suitable for applications, where low-voltage dc sources and batteries are stacked to form a dc link. A variable-speed operation is done using a seven-level inverter scheme for a symmetrical six-phase IM, which is formed by three dc-link stacked capacitors cascaded with two low-voltage-capacitor-fed CHBs per phase. Furthermore, the method is extended for an open-end IM to obtain a seven-level common-mode eliminated space vector structure using a single dc link. The generalization of this method for any stacked $n$ -level inverter without NP voltage deviation is also presented in this paper. The experimental results and analysis are included to validate the proposed method. [ABSTRACT FROM AUTHOR]

This paper proposes a new dc–ac converter with a reduced number of semiconductor switches and gate drive and control circuit components. A salient feature of this inverter is its pure sinusoidal line-to-line voltages with no need for output filter. Also, the proposed inverter improves the voltage utilization factor of the input dc supply compared to the four-switch three-phase inverter (first best topology in the literature from the number of switches point of view) and standard six-switch inverter with sine pulsewidth modulation. The proposed inverter is capable of operating with a wide range of output voltages from zero to the full value of the dc input voltage by appropriately altering the instantaneous duty cycle. A three-phase universal inverter with only three power switch has been proposed in this paper for the first time ever, to our knowledge. For the purpose of providing a good compromise between fast transient response and stability, a model predictive controller is proposed. All the design expressions have been derived. A comparison with other dc–ac converters is given to show the merits of the proposed converter. Finally, satisfactory circuit operation is confirmed by experimental results from a laboratory prototype. [ABSTRACT FROM AUTHOR]

This paper proposes a new family of multilevel inverter topology that is able to generate seven voltage levels by utilizing one or two floating capacitors and 10 power switches. This novel boost switched-capacitor seven-level inverter possesses voltage boosting capability with an achievable maximum voltage level 1.5 times the input direct current (dc) voltage. The generation of higher output voltage does not incur high-voltage stress on any power switch in this topology, as the peak inverse voltages of all power switches do not exceed the input source voltage. In addition, capacitor voltage balancing is not essential since the floating capacitors are effectively balanced during the charging and discharging processes. Furthermore, the proposed topology eliminates the need for multiple isolated dc sources, and a single dc source is sufficient in both its single-phase and three-phase topologies. The operating principle and steady-state analysis of the proposed topology are elaborated. Experimental results from a single-phase prototype are then presented to verify the validity of the proposed topology. [ABSTRACT FROM AUTHOR]

In this paper, a generalized switching modification method is proposed to reduce the root-mean-square (rms) current flowing into a dc-link capacitor in a dc–dc–ac structure consisting of a boost converter and a three-phase inverter. To analyze the current flowing into the capacitor, we analyze the currents at the respective converter and inverter sides. Based on this analysis, we derive an analytical method to find the modification time between the converter and inverter pulsewidth modulation (PWM) carriers through a Fourier series and approximation to facilitate real-time implementation. Real-time implementation of the modification time calculated by the derived method is described. To verify the validity of the proposed method, experimental results are presented based on a 1-kVA dc–dc–ac prototype. The proposed method has a better capacitor rms current reduction performance than the conventional method in various inverter power factors and PWM strategies. Especially, it has an excellent performance in mid-power factor level (0.95–0.1). [ABSTRACT FROM AUTHOR]

Three-phase voltage-source inverters typically feature a significant amount of dc energy storage to maintain a stiff dc bus. In these cases, the dc-link capacitor is sized to store enough energy to maintain several tens of cycles of ac output at the rated power. In this paper, we propose to reduce the size of the dc-link capacitor dramatically to store enough energy to provide just one high-frequency switching cycle of the ac output power. The dc bus is no longer stiff, and hence, classical sinusoidal pulse-width modulation cannot be used. However, the stored energy modulation (SEM) proposed herein synthesizes high-quality sinusoidal output voltage waveforms, even with such tiny dc-link capacitors. In SEM, the switching intervals of the interconnecting switches are carefully determined nonlinear functions of various operating parameters such as reactive component sizing, switching frequency, load levels, etc. This paper presents the analytical and detailed design development of the SEM approach along with circuit simulation, experimental results, and comparative evaluation of a dc-to-three-phase system example. [ABSTRACT FROM PUBLISHER]

The paper proposes a method of active switching harmonics current reduction in the dc-link capacitor of a two-level, three-phase, back-to-back converter. Based on the derived analytical solution for switching harmonic currents in the dc-link, it is shown that by specific control over the pulsewidth-modulated (PWM) carriers’ phase angles, the targeted harmonics of the rectifier and the inverter can be synchronized in phase such that their cancellation occurs in the dc-link capacitor. This synchronization is provided by harmonic phase feedback control. A three-step procedure to implement the method is detailed in the paper. The effectiveness of the proposed approach is verified experimentally. [ABSTRACT FROM AUTHOR]

This paper presents a model predictive control technique applied to a dual-active bridge inverter where one of the bridges is floating. The proposed floating bridge topology eliminates the need for isolation transformer in a dual inverter system and therefore reduces the size, weight, and losses in the system. To achieve multilevel output voltage waveforms, the floating inverter dc-link capacitor is charged to the half of the main dc-link voltage. A finite-set model predictive control technique is used to control the load current of the converter as well as the floating capacitor voltage. Model predictive control does not require any switching sequence design or complex switching time calculations as used for space vector modulation; thus, the technique has some advantages in this application. A detailed analysis of the converter as well as the predictive control strategy is given in this paper. Simulation and experimental results to validate the approach are also presented. [ABSTRACT FROM PUBLISHER]

This paper explores a power-conversion system for single-phase transformerless ac module application. A nonisolated high-gain dc–dc stage is coupled with a doubly grounded dynamic dc-link inverter to implement the microinverter topology. The front-end boost stage steps up the single-module voltage to a higher dc voltage, typically to 200 or 400 V as required for the following inverter stage. It is a hybrid of an interleaved boost and switched capacitor concept capable of achieving high gain while simultaneously maintaining reduced voltage and current stress, and thus lowering switching and conduction loss for most of the switches. By directly connecting the grid neutral to the photovoltaic (PV) negative, the doubly grounded voltage swing inverter has the advantage of zero capacitive-coupled common-mode ground currents, critical for transformerless PV inverters. The two dc links of the inverter stage share the double-line frequency power decoupling with a combination of higher value of mean voltage and relatively large 120-Hz ripple component–the dynamic dc-link approach. Through an optimization algorithm, the decoupling capacitance is minimized enabling an all-film capacitor implementation while satisfying the converter's operating constraints over a wide range of power factors. The simulation as well as experimental results from a GaN-based hardware prototype validate the converter's performance. [ABSTRACT FROM AUTHOR]

In this paper, a novel space-vector pulsewidth modulation technique for a five-level active neutral-point clamped (5L-ANPC) inverter is proposed to eliminate the common-mode voltage (CMV). For the 5L-ANPC inverter, which produces a good output voltage performance and lowdv/dt, the total 125 voltage vectors can be generated, among which the proposed scheme employs only 19 voltage vectors producing a zero CMV. Due to the limitation of voltage vectors selected, the dc-link capacitor voltages of the 5L-ANPC inverter cannot be balanced by themselves. Therefore, the capacitor voltages of the inverter should be controlled by choosing the redundant switching states appropriately. The validity of the proposed modulation scheme has been verified by simulation and experimental results. [ABSTRACT FROM AUTHOR]

Owing to low cost, small size, and low weight, transformerless inverters became prominent in single-phase grid connected photovoltaic (PV) systems. Key issues pertaining to these inverters include suppression of common mode (CM) leakage current and improvement of conversion efficiency. Achieving higher efficiency in single-phase grid-connected photovoltaic systems depends on the number of stages involved in feeding power to the grid, predominantly, if the PV array voltage is less than the peak value of the grid voltage. In this paper, an integrated dc–dc converter based grid-connected transformerless PV inverter is proposed which is aimed at maintaining high efficiency, even if the PV array voltage falls below the peak value of grid voltage (efficient operation at an extended input voltage range). A modulation strategy is discussed in order to minimize the flow of CM leakage current. Further, the efficiencies of certain transformerless inverter topologies are analyzed and compared with that of the proposed topology. Detailed simulation studies are carried out in MATLAB/Simulink environment to verify the analysis. Experimental results for a scaled down laboratory prototype are included as a proof-of-concept to validate the claims. [ABSTRACT FROM AUTHOR]

High-step-up dc/dc converters are widely required in grid-connected applications with renewable energy sources. An extremely high-ratio step-up nonisolated dc/dc converter, in the form of a harmonics-boosted resonant converter, is proposed in this paper. This proposed converter consists of a high-frequency dc/ac inverter stage that is followed by a passive ac/dc rectifier stage connected in cascade. Conventionally, such a dc/ac inverter is designed to output a pure sinusoidal ac voltage with an amplitude several times the amplitude of the input voltage. However, for the proposed converter, the harmonics-boosted inverter stage is designed to contain selected voltage harmonics that significantly boost the amplitude of its output voltage. This greatly increases the overall gain of the converter. The adopted ac/dc stage is a diode-capacitor rectifier, which is of high efficiency and easily extendable to increase the voltage gain. Importantly, the proposed converter involves only one active switch. With only one active switch, the driver's loss is minimized and the converter's control is simplified. Zero-voltage switching is applied to reduce the switching loss, which also allows the converter to operate efficiently at high frequency, and thus can be designed for high power density. The optimal design of the two converter stages and their combined voltage gain is investigated and reported. Besides, a design guideline of the proposed converter is provided. A prototype of a 57-time harmonics-boosted resonant converter with 3.3 V input voltage, 500 kHz switching frequency, and 21 W output power, is built. The experimental result shows that the achieved converter's efficiency is as high as 88.6%. [ABSTRACT FROM AUTHOR]

This paper introduces a high-gain single-stage boosting inverter (SSBI) for alternative energy generation. As compared to the traditional two-stage approach, the SSBI has a simpler topology and a lower component count. One cycle control was employed to generate ac voltage output. This paper presents theoretical analysis, simulation and experimental results obtained from a 200 W prototype. The experimental results reveal that the proposed SSBI can achieve high dc input voltage boosting, good dc–ac power decoupling, good quality of ac output waveform, and good conversion efficiency. [ABSTRACT FROM AUTHOR]

In this paper, a method is proposed to investigate the dc-link current and voltage ripple calculations in voltage source inverters by considering the reverse recovery of the antiparallel diodes. The impact of the diode reverse recovery transient on the dc-link current and voltage within the switching period is first analyzed. The analysis indicates that the current ripple rms value is affected by the value of inverter switching frequency, diode reverse recovery time, and current. However, the diode reverse recovery shows negligible impact on the dc-link voltage ripple calculation, since the difference between the voltage ripples calculated by the proposed and existing method is less than 1%. To evaluate the estimation accuracy of the dc-link current ripple rms value by the proposed method, the experiments are implemented and the comprehensive analysis is done under different operating conditions, including various power factors, modulation indexes, inverter output currents, and inverter switching frequencies. Experimental results show that the accuracy of dc-link rms current ripple calculation by the proposed method is in the range of $\pm$5% and increased by up to 7% compared with the existing method neglecting the antiparallel diode reverse recovery. [ABSTRACT FROM AUTHOR]

The hybrid modulation strategy using both low-frequency square-wave modulation and high-frequency pulse-width modulation can extend the stable operating region of a cascaded H-bridge converter. However, it does not control accurately dc voltages of converter but balances them by charging or discharging dc capacitors based on the state of system, which could aggravate fluctuation of dc voltages. If cascaded H-bridge converter is used in photovoltaic field, the aggravated fluctuation on dc capacitor voltages will result in further losses in energy harvesting of solar cells. To address this issue, a modified hybrid modulation strategy is presented in this paper. When dc-bus measured voltages are close to their reference voltages, these H-bridges operate in a zero mode. Adding appropriate zero state can prevent grid current charging or discharging the dc capacitors whose voltages have already reached their control goals. Therefore, the proposed technique is capable of suppressing dc voltage fluctuation, and, thus, improving the output power of solar cells. Simulation and experimental results validate the effectiveness and feasibility of the proposed method. [ABSTRACT FROM PUBLISHER]

This paper presents an optimized topology for a \text3-\phi three-level inverter with complete elimination of common-mode voltage (CMV). The proposed multilevel inverter (MLI) configuration is realized by modifying a T-structure \text3-\phi inverter. The proposed configuration is an optimized solution with respect to the pulse-width modulation strategy used for CMV elimination. The given three-level inverter structure uses only 16 power semiconductor switches, which is much lower than the existing configurations. A reduced number of power semiconductor devices results in a diminished number of driver circuits, less installation space, and low cost. Further, due to the complete elimination of CMV, the proposed MLI is free from issues such as electromagnetic interference and leakage current with a reduction in filter requirement. The presented topology is also compared with other existing topologies to prove its advantage. It is an optimized solution with respect to the dc bus voltage requirement and the total voltage rating of the devices or the components used in the system. Simulation and experimental results are presented to confirm the capability of the proposed MLI. [ABSTRACT FROM AUTHOR]

Three-phase inverters in uninterrupted power supply, electric vehicles, and hybrid electric vehicles use an intermediate dc-link electrolytic capacitor, which has reliability issues and is one prominent cause of inverter failure and limited life. The large volume of an electrolytic capacitor increases the size and cost of the system. Recent research on electrolytic capacitorless inverters using six-pulse modulation technique along with high-frequency power conversion has attempted to address this issue. However, closed-loop operation and control has some issues due to capacitorless dc-link. In this paper, closed-loop operation, design, and implementation of an electrolytic capacitorless inverter is presented. A proof-of-concept 1-kW hardware prototype has been built and tested in a laboratory under different loading conditions. In total, 98% rated efficiency of the inverter is obtained with total harmonic distortion within 2%. Transient results during start-up and load change are smooth, demonstrating safe operation of the inverter. [ABSTRACT FROM AUTHOR]

This paper presents the design and implementation of a simple neutral point potential (NPP) regulator for a three-level diode-clamped inverter employing a sine-triangle regulator in conjunction with a closed-loop controller with reduced switching losses. The regulator principle is based on adding a continuous variable offset voltage which regulates the midpoint potential of the dc bus. The novelty of the proposed NPP regulator is in the determination of the magnitude of variable offset voltage based upon the average value, peak-to-peak amplitude, total harmonic distortions, and third harmonic content in NPP. Aside from maintaining dc-bus voltage balance, the proposed regulator leads to a significant reduction in the voltage distortion at the NP, resulting in the reduction of the required dc-bus capacitance. It also reduces the switching losses of the inverter by inserting the “no-switching” zone within each half cycle of the fundamental voltage wave. Analytical, computer simulation, and experimental results verifying the approach are presented in this paper for various load power factor angles. [ABSTRACT FROM AUTHOR]

This paper deals with a new family of high boost voltage inverters that improve upon the conventional trans-Z-source and trans-quasi-Z-source inverters. The improved trans-Z-source inverter provides continuous input current and a higher boost voltage inversion capability. In addition, the improved inverter can suppress resonant current at startup, which might destroy the device. In comparison to the conventional trans-Z-source/-trans-quasi-Z-source inverters, for the same transformer turn ratio and input and output voltages, the improved inverter has a higher modulation index with reduced voltage stress on the dc link, lower current stress flow on the transformer windings and diode, and lower input current ripple. In order to produce the same input and output voltage with the same modulation index, the improved inverter uses a lower transformer turn ratio compared to the conventional inverters. Thus, the size and weight of the transformer in the improved inverter can be reduced. This paper presents the operating principles, analysis and simulation results, and compares them with those of the conventional trans-Z-source/-quasi-Z-source inverters. To verify the performance of the improved converter, a laboratory prototype was constructed based on a TMS320F2812 digital signal processor with 100 V dc input and 115 Vrms output voltage. [ABSTRACT FROM AUTHOR]

Switched boost inverter (SBI) is a single-stage power converter derived from Inverse Watkins Johnson topology. Unlike the traditional buck-type voltage source inverter (VSI), the SBI can produce an ac output voltage that is either greater or less than the available dc input voltage. Also, the SBI exhibits better electromagnetic interference noise immunity when compared to the VSI, which enables compact design of the power converter. Another advantage of SBI is that it can supply both dc and ac loads simultaneously from a single dc input. These features make the SBI suitable for dc nanogrid applications. In this paper, the SBI is proposed as a power electronic interface in dc nanogrid. The structure and advantages of the proposed SBI-based nanogrid are discussed in detail. This paper also presents a dq synchronous-reference-frame-based controller for SBI, which regulates both dc and ac bus voltages of the nanogrid to their respective reference values under steady state as well as under dynamic load variation in the nanogrid. The control system of SBI has been experimentally validated using a 0.5-kW laboratory prototype of the SBI supplying both dc and ac loads simultaneously, and the relevant experimental results are given in this paper. The low cross regulation and the dynamic performance of the control system have also been verified experimentally for a 20% step change in either dc or ac load of SBI. These experimental results confirm the suitability of the SBI and its closed-loop control strategy for dc nanogrid applications. [ABSTRACT FROM AUTHOR]

This paper focuses on the common dc-link voltage between a three-phase diode rectifier and a modular multilevel cascade inverter based on double-star chopper cells (MMCI-DSCC) for a medium-voltage motor drive. This motor drive can be operated even when no capacitor exists on the dc link. However, a nonnegligible, but predictable, amount of switching-ripple voltage occurs on the dc link. This paper achieves modeling and analysis of the switching-ripple voltage, thus making it possible to design a small-sized dc passive filter consisting of series connection of a film capacitor and a damping resistor. A 400-V, 15-kW down scaled system is used to confirm the effectiveness of the analysis and the dc filter. Experimental results show that the switching-ripple voltage can be attenuated satisfactorily by the dc filter, and that the power loss dissipated in the damping resistor is negligible, compared to the rated power of 15 kW. [ABSTRACT FROM AUTHOR]

Power switches and electrolytic capacitors are the most vulnerable components in the power electronic converters. Any failure in these components may result in severe damages, if no remedial action is employed. Prior to any remedy, the first step is fault diagnosis. In this paper, a new type of Rogowski coil sensor is proposed. The sensor captures the inductor current derivative, which contains suitable signatures for switch fault diagnosis and capacitor lifetime monitoring in nonisolated single-switch dc–dc converters. Using the captured signal, detection of switch open-circuit and short-circuit faults is realized by a simple logic circuit. Furthermore, a new capacitor lifetime monitoring technique is proposed, which employs this signal for calculating equivalent series resistance of the capacitor. The proposed sensor has some remarkable advantages. Due to its nonmagnetic core, the problem related to nonlinear response of magnetic cores at high frequencies will not be encountered. Furthermore, the proposed cost-efficient approach can be easily implemented even for already fabricated converters. The performance of the proposed sensor is evaluated using some finite-element simulations and experiments for a buck converter. The results confirm the capabilities of the sensor for switch fault diagnosis and capacitor lifetime monitoring in nonisolated single-switch dc–dc converters. [ABSTRACT FROM PUBLISHER]

This paper presents a new family of hybrid Z-source boost dc–dc converters intended for photovoltaic applications, where the high step-up dc–dc converters are demanded to boost the low-source voltages to a predefined grid voltage. Because the boost capabilities of the traditional Z-source networks are limited, the proposed converters are composed of combine traditional Z-source networks in different ways to enhance the boost abilities of the traditional Z-source networks. The new version of the proposed Z-source converters is termed as hybrid Z-source boost dc–dc converters to satisfy the traditional benefits of Z-source networks with stronger voltage boost abilities which can also be applied to dc–ac, ac–ac, and ac–dc power conversions. The performances of the proposed converters are compared with other Z-source networks behaviors. The simulation and experimental results of the proposed converters are validated at different operating conditions. [ABSTRACT FROM PUBLISHER]

In this paper, a new isolated high step-up dc–dc converter is proposed based on the quasi-switched-boost network. The proposed converter has the following features: 1) continuous input current; 2) reduced turn ratio of the isolated transformer; 3) increased reliability, as it can operate in either short-circuit mode or open-circuit mode without causing damage to the power converter; and 4) unchanged primary and secondary voltage waveforms of the transformer, although the shoot-through duty cycle is variable. Compared to the quasi-Z-source-based isolated dc–dc converter, the proposed converter uses fewer passive components. The operating principles, analysis, parameter design guideline, and comparison with the quasi-Z-source-based isolated dc–dc converter are presented. A 450 W prototype is built to test the proposed converter. The proposed converter is applicable for distributed power generation applications where a varying low dc input voltage is converted to a high stabilized dc output voltage with a galvanic separation requirement. [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]

In this paper, a novel cascaded seven-level inverter topology with a single input source integrating switched-capacitor techniques is presented. Compared with the traditional cascade multilevel inverter, the proposed topology replaces all the separate dc sources with capacitors, leaving only one H-bridge cell with a real dc voltage source and only adds two charging switches. The capacitor charging circuit contains only power switches, so that the capacitor charging time is independent of the load. The capacitor voltage can be controlled at a desired level without complex voltage control algorithm and only use the most common carrier phase-shifted sinusoidal pulse width modulation strategy. The operation principle and the charging–discharging characteristic analysis are discussed in detail. A 1-kW experimental prototype is built and tested to verify the feasibility and effectiveness of the proposed topology. [ABSTRACT FROM AUTHOR]

In this paper, initially a new dc/dc converter is proposed which can produce boosted multiple dc link voltages by using the novel switched-capacitor converter (SCC) and with reduced number of switches. In the proposed SCC, voltage of all capacitors is charged by binary asymmetrical pattern as self-balancing and without using any auxiliary circuits. The proposed SCC will boost the input dc power supply voltage without transformer by switching the capacitors in series and in parallel. Next, a new single phase switched-capacitor multilevel inverter (SCMLI) topology which uses the proposed SCC units as virtual dc links have been proposed. The proposed topologies reduce the number of power switches, diodes, isolated dc power supplies, size, and the cost of the system in comparison with conventional similar topologies. For example, by contribution of proposed SCMLI structure, 49 and 137 output voltage levels are made by only 14 and18 power switches and 3 and 4 isolated dc power supplies, respectively. To confirm the performance of proposed topology, various simulation results by PSCAD/EMTDC software and experimental tests are given. [ABSTRACT FROM AUTHOR]

This paper proposes a new space-vector pulsewidth modulation (SV-PWM) strategy for a three-level neutral point clamped inverter. The presented SV-PWM strategy makes it possible to control the neutral point voltage by optimum choice of switch sequence for any position and length of output voltage vector. The proposed solution takes into consideration the unbalance of the dc-link voltages. It also analyzes the influence of vector sequences on the predicted unbalance of the dc-link voltage. The solution allows selecting optimum vectors and their on-time durations in order to reduce quickly the dc-link voltage unbalance. The calculation of the space vector area proposed in this paper takes into consideration voltage unbalance and its influence on the length and position of vectors. The proposed approach assures properly generating the voltage output vectors, even in the case of the existing large voltage unbalance in the dc-link. The results of the experimental investigation of the proposed modulation strategy are presented in this paper. [ABSTRACT FROM PUBLISHER]

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

This paper describes a single-phase full-bridge inverter that possesses limited current ripple at the dc link while providing a sinusoidal square power at the ac output. This is achieved through the addition of an extra pair of switches and complementary control for the full-bridge inverter. The extra switches operate to prevent the double-line frequency ripple current from flowing into the input of the inverter. In doing so, the pulsation component of the sinusoidal square output power is confined to flow between the output capacitors and the load. Thus, the dc link input only supplies the dc component of the output power. Simulation and experimental results validating the proposed solution are presented. [ABSTRACT FROM PUBLISHER]

Local dc distribution systems or dc nanogrids for residential and commercial buildings are growing popular due to the increased focus on energy savings. Using low-voltage dc for the nanogrid provides various advantages such as easier integration with renewable sources and battery banks, increased savings, etc. Future systems would use renewable sources and storage devices to become self-sufficient in generation with bare minimum consumption from the grid. The objective of this paper is to develop an energy management system (EMS) to provide uninterrupted power supply to the dc loads and achieve self-sufficiency by minimizing grid power consumption. This is achieved by developing a control scheme for a cascaded two-stage bidirectional converter interface between the nanogrid and the ac distribution network. In addition, an empirical relation for power flow through the converter is obtained, and an optimal capacitor link voltage range is derived to achieve power transfer between rated limits. The efficacy of the proposed control algorithm for the EMS is analyzed and proved to be well suited for the self-sustained dc nanogrid. A 5-kVA prototype of the converter is designed and developed in hardware, and the system operation is verified with experimental results. [ABSTRACT FROM PUBLISHER]

In this paper, an analysis and calculation of the dc-link current and voltage ripples are presented for a three-phase inverter with unbalanced load. A comparison of the dc-link average and root-mean-square (rms) currents between considering and ignoring high frequency harmonics of the output current is drawn. It is shown that high frequency harmonic currents have little effect on the dc-link current, and therefore, they can be ignored. Based on the symmetrical components method, the dc-link average and harmonic rms currents are derived, and the dc-link voltage ripple is compared between the balanced and unbalanced loads. It can be found that the dc-link current and voltage ripples consist of not only high frequency harmonics but also the double fundamental frequency harmonic, and the voltage ripple is independent of the positive-sequence component and determined by the negative-sequence component, under the unbalanced load. Experimental results are shown to verify the accuracy of the theoretical analysis. [ABSTRACT FROM AUTHOR]

Two stage-cascaded converters are widely used in dc–ac hybrid systems to achieve the bidirectional power transmission. The topology of dual active bridge cascaded with inverter (DABCI) is commonly used in this application. This paper proposes a coordinative control method for DABCI and it is able to reduce the dc-link voltage fluctuation between the DAB and inverter, then reduce the stress on the switching devices, as well as improve the system dynamic performance. In the proposed control method, the DAB and inverter are coordinated to control the dc-link voltage and the power, and this responsibility sharing control can effectively suppress the impact of the power variation on the dc-link voltage, without sacrificing stability. The proposed control method is also effective for DABCI in unidirectional power transmission. The effectiveness of the propose control has been validated by both simulations and experiments. [ABSTRACT FROM AUTHOR]

This paper presents an effective circuit configuration of a multilevel inverter that can increase the number of output voltage levels with a reduced number of circuit components. The proposed seven-level pulsewidth-modulation inverter consists of a single dc voltage source with a series of capacitors, diodes, active switches for synthesizing output voltage levels, and an H-bridge cell. After theoretical analysis, we carry out computer-aided simulations and experiments to verify the validity of the proposed approach. Here, we also introduce a modified switching strategy to solve the capacitor voltage unbalancing that occurs in series-connected capacitors. [ABSTRACT FROM PUBLISHER]

Photovoltaic (PV) inverters without the isolation transformer become more attractive due to higher efficiency and lower weight. However, it may have dc offset current problem and is critical to the power system. In this paper, a novel control strategy of suppressing dc current injection to the grid for PV inverters is investigated. It is based on the idea of accurately sensing the dc offset voltage of PV inverter output. Since dc component of the inverter output can be eliminated, dc injection to the grid can be effectively suppressed. Finally, the control scheme is verified by the experiment. [ABSTRACT FROM AUTHOR]

The objective of this paper is to propose a new inverter topology for a multilevel voltage output. This topology is designed based on a switched capacitor (SC) technique, and the number of output levels is determined by the number of SC cells. Only one dc voltage source is needed, and the problem of capacitor voltage balancing is avoided as well. This structure is not only very simple and easy to be extended to a higher level, but also its gate driver circuits are simplified because the number of active switches is reduced. The operational principle of this inverter and the targeted modulation strategies are presented, and power losses are investigated. Finally, the performance of the proposed multilevel inverter is evaluated with the experimental results of an 11-level prototype inverter. [ABSTRACT FROM PUBLISHER]

This paper presents a novel direct current-fed interleaved phase-modulated single-phase unfolding inverter for fuel-cell applications. Two active-clamped zero-voltage switching current-fed half-bridge isolated converters are interleaved in parallel input and series output configuration. Phase modulation is proposed to control these two converter cells, which generate a rectified sinusoidal pattern at the dc link. A simple H-bridge unfolding dc–ac inversion is used to produce single-phase sine voltage at line frequency switching using square-wave control. This not only simplifies the inversion stage in terms of modulation but also reduces the switching losses. Direct front-end current-fed based unfolding inverter is not reported in literature yet. Detailed analysis and design of the proposed direct current-fed single-phase unfolding inverter has been presented. Simulation waveforms using PSIM 9.0.4 are given to verify the presented analysis and design. Experimental results on a laboratory prototype rated at 200 W are demonstrated to support the investigation, to validate the accuracy of the proposed analysis and design, and to test the performance. [ABSTRACT FROM PUBLISHER]

This paper presents a detailed operation analysis, controller design, and realization of a high-power, bidirectional quasi-Z-source inverter (BQ-ZSI) for electric vehicle applications. The circuit analysis shows that with a bidirectional switch in the quasi-Z-source network, the performance of the inverter under small inductance and low power factor can be improved. Based on the circuit analysis, a small signal model of the BQ-ZSI is derived, which indicates that the circuit is prone to oscillate when there is disturbance on the dc input voltage. Therefore, a dedicated voltage controller with feed-forward compensation is designed to reject the disturbance and stabilize the dc-link voltage during a non-shoot-through state. An 85-kW prototype has been built. Both simulation and experimental results are presented to prove the functionality of the circuit and the effectiveness of the proposed control strategy. [ABSTRACT FROM AUTHOR]

It is important to improve the overall efficiency of a photovoltaic (PV) inverter when it is connected to the grid. Fundamentally, the conversion efficiency from dc to ac power of an inverter is important. However, in the presence of partial shading, maximum power point tracking (MPPT) on PV modules is more important than the conversion efficiency. In this paper, a new control method for a three-level inverter is proposed. With the proposed method, each dc-link voltage of the three-level inverter can be asymmetrically regulated. When PV modules are split into two and each split module is connected to the respective dc-link capacitors of the inverter, the asymmetric control can be helpful because separate MPPTs are possible. The effectiveness of the proposed method was examined through experiments with a T-type three-level inverter, where each dc-link capacitor was supplied by a PV simulator emulating two separate PV modules under different shading conditions. [ABSTRACT FROM AUTHOR]

In order to eliminate the common-mode (CM) leakage current in the transformerless photovoltaic (PV) systems, the concept of the virtual dc bus is proposed in this paper. By connecting the grid neutral line directly to the negative pole of the dc bus, the stray capacitance between the PV panels and the ground is bypassed. As a result, the CM ground leakage current can be suppressed completely. Meanwhile, the virtual dc bus is created to provide the negative voltage level for the negative ac grid current generation. Consequently, the required dc bus voltage is still the same as that of the full-bridge inverter. Based on this concept, a novel transformerless inverter topology is derived, in which the virtual dc bus is realized with the switched capacitor technology. It consists of only five power switches, two capacitors, and a single filter inductor. Therefore, the power electronics cost can be curtailed. This advanced topology can be modulated with the unipolar sinusoidal pulse width modulation (SPWM) and the double frequency SPWM to reduce the output current ripple. As a result, a smaller filter inductor can be used to reduce the size and magnetic losses. The advantageous circuit performances of the proposed transformerless topology are analyzed in detail, with the results verified by a 500-W prototype. [ABSTRACT FROM AUTHOR]

In this paper, several modular converter topologies based on a switched-capacitor-cell concept are introduced for high-power applications. Two types of switched-capacitor cells, including the full cell and the half-cell, are discussed. The full cell can be used for dc–ac inversion, and the half-cell is utilized in both dc–dc and dc–ac applications. A rotational charging scheme is adopted for the half-cell-based dc–dc voltage multiplier to eliminate the large output capacitor that exists in many traditional switched-capacitor topologies. A soft-switching scheme, which does not require extra components, is adopted to reduce the switching loss and electromagnetic interference. A variable switching frequency control scheme is proposed to realize soft switching for dc–ac inverters. The experimental results on a 2-kW prototype are presented to verify the proposed topologies. [ABSTRACT FROM PUBLISHER]

In this paper, a new three-phase, five-level inverter topology with a single-dc source is presented. The proposed topology is obtained by cascading a three-level flying capacitor inverter with a flying H-bridge power cell in each phase. This topology has redundant switching states for generating different pole voltages. By selecting appropriate switching states, the capacitor voltages can be balanced instantaneously (as compared to the fundamental) in any direction of the current, irrespective of the load power factor. Another important feature of this topology is that if any H-bridge fails, it can be bypassed and the configuration can still operate as a three-level inverter at its full power rating. This feature improves the reliability of the circuit. A 3-kW induction motor is run with the proposed topology for the full modulation range. The effectiveness of the capacitor balancing algorithm is tested for the full range of speed and during the sudden acceleration of the motor. [ABSTRACT FROM AUTHOR]

This paper is devoted to the step-up dc/dc converter family with a cascaded quasi-Z-source network (qZS-network). The cascaded (two-stage) qZS-network could be derived by the adding of one diode, one inductor, and two capacitors to the traditional quasi-Z-source inverter (qZSI). The proposed cascaded qZSI inherits all the advantages of the traditional solution (voltage boost and buck functions in a single stage, continuous input current, and improved reliability). Moreover, as compared to the conventional qZSI, the proposed solution reduces the shoot-through duty cycle by over 30% at the same voltage boost factor. Theoretical analysis of the two-stage qZSI in the shoot-through and non-shoot-through operating modes is described. The proposed and traditional qZS-networks are compared. A prototype of a step-up dc/dc converter with the cascaded qZS-network was built to verify the theoretical assumptions. The experimental results are presented and analyzed. Finally, a further optimization method of the cascaded qZS-network is proposed, and some practical design issues are discussed. [ABSTRACT FROM PUBLISHER]

The output voltage quality of some of the single-phase multilevel inverters can be improved when their dc-link voltages are regulated asymmetrically. Symmetrical and asymmetrical multilevel diode-clamped inverters have the problem of dc-link capacitor voltage balancing, especially when power factor of the load is close to unity. In this paper, a new single-inductor multi-output dc/dc converter is proposed that can control the dc-link voltages of a single-phase diode-clamped inverter asymmetrically to achieve voltage quality enhancement. The circuit of the presented converter is explained and the main equations are developed. A control strategy is proposed and explained in details. To validate the versatility of the proposed combination of the suggested dc–dc converter and the asymmetrical four-level diode-clamped inverter (ADCI), simulations and experiments have been directed. It is concluded that the proposed combination of introduced multioutput dc–dc converter and single-phase ADCI is a good candidate for power conversion in residential photovoltaic (PV) utilization. [ABSTRACT FROM PUBLISHER]