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This paper presents an isolated single-stage on-board electric vehicle charger without an intermediate DC-link. Based on an isolated current-source topology, the converter features soft-switching in semiconductors regardless of load variation for the full AC line voltage range. Moreover, it requires no external snubber or clamp circuits. The power factor correction and voltage regulation are provided by a relatively simple phase shift modulation, while the amount of circulating energy is kept at minimum. The charger is distinguished by its efficiency characteristic – the maximum is achieved in the constant power charging mode. The control method, component stresses, and design constraints of the topology are analyzed. The concept is verified using a 3 kW experimental SiC-based prototype, which reaches a peak efficiency of 96.4%. Moreover, the charger has demonstrated efficiencies above 95% with the THD of 4.1% when operating in constant power mode at the maximal power. [ABSTRACT FROM AUTHOR]

This paper proposes a capacitor voltage regulation method for the dual converter with a floating bridge for aerospace applications. This topology has previously been reported, but with a constrained voltage utilization factor due to the need for capacitor voltage regulations. In this paper, the effect of switching states on the voltage variation of capacitor is quantitatively modeled and an enhanced space vector modulation scheme with current feedback is proposed to achieve an active control of the floating capacitor voltages. This proposed method also allows further exploitation and utilization of converter voltage. The relationship between the allowed modulation index of dual converter and load power factor is obtained and expressed using a fitted polynomial equation. The advantages of the proposed method include boosted voltage utilization and superior performance in term of capacitor voltage balance. These advantages have been proven through simulation and experimental results on RL loads as well as with an open-end winding induction motor. The proposed modulation scheme can boost the converter voltage utilization by at least 10% while achieving full four-level operation. More importantly, the higher available voltage allows extending the constant torque region of the motor, the further beginning of field weakening operation could be postponed. [ABSTRACT FROM AUTHOR]

This paper presents two capacitor voltage balancing (CVB) strategies for modular multilevel converter (MMC) applications. Both balancing schemes are based on model predictive control and are designed to efficiently solve a constrained optimal control problem, where the predicted capacitor voltage errors are included in the cost function with the demanded output voltage of a cluster being forced through an equality constraint. The first method proposed in this paper computes specific modulation indexes for each module using the explicit solution of a relaxed version of the original optimization problem. The second approach proposed in this paper reduces the complexity of the original problem by linearizing the objective function and using an optimal sorting network based on a greedy algorithm to solve this approximation. Considering the structures of both solution approaches, they are integrated into modulation schemes based on phase-shifted and level-shifted pulsewidth modulation algorithms, respectively. Experimental results obtained from a nine-cell single-phase MMC prototype demonstrate the good performance achieved with the proposed methodologies, as well as the implementation simplicity offered by the proposed CVB algorithms. [ABSTRACT FROM AUTHOR]

To support the development of high-frequency ac microgrids in terms of compact design, high-voltage gain and low total harmonic distortion (THD), a buck–boost dual-leg-integrated step-up inverter is proposed in this paper. The inverter is formed by integrating a buck–boost converter into a conventional single-phase full-bridge inverter by sharing the upper switch and the body diode of the lower switch in both bridge-legs. Consequently, the component count is significantly reduced over the step-up inverter counterparts. In addition, to address the drawbacks of hybrid modulation methods adopted by existing dual-leg-integrated inverters, such as double-variable control, and high THD of output voltage/current at high input voltage and heavy load conditions, unipolar frequency doubling sinusoidal pulse width modulation scheme is adopted in this inverter. As a result, the modulation ratio M becomes the only control variable to regulate the output voltage/current and the control is simplified. The THD of the proposed inverter output can remain low throughout the entire input voltage range and load power range. This paper presents the topology derivation procedure, operation principle, and steady-state characteristics of the proposed inverter. To validate the effectiveness of theory, experimental results of a 400 W hardware prototype, where the output voltage frequency is at 500 Hz, are reported. [ABSTRACT FROM PUBLISHER]

The conventional three-level inverter only has voltage buck capability. The quasi-Z-source three-level T-type inverter (QZS 3LT $^2$ I) has been proposed to realize voltage buck–boost operation. In this paper, we further propose a novel modulation scheme for the QZS 3LT $^2$ I to realize voltage boosting, reduce the common-mode voltage (CMV), and control the neutral-point voltage balance simultaneously. The proposed scheme adopts a large vector, a medium vector, a small vector with low CMV magnitude, a zero vector, and a shoot-through vector to generate the output voltage. According to sector number and neutral-point voltage difference, a p-type or n-type small vector with low CMV magnitude is properly selected to balance the neutral-point voltage. Shoot-through states are inserted within zero vector to boost the dc input voltage without affecting the ac output voltage. Dwell times of basic vectors are calculated through the revised volt–second balance equation. Furthermore, a coordinate control strategy between neutral-point voltage balance and voltage boosting is proposed. Doing so, the CMV magnitude can be restricted within one-sixth of dc-link voltage and neutral-point voltage imbalance can be effectively mitigated. The effectiveness of the proposed scheme is verified by simulations and experiments. [ABSTRACT FROM AUTHOR]

The three-level full-bridge (TLFB) dc−dc converter has been widely used in high-voltage, high-power applications. In the experimental test, the neutral-point voltage deviation appears; moreover, it has also been found out that if the flying capacitors are introduced, the input capacitor voltages could realize self-balance even if no active balancing solutions are adopted. In the previous publications, the role of flying capacitors is generally considered to extend the range of soft switching; however, the self-balance ability has not been mentioned or investigated in any publications thus far. In order to fill this gap, this paper provides the detailed mode operation analysis of the TLFB converter and reveals the cause of the imbalance. In addition, the mechanism of the self-balance ability provided by the flying capacitors is explained in detail, which gives a deep insight into the converter. At last, the influence factor of the voltage error in steady state has been analyzed, and the specific expression of the voltage error is also derived. The feasibility of the theoretical analysis is verified by the simulation and experimental results. [ABSTRACT FROM AUTHOR]

This paper presents the topology and modulation technique of a three-phase three-level modified Z-source neutral-point-clamped (MZS-NPC) inverter, which combines a modified Z-source impedance network and a three-phase three-level NPC inverter. The boost factor of the proposed MZS-NPC inverter is twice as high as the three existing representative topologies combing an impedance network with a three-level NPC inverter. A modulation scheme for the proposed topology, based on a maximum boost control method, is designed to achieve the maximum voltage gain with simple implementation and to balance the dc-link neutral-point voltage. A closed-loop control of the ac load voltage in the fuel-cell or photovoltaic applications based on the proposed inverter is realized, in order to supply a desired voltage to the critical load in islanding mode of a microgrid. The boosting ability and operation validity of the proposed topology and modulation technique are demonstrated with simulation and experimental results. [ABSTRACT FROM AUTHOR]

This paper presents an approach for dealing with the control of five-level, diode-clamped rectifiers. The control of such converters is challenging, as voltage balancing among capacitors is not a trivial task. Some of the existing approaches that cope with this problem use specific modifications of one of the traditional modulation techniques, such as using redundant vectors in space vector modulation (SVM). The main feature of the proposed technique is that part of the modulation is considered in the system equations and, in this way, the voltage balance can be solved designing a specific controller for this problem. As a result, several levels are used within a switching period. Furthermore, it is shown that the proposed approach hardly affects the control of active and reactive powers and total dc-link voltage in such a way that the well-known direct power control can be applied. As a consequence, the resultant modulation stage is simpler than other techniques based on, e.g., SVM. The effectiveness and good performance of the system under the proposed control approach are validated by both simulation and experimental results. [ABSTRACT FROM AUTHOR]

In this paper, a highly efficient isolated resonant converter with a novel modulation method is proposed for delivering power from photovoltaic (PV) modules to the dc microgrid. The proposed modulation method allows the converter to boost low input voltages and regulate a wide input voltage range. The converter design is based on a series resonant converter (SRC) that operates at the resonant frequency to achieve highest efficiency under nominal input voltage condition. Under shadowed or low irradiance conditions of PV panels, the converter will operate with the proposed “double-pulse duty cycle” modulation method to step up the voltage for the dc microgrid connection. With the proposed modulation method, the output switches serve for both synchronous rectification and voltage boost function. This method enables a higher voltage boost ratio than the SRC without adding additional switches while operating at the resonant frequency. A 300-W hardware prototype with gallium-nitride devices is built to verify the performance of the proposed converter and modulation method. The converter achieved a peak efficiency of 98.9% and a California Energy Commission weighted efficiency of 98.7% under nominal input voltage condition. [ABSTRACT FROM AUTHOR]

The hybrid modular multilevel converter with cascaded full bridges (HMMC-CFB) is a recently proposed dc fault tolerant converter topology for high-power applications. It has a director part (DP) consisting of a series of connected half-bridge submodules, and a wave-shaping part (WSP) composed of a series of connected full-bridge submodules (FBSMs). The submodules in DP avoid high voltage stresses and improve synchronization between DP and WSP by slowing down the change rate of DP output voltage. This slowdown is achieved by using a trapezoidal reference signal for DP. The WSP attenuates the voltage harmonics produced by DP. However, the energy exchanged by WSP changes with modulation index, which may cause improper voltage regulation of the submodule capacitors. This paper proposes a new control technique to regulate the energy exchanged by WSP, which uses a variable slope trapezoidal reference signal of DP. To obtain this slope, the feedforward and feedback controllers are used. The feedforward controller gives the value of slope depending on the modulation index (mv) to keep the energy exchanged by WSP nearly equal to zero, whereas the losses and nonideality of the converter are taken care of by the feedback controller. This technique guarantees proper voltage regulation of the submodule capacitors for all modulation indices. The efficacy of the proposed technique is confirmed using simulations and experimentations. This paper also presents a circulating current suppressing controller for HMMC-CFB. The proposed control schemes and dc fault tolerant capability of HMMC-CFB are tested on a grid-connected model built in PSCAD. [ABSTRACT FROM AUTHOR]

In this paper, a new space vector pulse width modulation method to extend the linear modulation range of a cascaded five level inverter topology with a single dc supply is presented. Using this method, the inverter can be controlled linearly and the peak phase fundamental output voltage of the inverter can be increased from 0.577 to 0.637 V\text{dc} without increasing the dc bus voltage and without exceeding the induction motor voltage rating. This new technique makes use of cascaded inverter pole voltage redundancy and property of the space vector structure for its operation. Using this, the induction motor drive can be operated till the full speed range (0–50 Hz) with the elimination of lower order harmonics in the phase voltage and phase current. The five-level topology presented in this paper is realized by cascading a two-level inverter and two full bridge modules with floating capacitors. The inverter topology and its operation for extending the modulation range is analyzed extensively. Simulation and experimental results for both steady-state and dynamic operating conditions are presented in this paper. [ABSTRACT FROM AUTHOR]

The matrix converter (MC) is a direct ac–ac power converter without an intermediate dc link. It has several attractive features, such as high power density, four-quadrant operation, and bidirectional power flow. However, the application of MCs in high-voltage and high-power systems is still limited by the device voltage levels. It is well known that the multilevel power converter technology can be a solution to enhance the voltage rating and improve harmonic performance in many applications. Therefore, an application of a multilevel topology based on a direct ac–ac power converter is proposed in this paper. This paper first introduce the topology structure, the switching pattern grouping method, and the proposed output voltage modulation method for a five-level capacitor clamped multilevel matrix converter (5LMC). Amplitude coefficient adjustment is also introduced as a part of modulation procedure to simplify the duty cycles calculation. Simulation from MATLAB/Simulink is given to demonstrate the theoretical work. Experimental results from a five-level matrix converter prototype are presented to validate the theoretical findings. [ABSTRACT FROM AUTHOR]

This paper proposes a new topological configuration for a unified power quality conditioner (UPQC). Generally, the power structure of the three-phase three-wire UPQC consists of two back-to-back connected six-switch inverters. For this configuration, out of 12 switches, six of the series inverter switches will be underutilized most of the time. To improve the semiconductor utilization and consequently to reduce the total switch count, this paper proposes a new reduced switch topology for the UPQC. The proposed topology is realized using only ten switches and retains all the performance merits of the 12-switch UPQC while minimizing its underutilization without increasing the switch VA rating. The paper provides a detailed analytical study and evaluation by comparing the proposed topology with the twelve- and nine-switch-based UPQC system configurations. The feasibility of the proposed topology is validated through experimental investigation. [ABSTRACT FROM AUTHOR]

This paper presents a modular multilevel series/parallel converter (MMSPC) with intermodule switched-inductor power transfer. The switched-inductor voltage conversion feature allows controllable and efficient transfer of energy between modules with nonnegligible voltage difference, providing both step-down and step-up functionalities. Thus, this converter can accurately control and rapidly adjust the voltage of each module to generate an ac output voltage waveform with a controllable number of levels, increasing the quality of the output. Moreover, the intrinsic dc–dc conversion feature can generate a dc controllable output voltage and enable new applications. In this text, we specifically demonstrate how the flexibility of obtaining both ac and dc output with the same setup renders the topology promising for battery energy storage systems and dc microgrid applications. Experimental results validate the topology and concept of an MMSPC with intrinsic switched-inductor conversion. [ABSTRACT FROM AUTHOR]

This paper presents new space vector pulsewidth modulation (PWM) strategies for a single-phase three-level buck-boost neutral point clamped inverter coupled with impedance-source (IS) network. These strategies can be implemented for systems with any IS network with neutral point. The case study system is based on the quasi-Z-source inverter with continuous input current. To demonstrate an improved performance, the strategies are compared with a traditional PWM strategy. The advantages lie in reduced switching number, without output voltage quality distortion. The simulation and experimental results confirm the theoretical predictions. [ABSTRACT FROM AUTHOR]

An isolated single sourced multi-output dc/dc converter with a high-frequency link was proposed before to feed different cells of the Asymmetrical Cascaded H-bridge (ACHB) inverter. One of the fundamental advantages of the ACHB is that the main H-bridge is commutated with fundamental frequency, passing the majority of the inverter power. However, the isolated dc/dc converter needs to be connected to the main voltage source with high-voltage/high-frequency switches, which limits the power capability and the efficiency of the converter. In this paper, a switching pattern based on nearest level modulation method is proposed to command all the power to be transferred through the main H-bridge. Therefore, the power circulates between the auxiliary H-bridges with no need for high-voltage switches. As a result, a single-input single-output auxiliary converter is needed with only 5% of the power rating. This solution reduces cost and size while it improves the efficiency of the converter. Furthermore, the architecture makes the inverter more suitable for high power and high-voltage applications. The inverter switching strategy is based on programmable firing angles. The main dc-link of the grid connected inverter is controlled to achieve maximum power point tracking, while the dc/dc isolated converter is controlled to regulate the auxiliary dc-links. The proposed topology is verified by simulation and experimental results using a 1.5 kW hardware prototype. [ABSTRACT FROM AUTHOR]

This paper proposes a novel 11-level improved active-neutral-point-clamped (11L-IANPC) converter for ground power unit (GPU) application. This hybrid topology consists of the 5L-ANPC and the proposed low-voltage submodule. The proposed 11L-IANPC converter possesses only one flying capacitor (FC) and reduced number of high-frequency switches. Hence, voltage diversity and ratings, stored energy, and the number of costly and bulky FCs are significantly decreased. Moreover, operating the augmented submodule at the low voltage and power leads to doubling the number of output voltage levels, whereas the low extra cost and size are imposed on the proposed converter. In addition, suggested sensorless switching method leads to self-balancing of FC and significantly amends the output voltage frequency spectrum. These improvements cause significant reduction in control complexity of the proposed 11L-IANPC converter, remarkable decrease in size of the bulky and costly output LC filter, and improving the dynamic and steady-state performance of the proposed static GPU. The simulation and experimental results validate the feasibility of the proposed converter as well as its suggested modulation and control method. [ABSTRACT FROM AUTHOR]

This paper proposes a control method for a five-level hybrid flying-capacitor (5L-HFC) inverter, of which structure stems from the conventional five-level active neutral-point-clamped (5L-ANPC) topology by dividing the dc-link stage into three series-connected capacitors. In this inverter, the voltage stress on the power switches connected to the dc link is reduced by a half compared with that of the 5L-ANPC topology, thus the lower number of equally voltage-rated power devices can be employed. Also, the power losses in the 5L-HFC inverter are more evenly distributed than in the 5L-ANPC. In order to balance the dc-link capacitor voltages, a third-order harmonic offset injection is applied. When a diode rectifier is used to supply the dc bus voltage, the balancing method is not effective if the modulation index is higher than 0.64. Thus, an auxiliary circuit is needed to support the balancing of the dc-link capacitor voltages. However, the unbalancing problem can be overcome in a full-range operation without the auxiliary circuit if the back-to-back configuration is utilized. Finally, simulation and experiment results have verified the performance of the 5L-HFC inverter with the proposed control method. [ABSTRACT FROM AUTHOR]

This paper presents a new application of power and voltage balance control schemes for the cascaded H-bridge multilevel inverter (CHMI)-based solid-state transformer (SST) topology. To reduce load on the controller and simplify modulation algorithm, a master–slave control (MSC) strategy is designed for the dual active bridge (DAB) stage. The master controller executes all control and modulation calculations, and the slave controllers manage only device switching and protection. Due to the inherent power and dc-link voltage unbalance in cascaded H-bridge-based SST, this paper presents a compensation strategy based on three-phase dq decoupled current controller. An optimum zero-sequence component is injected in the modulation scheme so that the three-phase grid currents are balanced. Furthermore, to tightly regulate the output voltage of all the DAB modules to target value, a dynamic reference voltage method is also implemented. With this proposed control method, the three-phase grid currents and dc-link voltage in each module can be simultaneously balanced. Finally, simulation and experimental results are presented to validate the performance of the controller and its application to microgrid SST. [ABSTRACT FROM PUBLISHER]

Impedance-source networks cover the entire spectrum of electric power conversion applications (dc-dc, dc-ac, ac-dc, ac-ac) controlled and modulated by different modulation strategies to generate the desired dc or ac voltage and current at the output. A comprehensive review of various impedance-source-network-based power converters has been covered in a previous paper and main topologies were discussed from an application point of view. Now Part II provides a comprehensive review of the most popular control and modulation strategies for impedance-source network-based power converters/inverters. These methods are compared in terms of theoretical complexity and performance, when applied to the respective switching topologies. Further, this paper provides as a guide and quick reference for researchers and practicing engineers in deciding which control and modulation method to consider for an application in a given topology at a certain power level, switching frequency and demanded dynamic response. [ABSTRACT FROM AUTHOR]

This paper presents a dual modular multilevel converter (MMC) topology that utilizes energy exchange between adjacent-arm submodules (SMs), operating with out-of-phase modulation. The proposed configuration is applicable to medium-voltage high-power variable-speed drives incorporating open-end stator winding machines. A novel concept of power decoupling between adjacent-arm SMs in the dual MMC topology is realized through high-frequency transformer-based dc–dc converter modules. This concept offers a significant reduction in the sizing requirement of the SM capacitance and the stored energy in the MMC system, while avoiding the problem of wide voltage fluctuations of SM capacitors, especially at low operating frequencies. The proposed configuration can produce dc voltage; therefore, a machine speed range from zero speed to the rated speed is possible under the rated torque operating condition. The operating principles of the proposed dual MMC configuration are elaborated and necessary mathematical analysis is derived. Simulation and experimental results verify the concept of the proposed drive configuration. [ABSTRACT FROM AUTHOR]

Microinverters for grid-connected photovoltaic (PV) power conversion systems often require voltage boost due to the low dc voltage of the PV panels. A high-frequency (HF) transformer-isolated differential-mode Ćuk inverter (DMCI) is an attractive topology due to its inherent voltage boost capability and high power density. One of the significant operational issue of the DMCI addressed in this paper is the presence of lower order harmonic distortion in the injected grid current. It is shown that lower order odd and even harmonic voltages are generated with this topology. This problem is accentuated due to the low damping offered by the grid to harmonic voltages. A systematic low-complexity control design is proposed to address this issue. It is shown experimentally that the DMCI operates stably with effective attenuation of the lower order harmonics using the proposed design. Practical operational issues of the DMCI with fast switching GaN field-effect transistor (FET) devices are analyzed and solutions are proposed. It is shown that there can be significant HF noise generation in the DMCI with a frequency range higher than the switching frequency. Practical solutions for resolving HF issues using a combination of circuit layout design and additional passive components are proposed and validated. All of the experimental results are demonstrated on a 500-W GaN-FET-based microinverter prototype. [ABSTRACT FROM PUBLISHER]

This paper gives a comprehensive comparison of multilevel high-frequency-link (HFL) dc transformer (abbreviated MDCT) based on modular multilevel converter (MMC) and multilevel-dc-link dc transformer (abbreviated ADCT) based on dual-active-bridge (DAB) for medium-voltage dc (MVDC) application. The topology, operation, HFL voltage and current, active and circulating power, characteristic currents, switching behaviors, and power loss are analyzed in detail. Both MDCT and ADCT have fault treatment ability for MVDC application. However, the installation and commissioning of ADCT are more flexible and simpler. In addition, the MDCT needs more switches and high-frequency (HF) inductors than ADCT in the MVDC side with the same voltage level, but the number of HF transformer can be reduced. Compared with MDCT, the ADCT has higher power transfer ability and lower circulating power, lower HFL voltage, and RMS current and peak values with the same transmission power in the MVDC side. However, the arm RMS and average currents of MDCT are lower than those of ADCT in the MVDC side. The switching performance of MDCT deteriorates when the MVDC voltage fluctuates, but the switching behaviors of half bridges are added to ADCT. The loss of ADCT almost keep the same when the MVDC voltage fluctuates, but the loss of MDCT changes a lot. Finally, a small-scale prototype platform with 1 kW/450 V/150 V is built and experimental results verify the correctness and effectiveness of the theoretical analysis. [ABSTRACT FROM PUBLISHER]

This paper proposes a new nine-level inverter for medium- and high-power applications. The proposed topology comprises of a three-level (3L) active neutral-point-clamped (ANPC) inverter connected in series with a floating capacitor (FC) fed H-bridge. Besides, two additional switches operating at line frequency are appended across the dc link of the 3L ANPC structure. Compared with conventional hybrid cascaded inverters, the primary advantage of this addition is doubling of the resulting root mean square output voltage. This amelioration is achieved while preserving the standard 3L ANPC and H-bridge structures with minimum topological modification. A simple logic-gate-based voltage balancing scheme is developed to regulate the FC voltage. The proposed voltage balancing method is independent of load power factor, inverter modulation index, and can balance the voltage across FC instantaneously. The step-by-step formulation of logical expressions for the generation of gating pulses is deliberated in detail and can be generalized for any $n$-level inverter. Further, simulation results as well as the experimental measurements obtained from the laboratory prototype are presented to validate the effectiveness and practicability of the proposed configuration. Finally, the notable merits of the proposed inverter over the prior art topologies is established through a comprehensive comparative study. [ABSTRACT FROM PUBLISHER]

Grid-connected power conversion systems for renewable energy sources must fulfill several requirements, e.g., the high efficiency, the reduced cost and complexity, and, quite often, the boost capabilities that is usually achieved using a front-end dc–dc boost converter before the inversion stage, leading to a two-stage architecture. Meanwhile, single-stage power conversion systems, which perform the boosting operation within the inversion one, offer some potential advantages, in terms of reducing the complexity and the volume of the whole system. Among several proposed options, the split-source inverter (SSI) has been recently proposed by Abdelhakim et al. as an alternative option with some interesting features to the commonly used Z-source inverter. Taking into account that the SSI is controlled by a single parameter, i.e., its dc and ac sides are controlled by the modulation index, it is of paramount importance to investigate its control scheme in grid-connected mode, which has never been studied yet. Hence, this paper models the SSI dc side and proposes a modified modulation scheme combined with the commonly used synchronous reference frame control technique to achieve a decoupled control scheme of the SSI in grid-connected mode, i.e., the dc and the ac sides of the SSI can be controlled independently, which is convenient for many applications. The introduced control scheme is analyzed and simulated using a MATLAB/Simulink model, where a reduced scale 1-kVA grid-connected SSI is designed and simulated for the sake of experimental validation. Finally, the designed system is implemented experimentally to validate and verify the reported analysis and simulations. [ABSTRACT FROM PUBLISHER]

Full-bridge single-stage (FBSS) ac-dc converters allow to regulate both the output voltage and the input current that achieves a near sinusoidal waveform using only the four bridge transistors. Independent of this feature, these converters still need to be optimized in order to become an interesting and attractive solution for modern switch mode power supplies with power factor corrector (PFC) function. One of the most important improvements needed is the downsizing of the dc bus capacitor C b with the inherent cost reduction. However, this action introduces complex issues in the regulation of the input current and it is also responsible for the generation of high output voltage ripple. The new contribution of this paper consists in the introduction of a set of power circuit optimizations and control techniques in a FBSS PFC converter that solves the referred issues in order to enable the reduction of the dc bus capacitor's size and cost. These procedures are based in the use of a free wheeling circuit that improves the light load operation and in the application of one shot nonlinear modulator, in order reduce the output voltage ripple even when the dc bus ripple is high. The possibility of using, in the proposed topology, a reduced ratio capacitance/watt lower than the typical values used in commercial applications (0.7-0.5 μF/W for 385-450 V, respectively), while maintaining the accurate input current regulation, is also theoretically proved. The developed concepts, solutions and design criteria are detailed described in the paper. The correspondent theoretical study is verified trough experimental results token in an optimized FBSS topology prototype. [ABSTRACT FROM AUTHOR]

Multilevel inverters are receiving more attentions nowadays as one of preferred solutions for medium- and high-power applications. As one of the most popular hybrid multilevel inverter topologies, the five-level active-neutral-point-clamped inverter (5L-ANPC) combines the features of the conventional flying-capacitor type and neutral-point-clamped (NPC) type inverter and was commercially used for industrial applications. In order to further decrease the number of active switches, this paper proposes a seven-switch 5L-ANPC (7S-5L-ANPC) topology, which employs only seven active switches and two discrete diodes. The analysis has shown a lower current rating can be selected for the seventh switch under high power factor condition, which is verified by simulation results. The modulation strategy for 7S-5L-ANPC inverter is discussed. A 1 kVA single-phase experimental prototype is built to verify the validity and flexibility of the proposed topology and modulation method. [ABSTRACT FROM AUTHOR]

In this paper, a small signal model is proposed for the new unidirectional three-phase T-type rectifier topology known as five-level T-Rectifier (5L T-RECT). The proposed model is obtained starting from the large signal analytical representation of the 5L T-RECT configuration. The derived equations have been simplified using the synchronous reference frame transformation; to this purpose, the average values over the fundamental period T0 are considered for the input phase voltages. After that, the converter steady-state and dynamic models are derived by means of the local linearization around the desired operating point. The transfer functions related to the inputs and outputs of the system are, therefore, obtained and depicted. The achieved 5L T-RECT model has been first verified using the linear analysis tool in the matlab/Simulink environment starting from the detailed switching model. Theoretical results exhibit a very good accuracy between the small-signal, the large-signal, and the switching models. Then, experimental activity is depicted to further validate the proposed small-signal model. [ABSTRACT FROM AUTHOR]

This paper proposes a method for calculating selective harmonic elimination (SHE) angle solutions applied to multilevel voltage waveforms (of more than three levels of voltage): Phase-shifted SHE (PS-SHE). This technique is based on the calculation of simple SHE angles, increasing the number of levels and minimized harmonics by means of phase shift application. Compared to classical calculation, continuous SHE solution can be achieved for the whole modulation index range. Added to this, dc-link voltages balancing strategy is proposed for converters based on single-phase H-bridge (HB) configurations with multilevel (more than two levels) arms, using SHE. It is based on a prediction of the neutral point current and a hysteresis band. This strategy does not increase the number of commutations and shares them equally among the arms inside the HB. The good performance of the two proposed techniques (PS-SHE and dc-link neutral point regulation strategy) are proven into a downscaled five-level HB neutral-point-clamped (5L HNPC) converter topology. The carried out tests prove the suitability of the proposed techniques. [ABSTRACT FROM AUTHOR]

This paper proposes a controlled transition full-bridge (CTFB) hybrid multilevel converter (HMC) for medium and high voltage applications. It employs a full-bridge cell chain-link (FB-CL) between the two legs in each phase to generate multilevel bipolar output voltage. The CTFB-HMC has twice dc voltage utilization or power density of conventional converters due to the bipolar capability of its full-bridge configuration. Hence, for the same power rating and same voltage level number, its total cells per phase are quarter that in modular multilevel converter (MMC), which reduces the hardware installation volume. Also, in the proposed converter, the total device number in the conduction paths is the same as in the half-bridge MMC, leading to low conduction losses. The FB-CL current of the CTFB converter has no dc component, which offers the potential to enhance the transient response. Comparative studies between the CTFB and other multilevel topologies are carried out to clarify its main features. The modulation strategies and parameter sizing of the proposed converter are investigated using a generic case. Simulation and experimental results are used to verify the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

The semicontrolled open-winding PMSG system has been widely investigated due to its simplified topology and easy control implementation. Nevertheless, compared with the conventional controllable converter structure, the current zero crossing phenomenon will last a longer time in the semicontrolled configuration, which is determined by the phase displacement between voltage and current. Since a long current zero crossing duration will lead to voltage pulse disturbance, serious electromagnetic interference, and output power fluctuation, it is necessary to reduce the zero crossing duration to improve the open-winding PMSG performance. This paper gives a detailed analysis on the zero crossing phenomenon of the semicontrolled open-winding PMSG system in the 3-D space vector modulation perspective. Meanwhile, a third harmonic injection method is suggested to reduce the zero crossing duration. It is also demonstrated that the torque and power pulsation are effectively improved, while the zero-sequence current amplitude does not increase. A proportional resonant controller is used to regulate the desired zero-sequence current. The proposed method is validated in a 1-kW semicontrolled open-winding PMSG experimental system with id = 0 control method. [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]

Historically, cascaded H-bridge, capacitor-clamped, and neutral point-clamped topologies have been used for medium- to high-voltage applications but the modular multilevel converter (M2LC) is becoming a popular alternative. However, in comparison to other topologies, control of the load current, which is inherently coupled with circulating currents, is more difficult in the M2LC topology. This paper proposes a modified M2LC topology that allows for decoupled control of circulating currents from the load current. Each arm of the modified topology comprises a plurality of half-bridge modules and one full-bridge module. The full-bridge module minimizes harmonic currents within the converter without affecting the load current. A state-space model, which is generalized per arm with an N number of half-bridge modules and one full-bridge module, is presented to accurately predict the behavior of the proposed topology. Theoretical as well as experimental results of a single-phase three-level 800-VA prototype converter are presented with a discussion to demonstrate the viability of both the proposed mathematical model and modified topology. A comparative investigation with respect to a conventional topology reveals that the proposed topology offers superior performance. [ABSTRACT FROM AUTHOR]

Modular multilevel converters have several attractive features such as a modular structure, the capability of transformer-less operation, easy scalability in terms of voltage and current, low expense for redundancy and fault tolerant operation, high availability, utilization of standard components, and excellent quality of the output waveforms. These features have increased the interest of industry and research in this topology, resulting in the development of new circuit configurations, converter models, control schemes, and modulation strategies. This paper presents a review of the latest achievements of modular multilevel converters regarding the mentioned research topics, new applications, and future trends. [ABSTRACT FROM AUTHOR]

Modular multilevel converter (MMC) has become one of the most promising converter topologies for future high-power applications. A challenging issue of the MMC is the voltage balancing among arm capacitors. A good overall control system is also vital for the MMC, which should be based on sound mathematical model, readily adaptable for different applications, and capable of high performance. This paper presents a general control structure for MMC inverters, which is suitable for both voltage-based and energy-based control methods, and includes voltage balancing between the upper and lower arms. A new method for voltage balancing among arm capacitors, which is based on an improved pulse-width modulation, is also presented. The proposed method avoids some major disadvantages found in present voltage balancing methods, such as dependence on computation-intensive voltage sorting algorithms, extra switching actions, interference with output voltage, etc. Furthermore, all switching actions are evenly distributed among power devices. The proposed control system as a whole can serve as a promising solution for practical applications, especially when the number of submodules is fairly high. Simulation and experimental results verify the effectiveness of the proposed methods. [ABSTRACT FROM AUTHOR]

This paper introduces a novel isolated hybrid resonant converter with smooth transition between multiple operating modes. With the simple addition of a bidirectional ac switch, the highly efficient series resonant converter operating in the discontinuous conduction mode is combined with a phase-shifted full-bridge buck converter and a pulsewidth-modulated boost converter in order to provide high power conversion efficiency over a wide input-voltage operating range utilizing a simple topology and simple control techniques. First, the topology is introduced, and the converter's operating modes are discussed. Next, closed-loop input-voltage controllers are designed for the different operating modes, and a smooth transition technique is introduced using a two-carrier modulation scheme. Experimental results are provided to verify the proposed system using a 300-W prototype that achieved a 97.5% California Energy Commission weighted efficiency with a 30-V input including all auxiliary and control losses. [ABSTRACT FROM AUTHOR]

Unbalanced grids introduce performance deterioration for Vienna rectifier topology by producing twice fundamental frequency ripples in dc-link voltage and input active/reactive power. A common current reference generation for the purpose of eliminating the input power ripple, such as dual-frame hybrid vector control, can maintain constant input power and eliminate ripples in dc-link voltage under light voltage unbalanced grids. Under severe unbalanced grids, this type of a control method will fail to work. This paper first analyzes the theoretical operation area of a constant power control method under unbalanced grids, and then a novel control method is proposed. The proposed control method can work under severe unbalanced grids by injecting a small amount of input power ripple and balance the performance of working area and output dc voltage ripples. Finally, the experiment results using the constant power control method are given and validate the performance of the proposed control method. [ABSTRACT FROM PUBLISHER]

A new scheme for nine-level voltage space-vector generation for medium-voltage induction motor (IM) drives with open-end stator winding is presented in this paper. The proposed nine-level power converter topology consists of two conventional three-phase two-level voltage source inverters powered by isolated dc sources and six floating-capacitor-connected H-bridges. The H-bridge capacitor voltages are effectively maintained at the required asymmetrical levels by employing a space vector modulation (SVPWM) based control strategy. An interesting feature of this topology is its ability to function in five- or three-level mode, in the entire modulation range, at full-power rating, in the event of any failure in the H -bridges. This feature significantly improves the reliability of the proposed drive system. Each leg of the three-phase two-level inverters used in this topology switches only for a half cycle of the reference voltage waveform. Hence, the effective switching frequency is reduced by half, resulting in switching loss reduction in high-voltage devices. The transient as well as the steady-state performance of the proposed nine-level inverter-fed IM drive system is experimentally verified in the entire modulation range including the overmodulation region. [ABSTRACT FROM PUBLISHER]

A novel H-bridge multilevel pulsewidth modulation converter topology based on a series connection of a high-voltage diode-clamped inverter and a low-voltage conventional inverter is proposed in this paper. A dc link voltage arrangement for the new hybrid and asymmetric solution is presented to have a maximum number of output voltage levels by preserving the adjacent switching vectors between voltage levels. Hence, a 15-level hybrid converter can be attained with a minimum number of power components. A comparative study has been carried out to present high performance of the proposed configuration to approach a very low total harmonic distortion of voltage and current, which leads to the possible elimination of the output filter. Regarding the proposed configuration, a new cascade inverter is verified by cascading an asymmetrical diode-clamped inverter, in which 19 levels can be synthesized in output voltage with the same number of components. To balance the dc link capacitor voltages for the maximum output voltage resolution as well as synthesize asymmetrical dc link combination, a new multi-output boost converter is utilized at the dc link voltage of a seven-level H-bridge diode-clamped inverter. Simulation and hardware results based on different modulations are presented to confirm the validity of the proposed approach to achieve a high-quality output voltage. [ABSTRACT FROM PUBLISHER]