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This paper presents the development, analysis, and performance evaluation of a new topology for an isolated dc power electronic converter (PEC). The proposed topology (called the reverse flyback dc PEC) is developed to process a discontinuous input voltage and produce a continuous output voltage. The reverse flyback dc PEC is operated based on charging the inductive element in the high-frequency transformer, while discharging the energy to the output side through on–off actions of the switching element, which is located on the secondary side of the high-frequency transformer. A prototype for the proposed reverse flyback dc PEC is constructed to evaluate its performance under different operating conditions. Performance results show that the reverse flyback dc PEC is capable of processing discontinuous input voltages with different duty ratios and maintaining continuous output voltages with a minor sensitivity to the load type of ratings. [ABSTRACT FROM AUTHOR]

This paper proposes a dual-function dynamic voltage restorer (DFDVR) with fault current-limiting capability. The new topology can operate under different modes: the short-circuit fault current-limiting mode and the compensation mode for voltage fluctuation. Different functions of the DFDVR are achieved by controlling a brake chopper circuit and antiparallel thyristors. During fault conditions, the antiparallel thyristors are deactivated to protect the dc-side capacitor, and the duration of the on- and off-periods of the semiconductor switch in the brake chopper circuit is controlled to adjust fault current amplitudes. During voltage sags, the antiparallel thyristors are activated, and the brake chopper circuit is turned off by controlling the gate turn-off thyristor in the brake chopper circuit, thus making the DFDVR similar to a conventional DVR. The control scheme and optimal parameter selection of the DFDVR are provided. The design methodology of the DFDVR was verified through simulations performed using the PSCAD/EMTDC software. The experimental results prove the capability and effectiveness of the DFDVR topology. [ABSTRACT FROM AUTHOR]

This paper presents a new reconfiguration module for asymmetrical multilevel inverters in which the capacitors are used as the dc links to create the levels for staircase waveforms. This configuration of the multilevel converter makes a reduction in dc sources. On the other hand, it is possible to generate 13 levels with lower dc sources. The proposed module of the multilevel inverter generates 13 levels with two unequal dc sources (2VDC and 1VDC). It also involves two chargeable capacitors and 14 semiconductor switches. The capacitors are self-charging without any extra circuit. The lower number of components makes it desirable to be used in wide range of applications. The module is schematized as two back-to-back T-type inverters and some other switches around it. Also, it can be connected as a cascade modular which leads to a modular topology with more voltage levels at higher voltages. The proposed module makes the inherent creation of the negative voltage levels without any additional circuit (such as H-bridge circuit). Nearest level control switching modulation scheme is applied to achieve high-quality sinusoidal output voltage. Simulations are executed in MATLAB/Simulink and a prototype is implemented in the power electronics laboratory in which the simulation and experimental results show a good performance. [ABSTRACT FROM AUTHOR]

This paper proposes a novel modular equalization architecture for series-connected electric double-layer capacitor (EDLC) modules, each consisting of multiple cells connected in series. Cell voltages in a module are equalized by an inductive voltage divider (IVD)-voltage multiplier (VM)-based cell equalizer, while module voltages are unified by switched capacitor converters (SCCs). Square wave voltages generated at switching nodes of the IVD-VM-based cell equalizers are utilized to drive the SCC-based module equalizers, realizing the switchless topology of SCC-based module equalizers. The required switch count of the proposed system can be halved compared to conventional systems, allowing simplified circuit. An experimental equalization test for three EDLC modules, each consisting of six cells in series, was performed from an initially voltage-imbalanced condition. Module and cell voltages were equalized at different rates, and the equalization performance of the proposed modular equalization system was successfully demonstrated. [ABSTRACT FROM AUTHOR]

This paper presents an improved H8 power converter for common-mode voltage (CMV) reduction and electromagnetic interference suppression. The proposed H8 converter can realize zero CMV variation when entering and leaving the zero state, which is mainly achieved by both the improvement of the structure and the control strategy. For the system structure, two switches are added on the dc bus to float the ac part of the three-phase converter in the zero state. Besides, additional capacitors are used to realize controllable CMV. For the control strategy, a simple control strategy is proposed for the H8 converter. It can automatically adapt to the flowing orientation of the load current to realize synchronous switching of the power switches, which effectively eliminates the impact of the dead time. Through analysis, simulations, and experiment, a comparison between the proposed H8 converter and the conventional H6 converter is performed. Results validate the effectiveness of the H8 topology. [ABSTRACT FROM AUTHOR]

Due to the zero-sequence currents in the four-wire systems, the three-phase currents become more complex on both amplitudes and phases in the unbalanced load conditions, so that the existing open-circuit (OC) fault diagnosis methods of the switching devices cannot be directly used. In this paper, an OC fault diagnosis strategy applied to four-wire T-type converter systems is proposed, which is implemented by decomposing the circuit model into a positive- and negative-sequence model and a zero-sequence model, and locating the OC fault based on the law of positive- and negative-sequence voltage error offsets and zero-sequence voltage error offsets. The proposed diagnosis method is suitable for both unbalanced load and unbalanced input voltage conditions. Meanwhile, the differences of fault-tolerant control between four-wire and three-wire systems are analyzed and compared. An effective fault tolerance strategy for inner OC faults applied to four-wire T-type converter systems is presented, which owns the ability to suppress dc bus imbalance. Simulation and experimental results are presented to verify the correctness of the proposed strategy. [ABSTRACT FROM AUTHOR]

Several applications need a high power, high output voltage ac/dc converter. The structure includes a dc/dc resonant stage, which is fed from a three-phase line. Due to standards, rectified dc input voltage varies largely from 400 to 750 V affecting the adversely overall design and current levels. In fact, losses in the inverter become unbearable if both switching frequency and transferred power are desired beyond a certain level. In those cases, it is necessary to connect several switches in parallel. As an alternative, the new switches can configure a new modular structure instead, adding more flexibility in the control to compensate input voltage variations. As a result, the required circulating current is reduced to a half, with benefits in total power losses. Moreover, the nature of the topology allows a reconfiguration of the resonant net (LCC) for low power, reducing even further the minimum circulating current under those conditions (fluoroscopy, for instance). In this paper, the new multilevel resonant topology is mathematically modeled and proposed for radiography and fluoroscopy. An example illustrates the design procedure for a given application at 100 kW, 50–150 kV. [ABSTRACT FROM AUTHOR]

In this paper, a developed structure is proposed for high step-up nonisolated noncoupled inductor based multiport dc–dc converters. The voltage gain per number of devices of the proposed topology is higher than that of similar topologies. This means that, by using the same number of devices, the proposed topology can generate higher gains than other structures. In other words, the proposed topology utilizes less number of devices for producing the same voltage gain, which leads to less total cost, size, weight, and complexity. Despite high voltage gain, the normalized peak inverse voltage (NPIV) on switches/diodes is low. Higher number of input ports leads to higher gains and lower NPIVs on devices. The load energy can be absorbed and stored in first input unit. Modularity, simple structure, continuous input currents, and low input current ripple are the other profits of proposed topology. Low/medium power applications are suggested for the proposed structure. Proposed topology has been explained and operational modes along with steady-state analysis have been discussed. For better verification, the proposed topology has been compared with several multiport high gain converters. Comparison results confirm the advantages of the proposed topology. Finally, the proper performance of the proposed topology has been validated by experimental results. [ABSTRACT FROM AUTHOR]

Three three-phase unidirectional open-end topologies with reduced active switch count are investigated in this paper. These configurations arise from the replacement of controlled switches by diodes, in order to reduce the system complexity. Furthermore, the costs are also reduced once less driver circuitry is needed. The proposed topologies make the ac–dc conversion of the power delivered by a permanent magnet synchronous machine operating at unity power factor. Each configuration is made out of two converters in which at least one is derived from the substitution of active switches in two-level legs or three-level neutral-point clamped legs. The proposed configurations have less switches, making it possible to obtain the same number of voltage levels (in relation with the conventional configurations) with half or quarter of the number of active switches. Also, the topologies are compared in terms of semiconductor power losses and harmonic distortion. The control strategy of the systems as well as a detailed model, simulation, and experimental results are presented. [ABSTRACT FROM AUTHOR]

Low-voltage dc distribution systems have gained significant attention over the last years, since they provide simpler and more efficient integration of distributed generators and storage devices, establishing a pathway to net zero energy buildings. In low-power units, transformerless utility interface is preferred to reduce footprint and losses. However, the lack of galvanic isolation introduces a common-mode (CM) path between the dc distribution bus and the utility service grounding, leading to the presence of high CM voltages at the dc bus feeders. The attenuation of the CM voltage reduces the touch voltage amplitude and leakage current, contributing to a safer environment. In this paper, a feed-forward active compensation of the CM voltage is proposed. It relies on utility voltage parameters, estimated by a phase locked loop, to generate a counter CM voltage; hence, it does not require previous knowledge of the system CM path model or the addition of voltage sensors. Experimental results show that this technique can attenuate the CM voltage to non-dangerous magnitudes without interfering with the microgrid differential mode behavior. [ABSTRACT FROM AUTHOR]

A switching-capacitor-based buck–boost converter (with common ground) for point of load applications is proposed in this paper. It is capable of operating in stand-alone buck or boost mode in addition to its primary operation of performing the buck–boost conversion. The striking feature of the proposed converter is low source current ripple content irrespective of its mode of operation (buck–boost, buck, or boost). First, feasible pulsewidth modulation schemes for the proposed converter are identified and thereafter the corresponding circuit performance analysis, steady-state analysis, and state-space modelling is established. Through steady-state analysis, voltage gain expressions are formulated and equations defining L-C components are derived in terms of their ripple quantities. The state-space models are used to formulate small-signal analysis and to obtain the relevant transfer functions required in the controller design. A voltage-mode/current-mode controller is designed, with a tradeoff in bandwidth, to control the proposed converter and transit it from buck to boost mode or vice versa seamlessly. A 30–55 W, 100 kHz, prototype point of load converter with 36-V input dc source is built to supply power at constant load voltage of either 48 or 28 V. The proposed converters’ effectiveness is demonstrated experimentally in terms of reduced source current ripple along with seamless transition from buck to boost mode and vice versa. [ABSTRACT FROM AUTHOR]

A new single-switch high step-up dc–dc converter is proposed, in this paper, for fuel cell vehicles. The proposed topology utilizes an L2C3D2 network to obtain high voltage gain and reduce the voltage stress on the power switch. Additionally, the proposed converter has a universal input voltage in order to suit the soft output characteristics of the fuel cell. Comprehensive analyses of the steady-state operation in continuous conduction mode and discontinuous conduction mode, and design considerations of the proposed converter are given. Finally, a 400 V/1.6 kW scaled-down prototype is developed to validate the effectiveness and feasibility of the proposed converter. [ABSTRACT FROM AUTHOR]

A 1-φ hybrid nine-level inverter (H9LI) topology has been proposed in this paper. The proposed H9LI topology uses a simple phase disposition pulsewidth modulation strategy to generate nine-voltage levels in the output. The main advantage of this topology is that it has a low switch count (ten switches) compared to the existing nine-level inverter topologies. To regulate the voltage across auxiliary capacitor, two innovative control techniques are proposed, which are integrated with the inverter modulation technique itself. Hence, it does not require any extra voltage balancing circuits to maintain the voltage across the auxiliary capacitor and input dc capacitors. A major advantage of these control techniques is that they eliminate the sensing of the coupled inductor current. Another significant advantage of H9LI is that loss distribution among all the power switches is more uniform compared to existing nine-level inverters. Due to low part count and absence of extra voltage balancing circuits, the H9LI achieves higher efficiency (η ≍ 94.5%) and lower cost. Furthermore, the requirement of filter size reduces due to the presence of coupled inductor in H9LI. The proposed 1-φ grid connected H9LI is verified through MATLAB/Simulink simulations and validated through experiments on a laboratory prototype of 400-VA rating. [ABSTRACT FROM AUTHOR]

In this paper, a high-voltage unipolar pulse power generator is introduced for electroporation applications. Operating principle of the proposed structure is based on the buck–boost (BB) converter. The generator is comprised of parallel modules connected to the converter through an SCR and is supplied by a low-voltage dc source. Each module consists of an insulated gate bipolar transistor (IGBT), two diodes, and a capacitor. In fact, the proposed topology is a combination of the Marx generator and BB (MG-BB) converter. In comparison with other modular MG-BB structures, the proposed topology achieves interesting advantages including simpler structure, reduction of IGBTs voltage rating, and reducing number of components (inductors and switches). In order to clarify the features of the proposed structure, it has been compared with other unipolar MGs considering different aspects including the number of circuit components, number of required input supplies, amplitude of the output pulse, and the maximum voltage across switches and diodes. To validate the effectiveness of the structure, simulation and experimental results are presented. The results confirm that the proposed topology is capable of generating unipolar pulses with desirable amplitude and repetition frequency using a low-voltage dc supply. [ABSTRACT FROM AUTHOR]

In this paper, a family of step-up resonant switched-capacitor converters (RSCs) with a continuously adjustable conversion ratio is proposed based on the Cuk dual-resonance core (DRC) featuring two resonant paths. By adopting the on-time fixed frequency modulation, the two resonant paths can conduct simultaneously and satisfy the charge balance of the flying capacitor during the overlapping period. As a result, the conversion ratio—upper bounded by two determined by the circuit configuration—can vary continuously and efficiently even at the light load condition (1/10 of the rated power). A comprehensive analysis—the operation principle, voltage-gain curve, and voltage/current stresses—about the DRC is given. In addition, the Cuk DRC was extended to the series–parallel switched-capacitor converter (SCC), Fibonacci SCC, and voltage doubler to form a family of step-up RSCs, whose voltage-gain curves of different topologies are derived. Moreover, a characteristic comparison between the Cuk DRC and the traditional “direct” and “indirect” resonant core is given. Then, a 48 to 62–94.6 V resonant core with peak efficiency 97.8% and maximum power 120 W under the open loop condition was built. The analyses were verified by both experimental and simulation results. [ABSTRACT FROM AUTHOR]

In this paper, a new nonisolated high step-up dc–dc converter is proposed. Active–passive inductor cells (APICs) are used to extend the topology. The ability to achieve high gains is the main merit of the proposed topology. The proposed converter operates based on parallel charging and series discharging of the inductors. The converter also achieves high step-up voltage gain with appropriate duty cycle and low voltage and current stress on the power switches and diodes. The proposed converter is analyzed in operation modes. The main parameters of the converter such as voltage gain, voltage stress of semiconductor devices are calculated to compare with other structures. Considering the output voltage ripple and filter size, the proposed converter is designed. Moreover, the losses and efficiency of the converter are calculated. The performance of the proposed converter is validated by experimental results. [ABSTRACT FROM AUTHOR]

This paper proposes a new diode-clamped multilevel inverter that can effectively balance the voltages of dc capacitors. For the proposed inverter, the inductors are inserted between the diodes and the main switches. Also, the voltage balance of the dc capacitors can be guaranteed by controlling the opening time of the corresponding main switches in particular modes. Thus, the parallel circuits on the dc side in the conventional inverters are canceled. Consequently, the proposed topology requires fewer switches, diodes, and capacitors, although it adds the compensation currents to the corresponding main switches. Both the simulation and experimental results demonstrate the suitability and applicability of the proposed topology. [ABSTRACT FROM AUTHOR]

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

This paper 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 an overview of resonant and hybrid switched-capacitor converters with a particular focus on multimode operation. The multimode approach is discussed as a tool to affect high efficiency and power density across a wide load range, provide variable regulation, and, as a general framework, to conceptualize the advantages and opportunities of the approach compared to more traditional dc–dc converters. A general analysis is provided to quantify the advantage of hybrid and resonant converters that factors in the tradeoffs between size and loss in the magnetic component and voltage stress on the active devices. A broader set of operating modes is presented that spans continuous and discontinuous conduction and includes resonant, quasi-resonant, and more traditional buck- or boost-like operation. A prototype flying-capacitor multilevel converter is presented to demonstrate the variety of operating modes and motivate important considerations such as voltage balance on the flying capacitors. [ABSTRACT FROM AUTHOR]

The trend toward higher switching frequencies and higher power densities in dc–dc conversion led the designers to rediscover resonant topologies. However, the analysis of these converters is often limited to a particular operating mode and/or topology. This paper wants to fill the gap by presenting a state-space-based analysis for a broad class of series-resonant converters including voltage-fed as well as current-fed topologies, either unidirectional or bidirectional. The proposed solution consists of a mathematical framework that solves the trajectory of state variables in the resonant tank, as well as the main characteristic functions such as voltage conversion ratio and transferred power. The matrix approach permits a flexible and compact formulation and easy implementation in computational tools such as MATLAB. The theoretical framework is applied to both voltage-fed and current-fed resonant topologies: the first is used to show the advantages of the proposed model respect to the first harmonic approximation, while a detailed analysis in terms of operating mode boundaries, delivered power, and voltage gain is provided for the second. Simulations and measurements on a 300-W prototype of the current-fed topology are used to validate the correctness of the proposed solution. [ABSTRACT FROM AUTHOR]

This paper presents a dynamic power flow management system for a solar photovoltaic (PV) system employing a single-stage single-inductor-based dual-input/output dc–dc converter feeding standalone dc loads backed up by a rechargeable battery. A time-sharing voltage-mode control scheme has been proposed for power flow management between solar PV, a battery, and a standalone dc load, and it also maintains a constant dc load voltage and performs maximum power point tracking operation of solar PV. The implementation of the control scheme has been described in detail. The steady-state performance of the single-stage converter has been explained with the relevant analytical expressions derived along with the characteristics. A state-space average model was developed for simulating the transient behavior and validating the working of the system for step changes in the input solar PV power and the dc loads. A hardware prototype of the proposed system has been fabricated, and the proposed controller has been implemented using the dSPACE DS1103 real-time interface board. The working of the proposed scheme for different levels of input solar insolation and dc load power demand has been satisfactorily demonstrated, and the corresponding results are also provided. [ABSTRACT FROM AUTHOR]

Many of the renewable energy resources, like offshore wind, utility PV farms, are located far away from the load centers, which requires dc power transmission system to efficiently deliver power. Voltage-source converter solution is required in many applications due to the stability and compensation requirement. This paper presents a new voltage source converter topology for medium to high voltage dc application, named modular embedded multilevel converter (MEMC). MEMC is based on a three-level topology structure and consists of series-connected insulated-gate bipolar transistor (IGBT) bridge stacks, like the popular modular multilevel converter (MMC) and series-connected thyristor or press-pack high voltage integrated gate-commutated thyristor or IGBT stacks. The basic operation principle, control solutions, and the methods to commutate the thyristors are explained in detail. Due to the three-level structure, the total number of IGBT stacks are reduced by half compared with MMC, leading to much lower energy storage, weight, volume, and system complexity. Also by replacing part of the IGBT stack in MMC with thyristor stack, both of the system conduction loss and switching loss can be further reduced. There are other topology variations of MEMC with a similar operational principle but different characteristics. [ABSTRACT FROM AUTHOR]

An adaptive control of DPWM implementable in clamped-three-level inverters with two strings of photovoltaic (PV) panels in cascaded connection is proposed in this paper. The proposed modulation is developed based on the so-called circuit-level decoupling concept. It is able to provide balance line voltage even under unbalanced dc links. The unequal dc voltages appeared due to asymmetric maximum point of power trackings (MPPTs) are controlled by proper injection of zero-sequence voltage to the common mode voltage, while the total dc voltage is regulated based on the voltage commands generated by the MPPT of each string. Thus, both PV strings are able to be operated based on their MPPTs while there is almost no low-order harmonic distortion at the inverter output current. Compared with the previous methods, the high capability of the proposed method is evaluated by simulation study and experimental tests. [ABSTRACT FROM AUTHOR]

This paper presents a new concept and approach for topology control and switching in distribution systems by extending the traditional circuit switching to laterals and single-phase loads. Voltage unbalance and other key performance indicators including voltage magnitudes, line loading, and energy losses are used to characterize and demonstrate the technical value of optimizing system topology on a per-phase basis in response to feeder conditions. The near-optimal per-phase topology control is defined as a series of hierarchical optimization problems. The proposed approach is applied to IEEE 13-bus and 123-bus test systems for demonstration, which included the impact of integrating electric vehicles (EVs) in the test circuit. It is concluded that the proposed approach can be effectively leveraged to improve voltage profiles with electric vehicles, the extent of which depends on the performance of the base case without EVs. [ABSTRACT FROM AUTHOR]

Inductive power transfer (IPT) for battery charging applications has significant advantages over the traditional plug-in system. Since misalignment between the primary and secondary windings is inevitable, it is of significance to improve the misalignment tolerance of IPT systems with constant-current (CC) and constant-voltage (CV) outputs for battery charging. In this paper, the load-independent output characteristic of the hybrid topology and the function switching between CC and CV of the reconfigurable topology are analyzed. Besides, a hybrid and reconfigurable IPT system with 3-D misalignment tolerance for CC and CV outputs is proposed, simplifying or even canceling control schemes. Moreover, a novel parametric design method is given for the IPT system, which can suppress the fluctuation of the output voltage/current within a certain range of misalignment. In order to validate the performance of the proposed topology, a 1-kW prototype is built, and the corresponding experiments are carried out. In the CC/CV mode, the system can operate with the longitudinal misalignment to 50% when the load varies from 36 to 480 Ω, and the fluctuation of the output current/voltage is within 5%. Similarly, the misalignment in Y- and Z-axis is 12.5% and 33.3%, respectively. [ABSTRACT FROM AUTHOR]

This paper presents a novel three-phase DC-link multilevel inverter topology with reduced number of input DC power supplies. The proposed inverter consists of series-connected half-bridge modules to generate the multilevel waveform and a simple H-bridge module, acting as a polarity generator. The inverter output voltage is transferred to the load through a three-phase transformer, which facilitates a galvanic isolation between the inverter and the load. The proposed topology features many advantages when compared with the conventional multilevel inverters proposed in the literatures. These features include scalability, simple control, reduced number of DC voltage sources, and less devices count. A simple sinusoidal pulse-width modulation technique is employed to control the proposed inverter. The performance of the inverter is evaluated under different loading conditions and a comparison with some existing topologies is also presented. The feasibility and effectiveness of the proposed inverter are confirmed through simulation and experimental studies using a scaled down low-voltage laboratory prototype. [ABSTRACT FROM AUTHOR]

This paper presents a new predictive power-factor-correction (PFC) controller for series-interleaved three-level boost (TLB) converters. Compared to the state-of-the-art TLB PFC controllers, where a two-cycle prediction and a detection of an operating region are necessary, the proposed controller achieves a low total harmonic distortion of the input current by using a single equation to predict the input current in all operating regions of the converter, in just one operating cycle. The average current control is achieved by sampling at the peak of the triangular carrier. The proposed PFC controller significantly reduces the distortion of the input ac current near the zero-crossing points, resulting in a low total harmonic distortion of the input current. The operation of the proposed controller was evaluated, and its stability and robustness to parameter changes was confirmed analytically. The controller operating principles were verified in simulations and validated by experiments on a medium-voltage 50-kW converter prototype. [ABSTRACT FROM AUTHOR]

A family of dimmable ac light-emitting-diode (LED) drivers fed from dc voltages, is presented in this paper based on zero-current-switching quasi-resonant converters. The proposed family of drivers is based on replacing the diode in the conventional converter topologies (i.e., buck, boost, or buck–boost) by a string of high-brightness LEDs (HB-LEDs). Hence, the HB-LED string will be working as the rectifier diode and the load, switching at the same frequency of the main switch. In this case, the output current, which is experimentally validated, shows a negative current peak due to the reverse-recovery effect of the HB-LEDs. In order to reduce the reverse-recovery effect on the HB-LEDs, the main switch of the proposed topologies is replaced with a full-wave resonant switch, which makes possible to reduce the di/dt during the turn-off of the HB-LED string, therefore the reverse-recovery effect is eliminated. Moreover, the dimming of the HB-LEDs is done by means of changing the switching frequency of the converter by varying the turn-off, while keeping a constant turn-on time. The proposed converters are suggested to be used in a postregulator stage of an ac–dc converter or as the interface between the low-voltage bus and the HB-LED string in a dc nanogrid. In order to validate the analysis, the proposed topologies have been experimentally tested on a constructed prototype with an output power of 7.5 W, that is able to achieve an electrical efficiency of 94.5% and a luminous efficacy of 110 lm/W at full load. Moreover, the analysis has been extended to a comparison in terms of reliability with the conventional topologies on a 700-h test. [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]

This paper investigates ac–dc–ac multilevel topologies for three-phase four-wire applications obtained from an interconnection of three-leg voltage-source converters. The topologies can be applied in line voltage regulators, universal active power filters, and uninterrupted power supplies. Operating principles, a pulsewidth modulation (PWM) technique, and an overall control strategy are developed. The PWM and control strategies are suitable to regulate the dc-link voltages and to reduce the harmonic distortion, switching stress, and power losses. Simulation results are used to compare the proposed configurations with a conventional solution in terms of harmonic distortion, semiconductor losses, and others characteristics. Experimental results are presented to validate the theoretical considerations and were obtained by using insulated-gate bipolar transistors with dedicated drives and a digital signal processor with appropriated plug-in boards and sensors. [ABSTRACT FROM AUTHOR]

In this paper, a fifth-order boost point-of-load converter is developed by cascading a modified fourth-order boost converter with a combination of L–C and diode. This topology has the following salient features: Single-switch topology, common ground between source and load, low-voltage stress across intermediate capacitors, and voltage gain same as other reported fifth-order boost converters with no common ground. Steady-state and dynamic analyses demonstrate the proposed converter's boosting feature and dynamic performance, respectively. A contoured robust Bode plot methodology is employed to design the robust voltage-mode controller to ensure load voltage regulation in the presence of uncertainties. The necessary and sufficient conditions under which the designed controller guarantees the load voltage regulation and robust stability are obtained. A step-by-step robust controller design procedure is outlined. The salient features of the proposed converter and its robust performance are studied analytically, using the MATLAB platform, and validated experimentally on a 60-W prototype module. [ABSTRACT FROM AUTHOR]

This paper investigates an ac–dc–ac multilevel power converter. The studied configuration is composed of two single-phase ac–dc–ac three-leg modules and series-connected H-bridges in the shared part of system. Because the proposed converter has shared legs between the input and output, it is employed in applications with same input and output frequency. Uninterrupted power supply and unified power quality conditioner are application examples for this converter. Such multilevel topology has lower dc-link voltage rating, which, consequently, presents low switch blocking voltages when compared to conventional topologies. System model, a space-vector pulsewidth modulation (PWM) strategy to symmetrical and asymmetrical dc-link voltages, and an overall control strategy to adjust the system variables are presented. A power flux analysis shows the operation zone in which the individual dc-link voltage balancing is possible. PWM and control strategies are developed to reduce the semiconductor total losses, harmonic distortion, and switching stress. Two ac–dc–ac multilevel conventional structures are used for comparison. Simulation and experimental results demonstrate the feasibility of the studied converter. [ABSTRACT FROM AUTHOR]

This paper investigates a multilevel inverter composed of series/parallel-connected H-bridges. The presented structure can be used for applications in which the use of semiconductor switches with low-voltage and low-current ratings is intended. A comprehensive system model, an overall control strategy to adjust the output voltage with constant magnitude and frequency, and a level-shifted PWM (LS-PWM) strategy based on a voltage vectors unidimensional analysis and a plane analysis are presented. The LS-PWM is capable of mitigating the low-frequency circulating current, thus generating multilevel voltage signals with low harmonic distortion, maximum number of levels, and low dv/dt. In addition, considering a wide range of values of voltages and currents and various power levels, the total converter losses are reduced compared with the conventional multilevel converters. Two multilevel conventional inverters with the same number of semiconductor switches are used for comparison. Simulation and experimental results demonstrate the feasibility of the studied converter. [ABSTRACT FROM AUTHOR]

This paper presents a nine-level transformer-based inverter requiring only eight switches. The envisaged structure consists of two standard H-bridges fed from a single dc source. Besides, a single-phase transformer is employed to aid the process of intermediate voltage level generation. An ad-hoc pulsewidth modulation scheme based on boolean logic form equations is developed to derive the gating pulses. An effortless extension of the proposed inverter to a higher number of voltage levels is also achieved by generalizing the switching functions. Furthermore, the superior performance of the proposed topology is demonstrated through a comprehensive cost-based analysis. Finally, the validation of the proposed topology is accomplished through experiments on a down-scale prototype, and the measurement results are included. [ABSTRACT FROM AUTHOR]

This paper proposes new angles constraint for selective harmonic elimination-pulsewidth modulation (SHE)-PWM utilized in single-phase inverter applications. The proposed angles constraint naturally eliminates all triplen harmonics, whereas they conventionally appeared in all single-phase output voltages. The harmonic amplitude formula is developed based on the obtained angles constraint, and then modified single-phase SHE equations are defined to eliminate only specified low nontriplen harmonics. Therefore, more harmonics would be eliminated with the same switching frequency in modified SHE-PWM. Five-level voltage waveform has been opted to implement the introduced method, but it can be applied on all multilevel voltage waveforms such as seven-level with even number of angles. Unlike the conventional SHE technique, THD is analyzable in modified SHE to find optimum values for switching angles in order to control noneliminated harmonic amplitudes and minimize THD. Moreover, the cancellation of triplen harmonics empowers a single-phase inverter to supply nonlinear loads beside linear ones. Some experimental tests are accomplished using a single-phase five-level modified packed U-cell (MPUC) inverter. Results are discussed to prove the excellent performance of a single-phase MPUC inverter under both normal and harmonic loads and accurate elimination of determined triplen and nontriplen harmonics by applying the presented angles constraint. [ABSTRACT FROM AUTHOR]

Direct power control (DPC) has gained much attention for medium-voltage applications due to its fast power control capability. However, a conventional static switching table based DPC can lead to unsatisfactory response when the converter is connected to an electric grid because it is commonly designed assuming ideal and constant voltages of the grid and the dc link. Therefore, the actual grid voltage and the actual converter dc-link voltage should be considered while designing the switching table. This paper proposes a novel dynamic switching table for the DPC, considering actual grid and dc-link voltages variation. The proposed dynamic switching table incorporates a new definition of power influence crossover angles of each converter space vector. The proposed scheme dynamically adapts the switching table by feeding forward the actual grid and dc-link voltages, and hence the converter's power is precisely controlled. The proposed technique is verified for the three-level neutral point clamped converters connected to a standard IEEE 9-bus test system. Moreover, the real-time simulations are performed in a real-time digital simulator, OPAL-RT. The obtained results verified the effectiveness of the proposed DPC strategy under different grid fault scenarios. [ABSTRACT FROM AUTHOR]

This paper proposes an improved dc transformer (NDCT hereinafter) based on switched capacitor with reduced switches for the integration of low-voltage dc energy storage systems and medium-voltage dc power distribution grid. The topology, phase-shift (PS) shoot-through and multiple PS modulations, and voltage, current, and power characterizations, as well as commutation characterization and control strategy, are proposed and analyzed comprehensively. Compared with the traditional schemes, the proposed NDCT not only can enhance reliability and flexibility but can increase voltage adjustment and power transfer capabilities as well. Moreover, the current ripple performance and soft-switching performance are improved, and the number and capacity of switches are reduced, thereby increasing the efficiency and cost of the system. Finally, an NDCT prototype is built. Experimental results verify the correctness and effectively of the proposed solution. [ABSTRACT FROM PUBLISHER]

This paper presents the active capacitor voltage-balancing (ACVB) methods based on the dynamic model for a five-level nested neutral-point piloted (NNPP) converter using hybrid carrier modulation. The traditional hybrid carrier modulation provides natural voltage balancing of floating capacitors and dc-link capacitors. First, the natural voltage-balancing ability under steady-state and ideal conditions is theoretically proved. However, there are accumulated errors and deviations of capacitor voltages in practical applications, especially under dynamic conditions. In order to address the accumulated errors and deviations of capacitor voltages, the dynamic models of floating-capacitor voltages and neutral-point voltage are established. Moreover, the ACVB method based on the dynamic model of the neutral-point voltage is proposed by injecting the zero-sequence voltage. And the ACVB method based on the dynamic model of floating-capacitor voltages is proposed by introducing the adjustment variables. The proposed ACVB methods have the advantages of simple formula, definite physical meaning, and high accuracy. Furthermore, the output voltage quality and current quality are evaluated in term of total harmonic distortion and the effect of model parameter mismatch on the proposed ACVB methods is presented. Finally, the comparative simulation and experimental results verify the correctness of the proposed ACVB methods based on the dynamic model under different conditions. [ABSTRACT FROM AUTHOR]

In this paper, a novel platform for the single phase switched-capacitor multilevel inverters (SCMLIs) is presented. It has several advantages over the classical topologies, such as an appropriate boosting property, higher efficiency, lower number of required dc voltage sources, and other accompanying components with less complexity and lower cost. The basic structure of the proposed converter is capable of making nine-level of the output voltage under different kinds of loading conditions. Hereby, by using the same two capacitors paralleled to a single dc source, a switched-capacitor (SC) cell is made that contributes to boosting the value of the input voltage. In this case, the balanced voltage of the capacitors can be precisely provided on the basis of the series–parallel technique and the redundant switching states. Afterward, to reach the higher number of output voltage levels, two suggested SC cells are connected to each other with a new extended configuration. Therefore, by the use of a reasonable number of required power electronic devices, and also by utilizing only two isolated dc voltage sources, which their magnitudes can be designed based on either symmetric or asymmetric types, a 17- and 49-level of the output voltage are obtained. Based on the proposed extended configuration, a new generalized version of SCMLIs is also derived. To confirm the precise performance of the proposed topologies, apart from the theoretical analysis and a complete comparison, several simulation and experimental results are also given. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive analysis of the current-stress optimization and soft-switching operation of the isolated bidirectional dual active bridge (DAB) dc–dc converter with the unified triple-phase-shift (UTPS) control. On this basis, the current-stress-optimized modulation scheme is proposed for DAB, which leads to the minimum current stress with the required transmission power and voltage conversion ratio in the whole load range. Moreover, the full soft-switching operation is achieved for the converter simultaneously. Distinct from the previous modulation schemes, the proposed optimized modulation scheme is deduced from a unified analysis of TPS where all effective switching modes are investigated. A novel algorithm based on the Karush–Kuhn–Tucker (KKT) conditions is originally proposed to derive closed-form solutions for the global optimal control parameters. This paper also presents a typical closed-loop control strategy for DAB with TPS control and detailed descriptions about the closed-loop operation. A laboratory prototype is applied, and the experimental results validate that the current-stress optimization and efficiency improvement are realized by applying the optimized modulation scheme. The experimental results also verify the effectiveness of the closed-loop control strategy for DAB with TPS control. [ABSTRACT FROM PUBLISHER]

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

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]

A four-level five-phase open-end winding (OeW) drive topology is introduced in this paper. The drive comprises a five-phase induction machine with open-end stator windings, supplied using two two-level voltage-source inverters with isolated and unequal dc-link voltages, in the ratio 2 : 1. The topology offers the advantages of a modular structure with fewer semiconductor components and has a greater potential for fault tolerance, as compared with an equivalent single-sided four-level drive. Due to the large number of switching states, development of a suitable space vector pulsewidth-modulation (PWM) method can be challenging. Hence, this paper examines the implementation of two-level-shifted carrier-based PWM methods. The effect of dead time on the drive performance is discussed, and it is shown that simultaneous PWM switching of both inverters can lead to degraded output phase voltage waveforms. Detailed analysis of this phenomenon is presented, a solution is proposed, and the modified modulation techniques are incorporated in an experimental setup, at first in conjunction with $V/f$ control. Once the proof of concept has been provided, full field-oriented control is implemented in this OeW drive topology for the first time; detailed experimental testing is conducted, and results are reported. [ABSTRACT FROM AUTHOR]

In this paper, we introduced an improved transformer-based parallel-resonant converter, suitable for high voltage, high power dc loads. The resonant capacitors are connected in parallel with diodes of the high voltage rectifier, thus restraining dv/dt stress in high voltage circuits. The LC tank resonant frequency is well beyond the switching frequency, reducing in this way the VA rating of LC components. With rated load, the output current of the IGBT bridge is equal to zero at switching instants, and the switching losses are very low. Proposed subresonant circuit requires lower primary current for the given output power and it has reduced IGBT losses. Experimental setup delivers 79 kW with an efficiency of 96.78%. The paper explains the switching states of the devised topology, and provides the guidelines for designing the power transformer, the LC tank and controls. Analytical prediction of the performance curves is verified both in laboratory and by the field tests with an electrostatic precipitator plant. [ABSTRACT FROM AUTHOR]

This paper is the continuation of Part I in which an online reference limitation strategy for shunt-connected converters is presented. This limitation strategy is successfully validated in this Part II of the paper by means of experimental results obtained in a laboratory setup. Two different experiment sets are carried out in order to check the two application scenarios described in Part I. On the one hand, the limitation strategy is implemented in the STATCOM application reducing the reactive power reference. On the other hand, the grid balancer functionality is implemented together with the new limitation strategy reducing the current references. In this last scenario, two different experiments are shown: 1) a switching-on of the converter; and 2) a voltage variation at the point of common coupling. In both functionalities, the corresponding reference limitations are activated due to overcurrent and overvoltage cases and the limitation due to the dc bus voltage oscillations is validated in the grid balancer functionality. [ABSTRACT FROM AUTHOR]

This paper presents nonisolated single-switch high step-up converters with low voltage stress. Based on the conventional flyback converter, one single-switch high step-up converter is derived. The voltage stresses on the switch and diodes are limited by using a clamping diode and voltage doubler structure. Also, to further reduce the voltage stresses of them, another single-switch high step-up converter is proposed simply by using one additional capacitor and rearranging the components. Thus, lower voltage-rated switch and diodes can be used, which results in higher efficiency. The operational principle, analysis and design considerations of each converter are presented in this paper. The validity of this study is confirmed by the experimental results from 24 V input and 250 V/125 W output prototype. [ABSTRACT FROM AUTHOR]

Multilevel converters are a proven solution for medium-voltage and high-power applications, including renewable energy conversion. Developing 6.6-kV converters is a key goal for the wind turbines industry. Considering the voltage rating of commercially available semiconductors, five-level converters are necessary to reach 6.6 kV. The five-level active neutral-point-clamped converter (5L-ANPC) is one of the most advantageous topologies among five-level multilevel converters. This paper presents a new 5L-ANPC topology that overcomes the features of the previously employed 5L-ANPC topology. Along this paper, the properties and working principle of this new 5L-ANPC are explained. Finally, the validity of the new converter is validated via simulation and experimental results. [ABSTRACT FROM AUTHOR]

In this paper, the conventional I- and T-type three-level neutral-point-clamped (3L-NPC) inverter for low-voltage renewable energy systems is first investigated. Literature research shows that the T-type inverter improves I-type's insulated-gate bipolar transistor (IGBT) $+$ IGBT current paths. However, the IGBT $+$ diode paths are the same. The calculation in this paper further reveals that the IGBT $+$ diode current paths dominate the conduction losses and even the whole semiconductor losses. Based on the aforementioned recognitions, a novel T-type inverter is presented as an alternative to be applied in the low-voltage renewable energy systems. In the proposed 3L-NPC, four CoolMosfets replace the IGBT $+$ diode middle bidirectional switch. In the proposed topology, there is no diode involved in the current path supposing the unity power factor. In this way, the conduction loss is expected to be reduced compared with that from the conventional T-type 3L-NPC, particularly in the low and medium power ranges. [ABSTRACT FROM PUBLISHER]

Leakage current minimization is one of the most important considerations in transformerless photovoltaic (PV) inverters. In the past, various transformerless PV inverter topologies have been introduced, with leakage current minimized by the means of galvanic isolation and common-mode voltage (CMV) clamping. The galvanic isolation can be achieved via dc-decoupling or ac-decoupling, for isolation on the dc- or ac-side of the inverter, respectively. It has been shown that the latter provides lower losses due to the reduced switch count in conduction path. Nevertheless, leakage current cannot be simply eliminated by galvanic isolation and modulation techniques, due to the presence of switches' junction capacitances and resonant circuit effects. Hence, CMV clamping is used in some topologies to completely eliminate the leakage current. In this paper, several recently proposed transformerless PV inverters with different galvanic isolation methods and CMV clamping technique are analyzed and compared. A simple modified H-bridge zero-voltage state rectifier is also proposed, to combine the benefits of the low-loss ac-decoupling method and the complete leakage current elimination of the CMV clamping method. The performances of different topologies, in terms of CMV, leakage current, total harmonic distortion, losses and efficiencies are compared. The analyses are done theoretically and via simulation studies, and further validated with experimental results. This paper is helpful for the researchers to choose the appropriate topology for transformerless PV applications and to provide the design principles in terms of common-mode behavior and efficiency. [ABSTRACT FROM AUTHOR]