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

A two-switch semiquadratic fifth-order buck converter belonging to a minimum-phase family is proposed in this paper. The proposed converter exhibits better dynamic performance, steady-state voltage gain in between conventional buck and quadratic buck converter. In view of this characteristic, it gives more bucking than the traditional buck converter. A time-domain analysis is formulated to predict the converter's steady-state performance. Also, the equations for designing the energy storage elements are established. Salient performance features, voltage bucking and source current ripples, of the proposed converter are compared to other competing/reported buck topologies. Transfer functions are obtained through state-space models, and then these are used in the controller design studies. The converter stabilization characteristics are studied through simulations. The analytical predictions and key features of the proposed converter are verified through experimental results. [ABSTRACT FROM AUTHOR]

Multiple output converters (MOCs) are widely applied to applications requiring various levels of output voltages due to their advantages in terms of cost, volume, and efficiency. However, most of the conventional MOCs cannot regulate multiple outputs tightly and they can barely avoid the cross-regulation problem. In this paper, the recently developed time-division multiple control (TDMC) method, which can regulate all of the outputs with a high accuracy, is used for a multiple output battery charger based on the phase-shift full-bridge topology to simultaneously charge three batteries. The proposed charger is able to charge three different kinds of batteries or three of the same kind of battery in different state of charges (SOCs) independently and accurately with the constant current/constant voltage (CC/CV) charge method. As a result, the strict ripple specification of a battery can be satisfied for multiple battery charges without difficulty. In addition, the proposed charger exhibits a high efficiency since the soft switching of all of the switches during the entire charge process can be guaranteed. The operating principle of the converter and the design of the controller, including the state-space average modeling, will be detailed, and the validity of the proposed method is verified through experiments. [ABSTRACT FROM PUBLISHER]

This paper presents the design, modeling, and control of an isolated dc-dc three-port converter (TPC) based on an interleaved-boost full-bridge converter with pulsewidth modulation (PWM) and phase-shift control for hybrid renewable energy systems. In the proposed topology, the switches are driven by phase-shifted PWM signals, where both phase angle and duty cycle are the controlled variables. The power flow between the two inputs is controlled through the duty cycle, whereas the output voltage can be regulated effectively through the phase shift. The primary-side MOSFETs can achieve zero-voltage-switching (ZVS) operation without additional circuitry. Additionally, due to the ac output inductor, the secondary-side diodes can operate under zero-current-switching (ZCS) conditions. In this study, the operation principles of the converter are analyzed and the critical design considerations are discussed. The dynamic behavior of the proposed ac-inductor-based TPC is investigated by performing state-space modeling. Moreover, the derived mathematical models are validated by simulation and measurements. In order to verify the validity of the theoretical analysis, design, and power decoupling control scheme, a prototype is constructed and tested under the various modes, depending on the availability of the renewable energy source and the load consumption. The experimental results show that the two decoupled control variables achieve effective regulation of the power flow among the three ports. [ABSTRACT FROM PUBLISHER]

Multilevel converter topologies for open-end stator winding medium-voltage (MV) induction motor drives have been researched from the last two decades. In this paper, a dual $n$ -level modular multilevel converter (MMC) topology has been proposed for open-end stator winding MV induction motor drives. The control requirements of the proposed system are low device switching frequency, minimal harmonic distortion of machine stator currents, elimination of common-mode voltages in machine stator windings, and maintaining floating capacitor voltages around their nominal value. Based on these requirements, an emerging modulation technique for MV induction motor drives known as synchronous optimal pulsewidth modulation has been developed for the proposed dual $n$L-MMC topology. The laboratory measurements from a dual three-level MMC fed 1.5-kW open-end stator winding induction motor drive demonstrate the performance of proposed technique. [ABSTRACT FROM PUBLISHER]

Modular multilevel converter (MMC) is very popular in medium-voltage applications, such as high-voltage direct current transmission, static Var generator, and motor drives. The arm capacitor voltage of MMC is usually constant and the output voltage is adjusted by regulating the pulse width modulation (PWM) index for switches in previous studies. In this paper, a novel flexible capacitor voltage control strategy for MMC as motor drives was proposed, with which the arm capacitor voltage was controlled flexibly according to the motor speed, by regulating the dc component and ac component of the PWM reference signal, and unsymmetrical control was used for the control of the upper arm and the lower arm in MMC. With the proposed control strategy, the circuit efficiency and the precision of the output voltage of the converter could be improved when the motor speed was low, and di/dt and d v/dt of the motor windings could be decreased. These proposals were implemented on a laboratory prototype, and experiments were carried out. The validity of the control strategy under both steady and dynamic states was verified. [ABSTRACT FROM AUTHOR]

Leakage current reduction of the single-phase transformerless cascaded H-bridge PV inverter is investigated in this paper. The high-frequency common-mode loop model of a typical single-phase cascaded H-bridge PV system is established. Based on the model, the main factors that affect the leakage current are discussed. The reason why the typical single-phase cascaded H-bridge inverter fails to reduce the leakage current is explained. In order to solve the problem, a cascaded topology based on the H5 inverter is presented, along with a new modulation strategy, which can ensure that the stray capacitor voltage is free of high-frequency components. In this way, the leakage current can be effectively reduced. Finally, a prototype with TMS320F28335DSP + XC3S400FPGA digital control is built. The performance tests of cascaded H-bridge and the proposed topologies are carried out. The experimental results verify the effectiveness of the proposed solution. [ABSTRACT FROM AUTHOR]

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

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

A new single-phase \uppi-\texttype 5-level inverter using 3-terminal switch-network (3TSN) is proposed in this paper. The topology is considered as a variant of T-type 3-level structure or dual-buck inverter with coupled inductors. This new inverter is suitable for multilevel power inversion with low dc-bus voltage. The merit of the proposed topology is to apply only four active power switches to achieve 5-level operation. Other benefits include double frequency operation of output inductor and equal division of the current that flows through power switches and filter inductor. Hence, it leads to high efficiency and low harmonics. These characteristics allow improvement of losses distribution and volume reduction of output filter inductor. The operation scenario with sinusoidal pulsewidth modulation (SPWM) is described in details. Meanwhile, the magnetic analysis and design are studied and discussed. Finally, a prototype is built to verify the theoretical analysis and demonstrate the benefits of the proposed topology. [ABSTRACT FROM AUTHOR]

This paper presents a modified two-level three-phase inverter for the reduction of the leakage current. With respect to a traditional two-level inverter, the proposed solution reduces the common-mode voltage (CMV), both in amplitude and frequency. Between the dc source and the traditional three-phase bridge, two active dc-decoupling devices and a voltage-clamping network have been added. A dedicated control strategy was developed adopting a modified space vector pulse-width modulation, oriented to the reduction of the CMV. Simulations showing the good performance of the solution are presented. A preliminary prototype was developed and experimental results are presented. [ABSTRACT FROM PUBLISHER]

In this paper, a reversible multilevel nine-leg converter for three-phase applications is investigated. This topology can be applied in line voltage regulators, power factor correction devices, and uninterrupted power supplies. It is composed of three single-phase three-leg converters with a leg shared by both load and grid sides. Suitable modeling, a pulse-width modulation (PWM) strategy based on a vector approach, and a control system are developed. The proposed PWM and control strategies are suitable to balance the dc-link voltages and to optimize the harmonic distortion, reducing switching stress and power losses. The investigated configuration is compared with two conventional topologies, including a neutral-point-clamped converter and has demonstrated that it presents some advantages in terms of voltage rating of the power switches, harmonic distortion, and semiconductor losses. Computer simulations and experimental results have been carried in the same operation conditions to verify the validity of theoretical considerations. [ABSTRACT FROM PUBLISHER]

This paper assesses the feasibility of three-phase pulse-width modulated (PWM) three-level voltage-source converters (VSC), namely neutral-point-clamped (3L-NPC) and T-type (3L-T) as alternatives to two-level converter (2L-VSC) for low-voltage multimegawatt renewable energy grid-connected converter applications. For this purpose, a novel design algorithm that takes switching frequency, capacity factor, modulation index, PWM scheme(s), and converter topology(ies) as input is unveiled to provide the design steps and performance benchmark for the specified topologies and modulation methods. Design of the LCL filter is also addressed, and equivalent output ripple performance criteria is used to benchmark the converter performances for a set of selected filter parameters. Main contribution of this algorithm is that it covers cost and operating factors of the design during the hardware design phase by introducing/modifying the terms of total cost of ownership (TCO) and return on investment (ROI) time considering the major energy markets. The design is detailed for 1-MVA system, and the results are summarized for 0.5 and 2-MVA systems. The study shows that 3L topologies perform more efficiently than 2L-VSC (T-type being the most prominent—with the shortest ROI), whereas the difference becomes much more prominent at the multimegawatt range, provided that all three yield equivalent outputs fulfilling the stringent grid codes. [ABSTRACT FROM PUBLISHER]

The flying-capacitor-based multilevel converter is one of the well-known breeds of the multilevel power converters. This paper proposes a new flying-capacitor-based multilevel converter to minimize the number of flying capacitors (FCs) and power switches. The advantage of the proposed FC-based multilevel converter in comparison with the conventional flying-capacitor multicell converter is that it needs fewer FCs. Also, in comparison with the stacked multicell converter, the proposed multilevel converter requires fewer semiconductor switches. In order to balance the voltage of the FCs in proposed multilevel converter, a new active voltage balancing method which is fully implemented using logic-form equations is presented. The proposed voltage balancing method measures output current and FC voltages to generate switching states to produce the required output voltage level, as well as balance the FCs voltages at their reference values. The output voltage of the proposed multilevel converter controlled with suggested active voltage balancing method can be modulated with any pulse-width-modulation (PWM) method, such as phase-shifted-carrier PWM or level-shifted-carrier PWM. Simulation results and experimental measurements of proposed FC-based multilevel converter are presented to verify the performance of the proposed converter, and its novel switching and modulation strategy, which is based on the active voltage balancing method. [ABSTRACT FROM PUBLISHER]

The unipolar sinusoidal pulse width modulation full-bridge transformerless photovoltaic (PV) inverter can achieve high efficiency by using latest superjunction metal–oxide–semiconductor field-effect transistor (MOSFET) together with silicon carbide (SiC) diodes. However, the MOSFETs are limited to use in transformerless PV inverter due to the low reverse-recovery characteristics of the body diode. In this paper, a family of new transformerless PV inverter topology for a single-phase grid-tied operation is proposed using superjunction MOSFETs and SiC diodes as no reverse-recovery issues are required for the main power switches for unity power operation. The added clamping branch clamps the freewheeling voltage at the half of dc input voltage during the freewheeling period. As a result, the common-mode voltage kept constant during the whole grid period that reduces the leakage current significantly. In addition, dead time is not necessary for main power switches at both the high-frequency commutation and the grid zero crossing instant, results low-current distortion at output. Finally, a 1-kW prototype is built and tested to verify the theoretical analysis. The experimental results show 98.5% maximum efficiency and 98.32% European efficiency. Furthermore, to show the effectiveness, the proposed topology is compared with the other transformerless topologies. [ABSTRACT FROM AUTHOR]

A hybrid pulse width modulation (PWM) strategy for the postfault grid-connected three-phase rectifier is proposed in this paper to achieve a reduced current stress on the dc-link capacitors. The capacitor current per sampling period is investigated, which consists of the effective duty ratio-based currents and the ineffective duty ratio-based currents. The currents introduced by the ineffective duty ratio are highly dependent on the allocation of the ineffective duty ratio. Therefore, this degree of freedom of the ineffective duty ratio allocation can be utilized to minimize the capacitor current. Then, the effect of the ineffective duty ratio allocation on the amplitudes of the capacitor current is analyzed. Based on this analysis, the optimized ineffective duty ratio allocations are proposed, where the ineffective duty ratios are flexibly allocated with respect to the vector angle of the ac current. Furthermore, a novel distribution of the vector plane is developed for the proposed hybrid space vector modulation (HBSVM) strategy. Moreover, the root-mean-square (RMS) values of the capacitor current are used to evaluate the performance of the proposed hybrid PWM strategy. The analytical results demonstrate that the proposed HBSVM strategy results in the reduced capacitor current RMS, which avoids a failure of the dc-link capacitors. Finally, the experimental results validate the effectiveness of the proposed HBSVM strategy. [ABSTRACT FROM PUBLISHER]

Four-level hybrid-clamped (4L-HC) inverter is a newly proposed topology which is suitable for high-performance medium-voltage drives. Each phase of this topology consists of eight switches and a flying capacitor and the dc-link is split into three parts by two neutral points. In order to ensure the topology operating properly, the voltages across the flying capacitors and three dc-link capacitors should be controlled and maintain balanced at their nominal values. This paper presents a decoupled voltage balancing method for this 4L-HC inverter, including the voltage balancing of dc-link capacitors and flying capacitors. A modified phase-shifted pulse-width modulation method is used to regulate the voltages of flying capacitors and the central dc-link capacitor. The relationship between the neutral-point currents and the output voltage is studied and the upper and lower dc-link capacitor voltages are balanced by injecting an optimum zero-sequence voltage. Simulation and experimental results are presented to verify the validity of this method. [ABSTRACT FROM AUTHOR]

The matrix converter (MxC) is a bidirectional direct ac–ac power conversion topology that can generate variable voltage and variable frequency output. It has low harmonics in input current and power factor control capability. In this paper, MxC concept is extended to medium-voltage (MV) level to provide a high-power drive that has bidirectional power flow capability and very low harmonics in input current and output voltage. MV MxC is implemented by connecting power cells in series which consist of three-phase input and single-phase output MxC. In this paper, detailed design of the MV MxC topology is described and the performance of the proposed topology is explained through experimental results. [ABSTRACT FROM PUBLISHER]

This paper presents a novel topology for a direct ac–ac power converter, called as the “three-to- k” phase matrix converter. The input to the proposed matrix converter configuration is a three-phase fixed voltage and a fixed frequency supply from the grid. The output is a variable voltage and variable frequency ac supply of any number of phases (k phase). However, the discussion is limited here for a k that is equal to odd number of phases. As an example, a “three-to-five” phase matrix converter is utilized for discussion and analysis. This paper also proposes two pulsewidth modulation (PWM) control techniques for the general topology of the “three-to- k” phase matrix converter. This is based on the so-called direct duty ratio PWM (DPWM). In one presented technique, the output voltage is limited to one half of the input voltage. For the other proposed scheme, the output voltage is enhanced to 78.86% of the input voltage. The proposed control algorithm is validated using simulation and an experimental approach. [ABSTRACT FROM AUTHOR]

In this paper, natural sinusoidal hybrid converter is presented for medium-voltage reactive-power control applications. Main high-voltage inverter that produces fundamental reactive current is a square-wave inverter. Several single-phase full-bridge converters are connected in series with this square inverter to eliminate harmonic voltages from the net output voltage of this hybrid converter. DC bus voltages of these cells are naturally controlled. Two different switching strategies are proposed for these series cells in this paper—one is pulse width modulation (PWM) type and the other is non-PWM type. Dc bus voltage of main high-voltage inverter is varied to have variable reactive power. Finally, experimental results are produced here to validate this hybrid topology and its proposed control strategies from a scale-down proto model. [ABSTRACT FROM AUTHOR]

The nongenerative-boost type rectifier, which is called the Vienna rectifier, is advantageous in terms of efficiency and current total harmonic distortion. Therefore, the Vienna rectifier is used in grid-connected applications such as telecommunication systems and wind turbine systems. Owing to the structural characteristics of the Vienna rectifier, various switching methods exist. Among these methods, a carrier-based discontinuous pulse-width modulation (CB-DPWM) method guarantees high efficiency compared to continuous pulse-width modulation methods; moreover, it is simple compared to a DPWM method based on space vectors. In this paper, the performance of the CB-DPWM method, its applicable region depending on the power factor and modulation index (Ma ), and its efficiency are analyzed in detail. Then, based on the analysis, a neutral-point voltage balancing method for the CB-DPWM method is proposed. The effectiveness and performance of the proposed neutral-point voltage balancing method are verified by simulation and experiment. [ABSTRACT FROM AUTHOR]

This paper proposes a new type of ac–ac converter which can operate as traditional noninverting buck and boost converters, and inverting buck–boost converter as well. The proposed converter uses six unidirectional current flowing and bidirectional voltage blocking switches, implemented by six reverse blocking insulated-gate bipolar transistors (IGBTs) or series mosfet–diode pairs, two input and output filter capacitors, and one inductor. It has no shoot-through problem of voltage source (or capacitor) even when all switches are turned-on, and therefore, pulsewidth modulation dead-times are not needed resulting in high-quality waveforms, and solves the commutation problem without using bulky and lossy RC snubbers or dedicated soft-commutation strategies. It has smaller switching losses because only two switches out of six are switched at high frequency during each half-cycle of input voltage, and it can use power MOSFETs as body diode never conducts, making it immune from mosfet failure risk which otherwise may occur due to poor reverse recovery problem of body diode. The noninverting buck–boost mode of the proposed converter can be used in applications with both step-up and step-down demand, while the inverting buck–boost mode can also be used in its application as dynamic voltage restorer. Detailed analysis of the proposed converter is given, and experimental results are also provided. [ABSTRACT FROM AUTHOR]

Photovoltaic (PV) energy conversion has been on the spotlight of scientific research on renewable energy for several years. In recent years, the bulk of the research on PV has focused on transformerless grid-connected inverters, more efficient than traditional line transformer-based ones, but more critical from a power quality point of view, especially in terms of ground leakage current. Neutral-point-clamped (NPC) inverters have recently gained interest due to their intrinsically low ground leakage current and high efficiency, especially for MOSFET-based topologies. This paper presents an active NPC (ANPC) topology equipped with 650-V silicon carbide (SiC) MOSFETs, with a new modulation strategy that allows to reap the benefits of the wide-bandgap devices. An efficiency improvement is obtained due to the parallel operation of two devices during the freewheeling intervals. Simulations and experimental results confirm the effectiveness of the proposed converter. [ABSTRACT FROM PUBLISHER]

This paper presents an MHz LLC resonant converter with load-regulating capability. Unlike the two-stage solution, most of input power is delivered to the load directly by the main transformer in the proposed topology. Moreover, only small portion of input power is converted by two stages: 1) auxiliary transformer and 2) a cascaded PWM dc–dc converter. Therefore, the sacrifice of the efficiency caused by the two-stage conversion is minimized. The operating principle of the proposed converter is analyzed, and a 1-MHz prototype based on the proposed converter is built-up to verify the high-frequency, high-efficiency, and output-regulating capability. [ABSTRACT FROM PUBLISHER]

In this paper, a new inverter topology is proposed for generating a multilevel dodecagonal voltage space vector structure for open-end winding induction motor (IM) using a single dc source. Dodecagonal voltage space vector structure eliminates fifth- and seventh-order harmonic voltages from phase voltage output and hence eliminates the fifth- and seventh-order harmonic currents through the motor leading to removal of the dominant sixth-order torque ripple generation in the motor over the entire modulation range. Multilevel space vector structure generates output voltage with better THD and low dv/dt. In the proposed topology, two three-level inverters drive an open-end winding IM, one inverter from each side. DC-link of primary inverter is from a dc source which delivers the entire active power, whereas the secondary inverter dc-link is maintained by a capacitor, which is self balanced during the inverter operation. The PWM scheme implemented ensures low switching frequency for primary inverter. Secondary inverter operates at a small dc-link voltage. Hence, switching losses are small for both primary and secondary inverters. Experimental results show the elimination of fifth- and seventh-order harmonic voltages over the entire modulation range, validating effectiveness of the proposed multilevel inverter scheme. [ABSTRACT FROM PUBLISHER]

In this paper, a three-phase multilevel power factor correction rectifier using the hybrid switched-capacitor concept is proposed. The converter is suitable for high-voltage-gain applications from conventional three-phase low-voltage sources. The three-level voltage operation reduces the weight and bulk of the magnetic devices. The main advantages of the proposed converter are low number of active switches, high voltage gain, sinusoidal currents, low voltage stress across all components, and simple control. Both steady-state and dynamic analyses are investigated. Experimental results for a 7500-W/220-V-to-1600-V laboratory prototype with maximum efficiency of 97.78% are presented and discussed. [ABSTRACT FROM AUTHOR]

This paper proposes three dynamic voltage restorer (DVR) topologies. Such configurations are able to compensate voltage sags/swells in three-phase four-wire (3P4W) systems under balanced and unbalanced conditions. The proposed systems use two independent dc links. Proposed configurations present advantages in terms of switch blocking voltages and consequently lower dc-link voltage rating. The complete control system, including the pulsewidth modulation (PWM) technique, is developed, and comparisons between the proposed configurations and a conventional one are performed. Simulation and experimental results are provided to validate the theoretical approach. [ABSTRACT FROM AUTHOR]

Multilevel inverters are gaining more attention in ac drive application due to their many attractive features. In the case of conventional neutral-point-clamped (NPC) or flying capacitor multilevel inverter configurations, active switches are connected in series to produce multilevel output voltage waveform. Therefore, if any one switch fails, the entire configuration has to be shut down; this will reduce the reliability of the system. A dual three-level inverter configuration for induction motor drive is proposed in this paper to improve reliability of the system. This topology is developed by feeding four-pole induction motor stator winding with four conventional two-level inverter modules. A level-shifted carrier-based third harmonic injection pulsewidth-modulation technique is used to produce the gating signals for the proposed configuration. By providing proper phase shift between carrier waves, multilevel voltage waveform is produced across the total motor phase winding, and first center band harmonics are also canceled. Thereby, the torque ripple will be considerably reduced compared with conventional NPC five-level inverter-driven induction motor drive. Finite-element analysis (FEA) is used to estimate the torque ripple when induction motor is supplied by the proposed configuration and conventional five-level NPC inverter configuration to show the effectiveness of the proposed converter. The proposed configuration is simulated using MATLAB/Simulink and experimentally verified using a laboratory prototype with a 5-hp four-pole induction motor drive. [ABSTRACT FROM PUBLISHER]

Eliminating the leakage current is one of the most important issues for transformerless three-phase photovoltaic (PV) systems. In this paper, the leakage current elimination of a three-phase four-leg PV inverter is investigated. With the common-mode loop model established, the generation mechanism of the leakage current is clearly identified. Different typical carrier-based modulation methods and their corresponding common-mode voltages are discussed. A new modulation strategy with Boolean logic function is proposed to achieve the constant common-mode voltage for the leakage current reduction. Finally, the different modulation methods are implemented and tested on the TMS320F28335 DSP +XC3S400 FPGA digital control platform. The experimental results verify the effectiveness of the proposed solution. [ABSTRACT FROM PUBLISHER]

This paper presents a voltage regulator topology, implemented using low-voltage devices, for converting high input voltage (>4.5 V) to low output voltages with fine-grain control (0.3 to 1 V). The topology merges a Dickson's switched-capacitor stage with a current-mode inductive buck stage, and optimizes the frequency of operations to reduce the overall passive size. The proposed two-stage hybrid regulator, designed in 130-nm standard digital process, operates from 4.8 to 6 V at input and regulates output voltage as low as 0.3 V with a maximum output power of 90 mW and a peak efficiency of 69%. [ABSTRACT FROM PUBLISHER]

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

The purpose of neutral-point voltage balancing algorithms in the three-level neutral-point clamped (3L-NPC) topology is to eliminate the voltage unbalance of top- and bottom-side dc-link voltages (neutral-point voltage). These algorithms are divided into dc unbalance and ac unbalance compensation methods. The dc unbalance causes distortion of output currents; therefore, this problem has to be solved. The ac unbalance implies that there is an ac ripple in the top- and bottom-side dc-link voltages. In applications using 3L-NPC topology, a large dc-link capacitor value is required to mitigate this ac unbalance problem. As a result, the size and the cost of applications become large and expensive. In this paper, a compensation method for mitigating the ac unbalance of the neutral-point voltage is proposed, which causes the dc-link capacitor value to be small, when a carrier-based pulse width modulation method is applied. The proposed method compensates the ac unbalance of the neutral-point voltage by adding an optimal compensation value to the reference duty signals. This compensation value is calculated simply by currents and reference duty signals. The calculation process of the optimal compensation value is discussed, and the effectiveness of the proposed method is verified with simulations and experiments. [ABSTRACT FROM PUBLISHER]

This paper proposes and evaluates an active voltage-balancing method for stacked multicell converters (SMCs) using phase-shifted pulse width modulation. The method is easy to implement and can be applied to SMCs with any number of levels. The proposed method balances the voltages of the capacitors by modifying the duty cycle of each switch of the SMC using a proportional controller. The direction of the output current and the crossed effect among the duty cycles of the switches is considered and used to improve capacitor voltage balance. The performance of the proposed voltage-balancing method is verified experimentally for different loads, such as linear and nonlinear loads, and under transient conditions. [ABSTRACT FROM PUBLISHER]

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

In this paper, a modified half-bridge (HB) resonant inverter topology with a dc-link neutral-point-clamped cell is proposed. A pseudo asymmetrical voltage-cancellation PWM method and a control strategy are introduced. The proposed topology can maximize the inverter output power factor, and minimize variations in the switching frequency. In addition, most switches are clamped to half of the dc input voltage at turn-off, increasing the overall efficiency of the system for a wide load range. The efficiency of the proposed inverter is improved up to 7% at light-load conditions compared with that of the conventional HB inverter. Informative expressions for performance comparison between the proposed inverter and its counterpart are provided. In addition, the losses in the inverter primary components are analytically analyzed in detail. For validation, a 120-W prototype is implemented, and experimental results are presented. [ABSTRACT FROM PUBLISHER]

Recently, novel direct pulse width modulated (PWM) ac–ac converters using coupled inductors with switching cell structure have been introduced as an alternative to the conventional ac–ac converter topology. The converters can effectively solve the commutation problem associated with the conventional direct PWM ac–ac converters. However, the two coupled inductors used in the topology make the converters less attractive for use in practical applications. This paper proposes magnetic integration of the discrete-coupled inductors in single-phase ac–ac converters. The dc offset fluxes generated by the common-mode currents are cancelled out perfectly when the windings on the common core are appropriately arranged, resulting in ac flux only. The proposed inductor shows significant improvements over discrete-coupled inductors, in that the proposed inductor does not have an air gap, it exhibits symmetrical winding currents, and it has smaller volume with large current handling capability. The proposed inductor can handle an unlimited amount of current due to the absence of core saturation caused by the current and is well suitable for high power ac–ac conversion applications. The performance evaluation and comparison of the experimental results show that the net volume of the coupled magnetic components can be reduced by more than 50% with the proposed integration scheme. [ABSTRACT FROM PUBLISHER]

Commutations existing in a brushless dc motor (BLDCM) drive system not only aggravate the torque ripple and reduce the power factor but also cause the catastrophic failure of a sensorless drive based on the zero-crossing detection of back electromotive force when the commutation duration approaches or exceeds 30 electrical degrees. For a sensorless BLDCM drive system with a long commutation time, it is necessary to shorten the commutation time. In this paper, a technique making the commutation time significantly reduced by means of a novel inverter topology is presented. The proposed topology is based on the idea of supplying higher dc-link voltage for the freewheeling phase. First, the dc link of the backward freewheeling path is decoupled from that of the forward energy flow path. The superiority of dc-link decoupling for commutation control is analyzed. Then, in order to provide adjustable voltage higher than the dc source voltage for the dc link of the freewheeling path, a double-layer C-dump converter is proposed. Compared with the traditional unipolar C-dump converter, it not only upraises the potential of the positive rail but also lowers the potential of the negative rail. Finally, the proposed inverter topology is verified by simulation and experimental results. [ABSTRACT FROM PUBLISHER]

This paper revisits the switched flow graph (SFG) technique. A general and unified equivalent SFG model of a three-terminal switcher encountered in regular and tapped inductor converters operating in the continuous conduction mode is proposed. The model can be applied to most PWM topologies and facilitates construction of a complete flow graph of a given converter. The approach can be helpful in theoretical analysis and derivation of analytical expressions of converter's small-signal transfer functions. The suggested methodology extends the previously proposed SFG analysis technique and alleviates the principal difficulties involved. Furthermore, the approach is straightforward and expeditious. Application guidelines and examples are presented and compared to simulation and earlier theoretical results. [ABSTRACT FROM PUBLISHER]

This paper proposed a fast, real-time and fair robustness scheme for single switch and double switches open-circuit fault diagnosis in pulse-width-modulated voltage source inverter (VSI) for vector-controlled induction motor drives based on three phase output currents, which is also easy to insert into the controlled algorithm as a subroutine without major modification. The concept of allelic points is proposed and corresponding functions are defined to describe the symmetry of the VSI physical topology under healthy and faulty conditions. The residuals between any two phase functions are applied as criterion for allelic points. Under healthy condition, three legs are symmetrical and the residuals are all closed to zero, when open-circuit fault occurs, the residuals will be larger than a predefined threshold, so it is used to detect fault occurrence. When fault occurs, the near-zero current samples per fundamental period will get large, its proportions in a period will be different when different fault classes occur. The fault can be located combined the functions and residuals based on the analysis of VSI topology. The simulations and experiments are carried out and the results show the effectiveness and the merits of the proposed method. [ABSTRACT FROM PUBLISHER]

This paper proposes a novel single-phase ac–ac Z-source converter based on the Γ-structure. The proposed converter uses a coupled transformer to produce the required gain. The obtained gain can be tuned by varying the turn ratio $\gamma _\Gamma$ of the transformer within the narrow range of $1 < \gamma _\Gamma < 2$. Also, the gain factor increases with decrease of the transformer turns ratio, $\gamma _\Gamma$ . Small transformer turn ratio results in more practical topology in some voltage gains. It makes the transformer design easier and reduces construction cost. Also, in the proposed topology, the input and output voltages share the same ground. In order to avoid voltage and current spikes on the switches, a commutation strategy is proposed and safe commutation is achieved without using a snubber circuit. The operating principles and steady-state analyses are presented to verify the operational concept of the proposed topology. Also, experimental results are given to verify the validation of the proposed converter. [ABSTRACT FROM AUTHOR]

The adverse effect of common-mode voltage (CMV) in pulse-width modulation inverters is widely acknowledged. Various approaches for mitigating CMV effect in PWM inverters have been proposed in the literature but they either show limited effect or impair the utilization of the drive. This paper proposes an active method for eliminating CMV in multilevel inverters which is independent on the inverter topology or its modulation scheme. In particular, the proposed method does not restrict the modulation index range of the drive. A detailed analysis of the active filter circuitry and a closed-form feed-forward control law are provided. Finally, selected simulation and experimental results are presented to validate the theoretical part. [ABSTRACT FROM AUTHOR]

In this paper, the performance of the new three-dimensional space vector-based switching signal generation technique for a grid-connected four-leg voltage source inverter used as a shunt compensator is proposed. The shunt compensator can be used for reactive power compensation, harmonic elimination, load balancing, and neutral current elimination in a three-phase four-wire grid-connected system. It is shown through experimental studies that switching losses in the four-leg voltage source inverter are appreciably reduced to a maximum of 33% in three-dimensional space vector modulation without NULL vector as the number of switches controlled at any instant of time is six out of eight. The new proposed technique is compared with three-dimensional space vector modulation with null vector. Experimental results are given to show the validity of the proposed switching control strategy. [ABSTRACT FROM AUTHOR]

Carrier-based pulsewidth-modulation (CBPWM) techniques are popular due to their simplicity, and have been widely researched for various three-phase inverter configurations. In this paper, two CBPWM techniques are proposed to reduce the common-mode (CM) voltage generated by the five-phase inverter. The five-phase inverters have more flexibility in reducing the CM voltage than their three-phase counterparts because they have more phase legs, hence finer control over the star-point voltage of the load. Two methods are proposed for the conventional two-level five-phase inverter to reduce the CM voltage; one utilizing adjacent modulating waveforms and the other utilizing nonadjacent modulating waveforms. The coupled inductor inverter (CII) uses coupled inductors to generate multilevel outputs. As the volt-second balance must be maintained across each coupled inductor, direct application of the proposed methods on the CII inverter will result in overcurrents in the coupled inductors. Hence, the proposed methods are further improved to ensure the volt-second integral over each switching period is zero. Moreover, the two proposed methods are designed to reduce switching events and prevent unexpected states occurring during the switching transitions. The performance and the switching strategy of both methods are verified by both simulations and experiments on a prototype of five-phase CII. [ABSTRACT FROM AUTHOR]

This paper proposes an indirect matrix converter (IMC) topology to supply a five-phase load directly from three-phase ac power sources without bulky electrolytic capacitors and explains its operating principle. Using the emerging topology, which combines the five-leg inverter into the rectifier stage of the conventional IMC, the three-to-five-phase IMC topology reduces the number of power switches and results in a simpler commutation compared with the conventional three-to-five-phase direct matrix converter. In addition, a simple approach to realize the carrier-based pulsewidth modulation (CBPWM) method for a three-to-five-phase IMC is presented, and the proposed CBPWM method is analyzed based on the space-vector approach. As a result, the IMC with the proposed CBPWM method can be more easily implemented compared with IMCs with the space-vector PWM method. A three-to-five-phase IMC control platform is realized by coordinating a TMS320F28335 DSP (Texas Instruments) with an EPM7128SLC84-15 field-programmable gate array (Altera). The simulation and experimental results are provided to verify the effectiveness of the CBPWM strategy. [ABSTRACT FROM AUTHOR]

A novel complementary phase disposition pulsewidth modulation method for the modular multilevel converter (MMC) with a limited number of submodules is proposed in this paper. Compared with the previous works, more practical issues have been considered, and the corresponding solutions have been provided. First, a new preset PWM signal mapping sequence and an improved virtual loop mapping (VLM) are used in the modulation. This method not only achieves a favorable capacitor voltage balance in the symmetry system but lowers the switching frequency of MMC's devices. Second, to further reduce the switching frequency, the unbalance margin of capacitor voltages is adopted to achieve the switching between the VLM and the selective VLM (SVLM). Moreover, the system robustness has been improved by considering the situation of symmetry losing, like cell fails; in these cases, the capacitor voltages of the upper and lower arms are balanced through the collaboration of the SVLM and the reconfigurable VLM. Finally, the effectiveness of the proposed method has been verified with simulation and experimental studies. [ABSTRACT FROM AUTHOR]

The Vienna rectifier, which is a nongenerative-boost type rectifier, is used in many applications such as telecommunication systems and wind turbine systems. The Vienna rectifier has a special operating requirement. Many switching methods considering this requirement were proposed. These methods generally take into account the Vienna rectifier's operation with the unity power factor because the Vienna rectifier aims to provide the power to the load. However, as the applications for the Vienna rectifier are diversified, control requirements have been suggested, including the dc-link voltage balance control and the novel control under severely unbalanced grids. In this paper, we propose a carrier-based pulse-width modulation (CB-PWM) method for Vienna rectifier operation with a variable power factor. The proposed CB-PWM method adds the compensation voltage to the three-phase reference voltages, depending on the power factor, to maintain the sinusoidal input currents of the Vienna rectifier. The performance and effectiveness of the proposed CB-PWM method are verified by simulation and experiment. [ABSTRACT FROM AUTHOR]

In this paper, an advanced control strategy for grid­tied photovoltaic (PV) cascaded H­bridge (CHB) inverter is proposed. The circuit topology consists of a proper number of power cells (H­bridge configuration) connected in series and supplied by individual PV modules. The adopted control method is a mixed staircase­PWM technique performed by means of a sorting algorithm to determine cells' switching state. The cells' state is related to the need of charging or discharging a particular cell much more than the others by calculating the voltage error at each dc­link (e.g., by considering the difference between the maximum power point tracking (MPPT) reference and the measured quantity). A dedicated P&O MPPT permits to control independently the voltage of each dc­link; thus, increasing the power extraction even in mismatched conditions. In order to prove the effectiveness and feasibility of the proposed approach, a set of experiments are performed on a laboratory prototype of a single­phase five­level PV CHB. The control section is implemented on FPGA by using a dSPACE real­time hardware platform; thus, obtaining fully dedicated digital circuits. Experimental results show good performance in terms of MPPT efficiency, total harmonic distortion, and power factor in both normal operation and mismatch conditions. [ABSTRACT FROM AUTHOR]

This paper investigates a dynamic voltage restorer (DVR) composed of two conventional three-phase inverters series cascaded through an open-end winding (OEW) transformer, denominated here DVR-OEW. The DVR-OEW operating with either equal or different dc-link voltages is examined. The proposed topology aims to regulate the voltage at the load side in the case of voltage sags/swells, distortion, or unbalance at the grid voltage. A suitable control strategy is developed, including space-vector analysis, level-shifted PWM and its equivalent optimized single-carrier PWM, as well as the operating principles and characteristics of the DVR. Comparisons among the DVR-OEW and conventional configurations, including a neutral-point clamped converter-based DVR, are furnished. The main advantages of the DVR-OEW compared to the conventional topologies lie on: 1) reduced harmonic distortion, 2) reduced converter losses, and 3) reduced voltage rating of the power switches. Simulated and experimental results are presented to validate the theoretical studies. [ABSTRACT FROM AUTHOR]

This paper presents a shunt power compensator based on the interconnection of three-phase two-level converters, and its comparison with two-level- and multilevel-based topologies. The shunt power compensator based on interconnected three-phase converter (ITC) is compared with compensators based on the two-level converter, three-level neutral-point clamped converter, and five-level modular multilevel converter. The comparisons were done in terms of components ratings, harmonic distortion, and semiconductor losses. Control strategies suitable to control the compensator and circulating currents, as well as the three-dc-link voltages are presented. The PWM strategy to generate the control reference voltages of the converter command is designed. Simulation and experimental results are presented. [ABSTRACT FROM AUTHOR]

This paper presents a single-phase ac–ac converter based on a modular multilevel cascade converter (MMCC) with double-star chopper cells (DSCC). The converter topology is composed of three DSCC legs, in which the middle leg is shared, and it does not present a common dc-link capacitor. It is suitable for nonregenerative or regenerative low-power and medium-power ac–ac conversions. A voltage-balancing control is presented for regulating the floating dc capacitor voltages. Furthermore, a grid current and load voltage control is presented to correct the input power factor and to ensure input/output sinusoidal waveforms. A phase-shifted carrier (PSC) pulsewidth modulation (PWM) commands submodules (SMs) using half of PSCs, preserving the characteristics of conventional modulation. Details about a downscaled prototype rated at 3.3 kW and 220 V are also presented. The experimental results allow validating the control strategies and the effectiveness of the proposed system. [ABSTRACT FROM PUBLISHER]