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

The circulating current in phase legs is an inherent phenomenon of modular multilevel converters (MMCs). The circulating current affects various aspects of MMC performance, such as power losses, capacitor voltage ripples, and the required current rating of semiconductors. Existing circulating current control methods can improve MMC performance in one aspect, but they may not implement the optimal performance in various aspects. Analytically analyzing how circulating current control affects MMC performance is essential. This paper proposes an improved steady-state analysis method that considers circulating current control. The influence of circulating current control is included by considering the effects of the second-harmonic component on reference voltages. Explicit analytical expressions for various electrical quantities can be derived, and the analytical calculation curves of some MMC performance indexes concerned under varying second-harmonic reference voltages can be obtained. Accordingly, the effects of circulating current control on MMC performance can be concluded, where a theoretical foundation for the accurate design of MMC parameters is provided. In addition, the obtained analytical calculation curves can be used to evaluate different circulating current control targets and find appropriate control targets to comprehensively improve MMC performance. Both simulation and experimental results verify the validity of the proposed steady-state analysis method and the corresponding conclusions. [ABSTRACT FROM PUBLISHER]

In this paper, a novel grid-connected high step-up inverter is proposed. The topology is composed of two stages. The first stage is a single-switch high step-up dc–dc converter with bipolar outputs, and the second stage is a conventional half-bridge dc–ac grid-connected inverter. Negative grounding of the photovoltaic (PV) module has resulted in elimination of unwanted ground leakage currents in the PV system. Simple structure, employing few semiconductor switches, simple control, and high efficiency are the features of the proposed topology. Theoretical analysis and principal operation of the circuit are discussed. An experimental prototype is implemented to verify the performance of the proposed inverter. The experimental results confirm the aforementioned features and the theoretical analysis of the converter operation. [ABSTRACT FROM PUBLISHER]

A three-phase single-switch discontinuous conduction mode (DCM) boost power factor correction (PFC) converter features zero-current turn on for the switch, no reverse recovery in the diode, a constant-switching-frequency operation, a simple control, and a low cost, which are suitable for low-to-medium-power and cost-sensitive applications. Due to the DCM, the energy transfer does not cover the whole switching cycle, the rms and peak values of the inductor current are large, and those of the switch and the diode are also large. This increases not only the current stress of the power components but also the conduction and switching turn-off losses, which lower the efficiency of the converter. An optimum utilization control of switching cycles is proposed in this paper to increase the critical boost inductance. The rms and peak current values of the main power components are reduced, and the conduction and switching turn-off losses are therefore decreased, leading to higher efficiency. The proposed method also slightly achieves an output voltage ripple reduction, and the input current harmonics comply with the standard of the International Electrotechnical Commission 61000-3-2 Class A. [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]

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]

In conventional control systems for a static synchronous compensator (STATCOM) based on a cascaded H-bridge multilevel converter, the action of individual voltage controllers that balance capacitor voltages can alter the output of a cluster voltage controller and a current controller due to a coupling effect. In this paper, first, the conditions that eliminate this coupling effect are derived, and then, a control system that enforces the derived decoupling conditions is proposed. It is also shown that an additional advantage of the proposed decoupled control system is that it enables the linearization of a cluster voltage control loop. Experimental studies on a single-phase seven-level STATCOM demonstrate the effectiveness of the proposed decoupled control system in improving the transient performance of the STATCOM. [ABSTRACT FROM AUTHOR]

This paper proposes a hybrid modulation strategy for asymmetrical cascaded multilevel converters operating under normal and faulty conditions on power cells. The proposed algorithm explores the advantages of both space vector (SV) and carrier-based modulation approaches. An SV is used for higher voltage cells to properly choose their voltage vectors in a way such as to avoid converter saturation, particularly under fault conditions. A generic algorithm to identify the domains of higher voltage vectors in which a reference lies, without the need for separation lines, is proposed. Then, to simplify the implementation of the algorithm, carrier-based modulation is employed for lower voltage cells, which switch with pulsewidth modulation. This suppresses the need for defining multiple switching sequences for different operational conditions, and it avoids converter saturation as much as possible, particularly under fault conditions on power cells. Simulation and experimental results for normal and faulty operational conditions are given, validating the theoretical analysis and demonstrating the good performance of the proposed hybrid modulation approach. [ABSTRACT FROM AUTHOR]

For discontinuous conduction mode (DCM) dc–dc converters with digital sensorless current mode (DSCM) control, an observed current error occurs, owing to a low-accuracy current observer. Moreover, a reference current error occurs due to a low-accuracy current controller or a finite dc gain of current loop. Conventionally, the observed current is compensated to increase current regulation accuracy, whereas the reference current error is neglected. However, for charge balance principle (CBP)-based DSCM (CBP-DSCM) control, this paper proves that the reference current should be compensated in a same quantity to that of observed current. Otherwise, single or unequal compensation leads to output voltage steady-state error. For this reason, a dual current error compensation strategy for CBP-DSCM control is proposed. It compensates the errors in a same quantity through a current error observer, which considers parasitics and calculates the current errors without approximation. To verify the proposed strategy, small-signal models with parasitics for both the converter and the controller are constructed by differential functions of key variables. Furthermore, converter stability is analyzed at typical operation condition, while the stability at various operation conditions is verified through robustness analysis. Finally, simulations and experimental results verify the analysis and the improved transient response of the converter. [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]

Power-hardware-in-the-loop (PHIL) simulations are used to test power hardware with the help of computer-based real-time simulations. Generally, buck-based power amplifiers that have good dynamic performance are used to construct a PHIL simulator because of their linear large signal control-to-output characteristics. However, their output voltage peak is limited to the applied dc input in the linear region of modulation. In this paper, a differential boost converter (DBC)-based power amplifier is proposed for PHIL simulations, which does not suffer from the aforementioned limitations of a buck-based amplifier. A conventional DBC exhibits highly nonlinear control-to-output behavior. A feedback linearization technique is used to linearize the DBC in a large signal and dynamic sense, which makes it suitable for PHIL applications. Using this power amplifier and a MATLAB/Simulink toolbox for real-time simulations, the PHIL simulator is constructed. Experimental results under various operating conditions of source voltages, such as unipolar, bipolar, transients in frequency, and the dc step, and various load conditions, such as reactive, nonlinear, and transient faults, are provided to confirm the efficacy of the proposed PHIL simulator. [ABSTRACT FROM PUBLISHER]

This paper presents high step-up dc-to-dc converter for low voltage sources such as solar photovoltaics, fuel cells, and battery banks. To achieve high voltage gain without large duty cycle operation, combination of coupled inductor and switched capacitor voltage doubler cells are used. By incorporating active clamp circuit, voltage spike due to the leakage inductance of the coupled inductor is alleviated and zero-voltage switching turn on of the main and auxiliary switch is obtained. Due to the use of MOSFETs of low voltage rating and soft turn on of the switches, conduction loss and switching losses are reduced. This improves the efficiency and power density of the converter. The proposed converter can achieve high voltage gain with reduced voltage stress on MOSFET switches and output diodes. Design and analysis of the proposed converter is carried out, and finally, a 500-W experimental prototype is built to verify theoretical analysis. [ABSTRACT FROM PUBLISHER]

A novel CLL resonant converter with a semi-bridgeless active rectifier (S-BAR) is analyzed, and its hybrid control strategy is proposed in this paper. This topology is developed by replacing rectifier lower diodes with synchronous switches and regulation by a phase-shifted pulsewidth-modulation signal. Theoretical and simulation results show that the performance of the proposed S-BAR is appropriate for resonant converters and secondary-side controlled infrastructure requiring a wide voltage range control at the secondary side. The hybrid control algorithm is obtained with the phase-shift and frequency tuning considering the voltage at the load terminal. High efficiency can be maintained by this proposed control, reducing conduction losses and providing zero-voltage switching soft-switching condition with a wide output voltage range. To confirm the performance of the proposed converter, experimental results are provided for which the output voltage/current range from 0 to 80 V/0 to 8.75 A with an input of 120 V and an average efficiency value of 93%. [ABSTRACT FROM PUBLISHER]

In this paper, a pulsewidth modulation (PWM) plus secondary-side phase-shift (SSPS) controlled full-bridge three-port converter (FB-TPC) is proposed for a renewable power system, which is derived by integrating two interleaved buck/boost circuits (IBBC) and a SSPS full-bridge converter (FBC), to interface the energy source, energy storage element, and output load simultaneously. The two switching legs are shared by the IBBC and FBC, which improves the active devices sharing ratio and power density. With PWM plus SSPS control scheme, decoupled power control can be realized and the converter can achieve wide input voltage range power conversion. In addition, zero-voltage switching (ZVS) of both the primary and secondary switches are achieved in a wide range. Furthermore, the circulating current can be greatly eliminated, which helps to reduce conduction losses. Moreover, the voltage stresses on the secondary rectifier are effectively suppressed since the power switches and diodes are clamped to output voltage. The operation principles, output characteristics, ZVS performances, and control strategy are analyzed in detail. Experimental results of a 600-W prototype are provided to verify the effectiveness and the advantages of the proposed converter. [ABSTRACT FROM PUBLISHER]

Phase-shifted carrier modulation is an industry standard in its application to multilevel H-bridge converters. The major advantage of this scheme over level-shifted and space vector modulation schemes is its inherent ability to evenly distribute losses between semiconductor devices. However, until now, its implementation has necessitated a capacitor voltage balancing scheme that degrades converter harmonic performance. This paper develops two phase-shifted carrier modulation schemes that avoid harmonic degradation by exploiting an extra degree of freedom in the available switching states. Simulation and experimental results are presented that confirm the correct operation of the modulation strategies. [ABSTRACT FROM PUBLISHER]

A new control technique for two-stage server power is proposed in this paper. The proposed technique will significantly reduce power consumption under the light-load condition. The basic idea of the proposed control technique is to control both the dc-link voltage of the power factor corrector (PFC) stage and the switching method of the full-bridge stage. Under the light-load condition, the output voltage of the PFC stage is no more fixed and is dynamically adjusted to significantly reduce the switching losses. Moreover, under the light-load condition, the full-bridge stage is with pulsewidth-modulation (PWM) and burst-mode control to reduce the circulating current losses. The former approach will reduce the switching losses due to the reduction of voltage across the power devices. The latter approach will dramatically reduce the circulating current losses caused by the phase-shift control method since phase-shift switching control is replaced by PWM switching control. Moreover, due to the reduction of the dc-link voltage, the switching losses for PWM and burst-mode control can be further reduced, as compared to those for fixed dc-link voltage. Experimental results of 480-W server power are presented. It is shown that the efficiency of the two-stage power converter can be improved up to 8% and 3.9% under light-load and 10% load conditions for \mboxinput voltage=110\ \mboxV, respectively. For the 220-V input voltage, the efficiency improvement using the proposed method is 6.4% and 4.2% under light-load and 10% load conditions, respectively. [ABSTRACT FROM PUBLISHER]

In this paper, the two-input buck converter is proposed as the dc/dc stage for photovoltaic (PV) cascaded converters. This converter is attractive for this application because it is cost effective and reliable and can achieve dual maximum power point tracking (MPPT) with only one power transistor. However, due to the simplified and integrated structure, the nonlinear characteristics of the converter and the two PV arrays complicate the control. By means of a small-signal modeling, the control theme of the two PV voltages is formulated, and the effect of the nonlinearities is presented. It is shown that, while fast voltage dynamics are achieved for the first input, the second-input voltage response depends on the second-stage converter control. Simulation and experimental results are reported to validate the theoretical analysis, showing the dual MPPT capability. [ABSTRACT FROM PUBLISHER]

The three-level boost power factor correction (PFC) converter has advantages of lower inductor current ripple and lower switch withstanding voltage compared with the boost PFC converter. Interleaved pulsewidth modulation had been used in the multiphase boost PFC converter. In the literature, interleaved current sensorless control (ICSC) for the multiphase boost PFC converters had been proposed. In this paper, the behavior of the three-level boost PFC converter is first analyzed. The results show that three-level converter has the same average equation as the interleaved boost PFC converter. Then, ICSC is modified for the three-level boost PFC converter with considering the voltage imbalance and the zero-crossing current distortion. The proposed modified ICSC (MICSC) is implemented in a field-programmable gate array board. Simulation results and experimental results are also provided to validate the proposed MICSC. [ABSTRACT FROM PUBLISHER]

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

This paper proposes an improved performance interactive distribution static compensator (DSTATCOM) to address the limitations of conventional current control mode (CCM) and voltage control mode (VCM) operations. The proposed interactive scheme provides smooth transfer of modes of operation while remaining connected in the distribution system. In normal operation, the DSTATCOM operates in CCM to make source currents balanced, sinusoidal, and at a unity power factor. During voltage disturbances, the CCM operation cannot improve load voltage. In that case, DSTATCOM operation is changed to VCM, which maintains a constant voltage across the sensitive loads. Hence, this interactive DSTATCOM ensures continuous, flexible, and robust operation of the load. Moreover, the filter current requirements are reduced in the proposed scheme, which reduces the losses in the filter and feeder, improves inverter efficiency, and requires a reduced-rating inverter for sag mitigation. The principle of operation and control for both operating modes is analyzed. The detailed process of the flexible transfer between the two modes is derived. Deadbeat predictive control algorithms for CCM as well as VCM operation are developed for fast operation during mode transfers. The performance of the proposed scheme is validated by both simulation and experimental results. [ABSTRACT FROM PUBLISHER]

Featuring high bandwidth and high efficiency, the switch-linear hybrid envelope tracking (SLH-ET) power supply has been gaining considerable attentions. This paper proposes a new configuration for SLH-ET power supply, which consists of a switching-mode converter with a step-wave approach and a linear amplifier connected in parallel. The switches in the switching-mode converter are operated only one time in every tracking period, leading to reduced switching loss and, thus, a higher efficiency. The number of the voltage levels and the voltage difference between the adjacent steps are analyzed in terms of the voltage synthesis accuracy and voltage total harmonic distortion. A full feedforward of the output voltage scheme is adopted to make the switching-mode converter provide the most load power and the linear amplifier only provide the ripple current that resulted by the switching-mode converter. Thus, the overall efficiency is improved. A prototype is built aiming for 300-kHz sine-wave tracking, with a 10–26-V output voltage and a 50-W peak output power. The experimental results show that the proposed configuration can obtain higher efficiency as well as high tracking bandwidth. [ABSTRACT FROM PUBLISHER]

Multiple-output Switched Mode Power Supplies (SMPSs) for personal computers (PCs) normally depict extremely bad power quality indices at the utility interface such as total harmonic distortion of the input current being more than 80%, power factor being lower than 0.5 and output voltage regulation being very poor. They violate the limits of harmonic emissions set by international power quality standards. In this paper, a nonisolated power factor corrected (PFC) converter is being proposed to be used at the front end to improve the power quality of an SMPS for a PC. The front-end converter is able to reduce the 100-Hz ripple in its output that is being fed to the second stage isolated converter. The performance of the front-end Zeta converter is evaluated in three different operating conditions to select the best operating condition for the proposed SMPS system. The performance of the proposed SMPS is simulated and a laboratory prototype is developed to validate its performance. Test results are found to be in line with the simulated performance under varying input voltages and loading conditions and all the results demonstrate its enhanced performance. [ABSTRACT FROM PUBLISHER]

This paper introduces the adaptive slope compensation method into the digital clamping current control at various input voltages to improve the power factor (PF) and the total harmonic distortion (THD) of the universal input. The controller conducts a phase-management mechanism for various input voltages and load conditions to raise the circuit conversion efficiency. The optimal switching timing for one- and two-phase operations can be determined from the power loss distribution. A digital signal processor chip TMS320F28035 is used to implement the digital platform. A 300-W laboratory prototype with a universal line voltage 80-V dc output voltage is designed and tested to verify the feasibility. The values of efficiency from light load (10% of rated power) to full load at 115- and 230-V inputs are greater than 95%. PF values from medium to full load are greater than 0.94. Input current harmonics also meet the norm of IEC 61000-3-2 Class D. [ABSTRACT FROM PUBLISHER]

While current-mode control of dc–dc converters provides numerous benefits over voltage-mode control, previous models of the control strategy have been limited to the form of classical control models. Through the use of a state-space averaged (SSA) model of current-mode control, both the open-loop and closed-loop circuit parameters of open-loop control-to-output frequency response, conducted susceptibility, input admittance, output impedance, and any other desired response can be easily obtained. In this paper, SSA models of current-mode-controlled converters are derived and presented for buck, boost, and flyback topologies operating in continuous conduction mode. The new model allows for simpler and more accurate modeling than possible with previous methods, facilitates the modeling of cascaded converters, and allows for the use of state-variable feedback and other modern control methods in applications that use current-mode control. [ABSTRACT FROM PUBLISHER]

A single-objective predictive control method that deals with four main control objectives applied to a multivariable single-phase three-level neutral-point-clamped converter operating as an active power filter is proposed in this paper. The four control objectives are to self-support the dc-bus voltage under load variations, to compensate the reactive power and the current harmonics, and to balance the dc capacitor voltages by using a predefined combination of the redundant switching states of the converter. The main contribution of the proposed method is that these objectives are accomplished without using weighting factors in the cost function, which eliminates problems such as multiobjective optimization or additional empirical procedures for determination of these factors. As a result, the method is easy to implement and rapidly selects the optimal voltage to improve the dynamic-state performance. Experimental results from a 2-kVA prototype are presented to prove that the method is valid for single-phase compensation. The well-known effect of model parameter errors' issue, which is inherent in predictive control methods, is also tested to confirm that the harmonic distortion in the grid current is below 5% even when the predictive model has a 25% error between actual and theoretically estimated grid impedance values. [ABSTRACT FROM PUBLISHER]

The modular multilevel converter (MMC) becomes attractive for medium- or high-power applications because of the advantages of high modularity, availability, and power quality. One of the technical challenges associated with an MMC is the balancing of the capacitors' voltages. In this paper, a voltage-balancing control method is proposed for the MMC under phase-shifted carrier-based pulsewidth modulation. The proposed voltage-balancing method uses the linearization method for pulse sorting without arm current measurement, which can control the capacitor charge transfer to balance the capacitor voltage in the MMC. In the proposed method, the voltagebalancing algorithm is implemented in each carrier wave period, which reduces the computational intensity and burden. In addition, the arm current can also be improved with the proposed method. The simulation studies with the professional tool PSCAD/EMTDC are conducted, and a downscale MMC prototype is also tested with the proposed method. The study results show the effectiveness of the proposed voltage-balancing method. [ABSTRACT FROM PUBLISHER]

This paper presents a power factor correction (PFC)-based bridgeless isolated Cuk converter-fed brushless dc (BLDC) motor drive. A variable dc link voltage of the voltage source inverter (VSI) feeding the BLDC motor is used for its speed control. This allows the operation of VSI in fundamental frequency switching to achieve an electronic commutation of the BLDC motor for reduced switching losses. A bridgeless configuration of an isolated Cuk converter is derived for the elimination of the front-end diode bridge rectifier to reduce conduction losses in it. The proposed PFC-based bridgeless isolated Cuk converter is designed to operate in discontinuous inductor current mode to achieve an inherent PFC at the ac mains. The proposed drive is controlled using a single voltage sensor to develop a cost-effective solution. The proposed drive is implemented to achieve a unity power factor at the ac mains for a wide range of speed control and supply voltages. An improved power quality is achieved at ac mains with power quality indices within the limits of the IEC 61000-3-2 standard. [ABSTRACT FROM PUBLISHER]

This paper analyzes the interleaved boost with coupled inductors (IBCI) converter, which is an isolated topology that is suitable for high step-up applications. Two main contributions are given: an exhaustive steady-state analysis and an accurate small-signal model. The former allows for deriving a closed-form noniterative design procedure for the power-stage active and passive components. In addition, it reveals an interesting equivalence with an apparently different converter, i.e., the single active bridge. Subsequently, the IBCI converter dynamic behavior is investigated, deriving a nonlinear average model that, under small-signal approximation, can be linearized around a given operating point and used for feedback controller design. A single photovoltaic module interface converter, rated for 300-W output power, is considered as a case study to validate the analysis outcome and the design procedure. Both are fully validated by measurements taken on the laboratory prototype. [ABSTRACT FROM PUBLISHER]

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

This paper proposes a novel multiple-input bidirectional dc–dc power converter to interface more than two dc sources of different voltage levels. This finds applications in hybrid electric/fuel cell vehicles (FCVs), where different dc sources of unequal voltage levels need to be connected with bidirectional power flow capability. The converter can be used to operate in both the buck and boost modes with bidirectional power control. It is also possible to independently control power flow between any two sources when more than two sources are actively transferring power in either directions. The operation, analysis, and design of the converter are presented with different modes of power transfer. The proposed converter is demonstrated for FCV application using real-time hardware-in-the-loop system. Experimental results for a 5-kW system are presented, validating the theoretical analysis. [ABSTRACT FROM PUBLISHER]

This paper presents a capacitor voltage balancing control applicable to any multilevel dc–ac converter formed by a single set of series-connected capacitors implementing the dc link and semiconductor devices, such as the diode-clamped topology. The control is defined for any number of dc-link voltage levels and converter legs (for single-phase and multiphase systems), guaranteeing the capacitor voltage control for any modulation index value and load (from idle mode to full power). The associated control loop small-signal transfer function is presented, from which optimum compensator design guidelines are derived. The improvement in control performance is verified through simulation and experiments comparing with a previous balancing control strategy in a four-level three-phase dc–ac conversion system. The satisfactory control performance is also verified through simulation in a four-level five-phase dc–ac conversion system. [ABSTRACT FROM PUBLISHER]

The modular multilevel converter (MMC) becomes attractive for high-voltage and high-power applications due to its high modularity, availability, and power quality. The voltage balance issue of capacitors is very important in the MMC, and balancing of the capacitor voltage is increasingly difficult as the switching frequency is reduced. In this paper, a voltage-balancing method is proposed for the MMC switched at grid frequency with reduced losses and does not rely on the arm current. By assigning the low-frequency pulses with different pulsewidths, the capacitor charge transfer in the MMC can be controlled for keeping the capacitor voltage balancing in the MMC. Simulations and experimental studies of the MMC are conducted, and the results confirm the effectiveness of the proposed capacitor voltage-balancing method. [ABSTRACT FROM PUBLISHER]

The average-current-controlled boost power factor correction converter may operate in all-continuous current mode (CCM), part-CCM/discontinuous current mode (DCM), or all-DCM mode in a half line cycle under different input voltage and load conditions, and the conducted electromagnetic interference (EMI) spectrum of the converter exhibits differences in these operation modes. In this paper, by analyzing the characteristic of the harmonics of the drain-to-source voltage of the power switch, the characteristics of the common-mode and differential-mode noise of the converter are revealed in different operation modes. The analyzed results can be used to guide the EMI filter design for the converter and ensure the conducted EMI satisfying the standard under all working conditions. [ABSTRACT FROM PUBLISHER]

Grid-connected power converters play a key role in several applications such as the integration of renewable energy sources and motor drives. For this reason, the development of high performance control strategies for this particular class of power converters has increasingly attracted the interest of both academic and industry researchers. This paper presents the predictive optimal switching sequence (OSS) direct power control (DPC) (OSS-DPC) algorithm for grid-connected converters. The OSS-DPC method belongs to the predictive-DPC family and provides the desired power references by calculating globally OSSs. To address computational and implementation issues, an efficient control algorithm, named reduced OSS-DPC, is introduced. The implementation of the proposed control strategy in a standard DSP is evaluated on a two-level power converter prototype working as a STATCOM. Experimental results show the algorithm's potential to provide high performance during both transient and steady states. [ABSTRACT FROM PUBLISHER]

This paper presents a real-time diagnostic algorithm for insulated-gate bipolar transistor open-circuit faults in three-level neutral-point-clamped rectifiers. This algorithm is based on the instant voltage error in the converter and requires only signals already available to the control system, avoiding the use of additional hardware. The algorithm is independent from the load and from the used control strategy and provides very fast detection and identification of the fault, with diagnostic times as low as two sample periods (in favorable conditions). Experimental results are presented for the operation of the rectifier with two distinct control and modulation strategies and in different conditions. Results show the algorithm's speed, effectiveness, and robustness. [ABSTRACT FROM PUBLISHER]

A single-switch nonisolated dc/dc converter for a stand-alone photovoltaic (PV)-battery-powered pump system is proposed in this paper. The converter is formed by combining a buck converter with a buck-boost converter. This integration also resulted in reduced repeated power processing, hence improving the conversion efficiency. With only a single transistor, the converter is able to perform three tasks simultaneously, namely, maximum-power-point tracking (MPPT), battery charging, and driving the pump at constant flow rate. To achieve these control objectives, the two inductors operate in different modes such that variable switching frequency control and duty cycle control can be used to manage MPPT and output voltage regulation, respectively. The battery in the converter provides a more steady dc-link voltage as compared to that of a conventional single-stage converter and hence mitigates the high voltage stress problem. Experimental results of a 14-W laboratory prototype converter with a maximum efficiency of 92% confirmed the performance of the proposed converter when used in a PV-battery pump system. [ABSTRACT FROM PUBLISHER]

In this paper, a seven-level single-carrier and multi-modulation-wave sinusoidal pulsewidth modulation (SCMM-SPWM) strategy is proposed. In the negative half cycle of the modulation waves (MWs), dc offsets related to the amplitude of the carrier are set on the three MWs, respectively, to apply the same comparison logics of the MWs and carrier during positive and negative half cycles of the MWs. Thus, it is implemented with only one digital signal processor chip without any other attached logical circuit or controller. The reason for generating the zero-crossing voltage pulse disturbance (ZCVPD) in this strategy is analyzed, and the elimination of the ZCVPD is proposed and verified by experimental results. The spectral characters of the conventional multi-MW-based SPWM and the proposed one are originally derived and compared with each other by simulation in detail. The theoretical analysis, simulation, and experimental results indicate that the output characters of the proposed strategy are identical to those of the conventional one; it means that the proposed strategy can replace the conventional one while with the benefit of significantly reducing the cost and bulk of the implemental platform. [ABSTRACT FROM PUBLISHER]

Conventional matrix converters (MCs) have limited voltage gain that is less than 0.866, whether for direct MC (DMC) or indirect MC (IMC). Existing Z-source (ZS)/discontinuous quasi-Z-source (qZS) DMCs and ZS IMCs achieved larger than 0.866 voltage gain; however, the former inherited the complex commutation from DMC, and the latter involved a ZS network in dc link and led to non-all-silicon solution. In this paper, ZS and discontinuous qZS networks of existing ZS/qZS DMCs are used for an IMC topology for simplifying commutation and having high voltage gain, but they require extra input filter to reduce current harmonics. A new continuous qZS IMC is proposed, where a qZS network integrates the filtering function of the grid side; hence, additional input filter is avoided in the proposed continuous qZS IMC. Three new IMCs are compared in detail, in terms of voltage gain, current ripple, voltage ripple, inductor current and capacitor voltage stresses, ZS/qZS switch current and voltage stresses, filtering function, input current total harmonic distortion (THD), output voltage THD, and efficiency. Their control and modulation methods are presented to achieve the desired performances. Experimental comparisons verify the theoretical analysis and that the proposed continuous qZS IMC is a promising topology. [ABSTRACT FROM PUBLISHER]

This paper presents a control scheme for the dynamic performance improvement of an AC/DC converter using the model predictive direct power control (MPDPC) with a duty cycle. In the MPDPC, the active and reactive power is simultaneously controlled with a single cost function. If either of the two control targets has a large power variation, the control weight is concentrated on one side, which causes mutual interference. Because of such mutual interference, the control dynamics of the AC/DC converter deteriorates. Due to the control weight being concentrated on one side using the single cost function, even if the control dynamics of the other side decreases, the dynamic performance of the system is improved by reconfiguring the cost function that has the weighting factor to minimize the decline of the system dynamics that is caused by the mutual interference. The effectiveness of the proposed control scheme is verified by comparing its results with those of the conventional MPDPC. The results are obtained through the simulations and experiments. [ABSTRACT FROM PUBLISHER]

Dynamic voltage restorer (DVR) is a definitive solution toward compensation of voltage sag with phase jump. Conventional DVR topologies, however, have dc links and two-stage power conversions. This increases its size, cost, and associated losses. Therefore, topologies without the dc link, mitigating sag by utilizing direct ac–ac converters, are preferable over the conventional ones. As no storage device is employed, compensation by these topologies is limited only by the voltages at the point of common coupling that is feeding the converters. In this paper, a direct-ac–ac-converter-based topology fed with line voltages is proposed. The arrangement provides increased range of compensation in terms of magnitude and phase angle correction. Detailed simulations have been carried out in MATLAB to compare the capability of the proposed topology with other similar topologies. Experimental results are presented to validate the capability of the topology to compensate various sags. [ABSTRACT FROM PUBLISHER]

This paper presents input-series–output-parallel (ISOP) configuration for single-phase front-end buck rectifiers (BRs). The configuration is especially suitable for traction applications, where the complete rectification system needs to withstand high ac voltages and supply medium-power loads. The primary rectification module of the proposed configuration is based on pulsewidth-modulated BR (current source inverter topology). The desired isolation, mandatory for ISOP connection, is provided at the dc stage through a medium-frequency/high-frequency transformer. Equal power sharing by modules is achieved from the ac side through input voltage and current sharing. The proposed control scheme is configured using two loops. While the outer loop regulates the output dc voltage and active wave shaping of the source current, the inner loop ensures stable voltage sharing. The performance of the proposed ISOP configuration is verified using numerical simulation. Experimental verification is achieved through a 2-kW grid-connected laboratory prototype. [ABSTRACT FROM PUBLISHER]

The propagation delay of a comparator and dead time causes the duty-discontinuity region near the boundary of the step-down and step-up regions in a non-inverting buck–boost (NIBB) converter. The duty-discontinuity region leads to an unstable output voltage and an unpredictable output voltage ripple, which might cause the entire power system to shut down. In this paper, a mode-transition technique called duty-lock control is proposed for a digitally controlled NIBB converter. It locks the duty cycle and eliminates the error between the output voltage and the reference signal by using a proposed fixed reference scheme that ensures the stability of the digital controller and output voltage. The experimental results that were applied to a field-programmable gate array-based platform revealed that the output voltage of the NIBB converter is stable throughout the entire transition region, without any efficiency tradeoffs. The input voltage of the converter that was provided by a Li-ion battery was 2.7–4.2 V, and the output voltage was 1.0–3.6 V, which is suitable for radio-frequency power amplifiers. The switching frequency was 500 kHz, and the maximum load current was 450 mA. [ABSTRACT FROM PUBLISHER]

This paper presents a power factor correction (PFC)-based bridgeless canonical switching cell (BL-CSC) converter-fed brushless dc (BLDC) motor drive. The proposed BL-CSC converter operating in a discontinuous inductor current mode is used to achieve a unity power factor at the ac mains using a single voltage sensor. The speed of the BLDC motor is controlled by varying the dc bus voltage of the voltage source inverter (VSI) feeding the BLDC motor via a PFC converter. Therefore, the BLDC motor is electronically commutated such that the VSI operates in fundamental frequency switching for reduced switching losses. Moreover, the bridgeless configuration of the CSC converter offers low conduction losses due to partial elimination of diode bridge rectifier at the front end. The proposed configuration shows a considerable increase in efficiency as compared with the conventional scheme. The performance of the proposed drive is validated through experimental results obtained on a developed prototype. Improved power quality is achieved at the ac mains for a wide range of control speeds and supply voltages. The obtained power quality indices are within the acceptable limits of IEC 61000-3-2. [ABSTRACT FROM PUBLISHER]

In a photovoltaic (PV)- or fuel-cell-based grid-connected power system, a high step-up dc–dc converter is required to boost the low voltage of a PV or fuel cell to a relatively high bus voltage for the downstream dc–ac grid-connected inverter. To integrate the advantages of the high voltage gain of a switched-capacitor (SC) converter and excellent output regulation of a switching-mode dc–dc converter, a method of combining the two types of converters is proposed in this paper. The basic idea is that when the switch is turned on, the inductor is charged, and the capacitors are connected in series to supply the load, and when the switch is turned off, the inductor releases energy to charge multiple capacitors in parallel, whose voltages are controlled by a pulsewidth modulation technique. Thus, a high voltage gain of the dc–dc converter can be obtained with good regulation. Based on this principle, a series of new topologies are derived, and the operating principles and voltage gains of the proposed converters are analyzed. Finally, the design of the proposed converter is given, and the experiment results are provided to verify the theoretical analysis. [ABSTRACT FROM PUBLISHER]

Pulse train (PT) control technique realizes the output voltage regulation of switching dc–dc converters by using preset high power control pulse PH and low power control pulse PL. In steady state, PH and PL in some successive switching cycles constitute a control pulse repetition cycle. The control pulse combination of PH and PL in the control pulse repetition cycle has a significant effect on the performances of PT controlled switching dc–dc converters. In this paper, by taking PT controlled discontinuous conduction mode buck converter as an example, the control pulse combination of PT controlled buck converter is studied. Some lemmas to reveal the control pulse combination are presented, and the combination of PH and PL in a control pulse repetition cycle is obtained. Based on which, the steady-state and transient performances of PT controlled buck converter are investigated. The control pulse combination-based analysis of PT controlled buck converter provides an effective way to understand the PT control technique in detail. [ABSTRACT FROM PUBLISHER]

This paper proposes a voltage balancing method for a flying capacitor multilevel converter based on the phase-disposition sinusoidal pulsewidth modulation (PD-SPWM). This voltage balancing method uses redundant switching states, which are determined by the minimization of a cost function. The implementation of the PD-SPWM using standard triangular carriers leads to additional switching events that are due to the transitions within the same voltage level, thus increasing the switching frequency of the power devices. Such drawback can be avoided by using sawtooth carrier waveforms. Another characteristic of the proposed voltage balancing method is that it does not require the tuning of parameters to achieve optimal performance. Simulation and experimental results confirm the robustness of the proposed method operating with different loads and transient conditions. [ABSTRACT FROM PUBLISHER]

The quasi-Z-source cascaded multilevel inverter (qZS-CMI) presented many advantages over conventional CMI when applied in photovoltaic (PV) power systems. For example, qZS-CMI provides the balanced dc-link voltage and voltage boost ability, saves one-third modules, etc. However, current research studies only disclosed control of single-phase qZS-CMI-based PV power systems, and there was no literature related to control of three-phase qZS-CMI-based PV power systems. In this paper, for the first time, three-phase qZS-CMI's control is proposed and demonstrated for application to PV power systems. The models of PV-panel-fed qZS H-bridge module and qZS-CMI-based PV power system are built to accurately design control algorithms for each module and the whole system. The proposed control method includes the distributed maximum power point tracking for each module, dc-link peak voltage balance control for all modules, and grid-tie control for the whole system; moreover, a new multilevel space vector modulation method is proposed for the three-phase qZS-CMI. Simulation and experimental results on a test bench with a three-phase seven-level qZS-CMI-based PV power system verify the proposed control and modulation methods. [ABSTRACT FROM PUBLISHER]

In this paper, a predictive control scheme is proposed for the low-voltage ride-through (LVRT) enhancement of direct-driven permanent-magnet-synchronous-generator-based megawatt-level wind turbines. The proposed method uses the turbine–generator rotor inertia to store the surplus energy during the grid voltage dips. The power conversion system is realized using a three-phase diode-bridge rectifier, a three-level-boost converter, and a neutral-point-clamped (NPC) inverter. The wind turbine requirements, such as maximum power point tracking, net dc-bus voltage control, balancing of the dc capacitor voltages, and reactive power generation, are modeled as the reference control variables. The generator- and grid-side cost functions are defined to deal with these control objectives. During each sampling interval, the control goals are achieved based on the minimization of cost functions. The coordination of boost and NPC converters and the exchange of reference control variables during normal and LVRT operation are formulated such that the power converters operate in a safe mode while meeting the grid code requirements. Simulation and experimental results are presented to validate the proposed strategy. [ABSTRACT FROM PUBLISHER]

For a sensorless predictive current controlled boost dc–dc converter, its small-signal model that contains a number of parasitic parameters, is derived in this paper. This model indicates that the type of system becomes type 0 even with the correction of voltage loop proportional–integral controller, leading to the existence of output voltage steady-state error. Then a self-correction differential current observer (SDCO) is proposed to eliminate this steady-state error and gain high transient response speed. The self-correction part of the SDCO makes the system become type 1 to achieve no steady-state error for output voltage, whereas the differential part can guarantee that the intermediate calculation results do not overflow. By carrying out a series of simulation verifications, further investigation proves that the proposed algorithm has good robustness. Finally, the effectiveness of the proposed algorithm is verified by experimental results. [ABSTRACT FROM PUBLISHER]

This paper presents a novel topology for the generation of adjustable frequency and magnitude pulsewidth-modulated (PWM) three-phase ac from a balanced three-phase ac source with a high-frequency ac link. The proposed single-stage power electronic transformer (PET) with bidirectional power flow capability may find application in compact isolated PWM ac drives. This topology along with the proposed control has the following advantages: 1) input power factor correction; 2) common-mode voltage suppression at the load end; 3) high-quality output voltage waveform (comparable with conventional space vector PWM); and 4) minimization of output voltage loss, common-mode voltage switching, and distortion of the load current waveform due to leakage inductance commutation. A source-based commutation of currents associated with energy in leakage inductance (termed as leakage energy) has been proposed. This results in soft-switching of the output-side converter and recovery of the leakage energy. The entire topology along with the proposed control scheme has been analyzed. The simulation and experimental results verify the analysis and advantages of the proposed PET. [ABSTRACT FROM PUBLISHER]