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High step-up converters are required for distributed photovoltaic generation systems, due to the low voltage of the photovoltaic source. In this paper, a new hybrid high voltage gain dc–dc converter is created by merging the standard boost converter with a coupled inductor and different switched-capacitor techniques. With a single switch and no requirement of higher duty cycle values, the proposed converter achieves a high voltage gain and high efficiency, in addition to lowered voltage and current stresses of the components. A 200-W prototype was implemented experimentally to evaluate the converter, which reached a maximum efficiency of 97.6%. [ABSTRACT FROM AUTHOR]

In a wireless power transfer (WPT) system via coupled magnetic resonances, the power transfer efficiency (PTE) drastically decreases with the transfer distance or the load changing. In this paper, the causes of efficiency degradation are analyzed, and an automatic impedance matching method based on the feedforward-backpropagation (BP) neural network is proposed to maintain the PTE at a reasonable level. To validate and test the performance of the proposed method, a WPT automatic impedance matching simulation system is implemented. Moreover, a prototype based on the proposed method is built and dynamic matching experiments were performed. The simulation results show that the algorithm efficiency of the proposed BP method is 108.5% higher than that of the genetic algorithm. The experimental results show that the PTE is improved up to 78.33% and this is closely maintained within a distance of 10–30 cm, which is consistent with the simulation result. [ABSTRACT FROM AUTHOR]

In this paper, the wear-out performance of an impedance-source photovoltaic (PV) microinverter (MI) is evaluated and improved based on two different mission profiles. The operating principle and hardware implementation of the MI are first described. With the experimental measurements on a 300-W MI prototype and system-level finite-element method simulations, the electrothermal models are built for the most reliability-critical components, i.e., power semiconductor devices and capacitors. The dependence of the power loss on the junction/hotspot temperature is considered, the enclosure temperature is taken into account, and the thermal cross-coupling effect between components is modeled. Then, the long-term junction/hotspot temperature profiles are derived and further translated into components’ annual damages with the lifetime and damage accumulation models. After that, the Monte Carlo simulation and Weibull analysis are conducted to obtain the system wear-out failure probability over time. It reveals that both the mission profile and the thermal cross-coupling effect have a significant impact on the prediction of system wear-out failure, and the dc-link electrolytic capacitor is the bottleneck of long-term reliability. Finally, the multimode control with a variable dc-link voltage is proposed, and a more reliable dc-link electrolytic capacitor is employed, which results in a remarkable reliability improvement for the studied PV MI. [ABSTRACT FROM AUTHOR]

In this paper, a hybrid switched-capacitor/switched-quasi-Z-source bidirectional dc–dc converter is proposed for electric vehicles (EVs) with hybrid energy sources, which has a wide voltage gain range in the bidirectional energy flows. Compared with the traditional quasi-Z-source bidirectional dc–dc converter, the proposed converter only changes the position of the main power switch and employs a switched-capacitor cell at the output of the high-voltage side. Therefore, the advantages of the wide voltage gain range and the lower voltage stresses across the power switches can be achieved. The operating principle, the voltage and current stresses across the power switches, and the comparisons with other converters are analyzed in detail. Furthermore, the parameter design of the main components, the dynamic modeling analysis, and the voltage control scheme are also presented. Finally, the experimental results obtained from a 400 W prototype validate the characteristics and the theoretical analysis of the proposed converter. [ABSTRACT FROM AUTHOR]

Modular multilevel-cascaded converter-based STATCOMs are scalable to higher voltages without requiring a step-up transformer with multiple windings and can be realized using a low switching frequency, giving lower harmonic content and, hence, a reduced filtering requirement. This paper presents a new injection technique to extend the operating ranges of modular multilevel-cascaded converters STATCOMs when used for negative sequence and reactive current compensation. A nonsinusoidal voltage or current containing a fundamental and its third-harmonic component is injected to achieve phase cluster voltage balance. This technique reduces the maximum dc-link voltage for the star configuration, and the maximum converter phase circulating current for the delta case, compared to applying only sinusoidal zero-sequence components for mitigating the same degree of load unbalance. The analysis is confirmed experimentally, showing that the third-harmonic injection can allow a significant improvement of STATCOM capability for simultaneous compensation of unbalanced load and reactive current. [ABSTRACT FROM AUTHOR]

Soft-switching inverters can achieve high efficiencies and low switchdv/dtanddi/dt, but often impose additional stress on the switches due to their resonant behavior. Multicell converters, on the other hand, can process high voltages by arranging the switches to share the stress. This paper proposes a buck–boost multicell soft-switching inverter with inherent cell voltage balancing. Both the current and voltage stresses are shared by the cells. Soft-switching conditions are achieved for all switching transitions without any need for auxiliary circuitry or clamps. A multiple-winding transformer transfers energy between the terminals and provides galvanic isolation. An analytical study and experimental results on a 1200-W prototype verify the operation of the inverter. [ABSTRACT FROM AUTHOR]

In this paper, a novel buck–boost converter with low electric stress on components and negative output voltage is proposed. The operational principle, steady-state analysis, and small-signal modeling of the proposed buck–boost converter in continuous conduction mode are presented. Comparisons among another five buck–boost converters and the proposed buck–boost converter are presented. It is found that the proposed converter's voltage gain is smaller than the other converters’ in step-down mode. Also, based upon the comparisons among the same kind and same number of components, the voltage and current stresses on the power switch of the proposed buck–boost converter are less than or equal to those of the comparative converters, and the voltage stress on the charge pump capacitor and the switching device power rating of the proposed buck–boost converter are always lower than those of other comparative converters. The efficiency of the proposed buck–boost converter is highest among those converters having the same number of elements. These advantages make component selection for the proposed converter much easier, and it can be used directly in applications needing a negative voltage source. Finally, simulation results and circuit experiments are given for validating the effectiveness of the proposed buck–boost converter. [ABSTRACT FROM AUTHOR]

In this paper, a sliding-mode control (SMC) strategy is proposed for three-phase grid-tiedLCL-filtered voltage source inverters in the natural frame. The SMC in the natural frame is based on controlling the sliding surface functions of phase-legsaandb. The sliding surface function of phase-legcis obtained from the sliding surface functions of phase-legsaandb. This eliminates the need for sensing capacitor voltage and grid current of phase-legc. The capacitor voltage references are generated by the proportional-resonant (PR) controllers which result in zero steady-state error in the grid current. The feasibility and performance of the proposed SMC strategy is investigated under steady-state, transient, unbalanced, and distorted grid conditions. Experimental results taken from a 9.8 kW system are provided to demonstrate the validity of the proposed SMC strategy. [ABSTRACT FROM AUTHOR]

Resonant converters with capacitive output filters are quite popular for their higher voltage gain and compact designs. But the majority of the converters underutilize the transformer as they are subjected to discontinuous currents. This discontinuous current possesses huge current ripples that produce huge core losses and aggravate the temperature rise of the transformer. This often leads to saturation of the transformer. This paper presents an LCC-T resonant dc–dc converter with a capacitive output filter operating all switches in the zero current switching (ZCS) switching mode and whose transformer current is a continuous sinusoidal with minimum stress on resonant tank components. This is achieved by bringing the transformer in series to a resonant inductor. The proposed converter is simulated in power simulation (PSIM) 11.0.1. A proof-of-concept model rated 288 W is designed and developed, and hardware results are presented as verification to theory. [ABSTRACT FROM AUTHOR]

This paper proposes a medium-/high-voltage high-power hybrid modular dc–dc converter to interconnect two different dc-voltage levels in medium-/high-voltage dc grids. The converter consists of half-bridge submodules (SMs) rated at a moderate voltage level, i.e., series connection of semiconductor devices is avoided while connecting two high dc-voltage levels. The proposed architecture provides self-balancing operation, i.e., unlike conventional modular converters, no need for capacitor voltage measurement, which enhances the system reliability and simplicity. Sequential charging/discharging of SMs capacitors is adopted in the proposed approach to ensure a self-balanced operation. The proposed architecture can provide a high conversion ratio as well as power transfer in both directions, i.e., bidirectional dc–dc converter. Detailed illustration of the proposed approach operational concept, design, and overall control system is presented. Simulation and experimental results are presented to show the viability of the proposed configuration and validate the claims. [ABSTRACT FROM AUTHOR]

Modular multilevel converter (MMC) has become a promising topology applied in medium/high-voltage applications due to its advantages. However, there are several challenges in the MMC, such as the appearance of harmonic circulating current. In this paper, a novel two-stage model predictive control (TSMPC) is proposed to suppress the harmonic circulating current. First, the mathematical model of the MMC is discretized to describe steady-state objectives including output currents, circulating currents, summation, and imbalance of capacitor voltages. Then, an optimal control options set consisting of inserted numbers is built by the front stage of TSMPC, while the inserted number applied to the MMC ultimately is selected from the above-mentioned set by the back stage of TSMPC. The proposed TSMPC can not only improve the control performance of harmonic circulating current but also ensure the overall control performance of the MMC system. In addition, a simplified rolling optimization method is proposed to reduce computation from the aspect of simplifying each control option prediction. An optimized search space method is also proposed to design the control options set to be evaluated from the aspect of ensuring the output current tracking and harmonic circulating current suppression. Finally, the effectiveness of the proposed method is validated by experiment results. [ABSTRACT FROM AUTHOR]

Generally, the small-signal model (SSM) of a modular multilevel converter (MMC) needs to consider the dynamics of equivalent arm capacitors, which inevitably increases the model order. In view of this, this paper proposes a general order-reducing approach based on balanced realization theory to reduce the SSM order of the MMC. In particular, two reduced-order models of an MMC-based HVdc grid are proposed with respect to different research objectives. To determine the potential minimum order of single MMC or MMC-HVdc grid, the criteria including singular values (SVs) of the frequency response, dynamic response in the time domain, and the largest absolute error of SVs are fully investigated. The simulation results of a four-terminal MMC-HVdc grid show that reduced-order models of the MMC and the HVdc grid can precisely predict both the stability and instability while the dynamic characteristics are retained. [ABSTRACT FROM AUTHOR]

For dc–ac modular multilevel converters (MMCs) in double-star configuration, this paper proposes a fast closed-loop control method based on optimized pulse patterns (OPPs). Thanks to the direct manipulation of the OPP switching instants, OPPs with discontinuous switching angles can be used, and the intrinsic cell capacitor voltage ripple is compensated for to preserve the OPPs’ superior harmonic performance. This model predictive pulse pattern controller is combined with a fast acting dead-beat circulating current controller and linked to an upper layer voltage balancing control scheme. The proposed control and modulation method is particularly suitable for medium voltage MMCs with a low number of cells. Despite operation at very low switching frequencies close to and including the fundamental frequency, a superior harmonic performance can be achieved. [ABSTRACT FROM AUTHOR]

The dc–dc modular multilevel converter (MMC), derived from the ac–dc MMC, is an attractive converter topology for interconnection of medium-/high-voltage dc grids. The dc–dc MMC generates an ac voltage component in each arm to drive an ac circulating current for maintaining the energy balance of its submodule capacitors. The power transfer capability of the dc–dc MMC and the amplitude of the ac circulating current are closely coupled with the available arm ac voltage headroom. As the voltage conversion ratio of the dc–dc MMC deviates from 0.5, the power transfer capability of the converter diminishes. This paper proposes an enhanced closed-loop control strategy, which increases the power transfer capability and at the same time reduces the ac circulating current of the dc–dc MMC. Performance and effectiveness of the proposed control strategy are demonstrated by simulation studies in the MATLAB/Simulink as well as experiments conducted on a laboratory prototype. [ABSTRACT FROM AUTHOR]

Discontinuous modulation applied to modular multilevel converters is an effective method for reducing the capacitor voltage ripples. In this paper, the discontinuous modulation is adapted and used in a motor drive application. For proper operation of the converter, a new energy controller is presented, which is suitable for operation with nonsinusoidal reference signals. Experimental results comparing the discontinuous modulation with other techniques operating at low motor speeds are shown. The results demonstrate the effectiveness of the discontinuous modulation on reducing capacitor voltage ripples and power losses. [ABSTRACT FROM AUTHOR]

Modular multilevel converters (MMCs) have been widely used in recent years due to their superior advantages in medium/high-voltage applications. The finite control set model predictive control (FCS-MPC) has shown high dynamic responses for the control of the MMC. However, with the existing FCS-MPC algorithms, the steady-state performances are degraded due to the irregular pulse patterns, especially under unbalanced grid conditions. In this paper, based on the discrete state-space model of the MMC, a modulated MPC (M2PC) algorithm is proposed to overcome the aforementioned drawback of the FCS-MPC. Compared to FCS-MPC algorithms, the M2PC accurately calculates and tracks the reference circulating current and adopts an effective modulation method, and, in turn, the proposed M2PC can obtain enhanced steady-state ac-side/circulating currents control performances under unbalanced grid conditions, with the high dynamic-state performances of the conventional FCS-MPC algorithms reserved. Experimental results regarding one typical FCS-MPC algorithm and the proposed M2PC algorithm are comparatively evaluated in detail for the steady/dynamic-state performances and pulse patterns by a downscaled prototype. The effectiveness and feasibility of the proposed M2PC are clearly validated by the experimental results. [ABSTRACT FROM AUTHOR]

This paper presents a modified modular multilevel converter with the three-terminal middle-cells inserted between arms and ac-side for medium voltage applications. It is intended to reduce the submodule capacitor voltage ripples by controlling the high-frequency powers flowing among arm branches for low-frequency output operations without common-mode voltage injected in ac-side. Due to the physical connection among the upper arm, the lower arm and ac-side, the middle-cell can be regarded as the excess degree of freedom to modify the dc-side and ac-side characteristics. Therefore, the common-mode voltage in ac-side can be eliminated by the inverse common-mode voltage produced by the middle-cell in ac-side. Moreover, owing to the unique structure of the middle-cell, the middle-cell capacitor voltage also results in a small ripple due to the high-frequency current flowing into it by proper control. The operation principle and control strategy of the middle-cell has been proposed in detail. Simulation and experimental results have verified the effectiveness of the proposed topology. [ABSTRACT FROM AUTHOR]

Capacitorless (CL) low-dropout regulators (LDO) have gained significant research interest for point-of-load voltage regulation without off-chip capacitors. While analog CL-LDOs can deliver superior power supply rejection (PSR), digital CL-LDOs are more scalable and efficient. To achieve the advantages of both types, this paper presents a digital CL-LDO with an analog PSR enhancer, delivering strong PSR without compromising scalability and efficiency. Load regulation is performed by an asynchronous digital feedback controller for fast transient response and scalable load drivability. PSR is achieved by a load-insensitive wide-bandwidth analog controller. A prototype chip of the analog-assisted digital CL-LDO is fabricated in a 130-nm CMOS process with an active area of 0.0645 mm2 , supporting load current up to 50 mA at nominal 1-V input and 0.8-V output. The measured PSR is better than –20 dB for frequencies up to 10 MHz, and the measured current efficiency peaks at 99.3%, with average current efficiency of 96.7% across 50× load range. The measured transient response to a full load step, with two values of load capacitance (100 pF and 10 nF), demonstrates the LDO's stable operation over a wide range of load resistance and capacitance. [ABSTRACT FROM AUTHOR]

Traditional control strategy for a power decoupling circuit typically involves a dedicate ripple power control loop, which makes it hard to achieve satisfied transient performance. Meanwhile, traditional single-phase ac–dc converters achieve active power decoupling function with extra power switches, which inevitably increased the cost of the system. In this paper, a controller based on automatic power decoupling concept is proposed for a dependent power decoupling circuit with no extra switches. Compared with the existing methods, the system controlled by the proposed controller has superior transient performance with simplified controller's structure. The controller parameter's design procedures will also be illustrated step by step with the help of the bode diagram. In comparison with traditional control methods, simulations and experiments verify the feasibility of the proposed control methods on the dependent power decoupling circuit. [ABSTRACT FROM AUTHOR]

In this paper, a quantitative evaluation of the flux-switching permanent magnet (FSPM) machine system reliability is carried out based on the Markov model. The evaluation model of the permanent magnet machine system consists of six main functional components and their dominant failure modes are counted. The performance of the FSPM machine system under each fault is simulated and compared with the reliability criteria to judge the reliability state of the machine system. The Markov model is used to calculate the FSPM machine system reliability. The influence of machine phase number, stator core topology, and hybrid excitation method on the machine system reliability is investigated. The experiments are presented to validate the accuracy of fault simulation. The reliability analysis results lay the foundation for the reliability design of an FSPM machine. [ABSTRACT FROM AUTHOR]

For a single-inductor dual-output (SIDO) dc–dc converter operating in continuous conduction mode (CCM), load variation of one output will affect the voltage of the other output, i.e., there exists cross regulation between its two outputs. To suppress the cross regulation of the SIDO dc–dc converter operating in CCM, a novel ripple based control technique, called capacitor current ripple (CCR) control technique, is proposed in this paper. The operation principle of the SIDO CCM buck converter and the proposed CCR control technique are presented. The small signal model of the CCR-controlled SIDO CCM buck converter is established by the state space averaging method. Bode plots based on small signal model show that the proposed CCR-controlled SIDO CCM buck converter significantly reduces cross regulation and improves the transient performance compared with the peak current mode controlled SIDO CCM buck converter. In addition, the effect of the variation of loads on the stability of the proposed CCR-controlled SIDO CCM buck converter is analyzed by eigenvalues analysis. Finally, experimental results are provided to verify the analysis results. [ABSTRACT FROM AUTHOR]

This paper presents an interleaved converter that benefits the coupled inductor and built-in transformer voltage multiplier cell (VMC). Compared with the other converters with only a built-in transformer or only a coupled inductor, the combination of these techniques gives an extra degree of freedom to increase the voltage gain. The VMC is composed of the windings of the built-in transformer and coupled inductors, capacitors, and diodes. The voltage stress of MOSFETs is clamped at low values and can be controlled via the turns ratio of the built-in transformer and coupled inductor that increases the design flexibility. Moreover, the energy of the leakage inductances, is recycled to the clamp capacitors which avoids high voltage spikes across MOSFETs. In addition, the current falling rate of the diodes is controlled by the leakage inductances, and the reverse current recovery problem is alleviated. Meanwhile, due to the interleaved structure of the proposed converter, the input current ripple is minimized and the current stress of the power devices is decreased. All of these factors improve the efficiency of the proposed converter in high-current and high-voltage applications. The principle operation and steady-state analysis is given to explore the advantages of the proposed converter. Finally, a 1.3-kW prototype with 50–600 V voltage conversion is built to demonstrate the effectiveness of the proposed converter. [ABSTRACT FROM AUTHOR]

The modular multilevel converter (MMC) is a promising topology for high-power drive applications. However, large voltage fluctuations can be produced in the floating capacitors when the machine operates with high stator currents at low rotational speed. To compensate these oscillations, relatively large mitigation currents are required to keep the capacitor voltages within an acceptable range. In this paper, a new integrated control scheme is discussed to regulate the voltage fluctuations. The strategy is based on closed-loop vector-control of the voltage fluctuations, maintaining them inside a predefined threshold. The proposed control system is also augmented using flux-weakening operation of the machine at low rotational speeds. An experimental prototype composed of 18 power cells, feeding a vector-controlled induction machine in the whole speed range, is used to validate the effectiveness and feasibility of the proposed control strategies. [ABSTRACT FROM AUTHOR]

In this paper, a new voltage balancing strategy based on improved carrier-phase-shifted pulsewidth modulation (CPS-PWM) scheme and fundamental frequency sorting algorithm (FFSA) is proposed. FFSA is a salient method which sorts the capacitor voltages at fundamental frequency and utilizes the different charging ability of driving signals to converge the capacitor voltages. Unfortunately, under the CPS-PWM scheme with high carrier frequency, 250 Hz or higher, FFSA cannot bring the capacitor voltage to the nominal value once the unbalance occurs, because there is a little difference remaining in the driving signal's charging ability. To avoid this disadvantage, an improved CPS-PWM scheme is proposed. In this scheme, driving signals with proper phase angle differences are selected to be dealt with logic and/or processing according to the sorting result of FFSA. With the logic processing, new driving signals with obviously different charging abilities are synthesized, which are assigned to the corresponding unbalanced submodules to achieve the balance of capacitor voltages. And several regions for logic processing are set up, where the proper phase angle difference is selected for each region in order to both guarantee the convergence speed and avoid the voltage oscillations. With the proposed scheme, FFSA can be adopted under CPS-PWM with high carrier frequency. Moreover, the merits of FFSA are inherited, such as the reduced computational burden and the elimination of arm current detection. Performance and effectiveness of the proposed strategy are validated by both simulations and experimental results. [ABSTRACT FROM AUTHOR]

Among the various topologies proposed in this literature, the modular multilevel converter (MMC) is considered the next generation of converters for medium- and high-voltage applications. This paper presents a comparison between two variants of MMCs for STATCOM applications: The double-star chopper cell-MMC and the single-delta bridge cell-MMC. These converter topologies are compared and benchmarked during positive and negative sequence compensation. The comparisons are supported by analytical results regarding minimum effective dc-link voltage, number of cells, current rating, energy storage requirements, and operation during unbalanced conditions. The dynamic behavior, power losses, and cost of both solutions are evaluated through simulation model of a 15 mega volt-ampère (MVA) MMC STATCOM. [ABSTRACT FROM AUTHOR]

The modular multilevel converter (MMC) is very attractive in a high-voltage dc (HVdc) transmission system due to its high modularity and scalability. It is also a promising candidate for medium-voltage applications. An MMC has many power devices that lead to a relatively low reliability based only on a direct failure rate calculation. The reliability of an MMC can be improved by redundant designs. Lots of redundant designs and strategies have been proposed in recent years, while their reliability improvements are hardly quantified in existing literature. In practice, reliability improvement with constraint costs is a challenge. In view of these, this paper proposes a reliability and cost assessment scheme for MMC redundant designs and strategies. Reliability and cost are quantified for comparison purposes. A medium-voltage application is used to demonstrate the reliability and cost assessment scheme. The reliability analysis is based on a combinatorial model and the Poisson process model. The cost analysis focuses on capital cost and power loss cost. The proposed reliability and cost analysis scheme provides a guideline for MMC redundant design and redundant strategy selection. [ABSTRACT FROM AUTHOR]

This paper proposes a delta-channel modular multilevel converter (MMC). It aims to overcome the issues of the conventional MMC during zero/low fundamental frequency operation. The proposed converter is characterized by the cross connection of both the upper and the lower three arms through two sets of delta-channel branches. These delta-channel branches timely redistribute power among three phase legs, leading to the minimized submodule capacitor voltage fluctuations, even at zero/low fundamental frequency operation. The inner power balancing through physical channels makes the converter inject no common-mode voltage. A 4160-V, 1-MW simulation model is performed in MATLAB/SIMULINK, and a 208-V, 5-kW experimental setup is constructed in the laboratory. Both the simulation and experimental results verify the feasibility of the proposal. [ABSTRACT FROM AUTHOR]

Irreversible electroporation (IRE) for disinfection applications involve exposing the specimen cell membrane to a pulsed electric field in order to kill harmful microorganisms. High-voltage (HV) pulses, of relatively short durations in range of few microseconds, are generated across the sample chamber. The HV pulse specifications such as voltage magnitude, waveform, repetition rate, and duration differ according to the conditions of the sample being processed. This paper proposes a new step-up power electronic converter topology for generating the required HV pulses from a relatively low input voltage. The converter consists of two main stages; the first stage is responsible for boosting the input voltage to the desired level using input-parallel/output-series connected dc/dc modules, while the second stage forms the required HV pulses with the proper magnitude, duration, and repetition rate using modular multilevel converter submodules. The proposed topology is able to produce the HV pulses with controlled voltage and current stresses across the employed semiconductor switches and diodes; hence, it can be implemented with the market-available semiconductor technology. Mathematical analysis of the proposed topology is developed, and MATLAB/Simulink simulation results explore operational conditions. Experimental results from a scaled-down prototype validate the functionality of the proposed system. [ABSTRACT FROM AUTHOR]

Maximum power point tracking (MPPT) is a basic and indispensable requirement for photovoltaic (PV) systems under normal irradiance and under partial shading conditions (PSCs). Although the simple perturb and observe algorithm is quite effective under normal conditions, it fails to recognize the global maximum operating point (GMOP) under the PSC. This paper explores the fast determination of GMOP under PSCs using a proposed high-speed MPPT module, which operates in conjunction with a boost converter. With this high-speed MPPT module, the tracking time of the MPPT controller is considerably reduced. The tracking accuracy and efficiency are significantly better than other techniques in the literature. The concept is first implemented on a PV system simulation model and the results are further validated with a prototype implementation of a 300 W PV-fed boost converter operated under various PSCs. The enthusiastic results were finally verified in an installation of a 2.5 kW PV system. The results demonstrate that the proposed high-speed MPPT controller outperforms both duty sweep and particle swarm optimization based MPPTs. [ABSTRACT FROM AUTHOR]

This paper presents a design methodology and its experimental validation for the input-admittance passivity compliance of LCL grid-connected converters. The designs of the LCL filter parameters and the discrete controller are addressed systematically, and suitable design guidelines are provided. The controller design is developed in the Z-domain, with capacitor-voltage-based active damping used as a degree of freedom to compensate for system delay effects. The role of resistive components in the circuit, which have inherent dissipative properties, is also discussed. As an outcome of the design, a passive input-admittance shaping is obtained. The theoretical development is further verified in a low-scale prototype supplied from a controllable grid simulator. For the sake of generality, different combinations of resonant to sampling frequency are tested. Experimental results fully prove the input-admittance passivity compliance. [ABSTRACT FROM AUTHOR]

The dc-link capacitors are important components that tend to be one of the weakest part of power converters. Thus, it is necessary to monitor the aging parameters of dc-link capacitors in valuable power electronic systems. This paper proposes a simple yet effective variable electrical network (VEN) condition monitoring method for dc-link capacitors in three-phase pulsewidth modulation (PWM) ac–dc–ac power converters. The capacitance (C) and equivalent series resistance of dc-link capacitors are estimated through the designed VEN unit during the discharging process. This VEN method does not need the current sensor or injecting signals into the control loop. The above property is favorable for the hardware and controller design. Besides, the designed monitoring circuit can be an external unit or a built-in unit which offers a flexible solution for electrical devices. When the designed VEN is used as an external unit, neither the hardware design nor the programs in the controller needs to change, which is practical and economic for electrical devices in use. Experiments are carried out in a 55 kW ac–dc–ac inverter with different capacitors. The experiment results prove the method to be effective and accurate. [ABSTRACT FROM AUTHOR]

In this paper, a nonisolated high step-down converter is proposed. Energy transfer capacitor and built-in transformer are employed to achieve a very high step-down conversion ratio. Due to the interleaved technique, small values of output inductance can be used, leading to a fast transient response. Furthermore, the use of a coupled inductor reduces inductor current ripples, which implies lower losses. Two main switches and two synchronous rectifiers are used in the converter and all can achieve zero-voltage-switching. As no floating switches are employed, grounded gate drivers and boost strap drivers can be used, avoiding the use of complex isolated gate drivers. In addition, if the switches are shorted, the high input voltage does not appear at the output; thus, the load is protected. A 48 V/1 V 30 A prototype was built, and experimental results are provided to verify the performance of the converter. [ABSTRACT FROM AUTHOR]

This paper presents an improved asymmetric half-bridge converter (AHBC) to enhance the output performance of a segmented-stator hybrid-excitation switched reluctance motor (SSHE-SRM) drive. Differences from conventional AHBC include an additional boost capacitor, a power switch, and two diodes added between the dc-bus and the AHBC. The static torque characteristic of a 12/8 SSHE-SRM is briefly analyzed and compared with a conventional SRM (CSRM). Based on the magnetic characteristic, the SSHE-SRM appears to have higher torque production capability. The improved AHBC is employed in order to increase the dc-bus voltage under dynamic operation. Higher voltage can be applied to phase windings and faster excitation and demagnetization currents can be obtained owing to the addition of capacitor voltage. Detailed simulations of the SSHE-SRM drive with the improved AHBC are carried out as well as compared with conventional AHBC. Finally, a 12/8 SSHE-SRM is prototyped. The SSHE-SRM drive based on the improved AHBC and conventional AHBC are experimentally tested. The measured results of static magnetic characteristic and dynamic performances are presented to validate the analysis and effectiveness of the novel converter. [ABSTRACT FROM AUTHOR]

Conventional two-level as well as multilevel voltage-source-inverter topologies with a hexagonal voltage-space vector structure generate low-order harmonics in the machine terminal voltages when operated beyond the linear modulation range in variable speed drive application. Progressing from hexagonal to a higher sided polygonal voltage-space-vector structure (VSVS) suppresses significant low-order harmonics throughout the modulation range. In addition, the linear modulation range will also be enhanced very near to the base speed. In this paper, for the first time, the generation of a multilevel 24-sided VSVS using a single dc source for induction-motor drives is proposed. A cascaded topology with a dc-source-fed flying-capacitor inverter and two low-voltage capacitor-fed H-bridge cells forms the power circuit. The features and advantages of the proposed scheme are validated through experimental results and discussions. [ABSTRACT FROM AUTHOR]

In previous research, the variable conductance of a parallel active power filter has been used for antiparallel resonance with parameter variations in power systems. Its disadvantages are many sensors, complicated harmonic detection, and complexity of the algorithm for successful accomplishment in antiparallel resonance. In order to eliminate such drawbacks, this paper presents the parallel active power filter based on source current detection for antiparallel resonance with robustness to parameter variations for power factor correction using capacitor banks. The proposed method employs only single harmonic detector and an open-loop shaping design for robustness to variations of source impedance and a sudden change of capacitor bank values for power factor correction. The proposed antiparallel resonance controller can be readily applied to both large-scale and laboratory-scale power systems without any change. The large-scale simulation and the laboratory-scale experiment results confirm the validity, the accuracy, and good performance for antiparallel resonance, harmonic suppression, and robustness to parameter variations in power systems. [ABSTRACT FROM AUTHOR]

In this paper, new techniques are presented to improve the performance of the optimal switching vector model predictive control. A well-defined analytic technique is proposed for the real-time adjustment of dynamic weighting factors, as well as a new objective function formulation. These techniques provide a dynamic controller behavior, automatically adapted to distinct operating points. This ensures better steady-state performance in different conditions while improving simultaneously the dynamic response. The proposed controller presents a lower computational load than the conventional formulation and its design requires less extensive testing. General guidelines are presented to guide the user in the controller design. Simulation and experimental results are presented, demonstrating the advantages and superior performance of the proposed controller. [ABSTRACT FROM AUTHOR]

The modular multilevel converter (MMC) has become the most promising converter topology for medium- and high-power applications. In this paper, a sliding mode control (SMC) based method is proposed for the MMC. Based on analysis of the system dynamics under the proposed control method, relations among control parameters and their validity conditions are obtained, which provide a guidance for systematic controller design. Compared with the conventional proportional-integral based method, the proposed SMC-based method provides comparable steady state performance and faster dynamic responses, without compromising the computational effort or requirement for precise system model. Simulation studies in the PSCAD/EMTDC software environment are carried out to validate the performance and effectiveness of the proposed control method in the context of an HVdc transmission system. A laboratory prototype is also developed to experimentally validate the proposed control method. [ABSTRACT FROM AUTHOR]

It is difficult for a single converter to handle the high voltages involved in dc–dc conversion with a high-voltage input bus. Input-series–output-parallel (ISOP) technology can be used to solve this problem. In this paper, an input voltage sharing control scheme based on peak current (IVSPC) control to guarantee power balance between the modules of the ISOP system is studied. Owing to the peak current control, the output voltage of the system has a good ability to suppress input bus perturbations, and it exhibits good dynamic characteristics even when the input voltage changes significantly with a high slope. The IVSPC control method has two kinds of loops: a common output voltage regulation (OVR) loop and individual input voltage sharing (IVS) loops. The OVR loop provides the same current reference component for all modules, whereas the IVS loops provide different components. The peak current reference signal for each module is the sum of the reference components from the OVR and IVS loops. The performance of the IVSPC control scheme is verified using an ISOP-connected prototype consisting of two flyback converters. [ABSTRACT FROM AUTHOR]

For the effective operation of a dynamic voltage restorer (DVR), a control strategy plays a significant role. This paper presents an enhanced control strategy for DVR using dual role cascaded delay signal cancellation (CDSC)-based dual vector control (DVC) under unbalanced and distorted grid conditions. Based on the numerical analysis, it is found that the CDSC prefilter is a promising solution when grid voltage is distorted by symmetric, asymmetric harmonics, and unbalanced sag. Mainly, the CDSC prefilter extracts instantaneous symmetrical components of the grid voltage required for voltage sags detection and generation of fundamental component of reference voltage for the DVR. A CDSC-based DVC algorithm with inductor current and capacitor voltage feedback is implemented in a synchronous reference frame, which tracks the fundamental DVR reference voltages. An extractor based on the modified CDSC strategy is designed to extract harmonics from load voltage during distorted grid conditions. These extracted harmonic components (nonfundamental) are added in phase opposition with fundamental component and fed to pulse width modulation block to generate reference voltages. Experimental studies are conducted on scaled down (100 V, 0.5 kVA) laboratory prototype DVR to verify the effectiveness of the proposed control algorithm under unbalanced and distorted grid conditions. [ABSTRACT FROM AUTHOR]

In this paper, a novel integrated interleaved dual-mode time-sharing inverter (IIDMI) is proposed for grid-tied transformerless photovoltaic (PV) applications. While the dual-mode time-sharing conversion technique ensures minimum losses, the IIDMI also retains the advantages of interleaved topologies, such as low total harmonic distortion of the ac current with reduced filtering requirements, increased power density, and reduced current and thermal stresses of power devices. The leakage current problem, which is a main concern with the transformerless PV inverters, is solved by increasing the frequency of the main side band of the common-mode voltage above the resonance frequency of the common-mode impedance, while avoiding high switching losses. The current control, especially at transitions between the buck and the boost modes of operation, is highly improved by utilizing a fast-response deadbeat control scheme. The working principles of the IIDMI are explained in detail, and a 2.2-kW experimental prototype is implemented to confirm the theoretical achievements. [ABSTRACT FROM AUTHOR]

In this paper, a family of automatic interleaved Dickson switched-capacitor converters (AIDSCC) and its zero-voltage switching (ZVS) resonant configuration are proposed. Different from the traditional Dickson switched-capacitor converter, the AIDSCC has symmetrical configuration with the features of automatic interleaved input current, small output voltage ripple, and lower peak capacitor voltage stress. To improve the line regulation capability, one small resonant inductor is inserted and two bulky capacitor banks are replaced by two much smaller resonant capacitors, forming the resonant AIDSCC. The transistors are ZVS turned on and diodes are zero-current switching turned off by operating above the resonance. With frequency modulation within a reasonable range, the voltage-gain range of the resonant AIDSCC is expanded significantly, while sacrificing the maximum efficiency due to the higher conduction loss. A 3X AIDSCC and a 3X resonant AIDSCC below 140 W were built to verify the analysis. [ABSTRACT FROM AUTHOR]

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

This paper presents a novel single-phase multicell converter for ac–dc power conversion, which is formed by a series connection of several full-bridge converter stages through passive components. The proposed topology employs a simple control scheme based on the carrier-based sinusoidal pulsewidth modulation technique. Detailed design procedure of the passive filter components are analyzed and discussed. An efficient optimization method based on a differential evolution algorithm is utilized to optimize the filter parameters. Considering the filter structure, active damping is introduced in the control scheme to improve the stability of the overall system, which is later verified by experiments. The systematic design approach of the controller parameter is also highlighted, focusing a specific set of goals. Experimental results for a 1-kW prototype are presented to further validate the concept. [ABSTRACT FROM AUTHOR]

Charging batteries of light electric vehicles require chargers with high efficiency and a high power factor. To meet this need, this paper presents a bridgeless single-power-conversion battery charger composed of an isolated step-up ac–dc converter with a series-resonance circuit. The bridgeless configuration reduces the conduction losses associated with the input diode rectifier, and the series-resonance circuit reduces the reverse-recovery losses of the output diodes by providing zero-current switching. In addition, direct and series-resonance current injections enable bidirectional core excitation by the transformer, thereby allowing high-power capability. The control algorithm derived from feedback linearization is also developed, which allows the proposed charger to correct the power factor and regulate the output power in a single-stage power conversion. This simple circuit structure leads to high efficiency and a high power factor. The theoretical concepts of the proposed charger are verified experimentally using a 1.7-kW prototype. [ABSTRACT FROM AUTHOR]

This paper investigates dc-link capacitor optimization for three-phase photovoltaic-based microinverters. This concept minimizes the storage capacitance by allowing greater voltage ripple on the dc link. Therefore, the microinverter reliability can be significantly increased by replacing electrolytic capacitors with film capacitors. However, this intentionally increased voltage ripple can introduce harmonic distortion on the output current of the inverter stage if it is not mitigated by the dc-link voltage controller. For this purpose, a robust and accurate dc-link voltage control is proposed to filter this ripple while regulating the dc-link voltage without using any additional circuit components. The experimental results on a 400-W three-phase half-bridge microinverter prototype validate the theoretical analysis of the dc-link capacitor optimization and show that a significant reduction of the dc-link capacitor requirement can be achieved. The proposed high-accuracy dc-link voltage controller is also implemented on this prototype to demonstrate very low harmonic distortion of the inverter output current while tightly regulating the dc-link voltage even during transients. [ABSTRACT FROM AUTHOR]

Usually, the parallel-compensated inductive power transfer (IPT) topology fed by a current-source inverter is controlled through variable switching frequency and fixed 50% duty cycle method. This enables the system to operate at resonance frequency, which drifts due to load and other parameter variations. Owing to this control constraint, the load requirements are fulfilled by adding extra dc–dc chopper at the output. This paper presents a new control technique for a parallel–series/series IPT network, fed from a full-bridge current-source inverter to meet the load demand directly by an inverter. Therefore, the extra chopper stage at the output side of the converter is eliminated. The control goals are achieved through a two-loop control method, where the inner input current loop controls the source current and the outer output current loop meets the load requirements. The detailed steady-state operation, converter design, small-signal modeling, and control are reported, and experimental results obtained from a 1.6-kW lab prototype are included to verify the mathematical analysis. [ABSTRACT FROM AUTHOR]

Conventional power supply systems for xenon lamps have only limited applicability in sintering, because sintering needs to drive the lamp itself as well as enable instantaneous and strong discharge of voltage and current for generating intense light. This implies that, for sintering applications, a method should be developed that would enable instantaneous and strong discharge of energy. In this paper, we propose a new xenon lamp sintering system with an additional capacitor charger and bank. The proposed system features three power supplies. Two power supplies, called the trigger and the simmer, ionize gaseous xenon using a 23-kV trigger pulse output and sustain the ionized xenon gas using a 2.5-kW simmer power supply. The used trigger is also specially designed to conduct high current through its transformer, and it makes the proposed system an outstanding high voltage blocking capability. Another 36-kW power supply charges a 130-mF capacitor bank with a high-efficiency resonant converter. In addition, some components such as the simmer blocking diode and the trigger output capacitor are introduced, because combining different power supplies causes operational problems. These components are analyzed with some circuits that show its features, and finally, the validity of the suggested system was confirmed in two steps. First, the simmer power supply and the capacitor charger were tested for the rated operating performance by using a resistive load condition. As a result, the rated operation of the simmer power supply was confirmed under the 2.5-kW output condition, and the efficiency of the capacitor charger was found to be greater than 96% at the rated 36-kW rated load condition. In addition, a pulse discharge current of 900 A was also observed with the equivalent resistor load through a pulsed discharge experiment of the capacitor bank, which was charged at 1500 V. The trigger power supply, whose equivalent resistive load was difficult to realize, was experimented directly using the real xenon lamp to check the stable trigger operation of the xenon lamp at its 23-kV output pulse voltage. After the verification using the resistive load condition, the real operation and performance of the combined xenon lamp power supply system that includes three kinds of power supplies were finally tested and verified by using the actual xenon lamp as a total system. [ABSTRACT FROM AUTHOR]

The conventional design of voltage-source power converters is based on a two-level half-bridge configuration and the selection of power devices designed to meet the full application specifications (voltage, current, etc.). This leads to the need to design and optimize a large number of different devices and their ancillary circuitry and prevents taking advantage from scale economies. This paper proposes a paradigm shift in the design of power converters through the use of a novel configurable device consisting on a matrix arrangement of highly optimized switching cells at a single voltage class. Each switching cell consists of a controlled switch with antiparallel diode together with a self-powered gate driver. By properly interconnecting the switching cells, the switching-cell array (SCA) can be configured as a multilevel active-clamped leg with a different number of levels. Thus, the SCA presents adjustable voltage and current ratings, according to the selected configuration. For maximum compactness, the SCA can be conceived to be only configurable by the device manufacturer upon the customer needs. For minimum cost, it can also be conceived to be configurable by the customer, leading to field-configurable SCAs. Experimental results of a 6 × 3 field-configurable SCA are provided to illustrate and validate this design approach. [ABSTRACT FROM AUTHOR]

There are technical challenges when the grid-connected current source converter operates under unbalanced grid voltage conditions. The negative sequence component of the unbalanced grid voltage would result in the low-frequency ripple at dc side, as well as current harmonics at ac side. It has an adverse impact on the system operation. In order to solve the problem, the system mathematical model is established in this paper. The limitation of the conventional control strategy is clearly clarified. And then, the improved control strategy is discussed from the viewpoint of constant instantaneous active power. In order to further enhance the system performance, a new control strategy is proposed. Instead of the complicated instantaneous power theory, the proposed solution is a direct control strategy. Both the low-frequency dc-side ripple and ac-side current harmonics can be significantly reduced with a simple control structure, due to the direct control concept. Finally, the comparison evaluation of the conventional and proposed control strategies is carried out. The experimental results verify the effectiveness of the proposed solution. [ABSTRACT FROM AUTHOR]

A new class of impedance networks is proposed in this paper. The proposed coupled-inductors-based impedance cells, called the series and the tapped switched-coupled-inductors, are employed within the (quasi) switched boost networks. The achieved impedance networks based on the proposed cells offer very high conversion gains with less-than-unity turn ratios (n < 1), which simplifies the realization of the magnetic element and at the same time reduces the number and size of passive components. The high boosting capability is achieved with small shoot-through durations that bring some additional advantages, such as low ratings of switching devices. The circuit analysis and operation concepts as well as a design procedure for the components of the proposed impedance networks are presented. Theoretical achievements are confirmed through experiments on a 220 W dc–dc converter laboratory setup. [ABSTRACT FROM AUTHOR]