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Four-level hybrid-clamped inverter is a newly proposed topology that can operate under a wide voltage range without switches connected in series. However, when it is applied in medium voltage high power conversions, the flying capacitors in each phase will occupy a huge volume and a high switching frequency is required to restrain the voltage ripples. In order to overcome this drawback, a four-level active neutral-point clamped inverter is discussed in this paper, which consists of only six switches and no diodes or flying capacitors are required. In order to balance the neutral-point voltages under the full power factor and modulation index range, a capacitor voltage balance method based on carrier-overlapped pulsewidth modulation is proposed in this paper. The upper and lower dc-link capacitor voltages are balanced by zero-sequence voltage injection and the central dc-link capacitor voltage is balanced by adjusting the duty cycles of switching signals slightly. Simulation and experimental results are presented to confirm the validity of this method. [ABSTRACT FROM AUTHOR]

This paper investigates the dependence of the supercapacitor Peukert constant on its terminal voltage, aging condition, and operating temperature. Recent studies show that the charge delivered by a supercapacitor during a constant current discharge process increases when the discharge current decreases if the discharge current is above a certain threshold, i.e., Peukert's law applies. By conducting extensive experiments using three supercapacitor samples with different rated capacitances from different manufacturers, this paper reveals that the Peukert constant increases when the initial voltage of the constant current discharge process is lower, the supercapacitor is more heavily aged, or the operating temperature is lower. The physical mechanisms accounting for the Peukert constant dependence are illustrated by analyzing an $RC$ ladder circuit model. When the supercapacitor terminal voltage is higher, the aging condition is lighter, or the operating temperature is higher, more charge is stored in the supercapacitor. Consequently, when the same discharge current is applied, the discharge time is longer and the branch capacitors are more deeply discharged. Therefore, the relaxation effects of the slow branches are reduced and the supercapacitor behaves more like a single capacitor rather than a distributed capacitor network, which ultimately leads to a lower Peukert constant. [ABSTRACT FROM AUTHOR]

In this paper, a new non-isolated two-input single-output dc–dc converter with high voltage gain is proposed. In the proposed converter, there are two three-winding coupled inductors used to achieve a high voltage gain and ripple-free input currents. The proposed converter has two switches, and their control pulses are the same as the control pulses of the two-phase interleaved converters with a phase shift equal to $\text{180}^{\circ} $. The voltage stresses of switches and diodes are reduced and are always lower than the high output voltage. The proposed converter is extendable to a four-input single-output converter in which the switches have the control pulses the same as those in four-phase converters with phase shifts equal to $\text{90}^{\circ} $. In this paper, the proposed topology is analyzed in all operating modes, and the values of current and voltage stresses of all switches and diodes, voltage gain, and required conditions for input current ripple cancelation are calculated during a switching period. Finally, the accuracy performance of the proposed converter is reconfirmed through experimental results for 225- and 298-W prototypes. [ABSTRACT FROM AUTHOR]

This article develops a series of improved Z-source dc–dc converters to realize additional voltage pumping and high power density through two propositions. Proposition 1 develops two improved positive- and negative-connected Z-source dc–dc converters (IPZSC and INZSC), using the same number of components as in the existing voltage pumping Z-source converter. Based on Proposition 1, Proposition 2 proposes four novel embedded Z-source dc–dc converters (EZSCs) by placing the source in a specifically designed position, which realizes lower voltage stresses across capacitors. Various technical aspects of the proposed EZSCs, including operations, power losses, and small signal stability analyses are detailed in this paper. Besides, comparisons between the proposed series of improved Z-source dc–dc converters and other existing Z-source dc–dc converters are thoroughly made to demonstrate the better performance of the EZSCs. Finally, experiments are conducted to well validate the effectiveness and superiority of the proposed converter circuits. [ABSTRACT FROM AUTHOR]

This article proposes a novel bidirectional isolated dc–dc converter with high voltage gain and wide input voltage, which can be applied to bidirectional power conversion systems. The proposed topology is composed of a bidirectional buck-boost converter and a forward-flyback converter; it has the advantage of higher voltage gain and has continuous current characteristic of the low-side port in step-up and step-down mode. In addition, the proposed topology also has the function of leakage inductance energy recovery, which can improve the efficiency of the converter, reduce the voltage surges on switches, and have the characteristics of zero voltage switching on certain switches. Finally, this paper implements a 500-W bidirectional dc–dc converter to verify the feasibility of the proposed topology. The low-side voltage of the proposed topology is 24, 48, and 55 V; the maximum efficiency in step-up mode are 94.2%, 95.6% and 96.9%, and the maximum efficiency are 92.6%, 94.2% and 94.5% in the step-down mode, respectively. [ABSTRACT FROM AUTHOR]

In data center and telecommunication power supplies, the front-end dc–dc stage is required to operate with a wide input voltage range to provide hold-up time when ac input fails. Conventional LLC converter serving as the dc–dc stage is not suitable for this requirement, as the normal operation efficiency (at 400 V input) will be penalized once the converter is designed to achieve high peak gain (wide input voltage range). This paper examined the operation of the LCLC converter and revealed that the LCLC converter could be essentially equivalent to a set of LLC converters with different magnetizing inductors that are automatically adjusted for different input voltages. In nominal 400 V input operation, the LCLC converter behaves like an LLC converter with large magnetizing inductor, thus the resonant current is small. In the hold-up period, when the input voltage reduces, the equivalent magnetizing inductor will reduce together with switching frequency reducing, thus the converter achieves high peak gain. In this paper, a new design methodology is also proposed to achieve optimal utilization of the two resonant capacitors for high power application. To verify the effectiveness of the LCLC converter for hold-up operation, comprehensive analysis has been conducted; a detailed step by step design example based on capacitor voltage stress is introduced; an experimental LCLC prototype optimized at 400 V, with input voltage range of 250–400 V and 12 V/500 W as output has been presented. [ABSTRACT FROM AUTHOR]

In this paper, a new structure for a nonisolated boost dc–dc converter is proposed. The proposed converter generates higher voltage gain than some conventional nonisolated boost dc–dc converters. In this paper, the voltage and current equations of the elements and voltage gain in continuous conduction mode and discontinuous conduction mode are extracted. Then, the critical inductance converter is extracted and the current stresses in the switches are calculated. To achieve high voltage gain, a generalized structure based on the proposed structure generates for dc–dc converters. Meanwhile, the root mean square current relations of devices are obtained for an extended structure. Finally, the results of PSCAD/EMTDC software and laboratory prototype are used to reconfirm theoretical concept. [ABSTRACT FROM AUTHOR]

This paper presents a novel six-pulse low-frequency (LF) fluctuating high-voltage dc-bus-based power system architecture for fuel cell vehicles (FCVs) application. A novel hybrid modulation scheme consisting of six-pulse modulation at LF scale and modified secondary modulation and 33% pulse width modulation at high-frequency (HF) scale is proposed. Three-phase ac waveforms for the propulsion system of FCVs are generated from LF fluctuating high-voltage dc bus. The proposed modulation technique significantly reduces the switching losses of the bidirectional dual-stage inverter: 1) soft-switching of both sides of the front-end current-fed full-bridge converter is realized; and 2) at any moment, only one leg of back-end three-phase inverter is switched at HF, while the other two legs are kept in on or off states. This tremendously reduces the bidirectional inverter's switching losses and improves the system efficiency. The LF fluctuating high-voltage dc bus allows the elimination of large electrolytic dc-link capacitor, which contributes to a more reliable and compact design. This paper presents the operation, analysis, and design of a bidirectional inverter implementing the proposed hybrid modulation technique. Simulation results obtained from power electronics simulation software PSIM and experimental results from the lab prototype clearly validate the effectiveness of the proposed modulation technique. [ABSTRACT FROM PUBLISHER]

The modular multilevel converter (MMC) has become a very attractive solution for interfacing high voltages in hybrid networks. The MMC enables scalability to different power levels, full controllability provided by insulated-gate bipolar transistors, and can achieve very high efficiencies by using a low-switching-frequency method as the nearest level modulation. However, the nearest level modulation requires a capacitor voltage-balancing algorithm, which can result in unbalanced loading for the power semiconductors in the different submodules. Particularly at low-power-factor operation, which could occur in the case of low-voltage ride through and of reactive power injection, the conventional algorithm is no more effective. This paper provides thermal stress analysis of the MMC in operation and proposes a thermal balancing approach, which is embedded in the capacitor voltage-balancing algorithm. The purpose of the thermal balancing is to achieve similar stress distribution among the different submodules to enhance the lifetime. The junction temperatures in the different submodules are studied for HVDC applications, and this paper proves experimentally that the thermal balance within the submodules is significantly improved. [ABSTRACT FROM PUBLISHER]

Cascaded H-bridge (CHB) based active power filters (APF) can compensate high-order harmonics in medium and high-voltage systems with relatively low switching frequency. This paper reveals that a severe dc capacitor energy unbalance can be induced by harmonic energy exchange if the frequency of APF output current coincides with the switching harmonic frequency of CHB cells. The mechanism of harmonic energy exchange is analyzed, and it is found that the dc capacitor energy unbalance is essentially affected by the carrier frequency of CHB. A noninteger ratio carrier frequency can be adopted to avoid the divergence of dc voltage, but there is still a significant low-frequency ripple on the dc voltage. This paper proposes an adaptive carrier frequency optimization method. By predicting the dc voltage ripple amplitude under different carrier frequencies, this method can adaptively select the optimal carrier frequency to minimize the dc voltage ripple. The proposed method is also proved to be robust against system parameter variations, and it can be implemented by a practical and simple linear computation method. Results obtained from simulation, experimental prototype, and field test are finally presented to verify the proposed adaptive carrier frequency optimization method. [ABSTRACT FROM AUTHOR]

This paper presents a voltage multiplier topology that is a hybrid between a Cockcroft–Walton multiplier and a Dickson charge pump. The Cockcroft–Walton structure exhibits significant output voltage drop under load as the number of multiplier stage increases. This is because all coupling capacitors are connected in series. Dickson charge pump mitigates this issue by connecting all capacitors in parallel. But this solution comes at the expense of large capacitor voltage stress at the last multiplier stage. The proposed hybrid structure arranges some capacitors in parallel and others in series, thereby achieving low output voltage drop and low capacitor voltage stress at the same time. We develop a model that predicts hybrid multiplier's performance and validates it experimentally. We also demonstrate a 60–2.25 kV dc–dc converter based on a 16-stage hybrid voltage multiplier which achieves a voltage gain of 12.8 while keeping the highest capacitor voltage stress to 660 V. [ABSTRACT FROM AUTHOR]

The Cuk dual resonance core (DRC) realizes overlapped dual resonance to regulate its output voltage. However, the DRC configuration was only applied to the Fibonacci switched-capacitor converter (SCC), series–parallel SCC, and voltage doubler. In this paper, the Cuk DRC is modified and then is extended to the Dickson SCC to form a multi-resonance-core-based (MRC) Dickson resonant switched-capacitor converter. All charging and discharging loops achieve soft charging, and so the inherent capacitor charge sharing loss and the high current transient spikes are eliminated. The modular configuration makes the MRC Dickson easy to be extended to a higher voltage level. The on-time fixed frequency modulation is adopted, all transistors being turned on with zero-current-switching (ZCS) operation and all diodes being turned off with ZCS operation. Most importantly, the conversion ratio of the MRC Dickson can be regulated continuously, widely, and efficiently even at light load condition, which is a huge advantage over the traditional Dickson SCC with limited control headroom. A comprehensive analysis of the operation principle, voltage-gain curve, component stress analysis, and output characteristic is provided. The converter operation principle and regulation capability were verified by both simulation and experiment. [ABSTRACT FROM AUTHOR]

The low-frequency fluctuation over the capacitor voltages seriously limits the development of medium-voltage variable-speed drives with a modular multilevel converter (MMC). Therefore, this paper presents an effective strategy of the low-speed and start-up operation for an MMC-based motor drive. The proposed strategy properly coordinates the improved injection and the reduced average capacitor voltage with high applicability. The specific interactions between the control parameters and the system metrics are analyzed to give the detailed steps of the parameters designing. Hence, based on the derivations, the proposed method enables the low-frequency operation under the nominal load torque with decreased injected components and reduced peak capacitor voltages. What is more, two start-up strategies that, respectively, aim at different objectives for the coordinated strategy are proposed, indicating satisfying control performances for the practical applications. The injected common-mode voltage and circulating current in the proposed method are designed to have a great reduction. Thus, the unfavorable risks for the motor are evidently decreased for better stability. The reduced peak current also lessens the high stress on switching devices with desirable reliability. The simulation and experiment results of an MMC-based motor drive prototype prove the effectiveness and superiority of the proposed method. [ABSTRACT FROM AUTHOR]

This paper proposes a new family of multilevel inverter topology that is able to generate seven voltage levels by utilizing one or two floating capacitors and 10 power switches. This novel boost switched-capacitor seven-level inverter possesses voltage boosting capability with an achievable maximum voltage level 1.5 times the input direct current (dc) voltage. The generation of higher output voltage does not incur high-voltage stress on any power switch in this topology, as the peak inverse voltages of all power switches do not exceed the input source voltage. In addition, capacitor voltage balancing is not essential since the floating capacitors are effectively balanced during the charging and discharging processes. Furthermore, the proposed topology eliminates the need for multiple isolated dc sources, and a single dc source is sufficient in both its single-phase and three-phase topologies. The operating principle and steady-state analysis of the proposed topology are elaborated. Experimental results from a single-phase prototype are then presented to verify the validity of the proposed topology. [ABSTRACT FROM AUTHOR]

Active pulsating power buffering (PPB) is an effective technique to reduce the energy storage requirement of a single-phase power-factor-correction (PFC) rectifier. Existing single-phase solutions with active PPB, however, generally suffer from high voltage stresses, leading to increased power losses as well as the need for high-voltage-rating semiconductor switches. Previous works have been focusing on two-level switching converter configurations, and thus have failed to address the high-voltage-stress problem. In this paper, a single-phase three-level flying-capacitor PFC rectifier with PPB-embedded switching is proposed. The flying capacitor not only clamps the voltage stresses of all power devices but also functions as a PPB capacitor. The operating principles, control methods, and design guidelines are detailed and the feasibility of the proposed converter is verified through a 48-W (48-V/1-A) hardware prototype. The proposed rectifier is shown to achieve nearly 50% reduction of the voltage stresses, 72% reduction of the buffering capacitor's volume, and 23.8% reduction of the magnetic core size, as compared to a state-of-the-art two-level solution recently proposed. This new approach of formulating single-phase PFC rectifiers with active PPB could dramatically boost the system's efficiency and power density whilst reducing cost. [ABSTRACT FROM AUTHOR]

A novel high step-down dc–dc converter with voltage demultiplier cell is proposed in this paper, which is widely used in the high step-down applications such as electric vehicle and digital circuits. The combination of switched-capacitor and coupled-inductor is employed to build extended voltage demultiplier in the proposed converter, which makes a quite higher voltage conversion ratio than that of the existing counterparts. Thus, the proposed converter can achieve extremely low output voltage with an appropriate duty ratio, and the extreme duty cycle is avoided. Accordingly, voltage stress on power switches is greatly reduced. Then, mosfets with low conduction resistance could be utilized to reduce conduction loss. Importantly, zero-voltage switching could be achieved for the main switch, which promotes the conversion efficiency further. In addition, the coupled inductor operates not only as a filter inductor, but also as a transformer when the main switch is in the off state, which reduces the volume of the magnetic core and improves the power density of the converter. The operation principle, performance analysis, design considerations of the proposed converter and performance comparison with recent counterparts are discussed in detail, and finally, an experimental prototype is built to verify the theoretical analysis and performance of the proposed converter. [ABSTRACT FROM AUTHOR]

In this paper, a two-stage transformerless multiple-output converter is proposed for applications requiring a high voltage step-down ratio. The proposed circuit transfers power via a current interface and the use of current-source-mode (CSM) converters, resulting in low voltage stress and drastically simplified control. The first stage of this configuration is regulated to provide a constant current to the second stage. The second stage consists of series-connected CSM boost converters. The high step-down ratio of the proposed configuration reduces the voltage stress in the switches of the second stage. The series-connected CSM converters are inherently independent of each other, leading to a very simple control scheme without the need for decoupling of the input voltage of the interconnected converters. Input voltage variation to the system will not affect the input voltage of the second stage. Load variation in one output will not affect the other outputs. If one or more CSM converters are shorted, there is no impact on other converters. These advantages enable a high scalability. Besides, the first stage of the proposed configuration can operate both in continuous conduction mode (CCM) and discontinuous conduction mode (DCM) with the same control strategy. This feature leads to a low control complexity and elimination of inductors. The performance of the proposed converter is illustrated with a laboratory prototype driving light emitting diodes (LEDs). [ABSTRACT FROM AUTHOR]

In high gain voltage conversion applications, the low-side switches usually suffer large current stress, resulting in dominate switching loss. In this paper, a general soft-switching method based on an advanced interleaved high-step-up converter, which features excellent performance but works in hard-switching, is presented to combat this issue by using a plug-play resonant circuit. Under this soft-switching method, the main switches reach zero-voltage switching (ZVS) turn-on and ZVS turn-off, and the soft-switching condition is derived. Meanwhile, the added auxiliary switches could be turned off under ZVS condition and turned on under zero-current switching condition as well. More importantly, due to its location out of the energy transferring path, the auxiliary circuit will never lead gain lost to the converter and maintain its other existing merits, such as current auto-balancing and diode inverse-recovery well. A 1-kW prototype is built and tested to verify the significant efficiency improvement and merits maintenance for the proposed converter considering active resonant soft switching. [ABSTRACT FROM AUTHOR]

This paper presents a digital control technique to achieve valley switching in a bidirectional flyback converter used to drive a dielectric electroactive polymer-based capacitive incremental actuator. This paper also provides the design of a low input voltage (24 V) and variable high output voltage (0–2.5 kV) bidirectional dc–dc flyback converter for driving a capacitive incremental actuator. The incremental actuator consists of three electrically isolated mechanically connected capacitive actuators. It requires three high-voltage (HV) (2–2.5 kV) bidirectional dc–dc converters to accomplish the incremental motion by charging and discharging the capacitive actuators. The bidirectional flyback converter employs a digital controller to improve the efficiency and charge/discharge speed using the valley switching technique during both charge and discharge processes, without the need to sense signals on the output HV side. Experimental results verifying the bidirectional operation of a HV flyback converter are presented using a 3-kV polypropylene-film capacitor as the load. The energy-loss distributions of the converter are presented when 4- and 4.5-kV HV mosfets are used on HV side. The flyback prototype with a 4 kV mosfet demonstrated 89% charge energy efficiency to charge the capacitive load from 0 V to 2.5 kV, and 84% discharge energy efficiency to discharge it from 2.5 kV to 0 V. [ABSTRACT FROM AUTHOR]

This paper proposes a new interleaved high step-up converter with coupled inductors. Interleaving configuration is employed at the input side to reduce the input current ripple and increase the power level. The series structure at the output side helps achieve a very high step-up voltage gain. Also, the proposed converter has very low switch voltage stress; thus, switching loss can be reduced and low-voltage-rating mosfets with small on resistance are allowed to lower the conduction loss. Due to the passive clamp performance, the leakage energy of the coupled inductors can be recycled and large voltage spikes across the switches are alleviated. Furthermore, with the aid of the leakage inductances, zero-current switching of the active switches can be achieved and the reverse recovery problem of the diodes is alleviated. The operating principles, performance analysis, and design considerations of the proposed converter are discussed. A prototype with 20-V input and 400-V output is built, and experimental results are provided to verify the theoretical analysis. [ABSTRACT FROM AUTHOR]

Impedance-source inverters using coupled inductors have been investigated as alternatives for providing high step-up voltages. However, leakage inductances of the coupled inductors have commonly led to lower overall effectiveness, in addition to generating high dc-link voltage spikes. The latter raises voltage stresses of switches, which in turn, may reduce the power levels of the inverters. A high step-up Y-source inverter has therefore been proposed in this paper to provide a high boost with a smooth dc-link voltage ensured by proper recycling of the leakage energy. These features have been verified by comparing simulation and experimental results of an existing Y-source and the proposed inverters. Factors compared are their respective boost ratios, voltage stresses, current stresses, and dc-link voltage spikes. [ABSTRACT FROM AUTHOR]

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

Modular multilevel converters are increasingly being considered or used for various medium voltage applications. Multiple control methods have been proposed for the control of the direct to three-phase modular multilevel converter. They differ one from another in the way the capacitor voltage ripples are handled, i.e., either neglected, estimated, reconstructed by filtering or measured. This has implications on the performance level that can be obtained. This paper provides insights on the advantages and drawbacks of each control method, in inverter and rectifier mode, with a fair and thorough assessment supported by extensive simulations, with converter ratings that are realistic for medium voltage applications. Finally, this works highlights the impact of the higher dynamics for medium voltage direct current (dc) applications compared to high voltage dc ones on the choice of the control method. [ABSTRACT FROM AUTHOR]

This paper explores the use of the flying-capacitor multilevel (FCML) topology in high step-up conversion. Compared to the conventional two-level boost converter, the FCML topology utilizes high energy density capacitors to facilitate inductors with storing and transferring energy during the conversion process, which brings features, such as lower voltage stress on the switches, reduced voltage stress on the inductor, and high effective switching frequency at the switching node. As a result, the total volume of the passive components in the converter is greatly reduced while maintaining high efficiency at high voltage gain. To demonstrate the potential high power density and high efficiency, a hardware prototype that converts 100 V to 1 kV with 820-W maximum output power is built. Such specifications require careful optimizations in many aspects of the converter to ensure a high power density and efficiency design. The implemented solutions and associate design process are presented in detail, with comparison with other state-of-the-art solutions. The hardware prototype has successfully demonstrated a peak efficiency of 94.1%, and 329 W/in $^3$ (20 W/cm $^3$) overall power density. [ABSTRACT FROM AUTHOR]

This paper proposes an indirect input-series output-parallel (I2SOP) dc–dc full-bridge converter system based on asymmetric pulsewidth modulation (APWM) control strategy for high input voltage applications. When a short-circuit fault occurs in a high input voltage dc bus, the proposed I2SOP system can disconnect from the dc bus effectively and avoid the input filter capacitors of constituent modules discharge compared with the traditional ISOP system, facilitating fault handling and protecting the input filter capacitors. Moreover, with the proposed I2SOP structure, it is easy to achieve redundancy design when one or a few constituent modules fail. The APWM control strategy is introduced to the I2SOP system rather than the classical phase-shifted control strategy for the basic full-bridge module to reduce the voltage stress of power switch and the filter requirement. The characteristics of input voltage sharing and output current sharing of the I2SOP system are also analyzed. A three-module I2SOP system prototype was built, and the experimental results verify the correctness and effectiveness of the proposed solution. [ABSTRACT FROM AUTHOR]

This paper presents three nonisolated high voltage gain dc–dc converters with ripple-free input current. The proposed converters combine coupled inductors and voltage-doubler structure (VDS) to achieve high step-up of input voltage. An active clamp circuit is used to suppress voltage spike of the switch caused by of the leakage inductor of the coupled inductor. VDS is placed in the secondary winding of the coupled inductor that clamps the diodes voltage stress. Working principle and design methodology of the proposed converters are presented in detail. Experimental results for a 300 W laboratory prototype, 48 V input voltage, and regulated output voltage of 400 V, are shown to validate the operation of proposed converters. [ABSTRACT FROM AUTHOR]

The ultra-high voltage gain dc–dc converters are extremely required because of the low voltage level of many nonpolluting power resources. This paper proposes an ultra-high voltage gain converter based on an interleave technique and using three-winding coupled inductor and voltage multiplier cell. The interleave technique is useful for reducing the size of the filter components. In the proposed converter, high voltage gain is achieved without extreme duty cycle of solid-state switches. The voltage stress across the semiconductor devices can be reduced by increasing the turn ratio of the secondary of the coupled inductors. In addition, because of the implementation of the interleave structure, peak-to-peak variation of the main input current and switching losses are substantially reduced. The steady-state principles of the proposed converter in continuous conduction mode operation are given. Also, design equations are presented. Validity and performance of the proposed converter are surveyed by simulation and experimental results of a 120 W prototype. [ABSTRACT FROM AUTHOR]

This paper investigates the diode reverse recovery process and reduction of a half-wave (HW) series Cockcroft–Walton (CW) voltage multiplier based on the steady-state analysis for high-frequency high-voltage (HV) generator applications. The diode reverse recovery process for a multistage voltage multiplier is analyzed after the introduction of steady-state operation. The diode reverse recovery problem is the bottleneck to further increase the circuit operation switching frequency for achieving high power density and short HV pulse rise and decay times. The diode reverse recovery problem is mainly caused by the diodes in the first-stage voltage multiplier. It is suggested that the most effective and economic way to alleviate the diode reverse recovery problem is by employing diodes without reverse recovery such as silicon carbide Schottky diodes in the first stage only. The silicon carbide Schottky diode without reverse recovery needs to be used only in the first stage of the voltage multiplier to effectively mitigate the reverse recovery problems at high frequency. The 300 kHz switching frequency three-stage voltage multiplier circuit hardware prototype experimental results finally validate the analysis. A technology demonstrator of a 300 kHz 8 kW 160 kV HV generator based on the proposed hybrid silicon carbide and silicon diode solution for the HW series CW voltage multiplier is provided finally. [ABSTRACT FROM AUTHOR]

In this paper, a unified equivalent circuit model which can simplify the design and analysis of a family of high-voltage (HV) generation architectures based on the series–parallel (LCC) resonant converter is proposed. First, four HV generation architectures are reviewed in terms of the modularization level of HV transformers and rectifiers. Next, the steady-state, unified equivalent resistor and capacitor (RC) model that can be easily embedded into the resonant tank to replace the complex HV transformers and rectifiers is derived. The generic model can be applied to the HV generators with different architectures, different voltage multiplier topologies, stage, and polarities number. Further analysis of the power factor of the resonant tank, the voltage gain of HV generators, and electrical stresses of power components is achieved with the derived equivalent circuit model. The analysis reveals the inherent circuit properties among HV generators with different configurations. Subsequently, a comprehensive design methodology considering the power factor, conduction angle, and quality factor is presented, which leads to low electrical stresses on the components and high efficiency. Furthermore, the parameter selection constraint based on the power factor, conduction angle, and quality factor is derived, which can ensure the effective design outputs. Finally, the proposed unified equivalent model and comprehensive design methodology are validated by the experimental results of a 250 V input, 20 kV output 500 W HV generator hardware prototype with distributed transformers and voltage multipliers. [ABSTRACT FROM AUTHOR]

The modular multilevel matrix converter (M3C) is a promising topology for high-voltage high-power applications. Recent researches have proved its significant advantages for adjustable-speed motor drives compared with the back-to-back modular multilevel converter. However, the branch energy balancing in the M3C presents great challenge especially at critical-frequency points where the output frequency is close to zero or grid-side frequency. Generally, this balancing control depends on the appropriate injection of inner circulating currents and the common-mode voltage (CMV), whereas their values are hard to determine and optimize. In this paper, an optimization-based predictive control method is proposed to calculate the required circulating currents and the CMV. The proposed method features a broad frequency range balancing of capacitor voltages and no reactive power in the grid side. For operation at critical-frequency points, there is no increase on branch voltage stresses and limited increase on branch current stresses. A downscaled M3C system with 27 cells is designed and experiment results with the R–L load and induction motor load are presented to verify the proposed control method. [ABSTRACT FROM AUTHOR]

The five-level active neutral-point-clamped (5L-ANPC) converter is becoming an attractive topology of multilevel converter family. A novel SVPWM algorithm based on line voltage coordinate was studied in this paper to overcome shortcomings of the traditional algorithm. Through coordinate transformation, steps of determining the basic vectors and the solution about the basic vector corresponding action time are simplified. Combining with the characteristics of 5L-ANPC converter and the new control algorithm, a method of controlling the voltage balancing of dc-link capacitors and floating-capacitors is proposed. According to the voltage of dc-link capacitors, the suitable switching sequence which can balance the voltage of dc-link capacitors is chosen. The high common-mode voltage will affect the service life of motor and reduce the reliability of the system especially in high-voltage converter. The common-mode voltage is also reduced by choosing the right switching state in this paper. The validity of the proposed method was proved by the experimental results. [ABSTRACT FROM AUTHOR]

This paper discusses an alternative approach to designing LED drivers based on high-voltage operation. Compared with the conventional approach of driving LEDs with low voltage and high current, the alternative approach aims to deliver the same power to LED load with high voltage and low current so that small and nonelectrolytic capacitor can be used. High-voltage operation also facilitates the use of simple PFC preregulators such as boost or SEPIC converters as single-stage LED drivers. This paper begins with the derivation of the relationship between the nominal output voltage and output capacitor's size of a PFC preregulator for achieving a given output voltage ripple's size, followed by a review of the recently emerged high-voltage LED packages suitable for the proposed application. This paper also discusses the flicker and colorimetric performances of LED light sources under the influence of large current ripple when nonelectrolytic capacitor is used. The method of third-harmonic current injection to the input current of LED drivers is also incorporated as an option for further reducing the output capacitor's size while meeting a specified flicker limit. Finally, a design example of high-voltage LED driver based on a boost PFC preregulator with third-harmonic current injection is presented and verified experimentally. [ABSTRACT FROM PUBLISHER]

The modular multilevel converter (MMC) is an emerging and highly attractive multilevel converter topology for high-voltage and high-power applications. This paper proposes the control method of parallel-connected modular multilevel converters (parallel-MMCs), which assumes that the multiple MMCs are directly connected at both ac and dc sides to effectively enhance the power rating as expected. Two key problems were first solved for the parallel-MMCs under the normal operation conditions: voltage balancing of submodules and mitigation of circulating currents, where the novel transformed third-order harmonic resonant controller in the synchronous reference frame was employed to mitigate the dominant second-order and fourth-order circulating currents and a sixth-order harmonic resonant controller is used to attenuate the zero-sequence sixth-order circulating current existed in all phase currents per MMC. Considering the high risk of switches fault in the parallel-MMCs, the fault-tolerant operation schemes were then proposed in this paper to address the major concerns of open-circuit and short-circuit switch fault in a submodule, respectively. Carefully controlling the healthy submodules and the corresponding phase arms, the parallel-MMCs can successfully maintain their balanced capacitor voltages and mitigate the circulating currents with the qualified output waveform obtained. In addition, the parallel configuration of MMCs provides the unique solution for the short-circuit switch fault operation which was seldom discussed in the published literature works with respect to the MMC fault-tolerant operation schemes. MATLAB simulations and the constructed experimental prototype have verified the performance of the proposed control strategy. [ABSTRACT FROM AUTHOR]

Modular multilevel converters (MMCs) have become increasingly interesting in dc-dc applications, as there is a growing demand for dc-dc converters in high-voltage applications. Power electronics transformers can be used for high step-down ratio dc-dc power conversion, with high power rating and efficiency achieved. However, this arrangement requires a large number of high isolation voltage transformers and a complicated balancing control scheme. To provide a simple solution with inherent voltage balancing, this paper presents a new resonant MMC topology for dc-dc conversion. The proposed converter achieves high-voltage step-down ratio depending on the number of submodules. The converter also exhibits simplicity and scalability with no necessary requirement of high-voltage isolation transformers. By using phase-shift control, a much higher converter operating frequency is achieved compared to the switching frequency. Resonant conversion is achieved between the series inductor and submodule capacitors. The operation principle and theoretical analysis are presented in this paper, which have been verified by experimental results based on a bench-scale prototype. [ABSTRACT FROM AUTHOR]

High-voltage direct current (HVdc) grid which incorporates multiple dc transmission lines will have extensive application since it has better operating flexibility and enhances the power trade. DC/DC converters are important components in the HVdc grid. The buck/boost modular multilevel dc/dc converter (MMDCC), which uses half-bridge submodules to reduce the voltage stresses across the power switches, is a good choice for the nonisolated applications in the HVdc grid. This paper proposes a pulse width modulation (PWM) control scheme for the buck/boost MMDCC, which uses much smaller submodule capacitors than those in the existing phase-shifted (PS) control scheme, thus reducing the converter volume and weight significantly. The operating principle of the proposed PWM control scheme is elaborated, along with the submodule capacitor voltage balancing strategy and the closed-loop control flowchart. Besides, the capacitance requirement of the buck/boost MMDCC in the PWM control scheme is calculated and compared to that in the PS control scheme, showing a dramatic reduction. The reason for the capacitance requirement difference of the two schemes is also explained. Simulation and experimental results validate the effectiveness of the proposed PWM control scheme and its ability to reduce the submodule capacitance. [ABSTRACT FROM AUTHOR]

A capacitor voltage balancing method for a modular multilevel dc (MMDC) converter is proposed. The MMDC inherits the desirable features of both a modular multilevel converter (MMC) and a dual active bridge, namely high voltage capability, fault tolerance, zero-voltage switching-on of all the power devices, and a wide operating range. These features are ideal for a dc transformer in any dc distribution system. One key MMDC control issue is balancing of submodule capacitor voltages. Conventional MMC balancing techniques cannot be used as arm currents of an MMDC change direction within each switching cycle. This paper establishes that the average capacitor voltage of each arm is self-balanced and proposes a method to balance voltages within an arm by assigning the gate signals with higher charge difference to the submodules with lower voltages and vice versa. Charge difference is obtained by the voltage difference, hence only the SM capacitor voltages are required for balancing control. Different from the existed methods, the proposed technique is not limited by voltage gain or load conditions. Simulation and experimental results show that capacitor voltages are balanced under different voltage gains, different output power, and also when the MMDC starts up, hence ensuring the stable MMDC operation. [ABSTRACT FROM PUBLISHER]

The modular multilevel converter (MMC) is attractive for medium- or high-power applications because of the advantages of its high modularity, availability, and high power quality. Reliability is one of the most important challenges for the MMC consisting of a large number of power electronic devices. The diode open-circuit fault in the submodule (SM) is an important issue for the MMC, which would affect the performance of the MMC and disrupt the operation of the MMC. This paper analyzes the impact of diode open-circuit failures in the SMs on the performance of the MMC and proposes a protection scheme for the MMC under diode open-circuit faults. The proposed protection scheme not only can effectively eliminate the possible caused high voltage due to the diode open-circuit fault but also can quickly detect the faulty SMs, which effectively avoids the destruction and protects the MMC. The proposed protection scheme is verified with a downscale MMC prototype in the laboratory. The results confirm the effectiveness of the proposed protection scheme for the MMC under diode open-circuit faults. [ABSTRACT FROM PUBLISHER]

DC grid technology is regarded as a promising solution for future electric networks integrating a great amount of renewable energies. It calls for high-efficiency dc–dc converters with high voltage step-up ratio to interconnect medium-voltage (MV) dc distribution grids and high-voltage (HV) dc transmission grids. This paper presents an isolated bidirectional soft-switching dc–dc converter combining two-level converters in parallel on the MV side and a modular multilevel converter (MMC) on the HV side. A dedicated control method of the proposed converter is presented. By the proposed method, a certain reactive current is injected into the MV side by the MMC to ensure soft-switching on the MV side. The proposed converter presents low power-semiconductor total device rating and low semiconductor losses over a wide power range at variable input and output voltages. Simulation of a 50 kV/400 kV, 400 MW converter is conducted to evaluate semiconductor losses and verify the validity of this work. [ABSTRACT FROM PUBLISHER]

This paper presents a dc–dc boost converter topology for low input and high output voltage applications, such as photovoltaic systems, fuel cell systems, high-intensity discharge lamp, and electric vehicles. The suggested configuration consists of a three-winding coupled-inductor, a single switch and two hybrid voltage multiplier cells. Furthermore, two independent hybrid voltage multiplier cells are in parallel when the single switch S is turned on, and they are in series when the switch S is turned off. So, the advantages of the proposed converter structure are summarized as follows: 1) A coupled inductor with three windings is introduced in the presented converter structure. The two secondary windings of the coupled inductor are, respectively, used to form a hybrid multiplier cell on the one hand, on the other hand, it increases the control freedom of the voltage gain, enhances the utility rate of magnetic core and power density, and reduces the stress of power components to provide a stable constant dc output voltage. 2) The two hybrid multiplier cells can absorb synchronously the energy of stray inductance, which not only reduces the current stress of corresponding diodes, but also greatly alleviates the spike voltage of the main switch, which improves the efficiency. 3) The two hybrid multiplier cells are connected in series to supply power energy for the load, so the voltage gain is extended greatly due to this particular structure. Thus, low-voltage low-conduction-loss devices can be selected and the reverse-recovery currents within the diodes are inhibited. The operating principles and the steady state analyses of the proposed converter are discussed in detail. Finally, a test prototype has been implemented in the laboratory, and the simulated and experimental results show satisfactory agreement with the theoretical analysis. [ABSTRACT FROM AUTHOR]

This paper deals with a new family of high boost voltage inverters that improve upon the conventional trans-Z-source and trans-quasi-Z-source inverters. The improved trans-Z-source inverter provides continuous input current and a higher boost voltage inversion capability. In addition, the improved inverter can suppress resonant current at startup, which might destroy the device. In comparison to the conventional trans-Z-source/-trans-quasi-Z-source inverters, for the same transformer turn ratio and input and output voltages, the improved inverter has a higher modulation index with reduced voltage stress on the dc link, lower current stress flow on the transformer windings and diode, and lower input current ripple. In order to produce the same input and output voltage with the same modulation index, the improved inverter uses a lower transformer turn ratio compared to the conventional inverters. Thus, the size and weight of the transformer in the improved inverter can be reduced. This paper presents the operating principles, analysis and simulation results, and compares them with those of the conventional trans-Z-source/-quasi-Z-source inverters. To verify the performance of the improved converter, a laboratory prototype was constructed based on a TMS320F2812 digital signal processor with 100 V dc input and 115 Vrms output voltage. [ABSTRACT FROM AUTHOR]

In the integrated reconfigurable converter (IRC) topology for high-voltage series-connected battery module systems, the converter can be reconfigured into a range of operating modes: “feeding a load” mode, “battery modules balancing” mode, “regenerative” mode, “charging” mode, and “backup” mode. In most battery applications, a battery-balancing system operates while another converter is used as a controllable power interface between the battery system and a load. However, during the conventional IRC operation, the “battery modules balancing” and “feeding a load” modes cannot be operated simultaneously. In this paper, a new balancing scheme is proposed that allows balancing the battery modules while they are powering the load. The proposed balancing strategy is able to distribute different amount of load between the battery modules based on their state of charge (SOC). When the load is disconnected, the battery modules can be still balanced using the conventional “battery modules balancing” mode. A scaled down prototype of the IRC is implemented with three series-connected battery modules. Experimental results are provided to verify the viability of the proposed balancing method. [ABSTRACT FROM AUTHOR]

Bipolar repetitive high-voltage pulse generators are commonly used in modern pulsed power applications. Conventionally, bipolar high-voltage pulses can be generated by adding a high-voltage H-bridge at the output stage of a unipolar high-voltage pulse generator which increases complexity and cost of the bipolar high-voltage pulse generator. In this paper, a boost-inverter-based bipolar high-voltage pulse generator with high-voltage gain is proposed. The proposed generator can provide high-voltage bipolar output pulses with the desired specifications from a low input dc voltage. The proposed generator is based on employing two bidirectional boost dc–dc converters, where the load is connected differentially between the boost converters’ output terminals. In the proposed approach, four controlled switches are required. Only two out of these four switches are rated at the high-voltage output level which affects positively the system cost. A detailed illustration of the proposed approach along with the design of its passive components is presented in this study. Simulation and experimental results are used to validate the proposed approach. [ABSTRACT FROM AUTHOR]

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

Recent advancements in renewable energy have created a need for both high step-up and high-efficiency dc–dc converters. These needs have typically been addressed with converters using high-frequency transformers to achieve the desired gain. The transformer design, however, is challenging. This paper presents a high step-up current fed converter based on the classical Cockcroft–Walton (CW) multiplier. The capacitor ladder allows for high voltage gains without a transformer. The cascaded structure limits the voltage stresses in the converter stages, even for high gains. Being current-fed, the converter (unlike traditional CW multipliers) allows the output voltage to be efficiently controlled. In addition, the converter supports multiple input operation without modifying the topology. This makes the converter especially suitable for photovoltaic applications where high gain, high efficiency, small converter size, and maximum power point tracking are required. Design equations, a dynamic model, and possible control algorithms are presented. The converter operation was verified using digital simulation and a 450-W prototype converter. [ABSTRACT FROM AUTHOR]

High-voltage-gain and wide-input-range dc–dc converters are widely used in various electronics and industrial products such as portable devices, telecommunication, automotive, and aerospace systems. The two-stage converter is a widely adopted architecture for such applications, and it is proven to have a higher efficiency as compared with that of the single-stage converter. This paper presents a modular-cell-based morphing switched-capacitor (SC) converter for application as a front-end converter of the two-stage converter. The conversion ratio of this converter is flexible and variable and can be freely extended by increasing more SC modules. The varying conversion ratio is achieved through the morphing of the converter's structure corresponding to the amplitude of the input voltage. This converter is light and compact, and is highly efficient over a very wide range of input voltage and load conditions. Experimental work on a 25-W, 6–30-V input, 3.5–8.5-V output prototype, is performed. For a single SC module, the efficiency over the entire input voltage range is higher than 98%. Applied into the two-stage converter, the overall efficiency achievable over the entire operating range is 80% including the driver's loss. [ABSTRACT FROM AUTHOR]

Transformer parasitics such as leakage inductance and self-capacitance are rarely calculated in advance during the design phase, because of the complexity and huge analytical error margins caused by practical winding implementation issues. Thus, choosing one transformer architecture over another for a given design is usually based on experience or a trial and error approach. This paper presents analytical expressions for calculating leakage inductance, self-capacitance, and ac resistance in transformer winding architectures (TWAs), ranging from the common noninterleaved primary/secondary winding architecture, to an interleaved, sectionalized, and bank winded architecture. The calculated results are evaluated experimentally, and through finite-element simulations, for an RM8 transformer with a turns ratio of 10. The four TWAs such as, noninterleaved and nonsectioned, noninterleaved and sectioned, interleaved and nonsectioned, and interleaved and sectioned, for an EF25 transformer with a turns ratio of 20, are investigated and practically implemented. The best TWA for an RM8 transformer in a high-voltage bidirectional flyback converter, used to drive an electro active polymer based incremental actuator, is identified based on the losses caused by the transformer parasitics. For an EF25 transformer, the best TWA is chosen according to whether electromagnetic interference due to the transformer interwinding capacitance, is a major problem or not. [ABSTRACT FROM AUTHOR]

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

An advanced hybrid LLC series resonant converter with integrated flying-capacitor cell is proposed in this paper to enable the high step-down conversion in the high input voltage applications. The inherent flying-capacitor branch in the primary side can effectively halve the primary switch voltage stress compared with the half-bridge LLC converters. And the input voltage can be shared equally and automatically between the two series half-bridge modules without additional balance circuit or control strategies due to the built-in flying-capacitor cell. Moreover, the inherent soft switching performance during wide load range that exists in the LLC converters is still kept to reduce the switching losses, which ensures the high efficiency. Besides, the proposed converter can be extended to further decrease the switch voltage stress by employing stacked connection. Finally, a 500 ∼ 640 V-input 48 V-output 1 kW prototype is built and tested to verify the effectiveness of the proposed converter. The results prove that the proposed converter is an excellent candidate for the high input voltage and high step-down dc/dc conversion systems. [ABSTRACT FROM PUBLISHER]

Featuring high efficiency, low harmonic distortion, high modularity and scalability, the modular multilevel converter (MMC) is particularly suitable for high voltage direct current transmission applications. As an advanced control strategy, model predictive control (MPC) has the advantage of direct modeling and fast dynamic response. It can simultaneously control multiple variables through an appropriate cost function. The conventional MPC can achieve an optimal control objective by evaluating all the candidate switching states for the MMC; however, with increasing number of submodules, there is an increasing number of candidate switching states that place an enormous burden on the control. In this paper, a grouping-sorting-optimized MPC (GSOMPC) strategy is proposed for the MMC with the number of submodules for each arm increases to hundreds. It divides all submodules of each arm into M groups, with each containing X submodules. By the implementation of the first level and second level optimized MPC between groups and submodules, respectively, the computational load of each phase decreases from C2N^N to $2X + M + 3(N = M \times X)$. In addition, to reduce the strict requirements of control hardware for sorting and calculation, the proposed strategy is able to simultaneously control the submodule voltage, ac current, circulating current, and switching frequency. Applied to a 2.7-kV/60-kW MMC back-to-back dynamic test system, experimental results verify the feasibility and effectiveness of the proposed GSOMPC strategy. [ABSTRACT FROM PUBLISHER]

This paper proposes a soft-switched single switch isolated converter. The proposed converter is able to offer low cost and high power density in step-up application due to the following features: zero-current switching (ZCS) turn-on and zero-voltage switching (ZVS) turn-off of switch and ZCS turn-off of diodes regardless of voltage and load variation; low rated lossless snubber; reduced transformer volume compared to flyback-based converters due to low magnetizing current. Experimental results on a 100 kHz, 250 W prototype are provided to validate the proposed concept. [ABSTRACT FROM AUTHOR]