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A switching-state selection scheme for a five-level stacked multilevel inverter for open-end winding motor drive is presented in this article. Using the proposed scheme, converter can be operated with a single dc supply and with zero common-mode voltage. In addition, the switching transition of high-voltage switches occurs at zero-voltage conditions. The degree of freedom provided by the redundant switching-states and voltage vectors of the inverter topology is utilized to design the modulation scheme. The proposed switching-state selection leads to inherent capacitor balancing without using any extra sensors and fundamental frequency switching of the high-voltage switches of the topology. The modulation scheme uses triangular carrier comparison and, hence, avoids the complexity of subsector identification and dwell time calculation. Half-wave symmetry in output waveforms is ensured by maintaining synchronous sampling with constant samples per fundamental cycle. The inverter topology and the effectiveness of the state selection scheme are experimentally validated on an open-end winding induction motor drive, and experimental results showing steady-state and dynamic operations are presented. [ABSTRACT FROM AUTHOR]

Here we demonstrate negative capacitance (NC) characteristics of a ferroelectric–dielectric (FE–DE) capacitor by means of a fully numerical, self-consistent simulation based on the Miller model (MM) and Poisson’s equation. Over the years, the Landau model (LM) has been widely used, which fits experimental data of spontaneous polarization versus electric field (${P}-{E}_{\mathrm {FE}}$) characteristics using a so-called “S-curve”; however, it cannot capture different transitions of polarization switching and can also fail to properly represent the material properties of certain FEs. To overcome such limitations of the LM, we have used the MM to simulate an FE–DE capacitor. Even though the MM seemingly fails to show steep switching characteristics due to the absence of the negative slope in the ${P}-{E}_{\mathrm {FE}}$ curve unlike the LM, our simulation exhibits the NC characteristics of FE–DE capacitors with significant internal voltage amplification. Notably, we explore the effect of different transitions of polarization switching by varying the coercive field of FE within the MM, and exhibit that greater NC characteristics can be achieved with a FE having a more abrupt switching transition. We have also investigated the impact of other material parameters of FE, such as saturation and remnant polarization, on the NC characteristics of FE–DE capacitors. Our results provide comprehensive insight into the mechanism of FE-DE capacitors, suggesting sophisticated engineering of material and device parameters to seek desired performance of NC devices. [ABSTRACT FROM AUTHOR]

LCC resonant converters have been widely adopted to achieve high power density and high efficiency. Due to high switching frequency and large reactive power in the resonant tank, the efficiency of LCC converters at light load decreases dramatically. Burst mode, which is commonly used in dc–dc converters to improve efficiency at light load, has not been applied to LCC resonant converters due to the oscillation of resonant tank during the burst off-time of burst mode. In this article, a simplified state model, which has only two state variables that can easily describe its state trajectory in the state plane, is proposed for LCC resonant converters with a capacitive output filter. Then, optimal state trajectory control of LCC converters for burst mode is proposed based on the state model, which can eliminate the resonance during the burst off-time. In addition, the transition from start-up mode to burst mode is proposed based on state trajectory control, which can complete this transition in one switching cycle. Finally, the proposed optimal trajectory control in burst mode is verified by an LCC converter prototype. [ABSTRACT FROM AUTHOR]

This article proposes a simple and fast active power device open circuit fault detection and localization technique. The proposed technique applies to the family of flying capacitor multilevel converters (FCMCs), including dc/dc FCMCs, single or multi-phase H-bridge FCMCs, and cascaded H-bridge multilevel converters. The localization technique needs to sense the voltage and direction of current at the output terminals of converters to detect and localize the fault. A circuit with multiple window detectors is utilized to track the output voltage level and current direction with high bandwidth. The algorithm compares the measured and expected terminal voltage, considering the commanded switch states and the terminal current direction. Once potential fault locations are identified, healthy switches are filtered out from the set of potential faulty switches over successive switching transitions. The proposed technique is experimentally validated on a single phase H-bridge FCMC. The switch state commands and pulsewidth modulation (PWM) is handled by a DSP while the fault detection and localization algorithm is implemented on a separate field programmable gate array (FPGA). The asynchronous operation of the DSP and FPGA is discussed. [ABSTRACT FROM AUTHOR]

Grid-tied photovoltaic (PV) installations with distributed maximum power point tracking (DMPPT) architectures include a dc–dc module integrated converter (MIC) for managing each PV panel, isolating it from the others, reducing the mismatching effect and maximizing the harvested power. In this article, the autotransformer forward converter with type-Zeta resonant reset (AFZ) is proposed as a DMPPT architecture's MIC candidate. The main characteristics of the AFZ converter are the high versatility due to its voltage step-up and step-down capability; the use of an optimized autotransformer with only two windings, reducing the complexity and power losses of this component; the good dynamic performances, like the forward converter ones; the low number of components and the simplicity and high feasibility associated to the use of just one active switch. Besides, soft switching transitions are achieved thanks to the autotransformer type-Zeta resonant reset. The steady-state theoretical analysis, considering the effect of the autotransformer leakage inductance, is presented. The converter is also studied in the frequency domain, obtaining the small-signal transfer functions. A design procedure based on the requirements of a 100-kW grid-tied photovoltaic installation is described, yielding in a 225-W prototype with efficiencies up to 95.6%. Experimental results validate the theoretical analysis. [ABSTRACT FROM AUTHOR]

Multiple insulated gate bipolar transistor (IGBT) open-circuit faults severely affect the reliable operation of modular multilevel converters (MMCs). The existing literatures have not provided an effective diagnosis algorithm for MMCs when multiple IGBT open-circuit faults simultaneously appear in one arm. This article presents a diagnosis strategy to handle that condition. Fault detection and estimation of the faulty submodule (SM) number is implemented by checking the value of the arm voltage error. The faulty SMs are located by observing when the transition of their switching functions leads to an obvious change of the arm voltage error. Meanwhile, the errors between the measured and predicted capacitor voltages are utilized to accelerate the localization. All of the faulty SMs can be quickly located one by one within several control cycles by using the proposed localization method. Simulation and experimental results demonstrate the validity of the proposed diagnosis strategy. [ABSTRACT FROM AUTHOR]

The purpose of this study is to present the concept and properties of a dual-active bridge dc–dc converter with a modified auxiliary-resonant commutated (MARC) pole concept, and to discuss preliminary test results of a high-power setup. In this approach, the dual-active bridge based on IGCT is considered. First, the soft-switching boundaries for the converter with lossless snubbers and high switching delays are introduced. Second, the MARC pole is presented to overcome this border to receive full soft-switching capability in the entire operation range of the dc–dc converter. This is of crucial importance since IGCTs will be destroyed in case of a snubber dump. The advantage of the modified circuit is the guaranteed switching under zero-voltage conditions without applying an additional boost current as needed in the classic auxiliary-resonant commutated pole (ARCP) approach. Thus, complexity is reduced and reliability is increased. Measurement results of the MARC are presented from a mega-watt dc–dc converter where the concepts are fully implemented. The results of large-scale systems impressively show how the ARCP reduced the impact of parasitic elements, which would normally affect the switching transitions tremendously. [ABSTRACT FROM AUTHOR]

In this article, a new pulsewidth modulation technique is proposed for the output voltage control and the dc-bus capacitors voltage balancing of a multipoint-clamped multilevel converter. The voltage equalization is achieved by allowing each converter's leg voltage to switch through multiple levels in a single modulation period (multistep operation). The approach is generalized with respect to the number of levels and phases and can be applied regardless of the converter operating conditions. Nevertheless, the multistep behavior generally leads to an increase of the average switching transitions rate. In the proposed method, this drawback is mitigated with an online adaptive selection of the number of switching levels. The algorithm is validated through an extensive hardware-in-the-loop testing and compared to other approaches. [ABSTRACT FROM AUTHOR]

In the no-load condition, LLC converter usually fails to regulate its output voltage although it operates at a high switching frequency. Till now, it is hard to obtain the exact relationship between design parameters and the maximum switching frequency for no-load regulation capability. In this paper, a specific criterion for no-load regulation of LLC converter is provided, without using active components or other modulation schemes. By analyzing the macroscopic switching period and microscopic switching transition in the no-load condition, it is shown that not only the peaking resonant current during the switching transition, but also the resonant tank design affect the no-load regulation of the LLC converter, which affects the no-load regulation capability. Furthermore, the relationship among design parameters is analyzed and the design guideline is also provided to achieve no-load regulation at the specified maximum switching frequency. To verify the effectiveness of the proposed design, 400 V input and 50 V/200 W output prototype is built and tested. [ABSTRACT FROM AUTHOR]

This paper proposes a three-phase, five-level, non-regenerative pulsewidth modulated rectifier using only two active switches (minimum required) per phase, which drastically reduces gate driver requirement and hardware complexity. It draws sinusoidal input current at close to unity power factor. All the semiconductor devices are rated at only one fourth of the dc-link voltage, and none of them requires any transient voltage balancing snubber. A total of 8 out of the 14 diodes per phase undergo soft switching transition under all operating conditions, which increases its efficiency. No extra hardware circuitry for balancing the flying capacitors (FCs) or the dc-link mid-point voltage are required, which further reduces hardware complexity and increases the conversion efficiency. The proposed topology does not need any sophisticated startup procedure for charging the FCs either, which solves the problem of semiconductor overvoltage during starting. A 3-kW laboratory prototype is built to experimentally verify the proposed topology. The maximum efficiency obtained from the prototype is 98.7%, and it is always more than 96% for the load range from 15% to its rated. [ABSTRACT FROM AUTHOR]

This article considers a medium-voltage static synchronous compensator (STATCOM) that is based on a delta-connected modular multilevel converter (MMC) and operates at switching frequencies of 150 Hz or less. Offline computed optimal pulse patterns (OPPs) facilitate the shaping of the grid current spectrum at such low switching frequencies. However, STATCOM applications require the injection of harmonics and negative-sequence currents, as well as fast power transients. In order to achieve this, a model predictive controller is designed, which modifies the switching transitions of the OPPs, inserts additional pulses if required, and controls the circulating current in the delta-connected MMC. [ABSTRACT FROM AUTHOR]

Initializing memory with zero data is essential for safe memory management. However, initializing a large memory area slows down the system significantly. The most likely cause for initialization to slow down the system is the limited DRAM initialization method. At present, the only way to initialize DRAM area is to execute multiple WRITE commands. However, the WRITE command slows the initialization because of its small granularity and data bus occupancy. In this brief, we propose an efficient in-DRAM initialization method inspired by the internal structure and operation of DRAM. The proposed method, called row reset, uses a DRAM row buffer to zero out a single DRAM row at a time. Row Reset allows for parallel initialization on multiple DRAM banks without using off-chip data transfer, thus reducing initialization time by up to 63 times. Row reset is a practical approach, because it can be implemented with existing circuitry in DRAM without additional area overhead. [ABSTRACT FROM AUTHOR]

The inherently low electrical conductivity of transition metal phosphides and most synthetic strategies rely on a multi-step post-processing process from an external phosphorus source, limiting their widespread application. Herein, we explore an in-situ activation and phosphating strategies to prepare CoP nanoparticles self-embedded in N, P-codoped hard carbon (CoP@NPHC) by using chitosan as nitrogen-rich carbon sources and phytic acid (PA) as trifunctional role of crosslinking/chelating agent, phosphorus source and activation reagent. Relying on the unique coordination ability of amino groups of chitosan with metal ions and the cooperative hydrogen bonding of chitosan with long chain structure and PA to form a 3D superstructure. Thanks to the highly dispersed CoP nanoparticles self-embedded in porous and highly conductive carbon skeleton, the CoP@NPHC exhibits high specific capacity of 694 mAh g−1 at 0.1 A g−1 and excellent rate performance. More importantly, a novel lithium ion capacitor is assembled using pre-lithiated CoP@NPHC as anode material and acid etched N, P-codoped porous carbon (NPAC) as the cathode material, which can provide a stable operating voltage of 4.2 V and high energy density of 139.2 Wh kg−1 at a power density of 394 W kg−1, as well as excellent capacity retention of 89.3% after 4000 cycles. [Display omitted] • CoP nanoparticles embedded in hard carbon is prepared via in situ phosphating method. • Phytic acid plays trifunctional role of cross-linker, phosphorus source and activator. • CoP@NPHC demonstrates a honeycomb carbon decorated with CoP nanoparticles. • Li-ion capacitor based on CoP@NPHC has wide operating voltage and high energy density. [ABSTRACT FROM AUTHOR]

This paper presents a control strategy using optimized switching sequences which results in capacitor voltage balancing of a three-phase neutral-point-clamped rectifier. In front end rectifiers, magnitude and lag angle of reference current vector (w.r.t supply voltage vector) varies depending upon amount of reactive power compensation and load current. Accordingly, the effectiveness of small and medium vectors (using SVPWM) for same switching state varies in each sector and its regions. This observation along with detailed analysis of current pattern for both the capacitors and their effect on neutral point voltage forms the basis of the proposed approach, which is to modify the reference vector for changing the number of sampling periods within each sector and its regions. The rectifier exhibits excellent performance in terms of other critical parameters like unity input power factor, low input current THD, minimum possible switching losses, reduced-rippled, and well-regulated dc-bus voltage, particularly, the capacitor voltage balancing. The proposed control algorithm is tested through exhaustive simulations and validated through experimental results obtained from a laboratory prototype of the rectifier. [ABSTRACT FROM AUTHOR]

The sorting algorithm is the most widely accepted capacitor voltage balancing strategy for a modular multilevel converter. This strategy offers to keep the balance among submodule capacitor voltages under all of the modular multilevel converter working conditions. However, this method generates unnecessary switching transitions in submodules, which results in high switching frequency and switching loss, and uneven distribution of switching transitions and switching loss among submodules (SMs). In this paper, a simplified switching loss balancing control strategy was proposed in order to handle these issues. The proposed approach adjusted the submodule selection process of the sorting algorithm by taking into consideration the number of switching transitions in addition to the capacitor voltages. Even distribution of switching transitions and switching loss was achieved, and the average switching loss was reduced at the cost of slightly increasing the capacitor voltage fluctuations. The effectiveness of the proposed approach was verified through both simulation and experimental results. [ABSTRACT FROM AUTHOR]