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As one of the promising power interfaces between the energy storage components and the dc link, dual active bridge (DAB) converters have gained extensive researches. Its reliability and healthy operation under one or even multiple unexpected open-circuit faulty conditions have become one of the main design challenges. Conventional fault detection (FD) and fault isolation (FI) methods exhibit obvious limitations in terms of detection speed, number of FD signatures, universality, accuracy, computational burden, and implementation cost due to the added sensors. To fill in this gap, this article presents a robust, fast, accurate, and low-cost FD and FI method for DAB converters, which is applicable under various operational conditions. The proposed method will adopt the differential switch node voltage between the primary and secondary bridge of DAB converters as the universal fault signature for complete FD and FI. The corresponding fault diagnostic circuit is simple, compact, low cost, and easy in implementation. This sensorless fault diagnostic technique can detect the switch open-circuit fault within a quarter of a switching cycle and realize the fault isolation accurately. A DAB prototype with a fault diagnostic circuit was designed, and main experimental results under various faulty conditions were provided to validate the advantages of the proposed method. [ABSTRACT FROM AUTHOR]

Pulse test techniques are widely adopted in characterizing both the static and dynamic performances of semiconductor devices considering various device structures and operating conditions. For gallium nitride (GaN) devices, due to the current collapse phenomenon, fast and accurate measurement of their key electrical parameters, such as dynamic ON-state resistance ${R}_{\text {ds}, \mathrm{\scriptscriptstyle ON}}$ , switching rising time, fall time, switching losses, and short-circuit (SC) robustness, becomes essential. This article presents a comprehensive review of state-of-the-art pulse test setup methods such as the double-pulse test (DPT), multiple-pulse test (MPT), and SC test (SCT) for the first time, which facilitates the GaN device structure design and practical applications in high efficiency and power density power converters. [ABSTRACT FROM AUTHOR]

In this article, an efficient model predictive control (MPC) using virtual voltage vectors for three-phase three-level converters is proposed. The proposed MPC achieves constant switching frequency by applying four voltage vectors, including one virtual voltage vectors and three other voltage vectors, in each control cycle. In addition, to reduce the computational burden, two-stage MPC approach is adopted. The first stage chooses one of six medium voltage vectors that minimizes the cost function. Then, in the second stage, these voltage vectors including virtual voltage vectors, which locate the same sector with the optimal medium voltage vector, are involved in the MPC optimization. The advantages of the proposed MPC over the classical MPC have been validated through experimental results. [ABSTRACT FROM AUTHOR]

Dual-active-bridge (DAB) converters have been widely recognized as one promising topology for high-frequency-link power conversion applications. However, one critical issue concerning DAB converters is the transient dc-bias current due to the voltage-second imbalance, which may occur frequently in typical dynamic operations of DAB converters such as the start-up, sudden load or output voltage change, and power flow direction change. Due to the high-frequency operation, the dc-bias current of DAB converters will impose more harm to magnetic components because of the limited range of operating flux density and possible magnetic saturation compared with the counterpart low-frequency dc-bias current. Over the past several years, extensive researches have been conducted to address the high-frequency transient dc-bias current of DAB converters under different phase-shift modulation strategies such as single phase shift, extended phase shift, and triple phase shift. In this article, a comparative review of typical dc-bias current mitigation strategies under typical phase-shift strategies for DAB converters is presented. An experimental evaluation of selected strategies under various scenarios is conducted in terms of the settling time, inductor current stress, efficiency, switching number, and implementation complexity. This article ends up with an overview of high-frequency dc-bias mitigation strategies and a discussion for the further optimization. [ABSTRACT FROM AUTHOR]

The dc power transmission system has been obviously attracting more research interests in recent years. In order to satisfy the high-reliability requirement of the dc power transmission system, the power converter should be able to keep uninterrupted operation after multiple unexpected faults. However, high fault-tolerant capability usually leads to the bulky redundant circuit, which increases the cost, volume, and complexity of the power converter. Thus, a fault-tolerant dual active bridge (DAB) converter is proposed to maintain the power transferring ability under multiple unexpected open-circuit faults (OCFs) conditions, which can significantly enhance the reliability of the dc power transmission system. By reconfiguring the central-tapped transformer and two symmetrical auxiliary inductors, the half-bridge conduction branch is built to maintain uninterrupted operation when a single or dual OCF has occurred. The proposed fault-tolerant strategy only requires four extra voltage sensors to detect and locate OCFs for the reconfiguration process. Thus, it significantly improves the system reliability with a low additional cost. Besides, the inductor current, transmission power, and the small-signal models of the proposed fault-tolerant converter have been presented. It proves the proposed fault-tolerant topology can smoothly switch between normal and postfault operation due to the constituency of the inductor current. Finally, the 250-W prototype is designed to verify the advantage of the proposed fault-tolerant DAB converter. [ABSTRACT FROM AUTHOR]

In this article, a low complexity finite-control-set model predictive control (FCS-MPC) based on the discrete space vector modulation (DSVM) is proposed for T-type three-phase three-level (3P-3L) converters. Different from the conventional FCS-MPC, 48 virtual voltage vectors (VVs) of the converter are constructed by real VVs based on the DSVM. Thus, the performance of 3P-3L converters is significantly improved and the peak amplitude of high-order harmonics concentrates at the sampling frequency. Furthermore, two-stage FCS-MPC based on virtual VVs is proposed to reduce the computation burden. Its first stage selects one of six virtual VVs that minimizes the current tracking error. Then, these candidate VVs located in the same sector as the optimal virtual VV selected in the first stage are evaluated in the second-stage optimization. Thus, the computational efficiency has been greatly improved. To verify the validity of the proposed control method and show its superiority over the conventional FCS-MPC, experimental results are presented. [ABSTRACT FROM AUTHOR]

With the increase of the component number, the power stress distribution among differential power processing (DPP) converters, control implementation, system cost, and reliability become the most challenging issues for a practical photovoltaic (PV) DPP system. This article introduces an improved power-rating balance (IPRB) control for the PV-to-bus based DPP architecture that ensures each PV submodule operate at its true maximum power point (MPP) while achieving more balanced power stress distribution and higher reliability. Specifically, a submodule-level finite-state-machine-based MPP tracking is implemented to guarantee always maximum power yield, whereas a string-level power-rating balancing (PRB) control is adopted to balance the unit-maximum proceeded power by DPP converters based on the built power flow model with respect to the string current. A comprehensive comparison of advanced control strategies for PV-to-bus DPP architectures, including least power point tracking, voltage equalization (VE) based PRB control, and the proposed IPRB, has been carried out with the mission-profile-based reliability assessment under different partial shading scenarios. Component-failure-rate-based reliability analysis shows that the PV-to-bus DPP architecture with the proposed IPRB control can significantly improve the system reliability. Main simulation and experimental evaluations are carried out to verify the effectiveness of the proposed control. [ABSTRACT FROM AUTHOR]

The derivation and implementation of multiple-phase-shift-based switching surfaces for a dual active bridge (DAB) converter is the main focus of this article. First, the mathematical models of multiple natural switching surfaces under different operation states of DAB converters are derived, which lays the foundation to achieve a fast transient response during startup, sudden voltage reference, and load changing conditions. Moreover, in order to improve the overall performance of DAB converters systematically, a minimum-current-stress boundary control (MBC) is proposed that can reduce the inductor peak current stress and achieve fast dynamic response simultaneously by using the multiple-phase-shift-based switching surfaces. The analytical derivation of the proposed MBC is presented together with the simulation and experimental evaluations, which shows the superior performance of the proposed MBC algorithm in terms of the efficiency and dynamic response improvement under various operating conditions. [ABSTRACT FROM AUTHOR]

Dynamic performance of maximum power point tracking (MPPT) algorithms is important to ensure high-power output under practical operating conditions. In this article, after reviewing three dynamic test procedures, including stepped operation procedure, day-by-day operation procedure, and EN50530 dynamic test procedure, three typical MPPT algorithms such as the fixed-step-size perturb and observe (P&O), variable-step-size incremental conductance, and hybrid-step-size beta method are evaluated experimentally under the EN50530 dynamic test procedure. Two dynamic EN50530 test sequences are adopted for the performance evaluation to cover different irradiance changing conditions. The PV model for EN50530 dynamic test sequences is built, and the effects of wrong-step changes by using three MPPT algorithms are analyzed systematically. The experimental comparison of three MPPT algorithms in terms of the tracking routines, accumulated energy, and tracking efficiency is presented. The research shows that the 0.5% fixed-step-size P&O may fail to track the MPP due to the tracking drift, whereas the beta algorithm exhibits the highest tracking efficiency under both dynamic sequences. The average tracking efficiency improvement of the beta algorithm compared with other two algorithms are experimentally measured as $\text{24.2}\%$ and $\text{18.8}\%$ , respectively. [ABSTRACT FROM AUTHOR]

Photovoltaic (PV) constant power generation (CPG) control is regarded as an advanced active power control by limiting the maximum feed-in power in order to avoid the adverse impacts of high-penetration PV systems such as overloading and overvoltage. Conventional CPG strategies show obvious limitations in terms of the dynamics response, oscillations during the steady state, and the estimation speed of limited power points (LPPs). In this article, a novel CPG control with the rapid approach to LPPs is proposed with the estimation of maximum power point (MPP), which guarantees fast converging speed in response to rapid changes in environmental conditions and low power oscillations for the steady state. Specifically, the proposed control allocates the operating point at the left-hand side of the MPP, which can not only avoid the instability issue but also simplify the MPP and LPP estimation according to the single-diode PV equivalent model. Furthermore, based on the estimated available power Pavi, the proposed CPG control contributes a direct solution in approaching the region around LPP or MPP, which improves the converging speed under environmental-changing conditions. Thus, regardless of the changes in irradiance or temperature, high-performance and reliable operation are ensured by switching the maximum power point tracking mode and CPG mode smoothly. The proposed control can be directly applied for the existing PV system and no additional hardware devices such as irradiance sensors are required, which is cost effective. A systematic comparison of the proposed control with other advanced CPG strategies was made under various scenarios and the advantages of the proposed control were validated experimentally. [ABSTRACT FROM AUTHOR]

A transient dc-bias current due to the voltage-second imbalance of isolated bidirectional dual-active-bridge (DAB) converters for the disturbance in line or load may result in the transformer saturation and oscillations in both sides dc currents. This article focuses on the transient dc-bias current elimination by using an improved triple-phase-shift (ITPS) control for DAB converters. The inductor peak current stress optimization is adopted in the proposed ITPS to determine the steady-state phase-shift variables. Originated from the dc-bias current model of DAB converters with the TPS control, the transient phase-shift adjustment strategy can be determined, which has the ability to improve the inductor current changing slope and shorten the settling time. Both simulation and experiments for different conditions are provided to evaluate main dynamic indexes such as the transient period, dc-bias current, and inductor current stress for three different transition cases. The proposed ITPS is proved as a promising solution in eliminating the dc-bias current, minimizing the transient current stress. [ABSTRACT FROM AUTHOR]

Differential power processing (DPP) is regarded as a promising architecture in solving mismatching issues among photovoltaic (PV) submodules. Although conventional total-minimum-power-point (TMPP)-based real-time optimization algorithm by using the distributed submodule-level maximum power point tracking and simultaneously the centralized total-minimum-power tracking shows effectiveness in maximizing the power yield. However, uneven power stress among DPP converters, large oscillations, high additional cost for communication among DPP converters, and complicated implementation hinder the practical application. This article proposed a low-complexity power balancing point-based optimization algorithm to reduce the system cost and size, improve the system efficiency, and realize the standardized modular design for DPP converters. Furthermore, simple submodule-level voltage equalization control is implemented to eliminate expensive communication and relieve the control complexity while guaranteeing high maximum-power-point efficiency. The proposed algorithm can reduce the power rating of DPP converters compared with conventional TMPP-based control, which is beneficial to the improvement of system cost, reliability, and lifetime. Both simulation and experimental results under various scenarios are provided to validate the advantages of the proposed algorithm. [ABSTRACT FROM AUTHOR]

Gallium nitride (GaN) high-electron-mobility transistors (HEMTs) are promising for the next-generation power switching applications due to their low on-resistance, high-frequency operation, and small gate capacitances, which are essential for the power density and efficiency improvement. However, with the increase of the switching frequency, the deadband effect will become a challenging issue for the high-efficiency converter design over a wide operation range. In this article, a comprehensive theoretical analysis and experimental verification of the deadband effect in the GaN-based dual-active-bridge (DAB) converters with multiple-phase-shift (MPS) control is presented. First, resonant transitions for various switching conditions with different initial currents by using MPS controls are discussed, and the effect of the stray capacitance of GaN HEMTs is analyzed. On this basis, the accurate boundaries among zero-voltage switching (ZVS), partial ZVS, and hard switching with MPS control can be obtained. A deadband compensation strategy is proposed by considering different switching conditions. Finally, a DAB prototype based on GaN HEMTs was built, and main experimental results were provided to verify the effectiveness of the proposed resonant transition analysis, ZVS boundaries, and the deadband compensation strategy. [ABSTRACT FROM AUTHOR]

As the “brain” of the modern photovoltaic power systems, dc solid-state transformers (SSTs) are playing an increasing important role in integrating different photovoltaic modules, batteries, and supercapacitors. This paper aims at improving the conversion efficiency of dc SST for a wide operating range by minimizing the backflow power of the dc SST system. First, the mathematical model of the backflow power from both input and output sides of dc SST is obtained. Then, the penalty function is derived and an enhanced triple phase shift control (ETPS) strategy is proposed to minimize the backflow power for various transmission power and voltage conversion conditions. A comprehensive comparison of the proposed ETPS with other advanced control strategies was carried out through theoretical analysis and experimental tests. Main experimental results are illustrated to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Differential power processing (DPP) is a promising architecture to solve the issue caused by mismatches among photovoltaic (PV) submodules. To eliminate the mismatch power losses, this paper presents an optimized PV-to-bus DPP system with submodule-level individual maximum power point tracking (MPPT) and module-level minimum-power tracking (MPT) simultaneous implementation according to the built mathematical model of the power processed by DPP converters with respect to the string current. Furthermore, a flexible time-sharing algorithm is adopted to reduce the number of MPPT units. Compared with other solutions, such as PV optimizer, the proposed scheme can reduce the effects of mismatches to the minimum regardless of mismatch conditions. The system cost is reduced since only one adaptive MPPT controller is required. Besides, the system efficiency is improved due to the true MPPT implementation and MPT control. Both simulation and experimental tests are provided to validate the effectiveness of the proposed scheme. [ABSTRACT FROM AUTHOR]

Power reserve control (PRC) without energy storage becomes essential for modern photovoltaic (PV) power plants to meet the increased ancillary service requirements such as grid frequency support. Conventional PRC strategies show obvious limitations to estimate the available maximum power point ($P_{\text{avai}}$), such as additional hardware requirements, implementation difficulty, and slow estimation speed. Originated from the linear characteristic of PV curves in the constant current region and a Lambert- $W$ function for voltage linear reference, $P_{\text{avai}}$ is estimated separately in separate steps rather directly measured or estimated. The proposed strategy does not requires any additional hardware such as the irradiance and temperature sensors, which realizes sensorless control with reduced cost. Furthermore, cumbersome procedures of curve fitting with sophisticated operating points sampling and key parameters determination in the real-time $P_{\text{avai}}$ estimation by using the conventional PRC methods can be also eliminated. In this strategy, the operating point with a curtailed power level is allocated at the left-hand side of the MPP, which guarantees the stability of PV systems under varying conditions. The developed strategy exhibits fast speed to estimate $P_{\text{avai}}$ , high robustness, and good compatibility with existing PV systems. Simulation and experimental results under various scenarios are provided to validate the effectiveness of the proposed strategy. [ABSTRACT FROM AUTHOR]

This paper presents a novel model predictive control (MPC) for the T-type single-phase three-level inverters. The cumbersome procedure in tuning of weighting factors is eliminated so that the implementation of the proposed MPC becomes easy. The constant switching frequency is achieved during the control implementation in order to facilitate the filter design. In order to optimize the distribution of the output current harmonics, multiple voltage vectors are employed in each control cycle with their application times setting inversely proportion to the respective cost function. The redundant small voltage vectors are utilized to balance the neutral point voltage of the inverter by directly regulating the upper and lower dc-link capacitors voltages. Finally, the proposed MPC algorithm is experimentally evaluated and compared with other two unfixed switching frequency MPC algorithms in terms of the steady state, transient performance, and parameter sensitivity. [ABSTRACT FROM AUTHOR]

This paper deals with an optimized three-level modulated phase shift control using particle swarm optimization (PSO) strategy based on the unified phasor analysis with an aim to improve the efficiency of the bidirectional dual active bridge (DAB) converter for the whole operation range. A unified mathematical model based on Fourier transform is built for the DAB converter. All possible operation states under the three-level modulated phase shift control are covered. Accurate complex mathematical expressions for the inductor current, the transmission power, and the reactive power are obtained. Both modulus and angle variables are illustrated with respect to the inner and outer phase shift angle with the phasor diagram. The proposed method is able to achieve the minimum reactive power under three-level modulated phase shift control by obtaining the optimal phase-shift angles directly. The cumbersome process of the optimal operation mode selection for different voltage conversion ratio and load conditions in conventional methods is overcome successfully, thus greatly simplifying the theoretical calculation and implementation difficulty. Simulation and experimental results in terms of the reactive power, soft-switching range, and efficiency are provided to verify the practical feasibility of the proposed method for the bidirectional DAB converters. [ABSTRACT FROM AUTHOR]

As key component for the flexible dc distributed power system, the dual active bridge (DAB)-converter-based solid-state transformer (SST) with high efficiency for a wide operating range is essential. However, with the traditional phase-shift control, high backflow power and current stress will significantly affect the conversion efficiency. In this paper, the backflow power characteristics in both sides of DAB-based SST converters are comprehensively analyzed. On this basis, complete transmission power, backflow power, and peak current mathematical models are established. Then, a minimum-backflow-power-based extended-phase-shift control strategy is proposed with the determination of optimal phase-shift pairs by using the Karush–Kuhn–Tucker function for various scenarios. The backflow power and current stress curves with different algorithms are compared. It shows the proposed control can improve the output power regulation flexibility, minimize the backflow power, and improve the efficiency in wide operating range. Finally, a DAB-based SST prototype was developed and the experimental results verified the effectiveness of the proposed control strategy. [ABSTRACT FROM AUTHOR]

When the photovoltaic (PV) string is under the partial shading condition (PSC), the conventional maximum power point tracking (MPPT) techniques may fail to track the global maximum power point (GMPP). Although some global MPPT (GMPPT) techniques have been proposed, they may overlook the GMPP and fail to detect the PSC occurrence. Therefore, a novel GMPPT technique is proposed in this paper by modifying the conventional beta method. The proposed technique is more accurate than the previous techniques since it can guarantee that all the peaks in the $\beta$ range and never overlook the GMPP. Furthermore, the proposed technique can inherently detect the PSC occurrence without setting any additional threshold parameters or periodical interruption, which is simpler and more effective. In order to verify the advantages of the proposed technique, a prototype with buck-boost converter was constructed. For a fair comparison, two popular GMPPT techniques were also implemented and tested in the same prototype under various scenarios. The performance improvement with the proposed technique for different PSCs has been validated by both simulation and experimental results. [ABSTRACT FROM PUBLISHER]

This paper presents a novel reactive-power minimization method under the three-level modulated phase-shift control to improve the efficiency for a wide operation condition. First, in order to unify all operation modes, a mathematic model of the dual-active-bridge converter with the three-level modulated phase-shift control by a harmonic analysis method is obtained. Then, the detailed analysis of the odd-order harmonic components of the active and reactive powers varied with the multiple control dimensions is presented. The soft-switching boundaries with respect to the voltage ratio and unified active power are specified. On this basis, a novel optimal three-level phase-shift (OPS) control strategy for minimizing reactive power is proposed. Experimental results of reactive power and operation efficiency among the proposed OPS method, and other methods are compared to verify the effectiveness of the OPS algorithm. [ABSTRACT FROM PUBLISHER]

Maximum power point tracking (MPPT) is essential to improve the energy yield of solar energy systems. However, conventional MPPT algorithms show obvious problems such as the conflict of the steady-state oscillations and dynamic speed, and the clash of high computational burden and accuracy. Originated from the beta method, which shows the advantages of fast tracking speed in the transient stage, small oscillations in the steady-state, and medium complexity of implementation, this paper proposed an improved beta method to further improve the overall performance, especially for practical applications. Instead of manually tuning key parameters such as the range of $\beta$ parameter and scaling factor $N$ for different operating conditions, an autoscaling factor is used, which make the method easier in practical implementation and suitable for wider conditions. The meteorological data of two distinct locations are used to verify that the $\beta$ parameters derived from photovoltaic (PV) modules are valid for one whole year under different environmental conditions. A PV system with the proposed MPPT method was built in MATLAB/Simulink, and different indices such as the rise time, the setting time, and the tracking energy loss are used to evaluate the performance of various MPPT algorithms. Finally, two experimental tests were carried out, including the indoor test with solar array emulator and the outdoor test with an actual PV module, respectively, to show the effectiveness of the proposed MPPT algorithm. [ABSTRACT FROM PUBLISHER]

Originated from analyzing nonactive power loss, a novel optimization method and modulation solution for bidirectional isolated dual-active-bridge (DAB) dc–dc converters are proposed in order to achieve high efficiency in a wide operating range. A comprehensive nonactive power loss model is developed, including both the nonactive components delivered back to the source and from the load. This paper points out that when the minimum nonactive power loss is achieved, zero-voltage soft switching can be naturally fulfilled. The optimal phase-shift pair obtained by the proposed method can keep low values of both root mean square (RMS) current and circulating power. Rather than using ideal power flow analysis, the nonactive power loss model directly embodies practical nonideal factors, including device voltage drops. Based on the analysis, an extended dual phase shift is proposed, and different operation cases are analyzed with comparison of performance indices. Experimental tests verify the theoretical analysis and show effectiveness of the proposed approach to achieve nonactive power loss minimization and efficiency improvement. [ABSTRACT FROM PUBLISHER]

A current-fed high-frequency alternating-current (HFAC) distributed power system is presented in this paper for medium- or high-voltage gate driving applications. The distributed gate driving modules (GDMs) at the high-voltage side are isolated from the low-voltage-side current-source power supply through magnetic coupling of current transformers (CTs), which are assembled by a high-voltage cable carrying HFAC and passing through the center of toroid magnetic cores. The centralized high-frequency current-source power supply is designed and composed of a two-stage resonant inverter and a double \Gamma-CL resonant network. The resonant network is parameterized by considering the tradeoff between the quality factor and component stress. Different magnetic core samples are tested and compared to construct the CTs for improving transmission efficiency. A 400-W prototype was built and experimentally evaluated with two load conditions, including resistive loads and practical GDMs. It showed significant improvements with regard to sinusoidal current output, system stability, and efficiency. Finally, the proposed current-fed HFAC power supply system was successfully applied to a practical solid-state fault current limiter, demonstrating the advantages of multiple outputs ( n > 10), high-voltage isolation, low harmonic distortion, high efficiency, easy installation, and flexible extensibility. [ABSTRACT FROM PUBLISHER]

This article proposes a fixed switching frequency (FSF)-based improved model predictive control (MPC) for a five-level active neutral-point clamped (5L-ANPC) converter. Compared to the conventional MPC for 5L-ANPC converter, the proposed MPC significantly reduces the computational burden while ensuring the balance of dc-link and flying capacitor voltages. The proposed MPC optimally selects the control voltage vectors to reduce common mode voltage (CMV), leading to a small CMV of the converter. Using three voltage vectors action per control cycle in MPC, FSF is achieved. Steady-state and dynamic performances of the proposed MPC have been evaluated by experiments. The results verify the feasibility and effectiveness of the proposed MPC method. [ABSTRACT FROM AUTHOR]

Compared with the conventional multilevel converters, the hybrid-clamped converter (HCC) reduces the number of power devices, which brings down the converter cost while enhancing its reliability for medium-voltage high-power applications. As one of typical medium-voltage HCCs, the single-phase, six-level HCC (6L-HCC) faces the main technical challenge of the voltage balance among five inner capacitors. Most of the existing pulsewidth modulation techniques cannot solve this problem. Advanced control methods that directly apply a selected voltage vector, such as the classical model predictive control (MPC), may fail to balance the inner capacitor voltages during low output frequencies. In view of this situation, this article proposes an improved MPC approach with autotuning weighting factors. It contributes to ensure excellent performance of 6L-HCC under all operating conditions with well-balanced inner capacitor voltages. Simulation and experimental results are proposed to verify the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

When electric vehicles encounter emergency, the dc-bus capacitor voltage in the motor drive system needs to be reduced as quickly as possible to prevent the passengers from secondary electrical injury. For the purpose of compactness and low cost, a novel discharge scheme by using the machine windings has come forth. Yet, the relevant research works are incomprehensive without considering the standstill cases and sensor fault issues. This article proposes a position sensor fault-tolerant winding-based dc-bus capacitor discharge method over the full-speed range. To achieve voltage discharge at high speed without using position sensor, an improved second-order sliding-mode observer based on continuous sigmoid function is presented. Moreover, an adaptive sine-wave-based position observer with high immunity to voltage change is proposed for discharge in the low and zero speed cases. In terms of the discharge procedures, deceleration-based and acceleration-based algorithms are designed and optimized aiming at the spinning and standstill situations, respectively. More specifically, they include voltage, current, and speed regulation methods. The proposed fault-tolerant discharge technique is verified by both simulation and experiments, which are conducted on a three-phase interior permanent magnet synchronous machines drive system. [ABSTRACT FROM AUTHOR]

An optimized model predictive control (MPC) method is proposed based on the selected switching states to control the four-level hybrid-clamped converter. The proposed method utilizes 64, instead of 512, switching states, compared with a conventional MPC, which greatly eases the calculation burden while achieving the high-quality regulation of output currents and the balance of capacitor voltages. The steady-state performance at both high and low frequencies is investigated, and results are compared with those by the traditional carrier phase-shifted pulsewidth modulation method. The dynamic response to the current or frequency step change is also evaluated. Both simulation and experimental results validate the feasibility and effectiveness of the optimized MPC method. [ABSTRACT FROM AUTHOR]

Passing cloud results in rapid changes of irradiance. The intermittency of photovoltaic (PV) power output has drawn serious concern especially for utility-scale PV system. Consequently, power ramp-rate control (PRRC) has been introduced to avoid significant PV power fluctuations. PRRC is usually implemented either by curtailing active power output or implementing energy storage system (ESS). However, current active power curtailment cannot deal with the irradiance ramp-down fluctuations, and the high cost of the ESS is still hindering its extensive application. In this paper, two innovative PRRC strategies are presented, which utilize the short-term forecasting. The first solution does not require any ESS, during the power ramp-down event, the PV generation will be curtailed before the actual shading occurs. The second solution requires only one-quarter of the energy capacity of the conventional ESS control strategy. To provide the PV generation forecasts, a dynamic model based on spatio-temporal theory is formulated. The effectiveness of the proposed forecasting model and control strategies have been verified through experiment and case studies. [ABSTRACT FROM AUTHOR]

The partial power processing (PPP) concept has been extensively employed in many two-port converters to achieve high efficiency and high-power density by modifying one of the original converter ports to be connected in series between input and output. This is attractive but is confined to two-port applications, and how to extend it to multiport applications is not clear. Hence, this article aims to explore a generalized PPP multiport scheme by arranging the connection of the module rather than the converter. For a PPP single-input(output)-N-outputs(inputs) converter, one terminal of all N+1 modules is connected together to construct a radial structure, and another terminal is series/parallel connected with the input/output port. Each module only needs to process partial power caused by the voltage or current difference between input and output. Therefore, the required power rating of components is effectively reduced, contributing to low cost as well as low power loss. In this article, a PPP single-input dual-output converter with active bridge modules is also taken as an example to be introduced in detail, designed and experimented upon, which validates that high efficiency and high-power density can be achieved. [ABSTRACT FROM AUTHOR]

Maximum power point tracking (MPPT) is required in PV power systems for the highest solar energy harvest. This article proposes a self-tuning scheme to improve the MPPT performance in terms of high accuracy and speed. The scheme adopts the reinforcement learning (RL) and Beta parameter for the highest MPPT performance. The tracking speed and accuracy are significantly improved since the RL algorithm is enhanced for high convergence speed, meanwhile, the guiding variable $\beta$ is introduced to constrain the exploration space. Simulation and experimental test are applied to validate the superior performance of the proposed solution following the EN50530 dynamic test procedure. [ABSTRACT FROM AUTHOR]

Novel normally-OFF AlGaN/GaN MIS-high electron mobility transistors (HEMTs) with a ZrOx charge trapping layer are proposed. The deposition of the ZrOx charge trapping layer on the partially recessed AlGaN in conjunction with the Al2O3 gate dielectric has been accomplished. The developed MIS-HEMTs exhibit a threshold voltage of 1.55 ± 0.4 V and a maximum drain current of 730 ± 6 mA/mm, while associated low ON-resistance of $7.1~\pm ~0.2~\Omega \cdot $ mm, for a gate to drain separation of 3 $\mu \text{m}$. The TCAD simulation results are presented to explore the charge trapping and de-trapping behaviors. Moreover, the devices exhibit a high breakdown voltage. The results indicate the merits of employing ZrOx charge trapping layer to realize the normally-OFF GaN devices with low ON-state resistance. [ABSTRACT FROM AUTHOR]

This article demonstrates the integrated comparators, hysteresis comparators, and sawtooth generators based on aluminum–gallium–nitride/gallium–nitride (AlGaN/GaN) metal–insulator–semiconductor high-electron-mobility transistors (MIS-HEMTs). The integrated circuits (ICs) exhibit thermal stability from 25 °C to 250 °C in both static and transient performances. The threshold voltage (Vth) in depletion (D)-mode MIS-HEMT is modulated from −8.9 to −2.4 V to optimize the performance of integrated comparator circuits. The comparator can realize a large and stable comparison range of 3–9 V and a high voltage swing of 9.1 V, while the hysteresis comparator exhibits a good noise-immunity ability and stable hysteresis output. The sawtooth generator with the hysteresis comparator features a high amplitude (6.1 V) sawtooth signal at 500 kHz to realize a compact structure applicable to the high-voltage mixed-signal circuits. These results show the feasibility of MIS-HEMT monolithic comparator circuits in conversion systems. [ABSTRACT FROM AUTHOR]

When electric vehicles (EVs) encounter an emergency, the voltage of the dc-bus capacitor in the surface-mounted permanent magnet synchronous motor (SPMSM)-based powertrain requires to be reduced as fast as possible. In order to eliminate the disadvantages and synthesize the advantages of the traditional machine-winding-based and external bleeder-based discharge techniques, this article proposes a hybrid discharge strategy that can achieve 5-s discharge in the minimum sacrifice of the bleeder size and weight for any EV drives. For the purpose of evaluating the size reduction of the new method, the individual bleeder-based scheme is modeled and analyzed at first. Then, the combined discharge method is developed, which contains two sequential procedures: bleeding resistor (BR) design and discharge control algorithm design. The BR design process has to be implemented under extreme condition. But concerning that the emergency might occur at the moment when the machine operates below the maximum speed, three different discharge modes including full-power, partial-power, and bleeder-based discharge modes are developed. The proposed discharge techniques are verified by experiments that are conducted on a three-phase SPMSM drive system used for EVs. [ABSTRACT FROM AUTHOR]

When the permanent magnet synchronous machine (PMSM) based electric vehicles (EV) are in the postcrash situations, the dc-bus capacitor voltage requires to be reduced quickly for the sake of electric shock risk prevention. Currently, due to the advantages of low cost, compact structure, and high reliability, the pure-winding-based discharge strategies are attracting increasing attentions. However, there are no theoretical criteria for judging whether a pure-winding-based method is suitable for bleeding a particular PMSM-based EV drive, not to mention the rules for opting for an effective discharge strategy among the instant nonzero d-axis, zero q-axis (NDZQ), long-cycle NDZQ, and the nonzero d-axis, nonzero q-axis (NDNQ) current control techniques. This article discusses the applicable occasions of the instant NDZQ, long-cycle NDZQ, and NDNQ discharge methods based on parametric analysis. On this ground the principles for determining whether an EV drive can adopt a pure-winding-based method for discharge are given. Meanwhile, the implementation procedures of the proposed criteria are detailed clearly. Finally, the proposed selection criteria are used for evaluating five different EV drives so as to select the corresponding winding-based discharge strategy for each system, and the effectiveness is verified by simulation or experiments. [ABSTRACT FROM AUTHOR]

Under partial shading conditions (PSC), the power-voltage (P–V) characteristic curve of a photovoltaic string exhibits multiple peaks, posing a big challenge to the problem of global maximum power point tracking (GMPPT). The traditional 0.8 VOC-model-based GMPPT method locates the global maximum power point (GMPP) locus by comparing the power at each local power peak. However, a considerable amount of time is required for iteratively scanning each 0.8 VOC vicinity. To address this problem, an improved 0.8 VOC-model-based GMPPT method is proposed in this article. A shading vector is introduced to characterize the PSC. The proposed GMPPT method estimates the 0.8 VOC region with the GMPP directly from the measured shading vector by the k-nearest neighbors approach and saves the time consumed in the comparison process used in the conventional method. Simulation and experimental results demonstrate that the proposed method is capable of tracking the GMPP efficiently and accurately under various shading patterns. [ABSTRACT FROM AUTHOR]

This article proposes a new finite control set model predictive control (FCS-MPC) strategy that simultaneously evaluates two targeting control objectives including speed and currents in a single cost function, achieving high-performance single-closed-loop control structure. Besides, aiming at the calculation delay problem of the model predictive control controllers, a novel calculation delay compensation method by predicting the current variation within the delay time is proposed. In this article, an improved machine model that is especially designed for the multiobjective FCS-MPC operation is illustrated at first. Then, a new cost function that can evaluate the tracking performance of speed and d-axis current and the steady-state performance of the q-axis current is developed. Compared with the conventional FCS-MPC approaches, extra speed controllers are not needed so that the proposed control topology becomes simpler. Then, in order to tune the weighting factors for the speed and currents in the cost function, an efficient handling strategy containing two implementation procedures, state variable normalization and balance of state sensitivity to voltage alteration, is developed. Finally, a brand-new computation delay estimation and compensation technique based on the dual sampling within a control period is proposed to reduce the current and torque ripples during the control process. Comparative simulation and experiments conducted on a three-phase 1.5-kW permanent magnet synchronous machine drive system are employed to verify the effectiveness of the proposed techniques. [ABSTRACT FROM AUTHOR]

The precision of position estimation is highly dependent on the accuracy of multiple current sensors, whereas the conventional error calibration strategies for current sensor accuracy uncertainty (SAU) problem have limitations regarding the position sensorless controlled drives. In order to solve this thorny problem, this article proposes a mutual calibration strategy for the multiple current sensors in an interior permanent magnet synchronous motor (IPMSM) drive. The proposed current sensor error calibration strategy takes full advantage of the correlation among the multiple current sensors themselves without using any complicated observers. Moreover, the traditional seven-segment space vector pulsewidth modulation technology is applied without modification. The only change is reflected in several sets of the artificially added current sampling points. The effectiveness of the proposed strategy is verified by experimental results on a 5-kW IPMSM motor prototype, which shows that the calibrated current sensors exhibit improved accuracy, and the position estimation accuracy is also guaranteed. [ABSTRACT FROM AUTHOR]

In order to enhance the control performance of the surface-mounted permanent magnet synchronous machines (PMSM) working under the low frequency situations, this letter innovatively proposes an accurate finite control set (FCS) model predictive current control (MPCC) method. First, a novel predicting plant model in the continuous-time domain based on the numerical solutions of the PMSM state-space model (differential equations) is developed. Without using the linear discretization implementation, the influence of the low control frequency can be eliminated completely. Besides, a brand-new calculation delay compensation method based on delay time prediction and current precompensation is designed for the proposed FCS–MPCC strategy. Finally, experiments are conducted on a PMSM test bench with the control frequencies of 2 and 1 kHz to comprehensively verify the proposed algorithms. [ABSTRACT FROM AUTHOR]

This paper proposes a perturbation estimation based nonlinear adaptive power decoupling controller for doubly fed induction generator based wind turbines (DFIG-WTs). Perturbation states are defined to include the nonlinearities, uncertainties of the system model, the cross-coupling between control loops, and external disturbances. Perturbation observers are designed to estimate the fast time-varying perturbation states. With perturbation estimation, the DFIG-WT system is fully decoupled, and an output feedback control can be designed for the control of rotor currents. Rotor current references are calculated based on the steady-state relation between active/reactive power and rotor current, and stator dynamic is ignored. The performance of the proposed controller is evaluated and verified via both simulation and experimental tests. [ABSTRACT FROM AUTHOR]

There has been growing interest in using photovoltaic (PV) energy harvesting technology to reduce reliance on mineral-based energy. Partial shading scenarios (PSS) significantly affect the electrical characteristics of a PV generator. However, a few studies have devoted to the detection and assessment of the PSS. In this paper, shading rate and shading strength are used to characterize the PSS. A shading pattern detection algorithm is proposed to estimate the number of shaded modules in a PV string and distinguish the PSS from uniform irradiation scenarios. A multiple-output support vector regression is applied to estimate the shading strength. In addition, the maximum power point voltage of the applied PV generation system can be predicted from measured data. Simulation and experimental validation show the feasibility of the proposed method in the face of various environmental conditions. It could be used as a preliminary step toward automatic supervision and monitoring PV generation system. [ABSTRACT FROM AUTHOR]

Plug-in hybrid electrical trucks (PHETs) are a kind of emerging transport solution to reduce greenhouse gas emissions. Switched reluctance motors (SRMs) are one of the popular choices for PHETs applications due to characteristics of rear-earth free, high starting torque, wide-speed range, and good fault tolerance. Usually, more than two converters are needed to achieve flexible energy conversion among multiple electrical energy components on board, i.e., generator, battery bank, and motor. High-power converters should be used to drive the trucks that occupy the limited on-board space. Furthermore, an extra converter is also needed to achieve ac grid connecting charging. All these converters make the on-board power electronics converter complicated. In this paper, a modular tri-port high-power converter for SRM based PHETs is proposed to combine the multiple electrical energy components into one converter. The modular tri-port high-power converter can not only support flexible energy flow, but also support parallel and series winding connections according to different conditions. Furthermore, ac grid connecting nodes are also developed in the drive, which allows the proposed converter to work as a grid connecting charger without extra facilities. The simulation and experiments are employed to verify the feasibility of the proposed converter and corresponding control strategies. [ABSTRACT FROM PUBLISHER]