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A method for the seamless transition of three-phase inverters switched between grid-tied and stand-alone modes of operation is presented in this paper. In this method, only the inverter current and voltage sensors are utilized, and no control over the grid-side static transfer switch is needed. The presented method contains two strategies for grid-tied-to-stand-alone and stand-alone-to-grid-tied transitions. In the stand-alone-to-grid-tied transition strategy, a novel algorithm is presented for estimating the grid angle nearly instantaneously, which allows the three-phase inverter to respond very quickly if the grid and point-of-common-coupling voltages are out of phase. This fast response allows the inverter to effectively eliminate the transient overcurrent that would normally occur if it was connected to the grid without first being synchronized. The fast response also allows the inverter to return to normal operation very quickly after such an event. The strategy for the seamless transition from grid-tied to stand-alone mode is also presented. These strategies have been verified through experiments, and the results are presented in this paper. [ABSTRACT FROM PUBLISHER]

This paper discusses a new circuit configuration and a new control method for a single-phase ac–dc converter with power factor (P.F.) correction and a power pulsation decoupling function. The proposed converter can achieve low total harmonic distortion (THD) on the input current and the power pulsation decoupling function between the input and output sides, which allows low output voltage ripple even on a small output energy buffer at the same time using an active buffer. Therefore, the proposed converter does not require large smoothing capacitors or large smoothing inductors. The buffering energy is stored by a small capacitor, which controls the variation of the capacitor voltage through the active buffer. In this paper, the fundamental operations of the proposed converter are investigated experimentally. The experimental results reveal that the input current THD is 1.44%, the rate of the output voltage ripple is 6.33%, and the input P.F. is over 99%. In addition, a maximum efficiency of over 96% is obtained for a 750-W prototype converter. [ABSTRACT FROM PUBLISHER]

An efficient converter topology for extracting maximum power from a photovoltaic module is presented in this paper. The proposed topology is implemented on a stand-alone battery charging system. A reversed buck–boost converter enabling parallel power processing (PPP) with a power switch referenced to the common return is the core of the charging system. Small-signal analysis of the proposed charging system is carried out to facilitate the design of a compensator for maximum power point (MPP) tracking. The simulation and experimental results confirm the validity of the model and verify the high efficient operation while tracking the MPP. The use of the PPP with split loads is also presented which would improve the converter size, efficiency, and step-down duty ratio. [ABSTRACT FROM PUBLISHER]

This paper presents single- to three-phase dc-link converters with a reduced number of controlled switches for either usual or reduced currents in switches of the rectifier. A suitable model and a control strategy, including a synchronization approach, are developed to obtain the maximum dc-link voltage utilization. Such a synchronization method, associated with the pulse-width-modulated generation signal, forces the input current to have the same phase angle as the input voltage. The main advantage of the proposed converters along with the synchronization method is the reduction of the zero-crossing distortion normally caused by the use of diodes. Simulated and experimental results are presented to confirm the validity of the theoretical expectations. [ABSTRACT FROM PUBLISHER]

High-brightness light-emitting diodes (HB-LEDs) are becoming omnipresent across all aspects of illumination products, due to their incredible characteristics such as efficiency, reliability, long lifetime, controllability, etc. This paper proposes power conversion topologies to drive medium to high power HB-LEDs in three-phase power grids when these connections are available. For that reason, an evaluation of several drivers for medium to high power HB-LEDs in three-phase power grids is done. Moreover, a new topology is proposed, which complies with IEC 1000-3-2 Class C requirements, achieves high power factor, low total harmonic distortion, and the capability to have a flicker free behavior while disposing of the bulk capacitor and having galvanic isolation. The HB-LED driver is based on a modular approach with several cells working together with their inputs connected to the three-phase network and their outputs connected in parallel generating a dc output. Each one of these cells is a dc–dc converter operating as a loss free resistor. In order to validate the concept, a prototype has been built by the use of flyback converters operating in discontinuous conduction mode. Furthermore, it operates in the full range of the European three-phase line voltage, which varies between 380 and 420 V, and it supplies an output voltage of 48 V with maximum power of 90 W. [ABSTRACT FROM AUTHOR]

In this paper, the zero sequence circulating current in open winding permanent magnet synchronous machine (OW-PMSM) drives with common dc bus is systematically analyzed for the first time. It is revealed that the zero sequence circulating current is affected by zero sequence back-electromotive force, cross coupling voltages in zero sequence from the machine side, pulse-width modulation induced zero sequence voltage, and inverter nonlinearity from the inverter side. Particularly, the influences from the cross coupling voltages in zero sequence and parasitic effect of inverter nonlinearity are investigated for the first time in this paper. Then, the synthetic model of the equivalent zero sequence circuit is proposed as well. Each cause is studied independently via analytical modeling, finite element analysis, and experiments. Meanwhile, to tackle this issue, the relevant suppression strategy using frequency adaptive proportional resonant controller is presented and tested on the 3 kW OW-PMSM platform. [ABSTRACT FROM AUTHOR]

The performance of a novel three-phase four-leg fault-tolerant T-type inverter topology is introduced in this paper. This inverter topology provides a fault-tolerant solution to any open-circuit and certain short-circuit switching faults in the power devices. During any of the fault-tolerant operation modes for these device faults, there is no derating required in the inverter output voltage or output power. In addition, overload capability is increased in this new T-type inverter compared to that in the conventional three-level T-type inverter. Such increase in inverter overload capability is due to the utilization of the redundant leg for overload current sharing with other main phase legs under healthy condition. Moreover, if the redundant phase leg is composed of silicon carbide metal-oxide-semiconductor field-effect transistors, quasi-zero-voltage switching, and zero-current switching of the silicon insulated-gate bipolar transistors (IGBTs) in the conventional main phase legs can be achieved at certain switching states, which can significantly relieve the thermal stress on the outer IGBTs and improve the whole inverter efficiency. Simulation and experimental results are given to verify the efficacy and merits of this high-performance fault-tolerant T-type inverter topology. [ABSTRACT FROM PUBLISHER]

This paper identifies possible topological reconfigurability of a T-type inverter for direct torque controlled (DTC) induction motor drives when an open-switch fault occurs. In open-switch fault, inverter current path is different than normal path. This causes undesirable inverter switching states. Since DTC is based on a voltage vector selection criterion, open-switch fault causes ambiguous torque control. Analysis of DTC drive under two different inverter open-switch fault conditions viz. half-bridge and neutral-point switch fault are presented. The operation of the inverter in DTC mode against faults is achieved by simple topological reconfiguration. [ABSTRACT FROM PUBLISHER]

Three-phase voltage-source inverters typically feature a significant amount of dc energy storage to maintain a stiff dc bus. In these cases, the dc-link capacitor is sized to store enough energy to maintain several tens of cycles of ac output at the rated power. In this paper, we propose to reduce the size of the dc-link capacitor dramatically to store enough energy to provide just one high-frequency switching cycle of the ac output power. The dc bus is no longer stiff, and hence, classical sinusoidal pulse-width modulation cannot be used. However, the stored energy modulation (SEM) proposed herein synthesizes high-quality sinusoidal output voltage waveforms, even with such tiny dc-link capacitors. In SEM, the switching intervals of the interconnecting switches are carefully determined nonlinear functions of various operating parameters such as reactive component sizing, switching frequency, load levels, etc. This paper presents the analytical and detailed design development of the SEM approach along with circuit simulation, experimental results, and comparative evaluation of a dc-to-three-phase system example. [ABSTRACT FROM PUBLISHER]

One of the main challenges of the solid-state transformer (SST) lies in the implementation of the dc–dc stage. In this paper, a quadruple-active-bridge (QAB) dc–dc converter is investigated to be used as a basic module of a modular three-stage SST. Besides the feature of high power density and soft-switching operation (also found in others converters), the QAB converter provides a solution with reduced number of high-frequency transformers, since more bridges are connected to the same multiwinding transformer. To ensure soft switching for the entire operation range of the QAB converter, the triangular current-mode modulation strategy, previously adopted for the dual-active-bridge converter, is extended to the QAB converter. The theoretical analysis is developed considering balanced (equal power processed by the medium-voltage (MV) cells) and unbalanced (unequal power processed by the MV cells) conditions. In order to validate the theoretical analysis developed in the paper, a 2-kW prototype is built and experimented. [ABSTRACT FROM PUBLISHER]

The control of an ultracapacitor (UC)-based dc–dc power supply is crucial to provide reliable energy backup to critical loads in the case of momentary power main failures. In this regard, smooth and seamless transition between charging and discharging controls of UC stack is of paramount importance. For ride-through applications where charging and discharging times are critical, provision of different control structures for charging and discharging subsystems is crucial. The conventional control techniques, though ensure seamless mode transition, does not allow different control structures for both the subsystems. This paper proposes an independent switch control strategy, which ensures seamless transition between charging and discharging control modes. The proposed control is based on pulse-width modulation blocking and is shown to ensure the fastest mode transition between control modes. The proposed control also elucidates an accurate method for identification of control modes, which is important to independent switch control. The advantages of the proposed control compared with conventional controls is presented in this paper. The proposed control strategy has been verified in simulations and experimentation, and the mode identification algorithm is found to work well. [ABSTRACT FROM PUBLISHER]

The successful mission of CubeSat require reliable and fault-tolerant electrical power system (EPS) that powers all the other subsystems and payloads. Several studies have shown that EPS failure has been one of the main contributors for the CubeSat mission failure. The main objective of this paper is to enhance the lifetime of CubeSats EPS by proposing a distributed EPS architecture and power-down mode. The distributed architecture consists of independent converters for maximum power point tracking operation of photovoltaic (PV) panels. This is possible by using gallium nitride field-effect transistors to reduce the converter footprint and placing the converters on the back-side of the PV panels. Also, single-inductor based $N$ -1 redundant converters for generation and load-side are proposed to provide uninterrupted operation during component failures. Thus, the proposed distributed architecture not only improves the reliability but also facilitates placement of redundant converters to achieve the fault-tolerant capability. To further reduce the electrical and thermal stresses on the semiconductor devices and thus, improve the EPS life span, a novel power-down mode is proposed for the power converters. In this mode, semiconductor devices are switched-off whenever the power processed is below the threshold level and/or no-load operation. Reliability block diagrams are illustrated to demonstrate the reliability improvement and calculations shows that the proposed distributed architecture has higher reliability than the conventional EPS architecture. All the proposed concepts are validated using a prototype developed based on the specifications of MYSAT-1, which is an 1U CubeSat launched by Khalifa University. [ABSTRACT FROM AUTHOR]

This paper proposes an electronic driver for public lighting systems. The input stage is based on the integration of two flyback converters with different polarities, in order to avoid the use of the input diode bridge rectifying stage. The output stage is a boost converter with an output current control. The proposed circuit is introduced and analyzed, and a design example for a 50-W light-emitting diode lamp is presented. The most relevant simulation and experimental results are also shown, in order to validate the idea. A comparison in terms of efficiency for the input stage is carried out between the proposed topology and the conventional flyback converter, showing an efficiency enhancement in the proposed converter. However, the most important advantage of the proposed converter is outlined in the final part of this paper. This advantage comes from the avoidance of the input diode bridge, thus enabling the bidirectional power flow at the input stage. Therefore, the topology can be used to deliver energy into the power grid. In recent lighting applications, the use of micro renewable generators in lighting points has made the use of special electronics to handle the energy flows in the ballast necessary. The present topology is an alternative to standard bidirectional input stages. [ABSTRACT FROM AUTHOR]

Common-mode voltage (CMV) in voltage-source inverters (VSIs) has been well defined and is frequently referred to in the literature. While often referred to, there is no real consistency with respect to how the CMV properties of an individual modulation scheme are evaluated, lacking tools to assess the relative merits or disadvantages of a certain topology or modification of a control scheme. The way that it is analyzed is still mostly a matter of the different authors' foci. In this paper, we propose a metric for the analysis of the CMV, aiming to fill the aforementioned gap. Thereby, the CMV in VSIs is quantified by the number of possible levels and the step sizes between different levels, as well as the respective frequencies of occurrence. The first two are given by the number of levels and the number of phases of the inverter. Depending on the modulation (control) schemes, all possibly available levels or a few of these levels are present in the CMV. We illustrate the use of the tool by applying it to thoroughly study the CMV properties intrinsic to the topologies of multilevel multiphase single- as well as double-ended diode-clamped VSI drive systems. As part of this analysis, we uncover new relationships concerning the existence of zero CMV level. Furthermore, we exemplarily apply the developed tool to the assessment of the CMV properties of selected pulse width modulation (PWM) control schemes and translate the findings into an interpretation of the endangerment of a given drive to suffer damage from inverter-induced bearing currents. The theoretical findings are supported by measurements. This paper also reviews the literature on CMV in multilevel multiphase VSI systems. With the proposed metric in mind, the CMV being mostly discussed as an element of different foci becomes even clearer, confirming again the need for the development of such a tool. [ABSTRACT FROM AUTHOR]

This paper reports on the continuing efforts of an IAS Working Group to investigate industry concerns with excessive stator fault-point burning damage in conjunction with various industrial generator grounding and ground fault protection practices. Previous working group efforts were reported in a series of papers discussing typical voltage bus connected industrial generator applications. These papers proposed a new method of grounding, called hybrid grounding, that offered the ability to limit damage while still providing the required level of ground fault current under all operating conditions. This new Working Group paper reports on the detailed design requirements for hybrid grounding. The paper reports the results of switching transient studies that formed the bases for recommended overvoltage protection. It also provides guidance in selection of equipment and fault protection required for hybrid grounding. The experience gained with several hybrid grounding applications is also reported. [ABSTRACT FROM AUTHOR]

Compared with the conventional hard switching battery equalizers, hierarchical battery equalizer based on the bipolar continuous-conduction mode buck–boost units could effectively reduce the switching loss and improve the conversion efficiency. This paper mainly addresses the key technical challenges associated with the optimal design of this battery equalizer. The inductor current is controlled to enter into the negative region. Thus, the mosfet body diode provides a freewheeling path for the inductor current during the dead band. This ensures zero-voltage switching turn-on of both power mosfets in each buck–boost unit without auxiliary snubbers. Therefore, the switching losses are significantly reduced. Meanwhile, the integral of the inductor negative current is precisely controlled to minimize the circulating current. This guarantees both minimized conduction losses and suitable equalization speed. Furthermore, an equalization algorithm, which compensates the battery internal resistance induced state-of-charge error, is proposed to improve the equalization accuracy. The operating principles and design considerations are analyzed in detail. An experimental prototype to balance four series-connected lithium-ion battery cells is implemented. The experimental results validate the design of the equalizer and demonstrate obvious efficiency enhancement over the conventional method. [ABSTRACT FROM AUTHOR]

Paralleled inverters have the merits of high power rating, improved reliability, and convenient maintenance. However, zero-sequence circulating current (ZSCC) will occur and lead to current distortion and system loss. The ZSCC control is more complicated when three-level topology is utilized and paralleled number is increased. Therefore, this paper proposes a simplified ZSCC suppression scheme for multi-paralleled three-level T-type inverters (3LT2Is). A novel equivalent model is developed and the ZSCC controller based on the new model is easier to implement. Thus, the number of paralleled inverters can be increased without complicating the control scheme and the inverters could be switched on or off optionally. Besides, Feed-Forward (FF) strategy is adopted to eliminate the ZSCC spikes caused by symmetrical three-level space vector modulation. The effectiveness of the proposed control scheme is verified by both simulation and experimental results. [ABSTRACT FROM AUTHOR]

This paper deals with the control and implementation of solar photovoltaic (PV) array-based multi-objective bi-directional charger beneficial for electric vehicle (EV), household load, and utility. For EV, the charger provides the charging facility. For household load, the charger acts as a standalone inverter, and for utility the charger acts as an active power filter. However, for providing the multi-functionality and the multi-mode operation capability of the charger, a reconfigurable control strategy is proposed. Moreover, an adaptive dc-link voltage strategy is proposed for achieving the optimum voltage at dc link under all voltage conditions for achieving minimum ripple in grid currents. The charger also uses a voltage synchronization strategy for achieving the seamless mode transition between the grid-connected and standalone modes. In grid-connected mode, the charger uses a double second-order generalized integrator-based positive sequence estimator along with the improved linear sinusoidal tracer-based algorithm for generating the balanced and sinusoidal reference grid currents, under the unbalanced and distorted grid voltages. The charger is implemented in the laboratory, and the performance is presented under various steady-state and dynamic conditions. [ABSTRACT FROM AUTHOR]

This paper proposes a high-frequency isolated dc/dc converter, whose switching frequency is 20 MHz. Meanwhile, the switch voltage stress is reduced based on optimal switch impedance. In the proposed converter, the switch can operate in ZVS condition, which can help to reduce the switching loss. A mathematical model of the proposed high frequency converter is built, which provides an effective design method for the system parameters. Meanwhile, the design method for PCB air-core transformer has been proposed and depicted. To verify the feasibility of the proposed converter and mathematic model, a 10 W prototype is built. [ABSTRACT FROM AUTHOR]

Three-phase voltage source pulsewidth modulation (PWM) rectifiers can achieve constant dc voltage and sinusoidal grid currents under ideal grid voltages. However, under unbalanced grid voltage conditions, there are ripples at twice the grid frequency in the dc voltage, and the grid currents become highly distorted. To address the aforementioned problems, control methods developed under ideal grid voltage conditions should be modified. Various techniques have been proposed in the literature to calculate the new current reference or power reference. However, most methods use conventional pq theory and only consider the grid-side power control. Hence, the dc voltage ripples are not completely eliminated. Furthermore, the derived mathematical expressions for reference calculations are usually very complicated. In contrast to current methods, this paper proposes a very simple yet effective direct power control (DPC) method based on extended pq theory. By analyzing the instantaneous extended power of the line inductance, a simple and concise power compensation is analytically derived and added to the original power references. As a result, the dc voltage ripples are significantly reduced, and the grid currents remain sinusoidal even under unbalanced grid voltage conditions. The proposed method is compared to conventional DPC methods, and its effectiveness is confirmed by the presented experimental results. [ABSTRACT FROM AUTHOR]

In this paper, a new zero-sequence current suppression control strategy for the five-phase open-winding fault-tolerant fractional-slot concentrated-winding interior-permanent-magnet (FTFSCW-IPM) motor drive system with a common dc bus is proposed. By unequal distribution of the zero voltage vector, the proposed method can well suppress the zero-sequence current caused by the dead-time effect that the conventional eliminating method cannot be achieved. First, the dead-time effect to the zero-sequence current is discussed. Then the zero-axis controller is designed to obtain the reference common-mode voltage. Last, according to the principle of the unequal zero voltage vector distribution, the switching sequence of the two inverters can be calculated, and the maximum modulation index is also first deduced in detail. The proposed method is proved by the simulation and experimental results. [ABSTRACT FROM AUTHOR]

The utilization of wide band gap devices has enabled high frequency operation of totem pole bridgeless PFC rectifier. However, most of the designs reported in the literature with frequency higher than 100 kHz operate under discontinuous conduction mode or critical mode to reduce the switching loss. This paper proposes a zero-voltage-transition (ZVT) technique for totem-pole PFC rectifier under continuous conduction mode operation which enables efficient operation at switching frequencies well above 100 kHz. A simple auxiliary circuit consisting of a small auxiliary inductor and two active switches is placed in parallel with the main input filter inductor to achieve zero-voltage-switching of the main switches. The auxiliary switches operate with zero-current-switching (ZCS) and conduct current as short resonant pulses only during the critical turn-on transition which results in very low losses in the auxiliary circuit. The timing of the auxiliary switches is adaptively controlled with respect to the grid voltage angle for optimized overall efficiency. The effectiveness of the proposed ZVT scheme has been validated through experiments based on a 2.4 kW 400 kHz hardware prototype with 98.35% peak efficiency. [ABSTRACT FROM AUTHOR]

In this paper, a highly reliable back-to-back (BTB) power converter is proposed for doubly fed induction generator-based wind turbines (DFIG-WTs). When a power switch open-circuit fault is encountered in either the grid-side converter (GSC) or the rotor-side converter (RSC), a four-switch three-phase (FSTP) topology is formed to avoid using redundant bridge arms, which reduces the power circuit complexity and minimizes the conduction and switching losses. A simplified space vector pulsewidth modulation technique is used to eliminate sector identification and complex trigonometric calculations. In addition, the influence of dc-bus capacitor voltage unbalance on the electromagnetic torque is analyzed in detail. The offset current components are calculated, and they are deducted from the reference values in the modified control strategies to suppress the dc-bus voltage deviation. Moreover, the power loss model of a BTB converter is analyzed in detail, and the efficiency study is performed in various post-fault situations. Simulations in MATLAB/Simulink are carried out to verify the performance of a DFIG-WT based on a FSTP BTB converter. Furthermore, the control hardware-in-the-loop setup with RSC and GSC separately simulated in a digital real-time simulator is applied for experimental verification of the proposed control strategy. [ABSTRACT FROM AUTHOR]

The switched shunting resistor circuit is a classical and practical passive equalization scheme that nevertheless suffers from the voltage imbalance after the charging process. It results from the discrepancy of the shunting resistor and the physical characteristics of supercapacitor (SC) cells. In this paper, the distributed voltage equalization control strategies with the proportional-integral (PI) observer for the switched shunting resistor circuit are analyzed and compared. First, the charging and equalizing system is modeled as the switched system and the system observability is proved. The decentralized control and consensus control are analyzed and their shortages are presented. Then, the leader–follower cooperative control is proposed to improve the charging time while keeping the equalization performance. Meanwhile, the PI observer is designed to estimate the internal capacitance voltage of an SC precisely to avoid the effect of equal series resistance. The control convergence is proved by using the Lyapunov stability and switched system theory. The experimental results show that the proposed method has much superiority and wide applicability than the existing methods for equalizing voltages of SCs. [ABSTRACT FROM AUTHOR]

This paper presents a new islanding detection method for synchronous distributed generation (DG). The proposed method is developed based on the combination of rate of change of exciter voltage (RCEV) and open–close circuit breaker (OCCB) at a DG connection point. Whenever the RCEV parameter is not sufficient enough to detect an islanding condition efficiently and correctly, the OCCB strategy will be triggered. The proposed OCCB strategy sends a switching command to one phase of the three-phase circuit breaker (CB), which connects the DG to the grid. In this way, the CB will be immediately opened and then closed. This switching condition will cause a variation in the value of RCEV. This variation is small for the conditions when DG operates in parallel with the main grid, whereas it will be large during the occurrence of islanding. The implementation of the proposed strategy is cost-effective because it only uses the CB at the DG output and does not require any extra equipment. The proposed approach is tested on two different systems including a hypothetical power system and the IEEE 33-bus test system in MATLAB/Simulink environment. The simulation results show that the proposed method eliminates the nondetection zone and also reveals high accuracy compared with previously introduced methods. Moreover, it has been proved that the performance of the proposed approach is not affected by DG capacity, DG location, the number of DG units, as well as network configuration. [ABSTRACT FROM AUTHOR]

A large grid-connected private industrial and residential 11 kV network in northern Australia has its own 11 kV diesel generators to supply essential loads during grid supply outages. The generators each have a neutral earthing resistor (NER). When islanded from the grid, one NER provides the system reference. Significant circulating current was causing overheating of the NER. This paper describes the investigation undertaken, the options considered for rectification and the results from commissioning of the implemented solution. [ABSTRACT FROM AUTHOR]

In this paper, in response to the open-circuit fault scenario in the grid-side converter (GSC) of doubly fed induction generator-based wind turbines (DFIG-WTs), a fault-tolerant four-switch three-phase (FSTP) topology-based GSC is studied. Compared with other switch-level fault-tolerant converter topologies, fewer switches, less switching and conduction losses, and simpler converter structure are derived. A simplified space vector pulse width modulation (SVPWM) technique is proposed to improve the output current quality and reduce the computational complexity in the control process. Unified expressions of duty ratios for the two remaining healthy bridge arms are obtained. In addition, the three-phase unbalance phenomenon caused by the capacitive impedance in the faulty phase is analyzed from the ac point of view, and a current distortion compensation scheme is illustrated. Furthermore, a dc-bus voltage deviation suppression strategy is proposed to maximize the dc-bus voltage utilization rate and mitigate the damage to the dc-link capacitors. Simulations are carried out in MATLAB/Simulink2017a to demonstrate the validity of the proposed SVPWM technique and compensation schemes in FSTP GSC for a 1.5-MW grid-connected DFIG-WT when different working conditions are considered. [ABSTRACT FROM AUTHOR]

In this paper, a multipulse ac–dc converter fed multilevel inverter (MLI)-based indirect vector controlled induction motor drive (IVCIMD) is proposed for medium-power application. A 54-pulse ac–dc converter is utilized at the supply side to suppress the input current total harmonic distortion, as per the IEEE-519 standard. Mainly three separate isolated transformers are utilized and each transformer is configured as an 18-pulse ac–dc converter. Due to the phase shift in primary windings, these three transformers are reconfigured as a 54-pulse ac–dc converter. A 15-level binary-based cascaded MLI is utilized at the motor side to enhance the required performance of IVCIMD. A 15-level inverter is switched at fundamental frequency, which ensures the very low switching losses in the proposed IVCIMD. A modified nearest level modulation strategy is proposed to achieve fundamental switching frequency. The performance of the proposed IVCIMD is simulated at various operating conditions by utilizing Simulink/MATLAB platform. Simulated results are validated with experimental results on a developed prototype in the laboratory to show its usefulness for medium-power applications. [ABSTRACT FROM AUTHOR]

This paper presents a methodology of the battery modeling based on experimental tests results. As a main contribution, authors conducted an analysis of the main constraints and effects of each parameter of the batteries model on its behavior and lifetime. This can help to improve the accuracy of the model. Due to its capability to model the recovery effect and the rate-capacity one, the kinetic battery model serves as the basis of the study. Results of experimental tests are used to realize the analysis and to define the suitable methodology of batteries parameters identification. These last can serve for prediction and estimation of the battery lifetime according to the actual operating conditions, particularly in microgrid and distributed systems. [ABSTRACT FROM AUTHOR]

Achieving high efficiency and high power density features of intermediate bus converter (IBC) in data center application is very critical. This paper proposes a nonisolated switched-tank dc–dc converter (STC) to meet the high requirement of IBC. The proposed STC has fixed voltage conversion ratio. Theoretical analysis provides the guideline for designing resonant tank and nonresonant tank as well as selecting proper deadtime for the proposed circuit. With resonant operation feature of the proposed circuit, zero current switching is realized on all switching devices to help the high-efficiency operation of the proposed converter. Through the proposed design methodology in this paper, power loss on switching devices and planar inductors can be minimized. In addition, detailed power loss analysis and breakdown provide hints for further efficiency improvement. Simulation has been performed to validate the operating principle of the proposed STC. A designed 6x STC (450 W nominal/600 W maximum) based on eGaNFETs is demonstrated. With 54 V typical input voltage, the output of the 6x STC is 9 V. The GaN-based prototype achieves a peak efficiency of 98.55%. Also, it achieves 97.18% efficiency and 750 W/in3 power density at 450 W. [ABSTRACT FROM AUTHOR]

This paper presents the operation principle and benefits of a novel power converter topology named three-level two-stage decoupled active neutral point clamped (3L-TDANPC) converter, which is implemented based on a hybrid utilization of silicon (Si) insulated gate bipolar transistors (IGBTs) and silicon carbide (SiC) metal–oxide semiconductor field-effect transistors (mosfets). The 3L-TDANPC converter can achieve high efficiency with limited number of SiC mosfet modules while keeping balanced loss distribution among the switching devices, which helps increase the converter power ratings. In addition, in this 3L-TDANPC converter, the SiC mosfet has a potential to ride through short-circuit fault because of the presence of Si IGBTs. The key challenges that are associated with system resonant current are investigated and the methods to damp such resonant current are proposed and explained in detail. The simulation and experimental results based on a 1-MW 3L-TDANPC converter prototype confirm the expected benefits of this proposed converter and the effectiveness of the proposed resonant current damping methods. [ABSTRACT FROM AUTHOR]

Advancing the turn-off angle of the phase current of brushless direct current (BLDC) motors is a common control practice to improve the operating behavior and energy conversion efficiency of such drives by, e.g., reduction of current peaks, copper losses, and breaking torques. This paper investigates a refined switching strategy for a single-phase BLDC motor with bifilar winding to increase the energy conversion efficiency of the system. In addition to advancing the phase current turn-off angle, the turn-on angle is delayed to improve the drive's performance and increase the efficiency even further. This efficiency increase of up to 20.6% is verified experimentally for a speed range from 3000 to 8000 rpm, translating into a reduction of copper losses of up to 37.4% or a decrease of current peaks by 27.4%. The focus is on sub-fractional horsepower single-phase BLDC motors with bifilar winding which, concerning this matter, have not drawn much attention in the literature yet. The findings show that the improved switching strategy can reduce current peaks, breaking torques, copper losses, and therefore increase efficiency over the speed range of interest for fan applications. [ABSTRACT FROM AUTHOR]

An adaptive control of DPWM implementable in clamped-three-level inverters with two strings of photovoltaic (PV) panels in cascaded connection is proposed in this paper. The proposed modulation is developed based on the so-called circuit-level decoupling concept. It is able to provide balance line voltage even under unbalanced dc links. The unequal dc voltages appeared due to asymmetric maximum point of power trackings (MPPTs) are controlled by proper injection of zero-sequence voltage to the common mode voltage, while the total dc voltage is regulated based on the voltage commands generated by the MPPT of each string. Thus, both PV strings are able to be operated based on their MPPTs while there is almost no low-order harmonic distortion at the inverter output current. Compared with the previous methods, the high capability of the proposed method is evaluated by simulation study and experimental tests. [ABSTRACT FROM AUTHOR]

In recent years, doubly fed induction machine (DFIM) is increasingly being preferred in variable speed pumped storage power plants due to its merits like partial-rated excitation system (cost factor), unity power factor, real and reactive power controls. In large-rated DFIM (250 MW), parallel-connected three-level neutral-point clamped (3L-NPC) back-to-back converter systems are employed as rotor excitation circuit to handle slip power requirements (–10% to +8.33% in Tehri PSPP, India). The power semiconductor device failure in the rotor excitation circuit may cause serious concerns in grid stability and system reliability. To ensure the continuous operation of a generating unit, this paper aims to design a redundant parallel leg configuration with six antiparallel IGBTs for a 3L-NPC back-to-back converter structure to acquire fault tolerant operation under power semiconductor device failure. Furthermore, an efficient active current sharing control strategy with fault tolerant operation is implemented for each converter to obtain better performance of the drive system. In fault tolerant operation, fault identification is computed based on a normalized phase currents average method with less computational effort and timely identification of open switch faults in both grid side converter and rotor side converter. The circuit reconfiguration under postfault operation is performed by antiparallel IGBTs with the help of fault tolerant control scheme. The effectiveness of a designed fault tolerant control scheme is validated through MATLAB/Simulink environment for a 250-MW DFIM system with 25 MW (5-channel) power converters. To ensure the trustworthiness of the simulation, an experimental demonstration is performed through a 2.2-kW DFIM laboratory prototype with a 2-channel 3L-NPC back-to-back converter structure. [ABSTRACT FROM AUTHOR]

This paper investigates ac–dc–ac multilevel topologies for three-phase four-wire applications obtained from an interconnection of three-leg voltage-source converters. The topologies can be applied in line voltage regulators, universal active power filters, and uninterrupted power supplies. Operating principles, a pulsewidth modulation (PWM) technique, and an overall control strategy are developed. The PWM and control strategies are suitable to regulate the dc-link voltages and to reduce the harmonic distortion, switching stress, and power losses. Simulation results are used to compare the proposed configurations with a conventional solution in terms of harmonic distortion, semiconductor losses, and others characteristics. Experimental results are presented to validate the theoretical considerations and were obtained by using insulated-gate bipolar transistors with dedicated drives and a digital signal processor with appropriated plug-in boards and sensors. [ABSTRACT FROM AUTHOR]

Flyback/forward derived power converters offer operational simplicity, but require active clamping circuits to reduce switch voltage stress and improve the converter efficiency. This paper presents an active clamping circuit technique, which additionally ensures enhancement in the converter voltage gain. This is enabled by the proposed auxiliary circuit, which introduces a charged capacitor in series with the primary source during the energizing interval. Two circuits are designed on this principle, and design and operation of both are presented for discontinuous conduction modes. It is shown that the voltage gain of these circuits increases with increase in the leakage inductance, which is an improvement over existing converters. Also, in one circuit primary (secondary) winding, rms current is similar to (lower than) that in a typical ideal flyback converter, leading to improvement in power density. Operation and analyses of this variant are experimentally verified with a 400-V laboratory prototype. [ABSTRACT FROM AUTHOR]

This paper presents a step in microlevel photovoltaic (PV) summation technology for combining unsymmetrical PV modules with differences in specification and age, relocation on nonfertile land, or multilocation mounting by designing an add-on modular hardware interface to a multi-input single-output (MISO) dc bus, using an MISO controller employing a suitable maximum power point (MPP) tracker under partial shading/long distance/mismatching PV module conditions along with a sensor-less PV vector control inverter (PV–VCI) driving a three-phase asynchronous squirrel cage induction motor dedicated to irrigation, with the facility of autoconfiguration/autotuning at the beginning. A PV source gets automatically added/removed in a ramp profile in proportion to the load in steps, thus keeping on only when required, enabling high efficiency, minimum heating, and prolonged life as that of a PV module. The contribution includes a reduced PV energy cost per watt by 24.10%, improved return on investment by 27.48%, improved water discharge yield by 11.06%, and improved MPP tracker impact by 14.59% with 90.88% MISO system efficiency compared to a normal scheme. [ABSTRACT FROM AUTHOR]

Inductive power transfer (IPT) is widely discussed as an alternative to contact charger for plug-in hybrid and electric vehicles. This paper analyzes a contactless battery charger back-end power factor correction (PFC) concept, reducing the primary-side circuit complexity and physical size. For that purpose, the main volume and loss factors of a contactless battery charger are identified, discussing the partitioning of tasks to perform a unity power factor operation. An analysis of the most commonly used front-end PFC and the proposed back-end PFC configuration is performed, with the aim of highlighting benefits and limitations of each variant. Moreover, performance of silicon (Si) and gallium nitride (GaN) devices has also been evaluated, defining the main advantages and drawbacks of both semiconductor technologies in different IPT scenarios. The study is verified experimentally on a 3.2 kW contactless battery charger. [ABSTRACT FROM AUTHOR]

This paper presents a nine-level transformer-based inverter requiring only eight switches. The envisaged structure consists of two standard H-bridges fed from a single dc source. Besides, a single-phase transformer is employed to aid the process of intermediate voltage level generation. An ad-hoc pulsewidth modulation scheme based on boolean logic form equations is developed to derive the gating pulses. An effortless extension of the proposed inverter to a higher number of voltage levels is also achieved by generalizing the switching functions. Furthermore, the superior performance of the proposed topology is demonstrated through a comprehensive cost-based analysis. Finally, the validation of the proposed topology is accomplished through experiments on a down-scale prototype, and the measurement results are included. [ABSTRACT FROM AUTHOR]

Pollution problems caused by fossil fuels have led to more investigations on renewable energy systems. Photovoltaic cells and fuel cells output low-level voltage than required; therefore, high gain dc–dc converters are used to boost this low voltage. The Z-source converter can be employed as dc–dc converter to boost the photovoltaic panel voltages. It also offers other advantages, such as clamped switched voltage, high voltage gain, isolation of energy source from the load, and positive polarity for output voltage; therefore, this is a good choice for high step-up applications. This paper presents analysis of a novel high step-up Z-source based dc–dc converter that has higher voltage gain than the Z-source converter. Furthermore, high efficiency, low device voltage stress, and wide voltage gain range make it a good candidate for photovoltaic and high voltage step-up applications. The proposed dc–dc converter is evaluated experimentally for converting 24-V dc input to 300-V dc output at 100 W and to validate the simulation results. [ABSTRACT FROM AUTHOR]

An optimal current control strategy for asymmetrical hybrid multilevel inverters (MLIs) is proposed in this paper enabling their use on motor drives, static synchronous compensators, and photovoltaic and wind generators, where a fast and precise current regulation is required. A key feature of these highly efficient converters is that an ac machine (motor or transformer) operates according to an open-end winding configuration, connected on one side to a main MLI and, on the other side, to an auxiliary two-level inverter (TLI). The first efficiently controls the main power stream operating at a low switching frequency, while the TLI acts as an active power filter, exploiting a conventional high-frequency two-level pulsewidth modulation (PWM) technique. The proposed control scheme optimally exploits the key features of the two inverters by suitably sharing the control task. In fact, a predictive current control is assigned to the MLI, which can be accomplished by low switching frequency operations, while the high switching frequency of the PWM-operated TLI is exploited to accomplish a fast and precise closed-loop current control, processing only a part of the power stream flowing through the system, thus producing low power losses. Simulations and experimental results confirm the consistency of the proposed approach. [ABSTRACT FROM AUTHOR]

This paper proposes new angles constraint for selective harmonic elimination-pulsewidth modulation (SHE)-PWM utilized in single-phase inverter applications. The proposed angles constraint naturally eliminates all triplen harmonics, whereas they conventionally appeared in all single-phase output voltages. The harmonic amplitude formula is developed based on the obtained angles constraint, and then modified single-phase SHE equations are defined to eliminate only specified low nontriplen harmonics. Therefore, more harmonics would be eliminated with the same switching frequency in modified SHE-PWM. Five-level voltage waveform has been opted to implement the introduced method, but it can be applied on all multilevel voltage waveforms such as seven-level with even number of angles. Unlike the conventional SHE technique, THD is analyzable in modified SHE to find optimum values for switching angles in order to control noneliminated harmonic amplitudes and minimize THD. Moreover, the cancellation of triplen harmonics empowers a single-phase inverter to supply nonlinear loads beside linear ones. Some experimental tests are accomplished using a single-phase five-level modified packed U-cell (MPUC) inverter. Results are discussed to prove the excellent performance of a single-phase MPUC inverter under both normal and harmonic loads and accurate elimination of determined triplen and nontriplen harmonics by applying the presented angles constraint. [ABSTRACT FROM AUTHOR]

This paper illustrates the application of a solving method of linear systems to a multilevel inverter. This study applies a generic pulsewidth modulation (PWM) method to a multilevel topology. This method finally highlights some specific modulation schemes. First, the study describes the mathematical model of the inverter leg. The leg is made of three level T-type structure. The model is extended to the three-phase inverter. The generalized inverse is used to generate the solution set of the conduction rates. Among the modulation strategies possible, three specific modulation schemes are proposed. The modulation schemes are applied to simulate a PWM three-phase inverter. Finally, some experimental results complete the analysis. [ABSTRACT FROM AUTHOR]

Current commutation from the load current path to the commutation path is the precondition to interrupt current successfully for hybrid direct current circuit breakers (DCCB). With remarkable current commutation performance, current commutation drive circuit (CCDC), mainly consisting of air-core transformer, fast-closing switch (FCS), and precharged capacitor, is proposed by us. In this paper, to eliminate the operating losses of CCDC and to avoid unrecoverable damage of FCS, CCDC used in hybrid DCCB for current commutation has been improved. Different submodules (SM) of commutation path in hybrid DCCB are analyzed, and experiments have been carried out on a hybrid DCCB prototype. Theoretical analysis and experiment results have shown that no matter which kind of SM is used, improved CCDC can ensure reliable current commutation in hybrid DCCB. In the end, by taking total cost of CCDC into consideration, a novel optimization method is proposed to design the parameters of CCDC. With this optimization method, CCDC for hybrid DCCBs with different rated voltage and current can be designed individually and its cost could be reduced significantly. [ABSTRACT FROM AUTHOR]

This paper proposes a multilevel flying capacitor dc/dc boost converter (FCBC) with a small capacitance of the flying capacitor for the reduction of converter size. In this paper, the design methods for the boost inductor and the flying capacitor in the n-level FCBC are principally and experimentally confirmed. Furthermore, the boost inductor is designed based on maximum product of voltage-time, regardless the number of level. Meanwhile, the minimum capacitance of the flying capacitor is designed based on the maximum switching device voltage stress, regardless of the output voltage ripple influences. Moreover, the achieved maximum efficiency of the designed three-level FCBC is 98.5% at the output power of 1 kW. Finally, the effectiveness of small capacitances of the flying capacitor in the three-level and five-level FCBCs is analyzed. The characteristics of the distorted voltage across the input voltage source and the boost inductor, and the distorted current to the output side (output capacitor and load) are investigated with several capacitances of the flying capacitors in the three-level and five-level FCBCs. As a result, it is experimentally confirmed that the distorted voltage is drastically reduced by increasing the number of level. Besides, the distorted current is almost the same although the number of level is increased. Therefore, based on the experimental results, it is shown that small capacitance of the flying capacitor can be used in the n-level FCBC without compromising the stability of converter operation. [ABSTRACT FROM PUBLISHER]

When medium-voltage reduced-voltage autotransformer (RVAT) motor starters fail, also referred to as Korndorfer starters, particularly ones in which there is no clear failure to the core or tap-to-tap but just layer-to-layer deep down in the windings, the results are almost always catastrophic. An offshore platform is used as an example to discuss site-specific solutions that are based on the recently developed switching transient analysis, sweep frequency-response analysis, and state-of-the-art electromagnetic transient program (EMTP) simulation techniques. This paper will explain how the power system, interrupter, and transformer interact and outline the steps to solve this long-standing problem as well as present the newly applied solutions. Since the implementation of these new solutions, no further failures have occurred. [ABSTRACT FROM PUBLISHER]

This paper presents the design and experimental results of a Thomson coil-based fast mechanical switch for hybrid ac and dc circuit breakers rated at 30-kV voltage and 630-A current. The compact design with optimized circuit parameters and geometric dimensions of components targets 2-mm travel within 1 ms when driven by a 2-mF capacitor bank precharged to 500 V. The use and design of a disc spring as the damping and holding mechanism is presented. Structural design of a complete switch assembly rather than just the actuator is given. Experimental results show that the switch can travel 1.3 mm in the first 1 ms and 3.1 mm in the first 2 ms when driven by a 360-V 2-mF capacitor bank. Such fast mechanical switches facilitate hybrid circuit breaker interruptions within 2 or 3 ms for ultra-fast and highly efficient protections in 5–35 kV medium-voltage dc as well as ac systems. [ABSTRACT FROM PUBLISHER]

This paper presents a hybrid pulse width modulation-based discontinuous modulation (D-HPWM) strategy with dc-link voltage balancing for a three-level neutral-point-clamped (NPC) traction inverter drive. The results are then compared with continuous-hybrid-PWM (C-HPWM) to check the performance improvement. The HPWM strategy uses both the advantages of carrier- and space-vector-based PWM strategies. The duty cycles are generated using the carrier-based strategy to reduce the computational time and complexity of the system and redundant vector states are used to keep the two dc-link capacitor voltages balanced. As discontinuous PWM (DPWM) reduces the switching losses considerably compared to the continuous PWM, the DPWM strategy is developed in this paper for the HPWM-based strategy. Detailed comparison studies are then carried out in MATLAB/Simulink and PLECS to show the conduction and switching loss distribution with change in modulation index for different power switches. A 54.0-kW surface permanent magnet synchronous machine (PMSM) is used for this simulation studies. Moreover, the total inverter loss and losses in each insulated gate bipolar transistor (IGBT) are also compared. Detailed experimental performance analysis is also carried out with a scaled down prototype of a 6.0-kW surface PMSM, NPC inverter, and real-time emulator DSpace, to show the capacitor voltage deviation with both control strategies. [ABSTRACT FROM PUBLISHER]

Parallel ac-link universal power converters are a relatively new class of power converters that can be configured as dc–dc, dc–ac, ac–dc, and ac–ac. These converters are extensions of a buck–boost converter in which the current of the inductor is alternating and the input and output can have any number of phases with any forms, voltage amplitude, or frequency. By placing a small capacitor in parallel with the link inductor, all the switches can benefit from soft switching. The main limitation of the parallel ac-link universal power converter is its large number of switches. A three-phase ac–ac configuration requires 24 unidirectional switches. This paper proposes two topologies based on the parallel ac-link universal power converters that significantly reduce the number of switches. One of the proposed topologies reduces the number of switches in a three-phase ac–ac configuration to 16. The other topology reduces the number of switches to 10. The latter can offer galvanic isolation with only a single-phase high-frequency transformer. This paper presents the principles of the operation of the proposed topologies and evaluates them through simulation and experiments. [ABSTRACT FROM AUTHOR]

In this paper, a novel multilevel dc–ac inverter is proposed. The proposed multilevel inverter generates seven-level ac output voltage with the appropriate gate signals’ design. Also, the low-pass filter is used to reduce the total harmonic distortion of the sinusoidal output voltage. The switching losses and the voltage stress of power devices can be reduced in the proposed multilevel inverter. The operating principles of the proposed inverter and the voltage balancing method of input capacitors are discussed. Finally, a laboratory prototype multilevel inverter with 400-V input voltage and output 220\ \textV\text{rms}/2\,{\text{kW}} is implemented. The multilevel inverter is controlled with sinusoidal pulse-width modulation (SPWM) by TMS320LF2407 digital signal processor (DSP). Experimental results show that the maximum efficiency is 96.9% and the full load efficiency is 94.6%. [ABSTRACT FROM AUTHOR]