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This paper presents a study of the losses in the integrated buck–flyback converter (IBFC) used as high-power-factor LED driver. The aim of the study is to investigate the possibilities of increasing the efficiency of the IBFC converter. The procedure of the improvement is done by obtaining the equations of the current through each component in terms of converter parameters. The current is found in an average value or rms value, depending on the type of the parasitic component, whether it is modeled by a parasitic forward voltage source or by a parasitic resistance, respectively. Using these equations and the parasitic model, the losses of each element of the converter are estimated. This paper proposes a technique to increase the efficiency of the IBFC by redesigning the converter parameters. Furthermore, this paper presents a case of study with a step-by-step efficiency enhancement process of an existing driver. The driver is operating under universal input conditions, and 38 V output, supplying an LED luminary of 26.5 W. The new design shows an improvement of the efficiency from 82% in the old design to 89% in the proposed one. Moreover, the new design shows an improvement in the power factor and the THD and a 50% reduction in the output current ripple. Furthermore, a reduction in the number of components has been achieved, as it is found by the analysis that by adjusting the converter parameters, one diode can be removed. Finally, the presented methodology is explained in detail so that it can easily be applied to other dc–dc converters. [ABSTRACT FROM AUTHOR]

This paper deals with the speed and position estimation for synchronous reluctance motors (SyRMs) and interior permanent-magnet synchronous motors (IPMs). A unified design and analysis framework for a class of back electromotive force-based observers is developed and the links between apparently different estimation methods are brought out. State observers equipped with a speed-adaptation law are shown to be mathematically equivalent to voltage-model-based flux observers equipped with a position-tracking loop. The error signal driving the adaptation law or the tracking loop is presented in a generalized form. Using the framework, a stabilizing gain design is reviewed and detailed design guidelines are given. Selected observer designs are experimentally evaluated using a 6.7-kW SyRM drive and a 2.2-kW IPM drive. [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]

Grid-tied inverters and associated control techniques have gained importance in the domain of distributed generation. Different methods of control have been compared in the literature depending upon the ability to meet total harmonic distortion limits, damping offered to resonant oscillations, and stable operation. Multiple-loop methods compared to their single-loop counterparts have proved to be highly effective for meeting the grid regulations. In the literature, while single-loop and two-loop control systems for LCL filter have been assessed, not much study on three-loop control (TLC) has been done, possibly due to the hardware complexity and cost imparted by the increase in the number of sensors. In this paper, a TLC structure for grid connected inverters is analyzed for stability and parametric variations. Robustness of TLC is compared with single-loop grid current feedback control and a two-loop control structure. An approach to estimate the state variables is proposed in this paper, which cuts down the number of sensors and cost of implementation. The performance of the system is analyzed through simulations and results are validated in a hardware setup, under dynamic and steady-state conditions, thereby showing that this is a promising approach. [ABSTRACT FROM AUTHOR]

Back electromotive force (EMF) self-sensing is commonly used in induction machine (IM) drive systems, which can be effectively controlled using deadbeat-direct torque and flux control (DB-DTFC). Accurate machine parameters are needed for back EMF self-sensing DB-DTFC drive systems. In this paper, an injection-based, real-time parameter estimation method for IM DB-DTFC drives, in the back EMF self-sensing mode, is proposed. The methodology for choosing appropriate frequencies for injection signals is introduced. With encoder-based velocity feedback, the proposed DB-DTFC injection method induces no additional torque ripple, compared to traditional d-axis pulsating voltage vector injection used in indirect field oriented control. However, in the self-sensing mode, the injected flux linkage induces an erroneous speed ripple, which causes a real speed ripple. This paper presents two approaches to eliminate the speed ripple. Finally, the injection-based real-time parameter estimation method for the system is experimentally evaluated. [ABSTRACT FROM AUTHOR]

High speed permanent magnet synchronous motors (PMSMs) are used in electric vehicles because of their intense power density. The high speed implies a significant electromotive force and requires flux weakening. The usual control algorithms realize flux weakening by adding a negative $I_{d}$ current component when the voltage required by the current regulation exceeds the maximum voltage depending on the battery. If the magnet can be totally defluxed, then it is better to use a maximum torque per volt strategy. Furthermore, there is no speed regulation in the control and the driver gives a torque reference. This reference value has to be limited by the attainable operating points; therefore, the battery power limit has to be taken into account in addition to the voltage and current limits. The d–q current references are calculated to minimize the total current magnitude required to reach the reference torque. This paper proposes a strategy to control a PMSM operating continuously since the speed zero up to the maximum speed without the switching algorithm, in order to take into account the different limitations (current, voltage, and power) and to expand the overspeed zone. In order to validate the proposed strategy, experimental results are shown for a low power machine. [ABSTRACT FROM AUTHOR]

In this paper, a simplified robust control is proposed to improve the performance of a three-phase current controlled voltage source inverter connected to the grid through an inductive–capacitive–inductive (LCL) filter. The presence of the LCL-filter resonance complicates the dynamics of the control system and limits its overall performance, particularly when disturbances and parametric uncertainty are considered. To solve this problem, a robust active damping method based on the linear active disturbance rejection control (LADRC) is proposed. The simplification is made possible by order reduction in the plant transfer function using Padé approximation. Simulation results show that the proposed LADRC-based current controller achieves high power quality and good dynamic performance, in the presence of parameters uncertainties as well as external disturbances. An experimental prototype is built to verify the effectiveness and practicality of the proposed control strategy. [ABSTRACT FROM AUTHOR]

This paper deals with a novel reduced sensor strategy, for two-stage single-phase grid connected solar photovoltaic system with a battery, where the dc-link voltage sensor is not required. Moreover, for maximum power point tracking (MPPT), a new “normal harmonic search” (NHS) algorithm is used, and for voltage source converter (VSC) control, a novel “power normalized kernel least mean square” (PNKLMS) algorithm is proposed. The PNKLMS algorithm is used for active load component extraction from the load current, even when the load current is characterized by linear or nonlinear behavior. Moreover, PNKLMS algorithm is used for reference grid current generation. The NHS algorithm is an improved version of the harmony search, which is inspired to the music composition technique and its searching ability is improved by using the normal probability distribution factor. Therefore, NHS reaches the global maximum power point very quickly and is suitable for online searching on hardware. Moreover, the extracted power is fed into the grid. For control of VSC, the proposed PNKLMS control technique is used, which maintains the power quality. The performances of NHS-based MPPT and PNKLMS-based control technique with reduced sensor approach are tested on a developed prototype. The satisfactory steady-state and dynamic performances of the NHS algorithm are demonstrated under variable irradiance and temperature during partial shaded conditions. Moreover, the performances of the PNKLMS algorithm, without using dc-link voltage sensor are demonstrated during overvoltage, undervoltage, harmonics distortion, and load nonlinearity condition, results of which have satisfied the objective of the proposed system and the IEEE-519 standard. [ABSTRACT FROM AUTHOR]

This paper presents a comparative study of harmonic current suppression control strategies for dc-biased vernier reluctance machines (dc-biased-VRMs). The back electromotive force waveforms of dc-biased-VRMs contain low-order harmonics. It leads to harmonic currents in phase windings. To eliminate the low-order harmonic currents, two types of representative architectures, namely closed-loop current control with proportional integral and resonant regulators and specific order harmonics compensation algorithm in multilevel rotating reference frame, are theoretically analyzed. The performance of the two architectures is compared in terms of accuracy, complexity, and dynamic performance for harmonic current suppression. The experimental results obtained are presented. It verifies that the two strategies have their specific advantages. [ABSTRACT FROM AUTHOR]

The paper aims to provide a guideline for rotor design of permanent magnet (PM) assisted synchronous reluctance machine (PMa-SynRM). Unlike interior PM machines, the PMa-SynRM is essentially an SynRM with dominant reluctance torque. The PMa-SynRM is often designed by directly embedding magnets into an SynRM rotor to improve the performance. However, how the PMs can be arranged in the rotor to enhance motor performance has not been fully discussed. This paper investigates the influence of several key factors concerning the PM arrangements, including number of PM layers, inserted positions, and PM sizes. The torque, flux linkages, power factor, and motor performance are comprehensively evaluated. Based on the analysis, a brief guideline is suggested for PMa-SynRM rotor design. Finite element analysis is used for evaluation and experiments are conducted to validate the analysis. [ABSTRACT FROM AUTHOR]

This paper presents a new least-mean-square (LMS) algorithm based deadtime compensation method to suppress the current distortion in permanent-magnet synchronous motor (PMSM) field-oriented control (FOC) drives. Compared to conventional average value compensations, the proposed method is robust to switching device parameter variations thanks to the online adaptation capability of the LMS algorithm. Similarly, the disturbance observer compensators are also immune to switching device parameter variations; however, varying motor parameters degrade their compensation performance. Without prior knowledge of switching device or motor parameters, the proposed method can directly reduce the deadtime current harmonics by generating compensation voltage references. In addition, the proposed method is easy to implement since it does not require voltage errors estimation or current harmonics extraction, which are necessary for disturbance observer and adaptive filter based methods. The proposed method is tested on a 2.5-kW voltage-source inverter PMSM drive controlled by an FOC algorithm. Its effectiveness is validated by both experimental results and spectrum analysis. [ABSTRACT FROM AUTHOR]

Many of the renewable energy resources, like offshore wind, utility PV farms, are located far away from the load centers, which requires dc power transmission system to efficiently deliver power. Voltage-source converter solution is required in many applications due to the stability and compensation requirement. This paper presents a new voltage source converter topology for medium to high voltage dc application, named modular embedded multilevel converter (MEMC). MEMC is based on a three-level topology structure and consists of series-connected insulated-gate bipolar transistor (IGBT) bridge stacks, like the popular modular multilevel converter (MMC) and series-connected thyristor or press-pack high voltage integrated gate-commutated thyristor or IGBT stacks. The basic operation principle, control solutions, and the methods to commutate the thyristors are explained in detail. Due to the three-level structure, the total number of IGBT stacks are reduced by half compared with MMC, leading to much lower energy storage, weight, volume, and system complexity. Also by replacing part of the IGBT stack in MMC with thyristor stack, both of the system conduction loss and switching loss can be further reduced. There are other topology variations of MEMC with a similar operational principle but different characteristics. [ABSTRACT FROM AUTHOR]

Many modern industrial plants are equipped with local generation and are designed to operate as a microgrid. Under normal conditions, the plant is connected to and often mainly supplied by the utility's network. However, during a disturbance on the utility side, it may island from the grid and continue supplying its load using available on-site generation. When this generation is not sufficient to supply the entire load (which is often the case), some of the noncritical loads must be shed so as to ensure that the remaining loads receive the required quality of service. The decision to island and the amount of load to be curtailed are determined based on the values of the frequency/voltage. In this paper, we first propose a hybrid undervoltage/under frequency islanding scheme for an industrial park consisting of multiple substations (microgrids) each supplying one or more industrial plants. It is assumed that once the park is islanded from the grid, the substations are instantly formed into multiple islands where all noncritical loads are automatically disconnected. This is done to ensure that individual islands are not affected by potential instability of their neighboring networks. However, once the individual islands are stabilized, it is possible to share their available generation capacities to maximize the total load served. This would mean connecting one or more islands together to form bigger ones. We formulate this as a network reconfiguration problem that tries to maximize the amount of load served by reconfiguring the network topology and using backup energy resources. The problem is solved and analyzed for a simplified version of an industrial park, both at steady state and during transients. [ABSTRACT FROM AUTHOR]

LLC resonant converter is a soft switching frequency modulated dc–dc topology with its switching frequency near the resonant frequency. However, in applications where a wide output voltage is desired, it is extremely difficult to tune its operation close to the resonant frequency. In this paper, a novel pulsewidth modulated LLC type resonant converter based on voltage quadrupler rectifier is proposed. The proposed converter always operates at the resonant frequency and is able to achieve a wide output voltage range by modulating the duty cycle of the secondary side auxiliary mosfet. This brings the benefits of the decreased circulating current and corresponding conduction loss, as well as the simplification of the parameters selection and magnetic component design. Zero-voltage-switching and zero-current-switching are realized among all power mosfets and all power diodes, respectively. Detailed circuit operation principles and modeling method are presented. A 1.3-kW converter prototype, generating 250–420 V output from 390-V dc-link is designed. Both the circuit functionality and the theoretical analysis are verified in the experimental results. [ABSTRACT FROM AUTHOR]

In this paper, we present modifications to the sphere decoder initially introduced in the work of Geyer and Quevedo and modified in the work of Karamanakos et al. that significantly reduce the computation times during transients. The relative position of the unconstrained solution of the integer quadratic program underlying model predictive control (MPC) with respect to the convex hull of the (truncated) lattice of integer points is examined. If it is found that the unconstrained solution does not lie within the convex hull—a phenomenon that is observed mostly during transients—then a projection is performed onto the convex hull. By doing so, a new sphere that guarantees feasibility and includes a significant smaller number of candidate solutions is computed. This reduces the computation time by up to three orders of magnitude when solving the optimization problem at hand. Nonetheless, the reduction of the computational burden comes at a cost of (mild) suboptimal results. The effectiveness of the proposed algorithm is tested with a variable speed drive system consisting of a three-level neutral point clamped voltage source inverter and a medium-voltage induction machine. Based on the presented results, the sphere decoding algorithm with the proposed refinements maintains the very fast transient responses inherent to direct MPC. Moreover, it is observed that the occasional implementation of suboptimal solutions does not lead to a deterioration of the system performance. [ABSTRACT FROM AUTHOR]

This paper presents the development, implementation, and performance evaluation of a new active dc link for permanent magnet generator (PMG)-based wind energy conversion systems (WECSs). The proposed dc link is developed based on the multiport converter (MPC) topology with two dc–dc power electronic converters (PECs) that have separate inputs and parallel-connected outputs. The first dc–dc PEC is designed as a boost converter, while the second dc–dc PEC is designed as a flyback converter. Each dc–dc PEC is operated and controlled independently to facilitate processing continuous and/or discontinuous input dc voltages. The performance of the MPC active dc-link is experimentally evaluated using a grid-connected 7.5-kW PMG-based WECS, when operated under different wind speeds and/or levels of power delivery to the host grid. Test results show that the proposed dc link can produce a high-quality-regulated dc output voltage over a wide range of wind speeds and levels of power delivery to the host grid. Performance results also demonstrate that the operation of the MPC active dc link has minor impacts on the operation and control of the generator-side and grid-side PECs. [ABSTRACT FROM AUTHOR]

This paper presents design, modeling, and control of a quasi-resonant zero-current switching boost converter used in a photovoltaic (PV) power based surface-mounted permanent magnet synchronous motor (SPMSM) for driving compressor loads of a refrigeration plant situated in remote locations. The solar-based refrigeration system is an attractive solution as cooling burden matches with the peak incident solar radiation. The field-oriented controlled voltage source inverter is employed for speed control of the SPMSM drive under variation in solar irradiation. The MATLAB/SIMULINK environment is used to model the control of a PV power based SPMSM drive. The performance of the developed system is investigated under wide changes in operating conditions. A prototype of an 800 W PV power based SPMSM drive is developed in the laboratory to validate the simulation results. [ABSTRACT FROM AUTHOR]

This paper proposes a new control method suitable for active power filters to reduce the dc capacitor voltage ripples associated with the third-order harmonic current compensation. The proposed method superimposes a negative-sequence fundamental current on the compensating current to cancel out the active power ripple caused by the third-order harmonic current. As a result, the proposed method has the capability to eliminate the dc capacitor voltage ripple at double the source frequency. Experimental results obtained by a 10-kW three-phase diode rectifier verify the validity of the proposed method. The proposed method exhibits a good suppression performance of the dc capacitor voltage ripple at double the source frequency. [ABSTRACT FROM AUTHOR]

This paper describes a new brushless and magnet-less synchronous generator where an induction machine (IM) is embedded in a synchronous machine (SM) to provide the excitation. Hence, this machine is named as brushless induction excited synchronous generator (BINSYG). To avoid the magnetic interaction between both IM and SM, they are configured for different number of pole pairs. A rotating uncontrolled rectifier (mounted on the shaft) is proposed to be used to rectify the rotor voltage of the IM to provide the excitation to the SM. Thus, by controlling the IM from stator side, field current of the SM can be controlled smoothly. As an example, in this work, SM and IM are configured for two pole and six pole, respectively. Practical winding-design-challenges and mutual interaction between IM and SM fields are analyzed briefly for 2/6 (SM poles/IM poles) pole BINSYG. Extensive finite element simulations of the proposed machine have been conducted using Maxwell-2D and these simulated results are obeying the theoretical analysis. A 3 kVA laboratory prototype of 2/6 pole BINSYG has been developed to evaluate the performance when IM is operated in the plugging mode for definite advantages. While a brushless configuration is proposed, brushes and slip-rings are used for the experimental machine, such that, rotor side windings of SM and IM can be accessed for the better understanding of the performance. Experimental results from this prototype confirm the theoretical and finite element method predictions. [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]

An improved hybrid unified power flow controller (IHUPFC) is developed in this paper to control the power flow and increase the utilization rate of the existing transmission lines. The IHUPFC is composed of an improved “Sen” transformer (IST) and a small capacity unified power flow controller (UPFC). After a detailed introduction of the structure and voltage regulation performance of the IST, this paper derives the capacity relationship between the IST and the UPFC. Then, this paper introduces the technology of the IHUPFC in power flow regulation and transmission capability improvement. Besides, the advantages of the IHUPFC in performance and structure are analyzed. The IST has simpler structure and larger power flow control area than a “Sen” transformer, and the IHUPFC provides a continuous active and reactive power flow control. Simulation and experiment studies are used to verify the practicability and superiority of the IHUPFC. [ABSTRACT FROM AUTHOR]

Recent works have shown that the state-feedback decoupling of capacitor voltage allows for drastic bandwidth enlarging of current controllers for grid-forming converters in islanded microgrids. Furthermore, Smith predictor and lead compensation have been also proved as very effective implementations for compensating the controller delays. These features are key to fulfill demanding requirements in terms of voltage regulation in islanded applications. This work deepens in the discrete-time domain modeling and implementation issues of the above-mentioned techniques. A full discrete-time and sensitivity analyses reveal phenomena not properly modeled in previous works, which limits the performance: the presence of high-frequency oscillations due to discrete poles with negative real part. Subsequently, proper design countermeasures (i.e., limit bandwidth) are proposed. Discrete implementation of the voltage controller is also addressed, and design guidelines are provided. Experimental tests in accordance with the high demanding standards for uninterruptible power supply systems verify the theoretical analysis. [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]

This paper describes the spatial mode, frequencies, the voltage reference update timing, and their interaction of pulsewidth modulation (PWM) harmonics, focusing on a distributed winding permanent magnet synchronous motor. We investigated the electromagnetic force generating the noise by using a couple of analyses between a circuit simulator and a two-dimensional finite element analysis. It was found that the electromagnetic noise and vibration result from a radial electromagnetic force spaced at the spatial zeroth mode of $f_{c}\pm 3f_{1},f_{c}$ , and ${{2}}f_{c}$ ($f_{c}$ : carrier frequency, $f_{1}$ : fundamental frequency of the current). We have shown that the radial electromagnetic force of frequency $f_{c}\pm 3f_{1}$ and ${{2}}f_{c}$ results from PWM harmonics. Also, the radial electromagnetic force of frequency $f_{c}$ evidently results from the voltage reference update timing of ${{1/ }}f_{c}$. The electromagnetic noise and the spatial mode are demonstrated in the experiment. [ABSTRACT FROM AUTHOR]

Inverter dead-time is known to make open-loop induction motor drives oscillatory, while operating at light-loads in particular. While dead-time compensation schemes exist, precise compensation of the same is often challenging as it involves factors such as device and driver delays and switching transition times, which are difficult to be quantified accurately. Hence, the effect of dead-time could be under or overcompensated. This paper presents a comprehensive analysis of the impact of such undercompensation and overcompensation on the stability of a 100-kW induction motor drive, along with experimental investigations of the same. The effects of undercompensation and overcompensation on the inverter output voltage are analyzed on a switching-cycle average basis. Further, small-signal models are proposed for an open-loop drive, when it is undercompensated and overcompensated. Stability analysis of the above motor drive is reported, which predicts oscillatory behavior with both under and overcompensation, over certain fundamental frequency ranges, respectively. Further, two different types of oscillatory behavior, characterized by different oscillating frequencies, are observed for the cases of under and overcompensation. The analyses are supported by simulations. Experimental investigations carried out also support the analyses and simulation results. [ABSTRACT FROM AUTHOR]

This paper presents an improved analytical model for estimating the high-frequency current ripple of interior permanent magnet synchronous machines due to pulsewidth modulation (PWM) switching. The proposed model accounts for the impact of slotting effect, magnetic saturation, and cross-coupling between the $d$ - and $q$ -axis. The model is subsequently used to investigate several factors that influence the PWM-induced current ripple. These include the PWM switching frequency, fundamental frequency (i.e., machine speed), dc-bus voltage, current control angle (i.e., γ angle), and the excitation current amplitude (i.e., saturation level). Experiments have been conducted to verify the analytical prediction results. These results show that the analytical model can predict the PWM-induced current ripple waveshape very well for many operating conditions and accurately estimate its rms value over a complete fundamental period. [ABSTRACT FROM AUTHOR]

The power oscillations at the input of constant power loads (CPLs) fed by LC filters is a well-known phenomenon in dc microgrids. The phenomenon happens because of the negative resistance characteristic exhibited by CPLs. The oscillations can be damped by inserting virtual resistances at the output of voltage-regulating converters to offset the negative resistance of the CPLs. However, large virtual resistances lead to a poor voltage regulation of the dc bus. This paper proposes a frequency-dependent virtual impedance comprising of a parallel RL branch, which solves the issue of poor voltage regulation. Further, the large signal stability of the system in the presence of the virtual impedance is also investigated through the Brayton–Moser mixed potential analysis. Detailed simulations and analysis of the frequency-domain interactions of the system are carried out and the effectiveness of the proposed technique is showcased. Experimental results from a 250 W prototype CPL are included to validate the proposed technique. [ABSTRACT FROM AUTHOR]

This paper presents a novel grid current control of a grid-connected voltage source converter with an LCL filter. The proposed control method uses an $\mathcal {H}_\infty$ synthesis method to shape the input admittance of the converter, to track a given current reference, and/or to limit the controller actuation at different frequency ranges. The converter admittance is shaped, both in magnitude and phase, following a model reference defined by the designer in the frequency domain. By specifying a low admittance magnitude reference, the optimization algorithm will obtain a controller that actively damp the filter resonance and attenuate/reject the grid voltage oscillations, either in a wide frequency range or concentrated at the main harmonic frequencies. Additionally, the proposed controller design methodology takes advantage of its admittance phase shaping capability to improve the system robustness in front of grid uncertainties and minimizing converter impact over grid stability due to its positive-real nature. The synthesized controller only measures the grid current and voltage to achieve the aforementioned results, reducing the number of sensors (and their associated cost) required for its implementation. Experimental results illustrate the correct behavior of the closed-loop system with the designed controller in time and frequency domain. [ABSTRACT FROM AUTHOR]

This paper proposes a zero-voltage ride-through (ZVRT) method and an LCL filter design method to meet the fault ride-through (FRT) requirements for a single-phase grid-connected inverter with a minimized LCL filter. A high inverter output current overshoot occurs at a grid voltage sag and a grid voltage recovery, when a low-inductance LCL filter design is employed in order to minimize the filter volume. In order to suppress the current overshoot, a high-speed gate-block operation and the design method of the minimized LCL filter are proposed. In particular, the filter design considers the delay time in the gate-block operation in order to clarify the reduction limitation of the inductance in the LCL filter. As a result, the maximum inverter output current overshoot is suppressed to 146% by the high-speed gate-block operation and the designed LCL filter, where the impedances of an interconnected inductor and a filter inductor are 1.0% and 0.78% of the inverter normalized impedance, respectively. Therefore, it is possible to meet the FRT requirements with the proposed ZVRT method even with the minimized LCL filter. [ABSTRACT FROM AUTHOR]

This paper highlights the power quality issues and explains the remedial measures taken by means of hybrid front-end third harmonic current injection rectifiers. Here, a zig-zag transformer is used as the current injection device so that the advantages pertaining to the zig-zag transformer are effectively utilized. The third harmonic current injection device along with three-level boost converter at the output stage will increase the dc-link voltage. With less boost inductance, generally half of the conventional boost converter inductance is sufficient to implement the proposed converter structure resulting in reduced ripple current and also the device rating is reduced by half of the output voltage. Moreover, the power quality is well improved using third harmonic current modulated front-end structure, which is well appropriate for medium/higher power applications. The experimental prototype of hybrid front-end converter is developed in the laboratory to validate the MATLAB simulation results. [ABSTRACT FROM AUTHOR]

This paper proposes a DC-side circuit configuration that improves the harmonic suppression ability of a 12-pulse diode bridge rectifier (DBR) using a zigzag configured autotransformer. The DC-side circuit uses a single-phase DBR along with interphase transformer which generates the required circulating current thereby modifies the DC currents at the DBR output, in turn shapes the input line current near to a sine wave. The proposed single-phase DBR is connected in parallel with the load which enables to reuse the harmonic energy thus improving the energy conversion efficiency. The zigzag configured autotransformer used for 12-pulse DBR possesses the inbuilt ability to hinder the zero-sequence components, which expel the need of zero sequence blocking transformer. The proposed configuration is analyzed, simulated in MATLAB Simulink and the simulation results are presented, which confirm the reduction of total harmonic distortion (THD) in the input line current thereby improving the power quality under large load variations. Furthermore, the viability of the proposed configuration is verified by experimental results, which confirm the suitability of the proposed configuration in industrial applications. [ABSTRACT FROM AUTHOR]

This paper presents a multiphysical model for a microtubular solid-oxide fuel cell (SOFC) using syngas as fuel. The proposed control-oriented syngas fuel cell model includes both hydrogen and carbon monoxide co-oxidation phenomena and is demonstrated through the electrochemical, fluidic, and thermal dynamic characteristics of the fuel cell. The developed model is validated experimentally under different operating conditions regarding different reaction temperatures, species partial pressures, and entire working range of current densities. As an important part of the model, the co-oxidation phenomenon of hydrogen and carbon monoxide is discussed in details. The developed model can be used in embedded applications such as real-time simulation, which can help to design and test the control and online diagnostic strategy for fuel cell power generation system in the industrial applications. [ABSTRACT FROM AUTHOR]

This paper presents theoretical and experimental discussions on low-voltage-ride-through operation of a modular multilevel single-delta bridge-cell (SDBC) inverter intended for utility-scale photovoltaic (PV) systems. Modern grid codes require grid-tied inverters to provide dynamic grid support during grid-fault events by injecting reactive current. This paper discusses decoupled positive- and negative-sequence reactive-current control, focusing on asymmetric voltage sags with imbalanced magnitude and phase relationships. The main objective is to present a feedforward control method based on calculation of the zero-sequence current required for achieving power balance during normal and grid-fault conditions. Moreover, this paper demonstrates a practical method that minimizes overcurrent stress in the three inverter clusters by adjusting active power drawn from PV arrays. Experimental results on a three-phase 12.6-kVA system prove that the SDBC inverter is capable of seamlessly operating through asymmetric voltage sags. [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]

In this paper, the damping ability of point of common coupling (PCC) voltage feedforward is analyzed in order to improve the stability of current control, in which interference with an LCL filter of a battery energy storage system (BESS) and synchronous inductance of a diesel generator is considered in a stand-alone microgrid. A BESS can be charged by a diesel generator when the state of charge of the battery bank is significantly insufficient and where the BESS operates with constant current constant voltage control and the diesel generator provides constant voltage constant frequency control. In this case, large synchronous when the diesel generator is in a steady state may severely cause the instability of current control. The stability analysis should be required to guarantee the paralleled operation between BESS and diesel generator. An equivalent circuit model of the diesel generator is needed to perform these processes. To bring availability of analysis, this paper considers a simple equivalent circuit model considering synchronous inductance in the steady state, and it has very large inductance corresponding 1 per unit. The resonance issue is attenuated by the damping ability of PCC voltage feedforward where it is possible to improve the stability by appropriately adjusting the gain of the voltage feedforward. The effects of the synchronous inductance and the feedforward loop are analyzed in the s-domain and z-domain. The gain of the voltage feedforward is determined to be 0.2 and 0.4 based on stability analysis. To verify the validity of the damping effect of PCC voltage feedforward, a demonstration site is constructed and the stability is verified through simulation and experiment with a full model, and total harmonic distortion of current is improved to 2.44%. [ABSTRACT FROM AUTHOR]

This paper discusses the energization and start-up process of modular three-stage solid-state transformers (SSTs) based on a cascaded H-bridge topology. A key element of the SST is the auxiliary power supply (APS) feeding the auxiliary circuitry. Redundancy and simpler implementation can be achieved by powering the APSs from the dc-link capacitors of cells, but at the expense of a more challenging start-up process of the SST. The first step of this process must be performed before APSs are operative. This can result in undesired transient events (inrush currents, voltage sags in the capacitors voltages, etc.), which could prevent a proper start-up of the SST or even jeopardize the power devices or other elements. A simple strategy for the energization and start-up of SSTs using this APS structure is proposed. The method is valid for both grid-forming and grid-feeding operations of the SST, regardless of the energization port and without the addition of any extra circuitry. Simulation and experimental results are provided. [ABSTRACT FROM AUTHOR]

In this paper, a fifth-order boost point-of-load converter is developed by cascading a modified fourth-order boost converter with a combination of L–C and diode. This topology has the following salient features: Single-switch topology, common ground between source and load, low-voltage stress across intermediate capacitors, and voltage gain same as other reported fifth-order boost converters with no common ground. Steady-state and dynamic analyses demonstrate the proposed converter's boosting feature and dynamic performance, respectively. A contoured robust Bode plot methodology is employed to design the robust voltage-mode controller to ensure load voltage regulation in the presence of uncertainties. The necessary and sufficient conditions under which the designed controller guarantees the load voltage regulation and robust stability are obtained. A step-by-step robust controller design procedure is outlined. The salient features of the proposed converter and its robust performance are studied analytically, using the MATLAB platform, and validated experimentally on a 60-W prototype module. [ABSTRACT FROM AUTHOR]

This paper is an experimental study on electroconvective flows produced by an asymmetric electric field in a cavity. It is part of a scientific project aiming to develop electrohydrodynamic (EHD) flow actuator in order to enhance heat transfer and mixing efficiency in fluidic and microfluidic systems. In this study, the EHD flow is obtained by applying a dc voltage between two electrodes (cylinder/plane) immersed in a working liquid. The produced velocity fields strongly depend on the applied voltage. Whatever may be the applied voltage, the fluid goes from the cylinder toward the plate or the other way round. The velocity fields obtained by particle image velocimetry for different potentials are analyzed in both cases with the usual mechanisms (injection and conduction) at the origin of the motion of the liquid. A discussion on the transition between injection and conduction phenomena is finally presented. [ABSTRACT FROM AUTHOR]

The disturbances including harmonics, distortions, transients, fluctuations, and dc offsets in the grid voltages and uncertain load currents, are the most challenging issues in the scenario of renewable sources based energy generating systems integrated to the conventional grid. A three-phase, double stage, grid tied solar photovoltaic based distributed generating (SPVDG) system fulfilling multiple objectives, is presented using an adaptive digital disturbance estimator (DDE) and a peak power tracking scheme. The adaptive DDE has the detection proficiency of all the harmonics and lumped disturbances resulting fundamental component estimation of the periodic signals such as grid voltages and load currents. This system deals with objectives such as reactive power compensation, load balancing, peak solar power extraction, operation at grid voltage sags and swells, estimation of harmonics, dc offsets, disturbances, etc. and their elimination. Moreover, this system ensures the active power flow from the SPVDG system to the local loads as well as the grid through a three-phase voltage source converter (VSC). An adaptive technique is used to adjust the dc-link voltage with respect to the grid voltage variation(s) that is advantageous in terms of losses in the VSC. A Lyapunov function candidate is considered to estimate the gains of the disturbance estimator confirming its parameter convergence. Considering the aforementioned objectives, SPVDG system with the proposed DDE-based control scheme, is simulated using Matlab/Simulink environment and then practically implemented using a prototype developed in the laboratory to confirm its performance under steady and dynamic conditions. [ABSTRACT FROM AUTHOR]

In copper electrorefining, process anomalies impair current efficiency and productivity. Short circuits produce nodules or dendrites in copper cathodes, impaired contacts at busbars elevate current densities dispersion and, open contacts result in blank cathodes and overcurrents at nearby electrodes. This paper presents an intercell topology composed by a base board, main anode–cathode connectors, and a capping board with secondary connectors snapped on top. With this segmented intercell configuration the resilience to anomalies is improved by reducing short-circuit occurrence and their magnitude. Anomalies are pinpointed in 60 s with the addition of light mass secondary connectors placed on the capping board. Moreover, the new topology is capable of surpassing anomalies even without assistance to sustain production. Finite-element modeling predicts the performance of the proposed innovation for fast detection of short and open circuits using thermography scans. The paper includes experimental results to validate the effectiveness of the secondary connectors in the detection of process anomalies. [ABSTRACT FROM AUTHOR]

Design of a transverse flux machine (TFM) with high power factor and high torque density is presented. Detailed analysis and verification of the benefit of TFMs over conventional radial flux machines, in terms of torque production capability, is described. A comprehensive investigation of the ideal torque production capability, power factor, and deviation from ideal cases is explained. Factors contributing to performance degradation are identified and a robust method is proposed to design and improve the machine performance. Simulation and experimental results are provided to validate the innovation and the robustness of the design process. [ABSTRACT FROM AUTHOR]

This paper presents a dual output power factor correction (PFC) converter for switched reluctance motor (SRM) drives. Here, a modified single-ended primary inductance converter (SEPIC) is proposed for a wide range of speed control and to achieve PFC at ac mains. The switching frequency of the converter is considered to be 20 kHz. The converter is designed to operate in the discontinuous conduction mode (DCM) of operation, which reduces the size of the output inductor. The DCM mode to obtain PFC also reduces the sensor requirement as compared to the continuous conduction mode (CCM), where two voltage sensors and one current sensor add to the drive cost. The drive is proposed for universal ac mains (90–270 V ac). Simulated and experimental results are demonstrated to validate the performance of the drive during different operating conditions. The input current total harmonic distortion is reduced to comply with an IEC 61000-3-2 standard. [ABSTRACT FROM AUTHOR]

Electrical power losses in distribution networks contribute significantly to the overall energy loss in power systems. Reducing network losses can help the power system become more energy efficient. The solid-state transformer (SST) is primarily being considered as a replacement to the traditional fundamental frequency transformer. This paper proposes the use of the dual-reactive power support feature of the SST to reduce radial distribution network losses. A planning algorithm using particle swarm optimization (PSO) is proposed to optimally locate and size the SST installations with an overall objective of reducing network losses. The proposed algorithm is implemented on a standard 33-bus radial distribution network and the results for multiple scenarios are presented. It is shown that by increasing the deployment of SST, the losses in the distribution network can be reduced considerably. [ABSTRACT FROM AUTHOR]

This paper presents a new methodology to manage the initialization process of fuel cells (FCs) as a main source in a microgrid. The startup aims to reduce the warming-up time, increase the FC efficiency, and decrease the time response. As a solution, the use of storage systems combined with an adaptive gain scheduling to absorb the power transients improve the microgrid stability and avoid the dc-link voltage collapse is proposed when we perform short circuits at the FC terminals. In the first analysis, we evaluate the mathematical model to obtain the gain of the interleaved boost with voltage multiplier (IBVM) as a function of the hydrogen pressure, membrane resistances, and temperature, i.e., the effect of the chemical variables on the IBVM terminal voltage. In the second part, an adaptive gain scheduling to compensate the short-circuit effects on the FC terminals is designed. To analyze the feasibility of the proposed technique, the frequency and step response for different gain scheduling is performed. Finally, we present a set of experimental results to support the theoretical study and demonstrate the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

The kinetic energy stored in the rotating mass of wind turbine generators can provide the effective power quality solution to the inertia-free stand-alone (IFSA) microgrid by improving its stability. In conventional power systems, the power released from the inertia of synchronous generators regulates the system frequency. However, the frequency does not vary much even when a large disturbance or a load change occurs in the IFSA microgrid with only converter-based generators. This paper proposes a new inertia control method for a type-4 permanent magnet synchronous generator wind turbine system in the IFSA microgrid by utilizing the measurement of the dc-link voltage of the converter and its derivatives, not by the system frequency. Several case studies are carried out to evaluate the performance of the proposed inertia control in the IFSA microgrid with electromagnetic transients program-based simulation. Also, its effectiveness is verified with the experimental results from the hardware-in-the-loop test implemented by the controller interface with the digital signal processor, which is connected to the real-time digital simulator. [ABSTRACT FROM AUTHOR]

The inertia-free stand-alone (IFSA) microgrid is the new small power grid without synchronous generators equipped in conventional power systems. In other words, this system has the only converter-based generators (CBGs) based on energy storage devices and renewable energies. Therefore, it requires a new CBG control to provide strong voltage reference for the CBGs connected to the point of common coupling (PCC). This is because the IFSA microgrid is subject to a weak system such that it cannot maintain its rated frequency and/or bus voltage with the conventional real and reactive power controllers, which usually get their references from the PCC. This paper proposes the innovative conceptual approach for distributed coordination in the IFSA microgrid by applying the synchronized global positioning system time to the CBGs. Moreover, it is verified that the proposed physical structure of the IFSA microgrid makes it possible for all CBGs to share the real and reactive powers effectively. As the result, the proposed CBG control can provide the robustness, which is strongly required in the IFSA microgrid, based on timely outage management and restoration process. Several case studies are carried out with the microgrid of 36 MW to verify the effectiveness of the proposed CBG controller. The simulation and hardware-in-the loop tests are carried out using the power system computer-aided design/electromagnetic transient design and control (PSCAD/EMTDC) and the real-time digital power system simulator (RTDS), respectively. [ABSTRACT FROM AUTHOR]

This paper proposes a framework for the design and analysis of a coreless permanent magnet (PM) machine for a 100 kWh shaft-less high strength steel flywheel energy storage system. The PM motor/generator is designed to meet the required specifications in terms of torque–speed and power–speed characteristics given by the application. The design challenges of a motor/generator for this architecture include: the poor flux paths due to a large-scale solid carbon steel rotor and zero-thermal convection of the airgap due to the operation of the machine in a vacuum. The magnetic flux in this architecture tends to be 3-D rather than constrained due to lack of a core in the stator. In order to tackle these challenges, several other parameters such as a proper number of magnets and slots combination, wire thickness, number of turns in each coil, magnets with high saturated flux density, and magnet size are carefully considered in the proposed design framework. Magnetic levitation allows the use of a coreless stator that is placed on a supporting structure. The proposed PM motor/generator comprehensive geometry, electromagnetic design, and mechanical dimensioning are followed by detailed 3-D finite-element analysis (FEA). The torque, power, and speed determined by the FEA electromagnetic analysis meet the application design requirements and constraints for both the charging and discharging modes of operation. Furthermore, the design and analysis of the coil holding structures are discussed. Finally, the motor/generator static thermal analysis is discussed in order to validate the proposed cooling system functionality. [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]

An improved model predictive direct power control (MPDPC) for three-phase grid-connected converters is proposed. In the proposed method, two voltage vectors are applied during a control period and their duty cycles are determined by a fuzzy logic-based modulator. The inputs to the modulator are the active and reactive power errors and the output is the duty cycle of the first (main) voltage vector. The fuzzy rules are developed based on expert knowledge and the fact that small/large power errors can be compensated by applying the main voltage vector for a small/large portion of the switching period. The candidate voltage vector pairs are examined on a control Lyapunov function and the pair that satisfy the closed-loop stability criteria are selected. The voltage vector pairs are then applied following a proposed switching pattern through which reduced average switching frequency is achieved. Comparative simulation and hardware-in-the-loop studies between the proposed method and a most recently introduced duty cycle-based MPDPC confirm that in addition to lower average switching frequency, better quality currents and active and reactive powers can be achieved under the proposed MPDPC. [ABSTRACT FROM AUTHOR]