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A phase-locked loop or phase lock loop (PLL) is, essentially, a closed loop control system, where its output signal (regulated) maintains a direct (chosen) relationship to the input signal (unregulated). If the phases of the input and output signals remain the same, their frequencies will also match. In its usual way, a PLL is an electronic circuit with filters and controllers that must be tuned each time, according to the input signal parameters. As a contribution and novelty, this paper introduces a new, easy, fast and highly efficient PLL algorithm, that it does not need to adjust every time the input signal changes. This makes it independent of the input signal it receives and, therefore, and in a certain way, universally applicable. In addition, the proposal is implemented exclusively by software, housed in a microcontroller, which also represents another novelty. As another remarkable feature, the proposed algorithm is very simple, with a very low computational cost, which makes it very stable, practically insensitive to noise, and very fast. These characteristics and the performance shown over a wide range of input signal frequencies, make the proposed algorithm suitable for use in different applications, from the electricity grid synchronization to the demodulation of frequency modulation, DC motor drives, etc. In addition to frequency and phase tracking, the developed algorithm generates the signal corresponding to the fundamental frequency of the input signal. Furthermore, the algorithm behavior is not affected by the input signal distortion and is independent of its initial phase. The performance and excellent behavior of the developed algorithm are evaluated through simulations and experimental tests. [ABSTRACT FROM AUTHOR]

This paper presents a new design of near-field focused metasurface for high-efficiency wireless power transfer with multifocus characteristics. A general synthesis procedure is outlined to design metasurfaces with desired multiple foci in the near-field zone. The unit cell of printed tridipole is used to realize the focused metasurface which has a large range of phase shift and is adapted to near-field focusing applications. Different feeding and focusing designs of the printed tridipole metasurfaces are proposed and analyzed. Two kinds of metasurfaces with 20×20 elements are designed, fabricated, and measured at 5.8 GHz. One is the single-feed and single-focus case, and the other is single-feed and two-focus case. Two-dimensional planar near-field scanning technique is implemented to measure the E-field focusing characteristics. Full-wave simulations and experiments demonstrate that the proposed focusing metasurfaces have a high wireless power transfer efficiency of 70%. The relative bandwidth with 50% power focusing efficiency is about 16%. The measured results are in good agreement with the theoretical designs and simulated results, which verify the feasibility and correctness of the proposed approach in this paper. [ABSTRACT FROM AUTHOR]

This paper presents a novel fabrication method that combines the advantages of fine-line lithography on flex substrate and 3-D printing to create practical RF components that can readily be folded. Photolithography and 3-D printing enable the fabrication of rigid-flex RF components, where 3-D printing is used to create thick rigid structures and photolithography is utilized to pattern the fine detailed conductor features on a flexible substrate. A coax-like structure is demonstrated as an example, and it is used to design a feed network to a foldable Vivaldi antenna array. This paper presents the detailed buildup of two-folded Vivaldi antenna arrays. [ABSTRACT FROM AUTHOR]

The influence of a filter inductor on the steady-state performance of a parallel-type resonant converter is elaborated and analyzed in this paper. By steady-state operation analysis, it is shown that the ripple current of the filter inductor results in an inaccurate prediction of fundamental harmonic approximation (FHA), and such problem would become serious when the filter inductance is small. In order to portray such feature, an improved fundamental harmonic approximation (IFHA) is proposed. Unlike an FHA equivalent circuit, an equivalent inductor is added to the ac resistance parallelly in an IFHA equivalent circuit. Due to that, the equivalent inductor branch takes account of the ripple current of the filter inductor, and the IFHA is expected to own higher accuracy and can be used in a parameter design procedure. In this paper, the equivalent inductor expressions of full-bridge rectifier and current-doubler rectifier are derived as examples. In order to verify the theoretical analysis, a 500 W LCC resonant converter is built as a prototype. The close-loop experiment results show that small filter inductance would lead to the failure of output voltage regulation and hard-switching operation of power switches. And open-loop experiment results show the IFHA gives more accurate predictions than those of FHA. [ABSTRACT FROM AUTHOR]

Many research works report the use of LCL filters for grid-interfaced PV systems. Indiscreet selection of passive LCL filter parameters may result in poor filtering and increased power losses. LCL filter parameter selection is critical to get a good performance and at the same time ensure that losses and costs stay low. This paper proposes a novel approach to design the LCL filter for a grid-interfaced PV system. A cost-based minimization approach on a cost per joule basis for each of the filter elements is explored to obtain the optimal filter design. Simulation results for a 10-kVA grid-connected inverter with an LCL filter are presented in order to verify the efficacy of the proposed design. The impact of designed filter parameters on the ripple current is also discussed in this paper. The total inductance of the LCL filter is varied and filter parameter values which give lowest cost is identified while meeting harmonic standard requirements and the fundamental voltage drop across the filter. Finally, the proposed design is also experimentally validated via a hardware prototype. Results validate the design method in terms of the harmonic attenuation and total harmonic distortion. [ABSTRACT FROM AUTHOR]

This paper proposes a new filter design method that can smooth the wind power generation output while keeping the energy capacity and power rating of the energy storage system (ESS) small. Wind power generation causes frequency fluctuations in power systems. Therefore, in many cases, the ESS is needed for smoothing the fluctuations of wind generator output. In order to improve the performance of the ESS controlled with the conventional low-pass filter (LPF), this paper investigates other types of filters. First, the relations between filter and energy capacity/power rating of the ESS are disclosed through the worst-case study. Then, the frequency fluctuation analysis of the power system with respect to the wind power generation is carried out in order to realize a pin-point smoothing. Finally, a metaheuristic optimization method is proposed for the multiobjective design of the filter based on these relations so as to achieve an optimal tradeoff between the output smoothing and energy capacity/power rating of the ESS. It is shown via simulation analysis with real wind data that the proposed method can suppress the frequency fluctuation of the power system effectively with the ESS having smaller energy capacity and power rating. [ABSTRACT FROM PUBLISHER]

The output voltage of power electronic converters is a very important quantity for dynamic control of power electronic systems. In electrical drives without electromechanical position or speed sensor, the terminal reference voltage is used to obtain the rotor position. Dead-time effects and semiconductor voltage drop lead to distortion in the actual output voltage and degrade the control performance when the back electromotive force magnitude is low. Thus, for stable low-speed operation, output voltage sensing becomes necessary. Due to the switching nature of power electronic systems, this is not a trivial task, especially when instantaneous measurement of the terminal voltage is required. In this paper, an instantaneous switching-period average voltage sensing technique is proposed that utilizes a combined approach of oversampling and filtering. Based on the theoretical analysis of the sampling- and filter-induced measurement distortion, a general solution for an optimal filter design is derived. The additional sensing circuit is integrated into the low-side gate driver of the converter outputs. This paper includes details about the hardware implementation and extensive verification measurements. [ABSTRACT FROM AUTHOR]

This paper presents the tradeoff study of heat sink and output filter volume of a GaN HEMT based single-phase inverter. The selected topology is three-level active neutral point clamped (ANPC) inverter, and the main aim is to explore the benefits of the GaN HEMTs at 600 V blocking class on the system level efficiency, and power density under the wide range of operating conditions. The paper starts by introducing the inverter topology, selected pulse width modulation scheme and followed by the device features, static, and dynamic characterization and continues with presenting and discussing the results of extensive experimental and analytical characterization. After this, the impact of GaN HEMTs on inverter volume is discussed in terms of heat sink and output filter volume analysis under different switching frequency and heat sink temperature conditions. The calculation of heat sink volume and single stage LC output filter volume are presented with respect to experimental results of the single phase prototype. The findings from static, dynamic characterization, and single phase prototype results clearly show that GaN HEMT has excellent switching performance under wide load current and heat sink temperature conditions. The high performance of the inverter leads to reduction of the combined total volume, including output filter and heat sink volume. [ABSTRACT FROM AUTHOR]

In this paper, a novel input/output (I/O) coupling multiplier circuit for conveniently increasing I/O coupling of a wideband coupled-resonator filter/diplexer is proposed. The multiplier circuit consists of a shunt capacitor and a negative phase shift. By appropriately shunt connecting a capacitor in the vicinity of an I/O port, the I/O coupling can be effectively increased. Compared to conventional approaches of increasing I/O coupling for a wideband application, using the multiplier circuit allows much less perturbing the resonant frequency of the first resonator. For many resonator configurations such as helical resonator, to which the tapping probe could not be adjusted continuously, the multiplier circuit provides a convenient way to control I/O coupling. In this paper, the working mechanism of the proposed circuit is well proved theoretically. The usefulness of the multiplier circuit has been demonstrated for coaxial combline cavity resonators and helical resonators, both for filter and diplexer applications. As a practical example, the multiplier circuit is applied to a wideband UHF helical resonator diplexer. [ABSTRACT FROM PUBLISHER]

This paper proposes a novel three-phase transformerless hybrid series active filter (THSeAF) based on voltage-fed type of converters (VSCs) to address major power quality issues related to residential and commercial buildings. This power quality compensator presents an affordable solution to overcome current-related issues as well as integrating renewables to ensure a sustainable supply to the loads. The controller is based on a novel combination of the synchronous reference frame and pq theory to extract voltage and current harmonics as well as voltage unbalances. A proportional resonant (P+R) regulator is producing gate switching signals for the three-phase THSeAF. The generated duty-cycle waveforms will produce compensating voltage to rectify harmonic currents initiated from typical nonlinear loads. The device ensures a reliable and dynamically restored power supply on the load's point of common coupling by means of three auxiliary dc supplies. This paper describes mitigation of power-quality-related issues of a microgrid systems and smart distribution grids along with the proposed solution to enhance the power system performances. A combination of simulations and experimental laboratory results are carried out to validate the study. [ABSTRACT FROM PUBLISHER]

High-frequency current harmonics injected into the point of common coupling, mainly at the switching frequency and its multiples introduced by the modulation of grid-connected converters, should be limited to comply with grid codes. This requirement can be satisfied by using trap filters with LC-traps tuned at the switching frequency and its multiples in replacement of conventional L filters. However, all existing trap filters are subject to certain problems, e.g., sensitivity to grid impedance variation and decreased high-frequency roll-off rate. In view of this, this paper presents a trap-LCL filter with its parallel resonant LC-trap located on the converter side, named as LT-C-L filter. The modeling and analysis presented in this paper show that the LT-C-L filter can be the most promising trap filter due to its advantages such as high roll-off rate, robustness against parametric variations of grid impedance and passive damper, satisfactory harmonic attenuation at the switching frequency, reduction of converter current total-harmonic-distortion, and flexible design of filter components through magnetic integration. A single-phase ac/dc grid-connected converter prototype has been built and tested in the laboratory, and experimental results are presented to verify the superiority of the proposed filter. [ABSTRACT FROM AUTHOR]

This paper targets the reduction of common-mode voltage in an indirect matrix converter (IMC) through an intelligent space-vector-based modulation technique. This mode of control results in lower dV/dt at the motor terminals, thereby, reducing voltage stress to windings; and reduced output voltage distortion resulting in lower machine losses. The conventional indirect space vector pulse-width modulation method of controlling matrix converters involves independent control of either the rectifying stage or the inverting stage of the converter. However, in this paper, by suitable selection of space vectors, the rectifying stage of the matrix converter generates different levels of virtual dc-link voltage. Therefore, the responsibility of formulating output voltages with a particular magnitude and frequency, which can be translated to different machine speeds, has been transferred solely to the rectifying stage of the IMC. Estimation of the degree of distortion in the three-phase output voltage is another facet discussed in this paper, which aids the sizing and designing of output passive filters. The analysis of output voltage distortion and the proposed modulation strategies have been substantiated by simulations in MATLAB/Simulink and experimentally verified on a scaled down laboratory prototype. [ABSTRACT FROM AUTHOR]

When designing a low electromagnetic interference (EMI) power electronic converter with high packaging density, its internal near-field coupling to an EMI filter is critical. In this paper, we investigated the near-field coupling between a noise source and a single-phase EMI filter. First, we measured the common-mode (CM) and differential-mode (DM) couplings separately using a four-port network analyzer. The DM coupling when the EMI filter was exposed to a magnetic field was larger than that when it was exposed to an electric field. On the other hand, the CM coupling when the EMI filter was exposed to an electric field was larger than that when it was exposed to a magnetic field. Second, we extracted parasitic coupling elements that determine the coupling magnitude of each mode of coupling. The coupling calculated by the extracted elements agreed with the measurement well. We identified the dominant coupling path between the noise source and the EMI filter. Finally, we studied the required shielding of the EMI filter to reduce the coupling efficiently. Consequently, we found that most of the coupling can be eliminated by shielding the dominant coupling path. [ABSTRACT FROM AUTHOR]

Compared with the conventional central shunt active power filter (SAPF), modular designed SAPF can track the harmonics more precisely and quickly with a compact and expandable structure, which makes it a better solution for harmonic mitigation. But there are very few paper discussed about the modeling and parallel resonance issues of modular SAPF parallel system. This paper provides a modeling of three-level SAPF, aiming to guide the modular design and research the parallel resonance control method. First, a simplified modular three-level SAPF modeling is proposed based on averaging impedance modeling and small signal linearization techniques. Then, the coupling issues between modules are researched, and a self-adaptive active damping method is proposed to suppress the system resonance. Based on the modeling results, an improved three-level SAPF module topology is proposed to construct the modular system. The theoretical analysis and experimental results verify that the module topology improvement together with the damping strategy can promise the compensating bandwidth, reliability, and fast, precise harmonics tracking ability. [ABSTRACT FROM PUBLISHER]

Wide bandgap semiconductor switches have been increasingly utilized to improve the power density and efficiency of power converters, as such devices are able to operate at very high frequencies, e.g., up to 100 MHz, with reduced power losses. However, such a high-frequency operation may impose a challenge to the digital control system, and the system clock frequency should be up to 100 GHz in high-precision applications, which is difficult to realize in low-cost microprocessors. Instead of using extremely high-frequency clocks, preprocessing-based solutions that utilize digital pulse-width-modulated (DPWM) dither techniques can also enhance the DPWM resolution with moderate frequency clocks. Unfortunately, this is usually achieved at the expense of introducing low-frequency harmonics, which may complicate system controller and output filter design. In this paper, an optimal dither technique is proposed to enhance the resolution of DPWM power converters. The concepts of positive dither and negative dither are first proposed in this paper. Furthermore, vector-diagram-based analysis indicates that with proper utilization of positive dithers and negative dithers and carefully selected dither sequences, the lowest order harmonic introduced by the conventional dither technique can be completely eliminated when the dither period is multiples of six switching periods. In other cases, the proposed optimal dither technique can produce minimized lowest order harmonic. Finally, experimental results obtained from a Gallium Nitride (GaN) devices-based synchronous buck converter validate the feasibility of the proposed dither technique. [ABSTRACT FROM PUBLISHER]

In conventional HVDC systems where the harmonic filters and shunt capacitors are installed at the ac grid side, the converter transformers inevitably suffer the detrimental impacts caused by harmonic penetration. In this paper, combined with an inductive filtering method, a parallel delta-connected filtering-winding scheme for 12-pulse converter transformer units is proposed to reduce the harmonic currents flowing through the transformers and, thus, to attenuate the harmonic effects on them. This paper describes the presented transformer configuration in terms of the wiring scheme of the 12-pulse converter transformer unit and corresponding flowing paths of different harmonic currents with the orders of 3,6n\pm 1\left(\mathrmn=1,3,5,\ldots \right), 11 and 13 in the filtering winding circuit. Then, the mechanism of the proposed scheme on harmonic suppression to the converter transformers is explained theoretically. In an attempt to validate the theoretical analysis, simulations based on PSCAD/EMTDC and experiments in a laboratory prototype system are performed to evaluate the harmonic eliminating performance of the proposed scheme. [ABSTRACT FROM PUBLISHER]

This paper proposes a control strategy for a three-phase three-wire thyristor-controlled LC -coupling hybrid active power filter (TCLC-HAPF), which can balance active power and compensate reactive power and harmonic currents under unbalanced loading. Compared with TCLC-HAPF with conventional control strategy, active power filters and hybrid active power filters which either fail to perform satisfactory compensation or require high-rating active inverter part for unbalanced compensation, a control strategy was proposed for TCLC-HAPF to operate with a small rating active inverter part for a variety of loads with satisfactory performance. The control idea is to provide different firing angles for each phase of the thyristor-controlled LC-coupling part (TCLC) to balance active power and compensate reactive power, while the active inverter part aims to compensate harmonic currents. First, the required different TCLC impedances are deduced. Then, independent firing angles referenced to the phase angle of voltage across TCLC are calculated. After angle transformations, final firing angles referenced to phase angle of load voltages are obtained. In this paper, a novel controller for TCLC-HAPF under unbalanced loading is proposed. Simulation and experimental results are provided to verify the effectiveness of the proposed controller in comparison with a state-of-the-art controller. [ABSTRACT FROM PUBLISHER]

Filter-based battery–supercapacitor hybrid energy storage systems (HESSs) are popular as a way of extending battery lifetime by diverging the high-frequency power variations to the supercapacitor. However, when a traditional supercapacitor voltage controller (SCVC) is employed in the filter-based HESS, precise sizing of the supercapacitor as well as finding filter parameters for the power allocation are challenging due to nonlinearities. These problems can be circumvented by using a supercapacitor energy controller (SCEC) proposed in this paper. The paper presents a method for selection of the SCEC and filter parameters as well as precise sizing of the supercapacitor for a given application. The proposed method is experimentally verified on a single-phase grid-connected HESS used to smooth the power delivered to the grid at the point of common coupling. It is also shown that the size of the supercapacitor when using the SCEC is significantly lower than the one estimated for the traditional SCVC. [ABSTRACT FROM PUBLISHER]

The current grid codes for distribution networks impose on operators to provide ancillary services, like fault ride through capability and reactive power compensation. In this context, generating units with power electronics interfaces could offer as an additional service the active compensation for harmonic and interharmonic currents introduced by other converters or distorting loads. Typically, the converters of these generating units do not have information on the distortion of either other loads or of the grid current. Thus, this paper presents a control algorithm for grid harmonics and interharmonics compensation that relies only on the measurement of the voltage at the point of connection of the unit. The reference for the compensating current is calculated from the harmonic components of grid voltage in the synchronous reference frame. The paper also addresses the influence on the compensation performance of the line impedance between the generating unit and the point of connection. Experimental tests on a laboratory setup fully validate the proposed compensation method. [ABSTRACT FROM PUBLISHER]

Repetitive control strategies have been commonly applied in pulse-width-modulated (PWM) voltage source inverters (VSIs) for many industrial applications. This paper presents a repetitive controller for voltage harmonic mitigation of VSI-based islanded microgrids. The phase delay in the overall control system, e.g., the delay caused by the digital duty cycle calculation, PWM generation, and repetitive controller, has to be compensated by elaborately designed phase lead filters in order to prevent control performance deterioration and system instability. Nevertheless, quantificational analysis and practical design of the time advance unit in such filters are hardly found in existing literature works. In view of this, this paper proposes an explicit analysis of the phase lead filters and a novel design method of the time advance unit in repetitive controllers to ensure system stability. Moreover, with the help of the proposed method, the overall system stability margin is predictable and improved controller performance is achieved as well. The proposed method is implemented experimentally to show the accurate stability margin calculation as well as the excellent steady state and dynamic performances of the repetitive control scheme. [ABSTRACT FROM PUBLISHER]

Harmonic resonance has become an important concern for the application of shunt capacitors in recent years. A potential solution to address this challenge is to convert a shunt capacitor into a passive filter. This paper presents design methods to configure a shunt capacitor as a C-type filter or a third-order high-pass filter with guaranteed resonance-free performance. The concept of resonance-free condition is first introduced in this paper. It is then used to develop filter design methods that always meet the resonance-free condition. The two filter configurations are also compared. It was found that the third-order high-pass filter has more advantages than the C-type filter. Another useful finding of this work is that the filter parameters, as determined using the proposed design methods, are independent of the system conditions. As a result, a lookup table for the filter parameters has been created to facilitate immediate use by the industry. [ABSTRACT FROM PUBLISHER]

This paper proposes an observer-based grid-voltage sensorless strategy that allows to implement the synchronization and control of an LCL grid-tied voltage source inverter. By using exclusively the measurement of the current injected to the grid, an observer estimates both fundamental positive- and negative-sequence components of the grid voltage, with a quality (in terms of total harmonic distortion and convergence speed) comparable to that obtained with a classic double second-order generalized integrator-frequency-locked loop (DSOGI-FLL). The unmeasured LCL filter states are also estimated by the observer, and they are used to implement a full-state feedback control strategy suitable for low resonance frequency LCL filters. The effectiveness of the scheme proposed here is demonstrated by comparison with a DSOGI-FLL and with a controller recently proposed in the literature. Experimental and simulation results that demonstrate the validity and effectiveness of the proposal are presented. [ABSTRACT FROM AUTHOR]

Due to the pulsating power at the inverter output terminals, the passive storage elements of the boost stage of the current-fed switched inverter (CFSI) contain a power frequency harmonic component (100 Hz), apart from dc and switching frequency components. In prior designs, the second harmonic component is suppressed by increasing the size of the input filter inductor and capacitor or by using additional circuits. This paper presents a complete characterization of a control-based approach to suppress the power frequency harmonic component in the input inductor current of a CFSI. It also presents a comprehensive characterization of the harmonic power redistribution. Using the proposed approach, it is demonstrated that the inductor value of a CFSI is reduced by 61% for the same peak-to-peak ripple. This leads to an improvement in the conversion ratio, efficiency, and power density of the overall converter. A SiC MOSFET-based CFSI with 75-kHz switching frequency is used to verify the proposed design philosophy. [ABSTRACT FROM AUTHOR]

The paper presents the performance of the modular multilevel converter (MMC) tapping cells associated with an ac filter in terms of efficiency and power density in a hybrid LV ac/dc microgrid application and compares it to the performance of the conventional topology used in LV application, i.e., the two-level voltage source converter (2L-VSC). A biobjective optimization based on the Genetic Algorithm is hence developed, providing details on designing the components of the LCL filter, the MMC, and the 2L-VSC. The MMC reaches an efficiency of 99.4% when the main dc-grid is left floating. However, due to its modularity and scalability, offering multiport connections option, the MMC tapping cells has the disadvantage of low power density. Exploring the filtering capability of the equivalent arm inductance of the MMC seen from the ac grid side, optimization design results show that higher switching frequencies allow a significant volume reduction of the inductive components of the MMC/LCL filter while higher switching frequencies have little impact on the switching losses of the MMC. This has the benefit of reducing the overall footprint of the converter and encouraging the use of the MMC in LV application. [ABSTRACT FROM AUTHOR]

In this paper, a bandpass frequency selective surface (FSS) based on substrate-integrated waveguide (SIW) technology is presented for airborne radome application. The proposed FSS element consists of a tapered cross-slot on either side of the substrate surrounded by metallic vias. The structure selectively allows the impinging electromagnetic (EM) wave through it in the specified frequency band. The element shows very stable frequency response for oblique incidence and the sharp roll-off performance characteristics at the edges of operating region in the rejection band. The −10 dB relative bandwidth (BW) of the element is 12.8% from 9.5 to 10.8 GHz with a very good insertion loss (IL) of 0.1 dB. Furthermore, the spectacular advantages of the FSS element based on SIW have been used for modeling the airborne radome application. The proposed radome structure is operating at 10 GHz with a relative 10 dB BW of 25.0% (8.20–10.6 GHz) with maximum (IL) better than 0.1 dB in its passband. The behavior of the FSS radome has been analyzed at different conformal sectors and thickness is optimized for optimal performance. The key parameters of radome such as transmission performance, radiation efficiency, and radar cross section (RCS) have been studied. Experimental verifications are carried out to prove the validity of the estimated results. The results show promising performance of the proposed FSS based on SIW technology for airborne radome application. [ABSTRACT FROM AUTHOR]

In this paper, a generic complex repetitive controller ($nk + m$ RC, $k\in \mathbb {Z}$), based on the inverse transfer function of the generalized delayed signal cancelation transformation is proposed. The presented complex controller can be designed for regulating different positive- and negative-sequence harmonic components through a space-vector error signal, with improved response time as compared to traditional repetitive controllers. An evaluation of the proposed control scheme stability, based on phase margin, Nyquist diagram, and sensitivity function is presented. The effects of the controller parameters on the system's stability and also on its dynamic response are shown and allow the definition of some control design guidelines. Experimental results are presented to validate the theoretical assumptions through applying the proposed controller for regulating the currents in a three-phase active power filter. [ABSTRACT FROM AUTHOR]

Resonant converters with capacitive output filters are quite popular for their higher voltage gain and compact designs. But the majority of the converters underutilize the transformer as they are subjected to discontinuous currents. This discontinuous current possesses huge current ripples that produce huge core losses and aggravate the temperature rise of the transformer. This often leads to saturation of the transformer. This paper presents an LCC-T resonant dc–dc converter with a capacitive output filter operating all switches in the zero current switching (ZCS) switching mode and whose transformer current is a continuous sinusoidal with minimum stress on resonant tank components. This is achieved by bringing the transformer in series to a resonant inductor. The proposed converter is simulated in power simulation (PSIM) 11.0.1. A proof-of-concept model rated 288 W is designed and developed, and hardware results are presented as verification to theory. [ABSTRACT FROM AUTHOR]

This paper proposes a hybrid modular multilevel dc–dc converter with dc fault ride-through capability. In each phase, the lower arm and shunt arm are composed of half-bridge submodules and full-bridge submodules (FBSMs) respectively, and the upper arm is composed of both types of submodules. The shunt arm eliminates the large ac filter required at the output of dc side. Moreover, it provides the bidirectional fault ride-through capability together with the FBSMs in the upper arm. Required kVA rating of the switches in the proposed topology is analyzed and compared to other topologies. With the optimal number of FBSMs in the upper and shunt arms designed by overmodulation, the proposed topology has a reduced kVA rating of switches, especially for the voltage conversion ratio above 0.54. A control strategy is presented to control the ac circulating current and balance the energy between the three arms. The performance of the proposed topology is validated by real-time simulation and a lab-scale test bench. [ABSTRACT FROM AUTHOR]

Output filters of the grid inverter usually have a large footprint in the total system. In order to increase the power density of the grid inverter, a passive integrated structure for the output filter with flexible multilayer foils is presented. Compared with a discrete output filter, the volume of the integrated filter is reduced by at least 20%. In this paper, the design of the integrated output filter is discussed. Then, a distributed electromagnetic component model of the integrated filter is used to verify the proposed design. Finally, a prototype of the integrated output filter is built and used in a grid inverter. Experimental results are included and compared with the results derived from the discrete output filter to prove the validity of this integrated filter design. [ABSTRACT FROM AUTHOR]

In this paper, a three-phase series hybrid active filter (SEHAF) interconnected with photovoltaic (PV) system and dc–dc boost converter is proposed to minimize sag, swell, and harmonics caused due to nonlinear power electronic loads. The SEHAF consists of a voltage source inverter (VSI) with a capacitor connected across it to provide consistency in managing and compensating the reactive power. This minimizes the sag, swell, and harmonics present in the source and load voltages. With the integration of PV, the voltage across the dc-link capacitor of VSI is controlled effectively, which helps in better compensation. Reference current generation is done using the proposed robust extended complex Kalman filter (RECKF) technique. The performance of the PV-integrated-HAF is analyzed using a synchronous reference frame with proportional-integral (PI) as well as fuzzy logic controller (FLC) and is compared with the proposed RECKF technique. The PV-integrated hybrid power system is developed using MATLAB/SIMULINK. Further, real-time digital simulation using OPAL-RT OP5142 is also carried out to support the simulation results. It is observed that the proposed control scheme provides better harmonic compensation compared to conventional PI and FLC. [ABSTRACT FROM AUTHOR]

An open velocity loop current regulated sensorless control scheme for both induction and permanent magnetic motor drives with an output sine wave filter and transformer is designed and implemented in this paper. The proposed control scheme provides a low-voltage drive solution for driving medium-voltage motors without substantially oversizing the inverter. Sufficient starting torque is guaranteed with controlled drive and motor current. Laboratory proof-of-concept tests and experimental results on an actual deep well have validated the effectiveness of the proposed control scheme [ABSTRACT FROM AUTHOR]

In this paper, a two-degrees-of-freedom control structure is proposed to minimize both total harmonic distortion and tracking error of inverter output voltage, adopting a resonant tracking controller and a modified uncertainty and disturbance estimator (UDE). Owing to the two-degrees-of-freedom feature of the proposed control strategy, tracking and disturbance rejection tasks are decoupled and treated almost independently. A time-delay action is introduced into a commonly adopted low-pass UDE filter to minimize the output impedance magnitude around the odd harmonics, which is typical to nonlinear loads. Once the disturbance is properly rejected, a tracking resonant controller is designed to force the output of the nominal system to follow a sinusoidal reference with near-zero amplitude and phase error. The performance of the proposed control structure is fully verified by the experimental results. [ABSTRACT FROM AUTHOR]

Contrary to the phase-locked loop (PLL), which has almost reached a mature stage of development in power and energy applications (particularly in three-phase systems), the frequency-locked loop (FLL) is not a mature technique yet. This is probably because of the implementation of FLLs in the stationary reference frame, which makes their modeling, tuning, and performance enhancement more complicated than PLLs. The aim of this paper is conducting a research on three-phase FLLs. Providing a review of recent advances, introducing the concept of inloop filters for designing more advanced FLLs, demonstrating the FLL modeling and tuning in the presence of an inloop filter, analyzing the advantages and disadvantages of using an inloop filter in the FLL structure, and establishing a connection between FLLs and PLLs are the main parts of this research. [ABSTRACT FROM AUTHOR]

This work presents a simple and accurate method for the calculation of both the self-inductance and the mutual inductance between thin-film capacitors, placed in close proximity in electromagnetic interference filters. From physical considerations regarding the impact of both skin and proximity effects, we approximate the currents flowing inside the capacitors at high frequencies by strip currents. This hypothesis is supported by electromagnetic simulations and measurements in this paper. On the basis of this model, we use analytical expressions to calculate both the self-inductance and the mutual inductance as a function of purely geometrical parameters such as the size of the capacitors, their orientation, and the distances between them. Because no previous impedance or network parameter measurements are required to estimate these inductances, this technique is suitable for the virtual prototyping design. We have constructed and measured several test boards to check the accuracy of the method and to identify its scope and limits. Also, in this work, we employ this technique to study the applicability to thin-film capacitors of a design strategy originally conceived to reduce the negative effects of the inductive parasitics of surface-mount capacitors. We demonstrate that this design strategy significantly improves the attenuation provided by filters with thin-film capacitors at high frequencies. [ABSTRACT FROM AUTHOR]

In this paper, a novel waffle-iron filter with transmission zeros at multiple frequencies, along with its design procedure, is presented. The proposed filter features a high-power behavior and a wide rejected band in a single compact structure by means of a set of transmission zeros that can also be placed close to the passband. Its design method rests on a divide-and-rule strategy, where the physical dimensions of the constituent design entities can be easily computed in a very short time. A novel high-power compact waffle-iron filter with transmission zeros at multiple frequencies has been designed as well as several classical waffle-iron filters with transmission zeros at one frequency only, using a detailed step-by-step procedure which avoids the brute-force optimizations needed until now. Multipactor and corona simulations have been conducted proving a high-power handling capability of 1.8 kW and 78.6 W, respectively. A prototype of the novel filter has been fabricated, obtaining a remarkable accordance between the simulated and measured results. [ABSTRACT FROM AUTHOR]

This paper presents a delta-sigma modulation control scheme for buck converters that features a reconfigurable loop filter with a scalable sampling frequency for effective switching noise reduction and high conversion efficiency. Depending on the load current, the proposed controller changes the sampling frequency along with the delta-sigma modulator (DSM) structure to transform between third- and second-order loop filters. Thus, it maintains a robust noise shaping capability and reduces the power consumption over a wide load range. The loop filters are implemented with a single op-amp resonator to reduce multiple integrators into a single element and enhance controllability of the resonance. More power-efficient operation is obtained by a switching node assisted deadtime controller (SADTC) that regulates the body-diode conduction. The proposed DSM-based buck converter was fabricated on a 180 nm CMOS. A spurious-free output spectrum with a noise floor below −81 dBm was achieved across all sampling frequencies. It operated at a wide range sampling frequencies of 3.75–15 MHz and regulated the output in the range of 1.0–2.4 V with input voltages of 2.5–5.5 V. The output voltage ripples were maintained under 19 mV. The converter showed a conversion efficiency of better than 80% over a load range of 1–1000 mA with a peak efficiency of 95.4% at 125 mA. [ABSTRACT FROM AUTHOR]

In this paper, the active differential-mode (DM) electromagnetic interference (EMI) filter topology for ac/dc converters is first briefly investigated. The active DM EMI filter model was developed based on the models of filter components including a current transformer, a high-pass filter, an operational amplifier, and a class AB amplifier. The system model including the active filter, ac/dc converter, and line impedance stabilization networks (LISNs) are explored. With the developed system model, the loop gain and insertion gain of the active filter are derived. Based on the loop gain, the stability of the active filter is investigated and the compensation is applied to achieve stability and good EMI reduction. Both simulations and experiments are conducted to validate the developed technique. [ABSTRACT FROM AUTHOR]

The second-order-generalized-integrator-based freq-uency-locked loop (SOGI-FLL) is a well-known tool for filtering and synchronization purposes in the power and energy applications. The SOGI-FLL, nevertheless, has a limited ability in rejecting the grid voltage disturbances. To deal with this problem, two advanced SOGI-FLLs have been proposed recently. In the first one, a SOGI-based filter is included inside the standard SOGI-FLL control loop, and in the second one, a SOGI-based filter is employed as the prefiltering stage of the SOGI-FLL. The small-signal modeling, tuning procedure, and detailed performance comparison of these advanced SOGI-FLLs have not been carried out yet. The aim of this paper is to cover these issues. [ABSTRACT FROM AUTHOR]

LCL-filter-based grid-tie inverters require damping for the current-loop stability. There are only software modifications in active damping, whereas resistors are added in passive damping. Although passive damping incurs in additional losses, it is widely used because of its simplicity. This paper considers the active damping in medium-voltage parallel inverters for wind turbines. Due to cost reasons, only minimal software changes are allowed and no extra sensors can be used. The procedure must be robust against line-inductance variations in weak grids. Double-update mode is needed so the resonance frequency is under the Nyquist limit. The bandwidth reduction when using active damping is also required to be known beforehand. Moreover, the design procedure should be simple without requiring numerous trial-and-error iterations. In spite of the abundant literature, the options are limited under these circumstances. Filter-based solutions are appropriate and a new procedure for tuning the notch filter is proposed. However, this procedure requires that the resistance of the inductors is known and a novel filter-based solution is proposed that uses lag filters. The lag filters displace the phase angle at the resonance frequency so that the Nyquist stability criterion is fulfilled. Simulations and experiments with a 100-kVA prototype validate the analysis. [ABSTRACT FROM AUTHOR]

This paper analyzes the accuracy of the zero-order hold (ZOH) model for the digital pulse width modulator (DPWM) in the s-domain. The s-domain model and the exact z-domain model for the current control of a single-phase inverter with an L-type filter are elaborated for quantifying the deviation of the ZOH model for the DPWM. The influences of the different computational delay and duty-cycle update modes on this deviation is analyzed in detail. The compensation method for this deviation of the ZOH model is proposed for accurately predicting the stability region of the control system in the s-domain. Simulations and experimental tests are executed to verify the effectiveness and correctness of the theoretical analysis. [ABSTRACT FROM AUTHOR]

In this paper, a novel buck–boost dc–dc converter with continuous input current is proposed. The voltage gain of the presented converter is higher than conventional converters, such as buck–boost, single-ended primary-inductance converter, Cuk, and Zeta converters. This converter works only by one switch and voltage stress across the switch is low. Input current of the proposed converter is continuous so a large filter at the input is not needed. Furthermore, continuous input current has made this converter suitable for renewable energy and fuel cell applications. In this converter, noninverting output voltage is obtained and high gain of voltage is achieved as well. So it can operate at wide output voltage range only by changing the duty cycle of the power switch pulse. The presented converter can easily controlled in continuous conduction mode operation, because of using only one power switch. In the following, the principle of operation and the mathematical analyses of the proposed converter are explained, finally, validity of the proposed dc–dc converter is verified by the experimental results. [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]

There are many different methodologies for a line startup, process transfer, line conversion, and process upgrade in semiconductor IC manufacturing. In our startup of a 200 mm bulk acoustic wave filter line converted from an existing 150 mm production line, a methodology of copy, scale, develop, and match (CSDM) was introduced. This methodology includes four phases of matching (unit qualification, short flow verification, pathfinder validation, and qualification lot process) between 150 mm and 200 mm process, different failure mode effects analysis (DFMEA) for the risk assessment of the differences between two processes, process flow breakdown with process blocks and sub-blocks, a decide, define, determine, and design method of process evaluation with short loop flow process monitors based on DFMEA assessment. Following this CSDM methodology throughout the conversion process ensures that both electrical and reliability performances of 200 mm product wafers match to those of the 150 mm line. The first 200 mm full flow pathfinder lot with electrical yield on parity to 150 mm line yield. In this paper, the application of this CSDM methodology is discussed in detail. [ABSTRACT FROM AUTHOR]

In this paper, a control strategy for the parallel operation of three-phase inverters forming an online uninterruptible power system (UPS) is presented. The UPS system consists of a cluster of paralleled inverters with LC filters directly connected to an ac critical bus and an ac/dc forming a dc bus. The proposed control scheme comprises two layers: 1) a local layer that contains a “reactive power-to-phase droop” in order to synchronize the phase angle of each inverter and a virtual resistance loop that guarantees equal power sharing among inverters; and 2) a central controller that guarantees synchronization with an external real/fictitious utility, and critical bus voltage amplitude restoration. Improved transient and steady-state frequency, active, reactive, and harmonic power sharing, and global phase-locked loop resynchronization capability are achieved. Detailed system topology and control architecture are presented in this paper. Furthermore, a mathematical model was derived in order to analyze critical parameters effects on system stability. The proposed control approach has been validated by means of experimental results obtained for several case-study scenarios. [ABSTRACT FROM AUTHOR]

The electric energy sector is moving toward extensive integration of renewable and clean energy resources, energy storage units, and modern loads via highly efficient and flexible multiterminal dc grids integrated within the traditional ac grid infrastructure. A voltage-source converter (VSC) is the main technology enabling the interconnection of dc and ac grids. In such demanding applications, dc-link voltage control is crucial to maintain system stability. However, the dynamics and control of VSCs considering the instantaneous power of both ac- and dc-side filters and dc grid uncertainties are not addressed in the current literature. Furthermore, as shown in this paper, the uncertainty in the effective dc grid parameters, including filter capacitance and dc-side inductance owing to connecting/disconnecting electric devices to/from the dc grid remarkably affects the converter stability and performance. To overcome these difficulties, this paper presents 1) a detailed small-signal model of the dc-link dynamics in grid-connected VSCs considering the instantaneous power of both ac- and dc-side energy storage components, and 2) a robust optimal dc-link voltage controller. The proposed controller ensures excellent tracking performance, robust disturbance rejection, and robust performance against operating point and parameter variation with a simple fixed-parameter controller. A theoretical analysis, comparative simulation studies, and experimental results are presented to show the effectiveness of the proposed control structure. [ABSTRACT FROM PUBLISHER]

This paper presents the analysis of possible transient overvoltages that can be generated during vacuum circuit-breaker (VCB) operation at the connection point of a photovoltaic powerplant. A typical switching event that is related to the VCB concerns energization and de-energization of the unloaded transformer. However, at the typical photovoltaic powerplant, the transformer is fed by an inverter equipped with LC (or LCL) filters that are necessary for limitation of harmonics and ripple in voltage and current. From the point of view of switching operations, the inductance and capacitance of the low-voltage (LV)-side connected filter affect the natural frequency of the transformer, which is reflected by different transient system response during VCB operation. In this paper, laboratory measurement of overvoltages generated during distribution transformer switching by means of VCBs is analyzed. The impact of the LC filter connected at the LV side on the overvoltages suppression was studied. Electromagnetic Transients Program–Alternative Transients Program simulations were conducted in order to verify the possibility of transients elimination by means of the additional series-connected RL choke at the transformer medium-voltage side. [ABSTRACT FROM PUBLISHER]