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Emulation of an electric machine allows the testing of a drive inverter and controller of an electric drive system, prior to the manufacture of a machine prototype. This paper presents the emulation of a variable flux machine (VFM). The VFM emulator system proposed in this paper uses a detailed look-up table-based machine model for the purpose of emulation. This allows the emulator to mimic all machine magnetic and geometric behaviors such as saturation and torque ripple. In addition, the machine emulator proposed in this paper uses high-performance high-bandwidth linear amplifiers as power amplifiers. This enables a high bandwidth; leading to a high accuracy machine emulation. A detailed control description for the proposed machine emulator system and a machine model look-up table data verification against a prototype machine is initially presented. Experimental results are then presented to validate the utility of the proposed VFM emulator system to emulate various machine transient behaviors at different magnetization levels. Experimental results obtained from the emulator are subsequently compared against the experimental results obtained from a prototype VFM drive to verify the emulation accuracy. [ABSTRACT FROM AUTHOR]

As the inverter-based generation replaces the conventional synchronous generators, it may also need to fill in the missing ancillary service support. One of these ancillary services is dynamic reactive power provision and voltage control. This paper analyzes optimal strategy of reactive and active fault-current support of the inverter-based generation leading to fast voltage recovery of the system. For the purpose of the analysis, new ramping active current controller able to emulate different behavior of active current injection is proposed. By optimizing its parameters for different case studies of the system, the conclusions about optimal behavior of the inverter based generation with respect to system parameters and operating conditions are drawn. It is observed that the optimal combination of active and reactive fault-current is the most sensitive to the dynamic load component penetration levels in the system. With the increasing penetration levels, the significance of active fault-current injection increases. The results show that with higher penetration levels of dynamic load component in the heavy load areas, the ramping down of the inverter-based generation active fault-current results in slower voltage recovery of the system. Following this conclusion, a recommendation on update of current European grid codes is proposed. [ABSTRACT FROM AUTHOR]

Low-inertia microgrids are prone to large frequency fluctuations due to high penetration of inverter-fed renewable sources. A virtual synchronous machine (VSM) is capable of handling these frequency fluctuations. VSM imparts inertial behaviour in grid-connected inverters with the help of an electric storage device. Most of the reported VSM control schemes use a constant inertia parameter that leads to an inadequate dynamic frequency response. In this paper, a fuzzy controller-based self-adaptive VSM control scheme is proposed. Here, the value of the inertia parameter is decided using fuzzy rules which take the penetration index of renewable energy, frequency deviation and rate-of-change-of-frequency as the input parameters. These rules are formulated with the help of the sample data obtained from simulations done in MATLAB/Simulink, where the inertial parameter is optimized using a genetic algorithm for various cases. The proposed method is validated for solar photovoltaic-fed microgrid test systems using power–hardware-in-the loop and the results indicate a reduction in maximum frequency deviation compared to the constant inertia parameter based VSM schemes. The introduction of renewable energy penetration level and fuzzy expert system in modifying the inertia parameter are the novel contributions in this paper. [ABSTRACT FROM AUTHOR]

Three-phase grid-connected inverter modeling depends on the equivalent resistance and inductance between the inverter and the grid. However, these parameters are not fixed during the operation of the inverter and vary with the operating conditions. In this paper, a new globally stable adaptive controller is proposed to estimate these values online and update the controller during its operation. A model reference adaptive system (MRAS) based on two fictitious quantities with no physical significance is utilized, namely $M = v \cdot i^*$ and $N = v^* \times i$ , where $v$ and $i$ are the steady-state values of voltage and current in synchronously rotating frame of reference. Detailed stability analysis of the proposed estimation technique has been presented using a Lyapunov energy function-based approach proving the global stability of the technique. Small-signal modeling and analysis of the proposed scheme has also been presented so as to understand the local dynamics of the system. The guidelines to select the parameter of the proposed MRAS system along with updating the controller are elaborated in this paper. Detailed simulation based on MATLAB/Simulink and PLECS, along with experimental studies through a Texas Instruments TMS320F28377S microcontroller, validates the feasibility of the proposed control architecture. [ABSTRACT FROM AUTHOR]

This paper highlights an immediate need for renewable generation developers, manufacturers, utilities and industry standardization institutes to jointly address a challenge of capacitor switching transient immunity in inverter-based wind or solar farms. The need was identified from wide-area operation records which showed partial or full generation loss in coincidence with routine utility-owned capacitor switching. The lack of a clear industry guideline has caused confusion to all involved parties. This paper recommends all entities to address this challenge collaboratively through enhanced equipment specification, design, and test before a well-defined industry guideline becomes available. [ABSTRACT FROM PUBLISHER]

Some inverter-fed motors, particularly at higher power ratings, are supplied with a shaft brush in order to help mitigate bearing currents. As more inverters are applied to motors in Class I Division 1/Zone 1 and Class I Division 2/Zone 2 locations, there is a need to understand whether a shaft brush can be safely applied in such an environment. This paper addresses the physics of why this is a concern and a methodology to evaluate the relative safety of two example cases. These issues are considered from the perspective of users, manufacturers of inverters and motors, and certifying bodies. The question posed in the title of this paper is answered by considering whether the addition of a shaft brush to an inverter-fed motor in a Class I hazardous location makes the system more safe or less safe. [ABSTRACT FROM PUBLISHER]

The staircase modulation strategy is the best choice for asymmetric cascaded H-bridge multilevel inverter (ACMI) because it makes the output voltage to present a high number of levels and makes one of the ACMI modules to operate at low frequency. However, the staircase modulation is usually employed without giving its deserved attention. This paper presents a clear understanding of the staircase modulation strategy and its applications in both isolated and grid-connected ACMI.  The main novelty of this paper is the obtaining of the switching function for each module. The principle of operation is carefully described, also indicating how to command the ACMI transistors. The output voltage of the two superior modules is evaluated for different values of iterations. Special attention is given to the power distribution among the ACMI modules when the staircase modulation is applied. It is demonstrated on how the power is processed in each module considering an ACMI with three modules. The analysis is presented showing the staircase modulation within a closed-loop control strategy for isolated and grid-connected modes of operation, showing that the content of this paper is valid for both modes. Experimental results clarify and show the efficacy of the content presented in this paper. [ABSTRACT FROM AUTHOR]

The grid-connected inverter is a key device in the renewable energy power generation system and large-scale energy storage system, which the operational stability and reliability are the basis for the efficient and safe application of electrical energy. A real-time fault diagnosis method of a three-phase for grid-connected application combining a mixed logic dynamic (MLD) model and finitecontrol set model predictive control (FCS-MPC) is proposed. This paper not only realizes the open circuit fault diagnosis and location of the switching devices in the main power circuit, but also discusses the threshold issues and post-fault operations. The advantage of the proposed method is that it directly uses the control data and measurement signals of the controller without extra sensors and calculation, which will shorter the fault diagnosis time and occupy less calculation resource of the main processor. Simulation results illustrate the quickness of the fault identification and accurate position with robustness to the interference of the diagnosis method. Finally, the effectiveness of the diagnosis method was verified by a 1500 W experimental prototype in a laboratory. [ABSTRACT FROM AUTHOR]

A large class of three-phase electrical power systems possess symmetry conditions that make it possible to describe their behavior using single-input single-output transfer functions with complex coefficients. In such cases, an extended root locus method can be used to design control laws, even though the actual systems are multi-input multi-output. In this paper, the symmetric conditions for a large class of power systems are analyzed. Then, the root locus method is revisited for systems with complex coeffcients and used for the analysis and control design of power systems. To demonstrate the benefits of the approach, this paper includes two examples: 1) a doubly fed induction machine and 2) a three-phase LCL inverter. [ABSTRACT FROM PUBLISHER]

Although the concept of a multiphase drive system dates back to the middle of the 20th century, the initial pace of development was rather slow, as witnessed by the first two surveys of the area published in the beginning of this century. However, considerably new developments have resulted in the last decade of the 20th century and the beginning of this century, leading to an authoritative survey of the asymmetrical six-phase drive control and subsequently of the review of the complete area. This also initiated the organization and subsequent publication of the first IEEE Transactions on Industrial Electronics "Special Section on Multiphase Machines and Drives" in May 2008, which commenced with another survey paper, and that contained 12 original research papers. Since the publication of this Special Section in May 2008, the level of interest and pace of developments in the area have further accelerated and substantial new knowledge has been generatedwith an ever-increasing number of published research papers and reported new industrial applications. Such a trend has been emphasized in a recent paper. It therefore seemed appropriate to revisit the area and organize this Special Section as a sequel to the first one. The call for the Special Section papers resulted in 51 submissions, almost twice as many as the total back in 2008, thus confirming a substantial growth of the area. Indeed, the amount of new knowledge acquired since the publication of the first Special Section in 2008 has meant that it was not possible to provide a complete and thorough survey of the field in a single review paper. [ABSTRACT FROM AUTHOR]

This paper is concerned with the use of a three-level inverter for a synchronous reluctance machine (SynRM). The SynRM suffers from a poor power factor due to poor machine saliency. This makes it harder to operate the three-level neutral-point-clamped inverter due to a strict requirement to have the two dc-link capacitor voltages balanced. This paper proposes a new nearest three vector modulation algorithm which can balance the two dc-link capacitors even at poor machine saliency ratio (poor power factor). In this paper, a method of sizing the two dc-link capacitors based on the machine power is also proposed. A comparison between two- and three-level inverters was conducted. The SynRM registered lower $d$-axis current ripple with a three-level inverter, indicating lower core losses in the machine. [ABSTRACT FROM PUBLISHER]

The modern photovoltaic inverter has an active power-reactive power (Watt-VAr) control curve that is part of its management modes. The Watt-VAr curve, whose settings can be remotely modified, regulates the inverter reactive power output in function of its active power. This paper proposes the optimization of inverter segregated linear decision rules (LDRs), starting from the legacy Volt-VAr optimization in distribution networks. As opposed to classical LDRs that are interfaced with Volt-VAr optimization, the segregated LDRs are piecewise linear continuous curves that directly satisfy the reactive power capability of inverters, and their multiple segments can capture the correlation in solar power variability. The paper presents linear programming formulations for optimizing the segregated linear decision rules using stochastic optimization, robust optimization, and distributionally robust optimization. The optimization schemes are demonstrated on both meshed and radial networks, and their performance is validated via Monte-Carlo simulation. [ABSTRACT FROM AUTHOR]

Motor current signature analysis (MCSA) has been widely used for fault diagnosis of induction motors (IMs) because of its non-invasiveness and comparatively low cost. However, the spectral leakage of the fundamental supply frequency can obscure the fault characteristic component when IMs operating at no-load or low-load conditions. In this paper, a broken rotor bar (BRB) fault diagnosis approach based on the third-order energy operator (TOEO) demodulated current signals is presented. The TOEO approach performs effectively in reducing the negative impact of the fundamental supply frequency spectral leakage and enhancing the BRB fault features. Theoretical and experimental results show that the TOEO approach can excellently reveal the fault characteristic frequency, instead of the sideband frequencies. Besides, the results are compared with the Teager-Kaiser energy operator (TKEO). The capability of the presented approach has several advantages over the TKEO, especially when the IMs are fed by an inverter. [ABSTRACT FROM AUTHOR]

This paper discusses systematic efficiency considering the efficiency of both a motor and airflow in an inverter-driven single-phase brushless direct-current (BLDC) motor with two different lamination designs for a cordless vacuum cleaner. In other words, multi-physical lamination design has to be conducted, and hence, the shape and placement of a whole electromagnetic structure are investigated in terms of a tradeoff between the electrical and mechanical efficiencies. In this paper, a single-phase BLDC motor for cordless vacuum cleaners is designed to satisfy starting and continuous torques by means of asymmetric air gap, and fluid analysis is performed to determine which shape of a single-phase BLDC motor has better system efficiency. The prototype of a single-phase BLDC motor has been tested, and the speed of the operation is ranged from 84468 r/min up to the rated speed of 100020 r/min. The motor efficiency of 94.7% has been measured to verify a good match with the estimated efficiency of 94.5%. [ABSTRACT FROM AUTHOR]

The nine papers in this special section focus on photovoltaic module and sub-module level power electronics. Grid connected photovoltaic energy systems have experienced an explosive growth over the last decade, with a cumulative installed capacity surpassing the 400 GW milestone as of 2017. Among PV system configurations, distributed module-level converter architectures can lead to a higher energy yield by mitigating partial shading, persistent shading (soiling, snow, bird droppings, and fallen leaves), mismatch, and aging, through a higher maximum power point tracking (MPPT) efficiency. Also, distributed electronics might be the key for implementing diagnostic and prognostic actions at a module level. Among these configurations, microinverters (also known as ac-module inverter), which connect a single PV module to the grid, and PV power optimizers, which are dc–dc converters performing the MPPT function at a module level, have attracted the academic and industrial interest in the last decade. So much so, that both microinverters and dc–dc power optimizers are commercialized by tens of companies around the world, with a great variety of circuit topologies, which comprise combinations of one or more power stages, interleaved converters, resonant converters, topologies with and without isolation, etc. [ABSTRACT FROM AUTHOR]

This paper examines metal–ferroelectric–insulator–semiconductor negative-capacitance FinFET (NC-FinFET) based VLSI subsystem-level logic circuits. For the first time, with the aid of a short-channel NC-FinFET compact model, we confirm the functionality and evaluate the standby-power/switching-energy/delay performance of large logic circuits (e.g., dynamic 4-bit Manchester carry-chain adder and the formal hierarchical 32-bit carry-look-ahead adder) employing 14-nm ultra-low-power NC-FinFETs. Our study indicates that the inverse Vds-dependence of threshold voltage (VT), also known as the negative drain-induced barrier lowering, of negative-capacitance field-effect transistor is not only acceptable but also beneficial for the speed performance of both the static and pass-transistor logic (PTL) circuits, especially for the PTL at low VDD. [ABSTRACT FROM AUTHOR]

This paper proposes a high-efficiency single-phase T-type boundary conduction mode (BCM) microinverter. The conventional full-bridge BCM microinverter has achieved zero voltage switching (ZVS) and thereby improved the efficiency, but it suffers from high switching losses under light load conditions. The proposed T-type BCM microinverter reserves ZVS and uses a multilevel technique to further decrease the switching losses. The BCM operation with multilevel technique will have too low switching frequency when the grid voltage approaches half of the dc link voltage. To solve this problem, this paper adopts a third operation mode for the T-type switching leg to maintain the switching frequency above a minimum value. The corresponding mode transitions are also detailed to ensure a smooth operation. Because of the turn-offdelay of the freewheeling transistor, the actual lower current boundary deviates from the programmed one, which will distort output current. To address this issue, this paper also proposes a boundary compensation method. A prototype has been built for performance verification, which can test both full-bridge and T-type topology. Compared with the full-bridge BCM microinverter, the proposed T-type BCM microinverter has a higher efficiency over the whole load range. [ABSTRACT FROM AUTHOR]

This paper proposes a vector control strategy for independent control of two permanent-magnet synchronous motors (PMSMs) using a single four-leg inverter (4LI). An expanded two-arm modulation to obtain a balanced three-phase output voltage is described. This paper also proposes a method to compensate for the fluctuations in the neutral point voltage of two split capacitors in the dc link. The experimental results show that independent speed and position control of two PMSMs can be achieved using a single 4LI with the proposed vector control method. [ABSTRACT FROM AUTHOR]

This paper presents a novel configuration for a high-Q tunable waveguide (WG) filter with a constant absolute bandwidth (BW). The key feature of this filter is that it is tuned by a single tuning element. This paper investigates the theory of coupling behavior of single septum and double septa to achieve constant absolute BW. The theory is presented for both the coupling matrix-based and inverter-based filter topologies. The filter design methodology is lucidly presented covering the design strategy adopted for interresonator coupling, input–output coupling and tuning element. The tuning mechanism of the proposed filter is explained with measurement results presented for a $Ku$ -band tunable WG filter designed at 15 GHz with a 2% BW to achieve 15% tuning range. The filter promises to be useful in emerging 5G millimeter-wave applications, where the filter size is very small to accommodate many mechanical tuning elements. Furthermore, the proposed design methodology is scalable, i.e., the tuning mechanism is independent of the filter order. [ABSTRACT FROM AUTHOR]

This paper presents a novel platform for accurate mathematical modeling of the propulsion system of electric cars. It provides, for the first time, a hardware-in-the-loop (HIL) real-time experimental verification case study of a General Motor Chevrolet Volt for power, control systems, and the mechanical systems. The contribution of this paper can be categorized into three approaches: First, each component of the powertrain is accurately modeled taking transient dynamics of all components of the electric vehicle into consideration. Further, a PSIM simulation platform is consequently developed to demonstrate the validity of this mathematical modeling. Finally, the Typhoon HIL is used to provide the experimental verification of the proposed model in real time, which precisely validates the viability of the model. HIL technology is used to prototype and test the proposed control system while simulating the power circuit on the HIL module platform. The permanent magnet synchronous motor and the power electronics hardware components are simulated in real time at which the parameters can be changed during the simulation. However, the control algorithm is generated as a C code and downloaded to the TI controller that exists on a digital signal processing board. The results from the simulation based on PSIM environment and hardware validations using HIL are in agreement, which validates the developed model. The performance has been investigated under different load operating conditions in real time to verify its robustness. The case study can be extended for any electric car as it provides a generic platform for modeling any propulsion system. [ABSTRACT FROM AUTHOR]

In this paper, we develop and examine permanent magnet synchronous motors (PMSMs) by use of both stator and rotor cores made of nanocrystalline magnetic materials (NMMs). We report core loss properties of the PMSM with the NMM under inverter excitation. In addition, we compare core losses of the PMSM with conventional non-oriented (NO) steel sheets under inverter excitation to discuss the core loss characteristics of the NMM motor. In average, under inverter excitation, the reduction ratio in core loss of the PMSM made of NMM is about 60% as compared with the core loss of the PMSM with NO sheets. In particular, the average decrease obtained by using NMM rotor core instead of NO rotor core is about 30%. [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]

The pump-back test is widely adopted in the industry for characterizing and qualifying high-power converters. One popular pump-back test configuration is to tie the dc links of two converters together and circulate the current through the inductor connected between the ac terminals. In this configuration, one of the converters operates in the voltage mode to generate the virtual grid and the other converter regulates the circulating current, where hysteresis control could be applied. However, the switching characteristics of hysteresis control are unique due to the pulsewidth modulation type voltage being the virtual grid. This paper contributes to analyzing the switching frequency characteristics of the hysteresis control in this pump-back test configuration. The switching frequency tracking phenomenon is revealed and reported in this paper for the first time. Theoretical analysis, simulation validation, and experimental demonstration are provided to support the major conclusions. [ABSTRACT FROM AUTHOR]

In this paper, the conventional I- and T-type three-level neutral-point-clamped (3L-NPC) inverter for low-voltage renewable energy systems is first investigated. Literature research shows that the T-type inverter improves I-type's insulated-gate bipolar transistor (IGBT) $+$ IGBT current paths. However, the IGBT $+$ diode paths are the same. The calculation in this paper further reveals that the IGBT $+$ diode current paths dominate the conduction losses and even the whole semiconductor losses. Based on the aforementioned recognitions, a novel T-type inverter is presented as an alternative to be applied in the low-voltage renewable energy systems. In the proposed 3L-NPC, four CoolMosfets replace the IGBT $+$ diode middle bidirectional switch. In the proposed topology, there is no diode involved in the current path supposing the unity power factor. In this way, the conduction loss is expected to be reduced compared with that from the conventional T-type 3L-NPC, particularly in the low and medium power ranges. [ABSTRACT FROM PUBLISHER]

The safety and reliability of inverters play a significant role in stable power electronic system operations. Considering a railway vehicle air-conditioning inverter as a case study, this paper presents a generic open-circuit fault diagnosis method that can be applied to various inverter and control schemes. First, a detailed model of three-phase output currents under both normal and fault status is derived, and then the concept of space trajectory is introduced based on the three-phase output currents. The open-circuit faults of the inverter lead to output phase current distortion. Therefore, different types of faults have different space trajectories, and the corresponding shape of the space trajectory is considered to be a fault feature. Then, the fault is located by the direction vector and center-of-mass coordinate. The effectiveness and reliability of the diagnosis method are verified and analyzed using a hardware-in-the-loop test platform. [ABSTRACT FROM AUTHOR]

Voltage imbalances are one of the most severe challenges in electrical networks, which negatively affect their loads and other connected equipment. This paper proposes a voltage support control strategy to mitigate the voltage imbalance in inverter-based low voltage distribution networks. The control scheme is derived taking in mind the following control objectives: a) to increase the positive sequence voltage as much as possible, b) to decrease the negative sequence voltage as much as possible, c) to inject the power generated by the primary source, and d) to minimize the output current of the inverter. The innovative contribution of the proposed solution is based on the design of a control algorithm that meets the aforementioned objectives without resorting to communications with other grid components. The theoretical results are experimentally validated by selected tests on a laboratory setup with X/R ratio close to one. [ABSTRACT FROM AUTHOR]

A novel single-phase transformerless dual-mode interleaved multilevel inverter (DMIMI) is proposed in this paper, which can inject a highly sinusoidal ac current to the grid even with the input dc voltage less than the peak grid voltage. Furthermore, dead-beat controllers are developed to directly calculate the optimal duty cycles in a digital control platform. As compared to the traditional dual-mode multilevel approaches, the DMIMI offers high efficiency, less number of components conducting simultaneously in each operation mode, and the capability of reactive power exchange. This paper presents the theoretical analysis and the experimental results obtained from a 1-kW prototype. The experimental results reveal that the proposed DMIMI can achieve high conversion efficiency and low leakage current as well as high quality grid current. [ABSTRACT FROM AUTHOR]

This paper proposes a new control scheme to eliminate the 3rd harmonic in the output currents of grid-following inverters under unbalanced grid conditions. Unbalanced grids adversely affect the performance of grid-following inverters due to the oscillations appearing on the DC-link voltage with a frequency twice the line frequency. The paper is based on instantaneous active reactive control (IARC) technique due to its advantages over other existing methods. However, the presence of severe asymmetrical 3rd harmonic distortions in the inverter output currents is the main challenge with IARC method, which impairs the power quality requirements. This paper enhances the IARC scheme by proposing a 3rd harmonic elimination approach by adopting a current reference generation method using the symmetric sequence components concept. Furthermore, the proposed scheme complies with the grid code requirements by injecting the requested reactive current. Finally, the proposed approach is evaluated by theoretical and simulation analysis and validated experimentally using a hardware setup. [ABSTRACT FROM AUTHOR]

This paper characterizes the sampling effect in digital sinusoidal pulse width modulation (SPWM) of voltage source inverter (VSI). The time-domain analysis presented in this paper establishes the relation between the fundamental frequency, carrier frequency, and the sampling frequency at different modulation indices of the SPWM. The analysis investigates the effect of sampling frequency of the digital controller on the output of the VSI. It is shown that the low-frequency harmonic components appear in the frequency spectrum of the VSI output voltage due to sampling. As a result, the output current of digitally controlled VSI is stepped in nature. The double Fourier integral solution of the switched waveform for inner and outer integral limits has been used to derive the expression. The integral solution is obtained using Jacobi-Anger expansions. The generalized results developed in this paper are useful to investigate the sampling effect in high switching frequency DSPWM. The proposed sampling effect has been analyzed for SPWM of single-phase H-bridge inverter. The analytical results are verified using simulation and experimental results. The experimental results have been obtained with the use of field-programmable gate array (FPGA) as a digital controller. [ABSTRACT FROM PUBLISHER]

The ability of an electrical drive to continue operation without tripping in spite of short-duration voltage sags or power supply interruptions is known as power failure ride-through capability. Critical production processes in industries require the drives to smoothly ride-through during momentary power interruptions. The reliability of the drive is dependent on the maximum duration for which a total power supply failure can be tolerated without process interruption. This paper presents a method to extend the duration of the ride-through in voltage-source-inverter-fed vector-controlled induction motor drives with a front-end diode bridge rectifier. The proposed method minimizes the losses in the system during the ride-through, thereby enabling a longer ride-through duration. The method only requires a modification of the control software and hence is easy to implement. This paper also briefly describes two conventional methods used for ride-through and compares the proposed method with the conventional methods to clearly bring out its advantage. Simulation study using MATLAB/PLECS verifies the effectiveness of the proposed method. Hardware implementation of the method on a 30-kW induction machine indicates an extension of up to 34% in the ride-through duration with the proposed method, as compared with the conventional method. [ABSTRACT FROM AUTHOR]

This paper presents real-time diagnosis for open-circuited (O-C) and unbalance faults in power electronic converters (PECs) connected to residential small wind systems grid-tied. The spectrum analysis along with the dc components of the voltage and current measurements available in the converter is utilized for the O-C fault detection, classification and localization of the power switching devices in the PEC, as well as the identification of the unbalance input voltage to the converter. The proposed methodologies in this paper require much fewer inputs compared to the previous researches; therefore, they avoid any additional sensors or hardware which include further costs and expenses on such systems. The experimental evaluations for the proposed algorithms are provided and demonstrate the effectiveness and the robustness of the proposed diagnostic algorithms in this paper. The PEC under study consists of three main subsystems: uncontrolled three-phase rectifier, boost chopper, and single-phase inverter. [ABSTRACT FROM PUBLISHER]

This paper develops a simplified phasor model for predicting harmonics present at the point of common coupling between a voltage-source power converter and the utility network. It employs the frequency coupling matrix (FCM) modeling technique. The FCM is experimentally determined without requiring access to converter internal details, such as control and output filter parameters, which are generally not available for converters used in distributed generation systems. Experimental measurements are conducted on a commercially available two-stage, three phase, grid-tied photovoltaic inverter to assess the accuracy of experimentally determined FCMs to predict the harmonic behavior of grid-connected converters. This paper considers two grid conditions for the experimental analysis: 1) when the grid is stiff and contains only background voltage harmonics and 2) when the grid contains harmonic grid impedances as well as background voltage harmonics. In all cases, a close match between the results predicted by the FCM approach and experimental measurements is achieved, thus demonstrating the practical viability of using experimentally determined FCM models for harmonic predictions. [ABSTRACT FROM PUBLISHER]

This paper presents an improved dc-link voltage balancing algorithm for a three-level neutral-point-clamped inverter by considering phase current direction. Detailed studies on the effects of change in load current direction on the dc-link capacitor voltages are presented. A maximum value of power factor is numerically derived, above which it affects the capacitor voltage balancing capability. Compared with the previously presented research work, the inputs to the space-vector pulsewidth-modulation block are the three phase currents and the difference between the two capacitor voltages. Depending on the states of the two dc-link capacitor voltages and phase current direction, redundant voltage vector sequences are selected. The selected vectors keep the capacitor voltage deviations within 5% of the total dc-link voltage. Two zero switching vectors (i.e., PPP and NNN) are also removed from all subsectors of the earlier proposed strategy, which one used to produce higher common-mode voltages. Detailed simulation and experimental results are presented in this paper for a 6.0-kW surface permanent-magnet synchronous machine. Both the simulation and experimental results show the required performance of the proposed system. [ABSTRACT FROM AUTHOR]

Capacitor-current-feedback active damping has been widely used in LCL-type grid-connected inverters. However, the damping performance is deteriorated due to the negative equivalent resistance resulted by the digital control delays, and thus the grid-connected inverter is apt to be unstable under the grid impedance variation. To address this issue, this paper proposes the capacitor-current proportional-integral (PI) positive feedback active damping method that can ensure a positive equivalent resistance almost within the Nyquist frequency, i.e., the full controllable frequency range. In theory, the proposed damping method can be implemented by feeding back the capacitor current through a PI function. However, the integral term will continuously accumulate the noise and dc bias arising from the feedback signal. To overcome this drawback, a more practical implementation solution is drawn in this paper. Furthermore, a straightforward design procedure is presented for the convenience of selecting the proper controller parameters. With the proposed damping method and its practical implementation, high inverter robustness against the grid impedance variation can be achieved. Experiments are performed on a 6-kW prototype and the experimental results are in well agreement with the theoretical expectations. [ABSTRACT FROM AUTHOR]

In this paper, we design a voltage-modulated direct power control (VM-DPC) for a three-phase voltage source inverter (VSI) connected to a weak grid, where the phase-locked loop (PLL) system may make the system unstable if the conventional vector current control (VCC) method is applied. Compared with the conventional VCC method, the main advantage of the proposed VM-DPC method is that the PLL system is eliminated. Moreover, in order to inject the rated real power to the weak grid, the VSI system should generate some certain amount of reactive power as well. An eigenvalues-based analysis shows that the system with the proposed method tracks its desired dynamics in the certain operating range. Both simulation and experimental results match the theoretical expectations closely. [ABSTRACT FROM AUTHOR]

This paper presents the bilateral operation of a transformer-less H-bridge inverter as a power flow controller and fault current limiter in low-voltage distribution network. A novel control strategy has been developed to initiate and activate the H-bridge inverter to control the power flow at point of common coupling (PCC). On the other hand, the H-bridge inverter operation like a short-circuit current limiter during grid disturbance event and its smooth reinsertion after fault clearance have also been clarified. Besides, an island mode control strategy incorporating synchronization controller, and proper coordination with flip flops have been implemented in order to synchronize the microgrid with the main grid before reclosing the circuit breaker. The results confirm: The effectiveness and feasibility of the novel control methodology in activating the real power flow; the inverter capability of minimizing the short-circuit current during fault and the successful resynchronization of the microgrid voltage source inverter (VSI) and the H-bridge inverter to the main grid. [ABSTRACT FROM AUTHOR]

In islanded microgrids, voltage source inverters working in parallel are expected to provide regulation of the local frequency while granting active power sharing. This paper presents a local control approach at each inverter based on an event-driven operation of a parameter-varying filter. It ensures perfect active power sharing and controllable accuracy for frequency restoration without requiring the exchange of control data between inverters over the communication network. This paper includes stability analysis and design guidelines for the control parameters using a modeling approach that considers the interaction between inverters. Selected experimental results on a three-inverter laboratory microgrid corroborate the effectiveness of the proposed control scheme, and outlines its advantages with respect to previous similar schemes and the performance cost that implies not using communications. [ABSTRACT FROM AUTHOR]

The supply-side current of an inverter-fed induction motor (IM) is easily accessible and less affected by noises than the motor stator current. This paper proposes a novel sensorless speed estimation method for an IM using the spectrum of the supply-side current. However, due to the influence of fundamental supply frequency, it is difficult to carry out the speed detection straight from the supply-side current signal. In this paper, an analytic model for characterizing the supply-side current of an inverter-fed IM using the modulation theory and the switching function concept is developed. Then, the Hilbert transform is applied to extract the speed harmonic component from the supply-side current. Finally, an interpolated Goertzel algorithm is put forward to enhance the estimation precision of IM speed. The performance of the proposed sensorless speed estimation method is proved by the speed estimation results obtained from hardware experiments of an IM fed by an inverter under different load conditions. [ABSTRACT FROM AUTHOR]

The automated and unattended design of balanced microstrip wideband bandpass filters by means of aggressive space mapping (ASM) optimization is reported in this paper. The proposed filters are based on multisection mirrored stepped impedance resonators (SIRs) coupled through quarter-wavelength transmission lines, acting as admittance inverters. Such resonant elements provide transmission zeros useful for the suppression of the common mode in the region of interest (differential filter pass band) and for the improvement of the differential-mode stopband (rejection level and selectivity). Due to the limited functionality of the inverters, related to the wide fractional bandwidths, the automated filter design requires a two-step process. With the first ASM, the filter schematic satisfying the required specifications (optimum filter schematic) is determined. Then, the layout is synthesized by means of a second ASM algorithm. Both algorithms are explained in detail and are applied to the synthesis of two filters, as illustrative (and representative) examples. With this paper, it is demonstrated that the two-step ASM optimization scheme (first providing the optimum schematic and then the layout), previously applied by the authors to wideband single-ended filters, can be extended (conveniently modified) to common-mode suppressed differential-mode bandpass filters. Thus, the value of this two-step ASM approach is enhanced by demonstrating its potential for the unattended design of complex filters, as those considered in this paper. [ABSTRACT FROM PUBLISHER]

This paper proposes a variable off-time control method for a single-phase microinverter operating in the discontinuous conduction mode (DCM) for efficiency improvement. First, the fixed off-time control method is analyzed. The concept is to fix the off-time of the active switch throughout a line cycle for all output powers and scale the on-time of the active switch to shape a sinusoidal output current. Then, based on the fixed off-time control method, a variable off-time control method is proposed to modulate the preset fixed off-time in order to decrease the switching frequency during ac line zero-crossings and light load conditions. Compared with existed fixed-frequency DCM control or boundary conduction mode control, the variable off-time control is more flexible to optimize the efficiency under different load conditions as the switching frequency range can be automatically adjusted according to the output power. The switching frequency is high at heavy loads to limit the maximum peak current and is low at light loads to increase the light load efficiency. In addition, a predictive on-time method is adopted to simplify inverter control and reduce hardware costs. The parameter design principle is detailed in this paper. A 300 W prototype is built to verify the performance of the proposed method. [ABSTRACT FROM AUTHOR]

This paper provides an experimental and theoretical discussion on dynamic braking for a medium-voltage induction motor fed by a modular multilevel double-star chopper-cell (DSCC) inverter. It is intended to apply the motor drive to large-capacity fans and compressors with a large moment of inertia. Each chopper cell consists of a bidirectional chopper and a braking chopper connecting a single small-rated braking resistor in series with a single IGBT. This configuration results in a “distributed” dynamic brake that provides a distinctive welcomed side effect of protecting all the bidirectional-chopper cells against sudden overvoltage. An experimental system rated at 400 V and 15 kW is designed, constructed, and tested to verify operating performance of the distributed dynamic brake. Experimental waveforms, along with simulated waveforms, confirm firmly that the distributed dynamic brake is feasible and effective in an induction motor fed by a medium-voltage high-power DSCC inverter for fans and compressors. Finally, this paper gives a design example of a distributed dynamic-braking resistor for the 11-kV, 12-MW induction motor driving a large-capacity fan equipped with a large moment of inertia. [ABSTRACT FROM AUTHOR]

This paper proposes a method to suppress the resonant current circulating between integrated half-bridge modules with phase-leg capacitors in two legs. This circuit configuration has the advantage of low stray inductance between power semiconductor devices and dc-link capacitors (phase-leg capacitors). This paper presents an analysis of the equivalent circuit for the circuit configuration that suggests that the dc-link capacitor current will increase depending on the relationship between resonant and switching frequencies. The capacitor current was experimentally evaluated under pulse-width modulation operation at switching frequencies up to 100 kHz using SiC-mosfet s. As a result, the resonant current may occur in the dc side when the resonant frequency between phase legs was close to either the fundamental or the third harmonic of the switching frequency. In order to suppress the circulating resonant current, a graphite bus bar is applied to the phase-connecting bus bar. Using the graphite bus bar, the capacitor current can be reduced by 35% without any influence from the ac-side output current. [ABSTRACT FROM AUTHOR]

The traditional evaluation method of vehicle noise can no longer meet the requirements of electric vehicle as the sound character of electric powertrain (E-PT) is totally different from that of internal combustion engine vehicles. This paper presents a complete investigation of the sound quality of an E-PT. An acoustic test is conducted to analyze the sound character of E-PT, based on which the acoustic origins of E-PT including electromagnetic noise, gear whine, and inverter switching noise are studied. After that the sound quality of E-PT is investigated by objective and subjective evaluations. Subsequently, a sound quality model of E-PT based on support vector machine is established. The relative error testifies the effectiveness of the prediction model. The influence of the main noise origins on the sound quality of E-PT is determined. Finally, the structure of gearbox housing is redesigned based on topology optimization to improve the sound quality. The main original contributions of this paper are not only the sound quality method developed for E-PT but also improvement feasibility of sound quality. [ABSTRACT FROM PUBLISHER]

In this paper, a new structure of Marx generator (MG) based on buck--boost converter is proposed to generate high-voltage pulses. In this structure, a single-phase inverter is employed to supply parallel diode--capacitor units by positive and negative values of the input dc source (±Vin). The main contribution of this paper is proposing a new switching strategy, by which a group of capacitors are charged properly. Finally, the charged capacitors are connected in series such that the output voltage is equal to summation of the capacitors' voltages. Considering specified value of the output voltage, the number of circuit elements in the proposed structure is reduced in comparison with other topologies of unipolar MG. Furthermore, voltage rating of switches and diodes in the proposed topology is lower than that of other unipolar MG structures. Design of the structure ensures that there is no need to connect the switches in series, when the number of stages is increased. To verify the performance of the proposed MG structure, simulation has been carried out in MATLAB/Simulink. Furthermore, a prototype of the proposed structure has been implemented in the lab. The simulation and experimental results confirm the capability of the structure for generating high-voltage pulses. [ABSTRACT FROM AUTHOR]

This paper describes the modeling, analysis, and design of a complete (dc-to-dc) inductive wireless power transfer (WPT) system for industrial moving applications. The system operates at 6.78 MHz and delivers up to 150 W to a load moving along a linear path, providing a quasi-constant dc output voltage and maintaining a zero voltage switching operation, regardless of position and load, without any retuning or feedback. The inductive link consists of an array of stationary transmitting coils and a moving receiving coil whose length is optimized to achieve a constant coupling coefficient along the path. Each Tx coil is individually driven by a constant amplitude and phase sinusoidal current that is generated from a GaN-based coupled load-independent Class EF inverter. Two adjacent transmitters are activated at a given time depending on the receiver’s position; this effectively creates a virtual series connection between the two transmitting coils. The Rx coil is connected to a passive Class E rectifier that is designed to maintain a constant dc output voltage independent of its load and position. Extensive experimental results are presented to show the performance over different loading conditions and positions. A peak dc-to-dc efficiency of 80% is achieved at 100 W of dc output power and a dc output voltage variation of less than 5% is measured over a load range from 30 to $500~\Omega $ . The work in this paper is foreseen as a design solution for a high-efficient, maintenance-free, and reliable WPT system for powering sliders and mass movers in industrial automation plants. [ABSTRACT FROM PUBLISHER]

This paper discusses and compares phase-shifted pulse-width modulation (PS-PWM) and level-shifted PWM (LS-PWM) in a modular multilevel single-delta bridge-cell (SDBC) inverter for utility-scale grid-tied photovoltaic applications. This three-phase SDBC inverter provides the capability of operating even under power-distribution imbalances not only among three clusters, but also among cascaded bridge cells in each cluster. The main focus of this research lies in analyzing the capability of operation under severe power-distribution imbalances and presenting power-balancing methods based on zero-sequence current injection, which result in an extended power-balancing capability. This paper highlights that LS-PWM is superior to PS-PWM in both power-balancing capability and harmonic performance at the ac side of the SDBC inverter when operating under power-distribution imbalances. Experimental results obtained from a three-phase 10-kW downscaled system show good agreement with those from the theoretical analysis. [ABSTRACT FROM AUTHOR]

This paper presents a different Finite Control Set – Model Predictive Control (FCS-MPC) for grid-connected three-phase bidirectional power inverters. These are typically used in dc or ac renewable-based microgrids (MGs), where bidirectional operation and fast dynamic response is required. The bidirectional grid-connected inverters are an essential part of MG, which inject energy into the ac grid or demand energy from it. The dynamic behavior of the system is a major concern since the current can suddenly change depending on the hierarchical controller. This paper proposes a different cost function using sliding mode theory, which offers a good dynamic response, reduced computational burden, and a parameter-free control model. The operation principle of the proposed controller is given and evaluated using a Hardware-In-the-Loop (HIL) system, but also experimentally with a 1kW laboratory prototype. The final results demonstrate the advantages of using this approach in grid-connected three-phase bidirectional power inverters in terms of dynamic response and reduced computational burden, making this solution technically attractive and viable. [ABSTRACT FROM AUTHOR]

Inverter transformers are one of the key components in a PV plant and their operating patterns are considerably different from that of transformers in a substation. Moreover, these transformers experience higher level of harmonics generated by the inverters. Therefore, investigating the ageing profile of the inverter transformer is a timely requirement. In this paper, the ageing of inverter transformers in a medium-scale solar PV plant is studied by utilizing various real-time measurements including load current, top-oil temperature (TOT), ambient temperature, moisture in top oil, solar irradiance and individual current harmonics. An updated moisture-dependent thermal model (MDTMH), with consideration of current harmonics is developed to estimate the hot-spot temperature (HST). The influence of weather conditions, which directly determine the load current of inverter transformers on the loss of life (LOL) of an inverter transformer is also investigated. Furthermore, the effect of current harmonics levels on the inverter transformer's HST and LOL is explored. Finally, comparisons of HST and LOL of inverter transformers connected to PV arrays with three different tracking technologies, i.e., fixed-tilt, single-axis and Dual-axis PV arrays are performed. [ABSTRACT FROM AUTHOR]

A recent paper by M. Zaky & M. Metwaly (doi: 10.1109/TPEL.2016.2583660) proposed a fuzzy logic controller (FLC) to mitigate the negative effects of motor parameter variation influence on indirect rotor field oriented control (IRFOC) without proposing a tuning method. However, neither rotor nor magnetizing inductances were investigated. Instead, the variation in stator resistance and load inertia—which have less effect on the orientation algorithm—is demonstrated. This correspondence introduces a typical system model with similar simulation platform and parameters. With identical tests, two errors to the original paper have been found. First, the reported speed which is in rev/min should be in rad/s. Second, the motor speed response to increasing inertia is opposite. The obtained results from the evaluation model confirm the claimed issues which conflict with the interpretations of the commented paper results. [ABSTRACT FROM AUTHOR]