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In this paper, an electric vehicle (EV) battery charger with interleaved Landsman converter (ILC) followed by a flyback converter, is designed and evaluated for improved power quality (PQ) charging of battery. A built-in wave-shaping is obtained at the charger front-end due to improved PQ characteristics of ILC. This PFC converter consists of two Landsman converter cells, which are designed in discontinuous conduction mode (DCM) to share the input and output currents. The current sharing at input results into lower input current ripple as well as peak current stress through the switch, is reduced. This, further improves the input current harmonics profile. Moreover, the reduced output voltage ripple gives reduced rms current in the output capacitor. A phase shift PWM scheme (PSPWM) is used for ILC and the duty cycle for the switches is selected below 50%. This allows the ripple cancellation at line and load sides. The interleaving at PFC stage as well as DCM based design ensures a low cost charging solution as compared to the conventional Landsman converter (CLC) based chargers in this power range. However, the flyback converter provides the current control during the charging of the battery in constant current (CC) and constant voltage (CV) regions. The harmonics spectrum of mains current follows the recommended PQ regulations over a range of varying line voltages and loadings. [ABSTRACT FROM AUTHOR]

The dc winding induced voltage in hybrid-excited machines can lead to dc winding current ripple and hence, fluctuating field excitation. It may also challenge the dc power source and increase the difficulty of machine control, especially at high speed. The dc winding induced voltage in a hybrid-excited switched-flux permanent magnet (HESFPM) machine is investigated in this article. The phenomenon and mechanism of the dc winding induced voltages under both open-circuit and on-load conditions are analyzed, with particular emphasis on on-load operation which consists of open-circuit induced voltage and armature current induced voltage, respectively. Two techniques, i.e., rotor step skewing and unequal rotor teeth, are proposed and comparatively investigated by the finite-element (FE) method to suppress the dc winding induced voltage under on-load condition. FE results show that the peak-to-peak value of on-load dc winding induced voltage can be effectively suppressed by 96.15% or 89.05% by rotor step skewing or unequal rotor teeth, respectively, while the average on-load electromagnetic torque can be maintained at 89.4% or 87.8%. A prototype HESFPM machine is built and tested to verify the FE results. [ABSTRACT FROM AUTHOR]

This article studies the voltage stress in random-wound machine windings under steep-fronted voltage excitations from inverter drives. The voltage stress in this article includes overshooting voltages between any two conductors in the windings, and overshooting voltages between individual conductors and the stator ground wall. This stress may accelerate insulation degradation in inverter-fed machines compared to traditional AC machines. A high-fidelity finite element (FE) model was used to analyze individual conductors of random-wound windings and predict the voltage stress during switching transients. Experimental validation of the model was conducted using a purpose-made random-wound three-phase winding, designed to allow access to multiple coils and parallel strands. Firstly, the voltage propagation and the voltage stress for both single-phase and three-phase windings were simulated and tested under Pulse Width Modulation (PWM) voltage excitations without a rotor. Both voltage propagations among all the coils and individual turns were measured and compared with simulated results. The voltage stress on each part of the machine stator winding insulation system was tested and studied. Then, similar simulations and tests were conducted with a demagnetized rotor installed to study how the rotor saliency affects the voltage propagation and voltage stress. The measured winding voltage propagations for all scenarios generally agree with the FE simulated results. [ABSTRACT FROM AUTHOR]

Direct power control (DPC) works well under ideal grid voltage conditions with accurate parameters. However, under unbalanced and distorted network conditions, significant power ripples and current harmonics arise in conventional DPC if no special measures are taken. Furthermore, the system performance further deteriorates if the inductance value differs from the actual value. To cope with the problems above, this article proposes an online inductance identification method for the DPC of a PWM rectifier under unbalanced and distorted network conditions. It is shown that the proposed method can guarantee sinusoidal characteristics of the grid current and reduce power ripples under unbalanced and distorted network conditions when the identification algorithm is enabled. The presented simulated and experimental results confirm the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

The automation of distribution systems will need a fast and efficient signal-processing tool in order to extract useful information from the power quality (PQ) monitors, smart meters, or Internet of Things, which are essential for real-time monitoring, detection, and faster decision-making capability of smart grids. This article proposes the application of the Hilbert–Huang transform (HHT) method for decomposition of the PQ data into its individual frequency components in order to separate the nonstationary voltage sag waveform containing the fundamental frequency component. After the decomposition of the data using the HHT method, an innovative fundamental frequency-based algorithm is proposed for the accurate detection of voltage sag starting and ending times, which are useful for accurate calculation of point-on-wave and voltage sag duration. The proposed algorithm is further extended for automatic detection of the transition segments to accurately calculate the time-varying and single event characteristics such as voltage sag magnitude and phase-angle jump. The composite method is referred to as the segmented Hilbert–Huang transform (SHHT). The limitations of the existing methods of voltage sag detection using the rms method, the fast Fourier transform method, and the waveform envelope method are also outlined in this article. Finally, the results of the detection and characterization of time-variant nonstationary voltage sag data using the proposed SHHT method is presented and discussed. [ABSTRACT FROM AUTHOR]

In this article, a fixed and smooth-switch-sequence modulation strategy is proposed to equalize the dc-link voltages among the cascaded rectifier. The structure of a single-phase three-level neutral-point-clamped cascaded rectifier is studied. Three core steps of this strategy are analyzed respectively, including carrier wave disposition calculation, fixed pulse generator, and voltage rank function. In addition, a criterion of the degree of the load unbalance is established in order to measure the voltage balancing boundary of the presented approach. The superiorities of the proposed control strategy embody the smooth switch sequence, the strong voltage balance capability, as well as the fixed switch sequence. Owe to these advantages, the cascaded rectifier could effectively reduce the switching frequency, achieve the goals of voltage balancing, and reduce the calculation burden of the controller when the number of cascaded modules is large. The effectiveness of the proposed strategy is verified by simulation and experiment results. [ABSTRACT FROM AUTHOR]

This article presents an optimal carrier-based voltage balancing scheme for three-phase three-level converters. The proposed scheme utilizes two available degrees of freedom, i.e., zero-sequence signal injection and virtual zero-level modulation (VZM), to eliminate the low-frequency neutral-point voltage oscillation. It is universally effective over the full power factor and modulation index range and easy to implement in digital controllers. The hybrid algorithm combines the merits of both approaches, which offers the optimal performance regarding controllability, switching device power losses, and output harmonics. The main drawbacks of VZM, i.e., the increased switching loss and high-frequency harmonics due to additional switching transitions, have been minimized in the proposed scheme. The performance of the proposed scheme is evaluated through simulation and experiment. [ABSTRACT FROM AUTHOR]

Axial–radial flux type permanent magnet synchronous machine can adjust air gap flux, which provides a new strategy for flux regulation of a permanent magnet motor. In this article, the structure of the ferromagnetic bridge is optimized by analyzing the magnetic circuit structure of Numerical anlysis of an axial-radial flux type fully superconducting synchronous motor (ARFTFSSM). The three-dimensional finite-element model of the motor is established by using the finite-element method, and the changes of air gap flux density and back electromotive force are compared through the finite-element prediction. The results show that the optimized ferromagnetic bridge has better magnetic regulation performance. On this basis, the eddy current distribution and eddy current loss of two kinds of ferromagnetic bridge structures are further compared and analyzed. Finally, the experimental results verify the accuracy of the calculation, and the research results can provide a reference for the further study of hybrid excitation motor. [ABSTRACT FROM AUTHOR]

Symmetrical and asymmetrical multilevel inverters (MLIs) have demonstrated its usefulness in a wide range of applications. This is accomplished due to the ongoing improvement by reducing the converter size and enhancement in the voltage quality. In this article, a generalized cascaded MLI structure is developed, which can operate in both symmetric and asymmetric modes. Comparative assessment in terms of the number of components and voltage stress warrants the design superiority. A new selective harmonic elimination (SHE) control using flower pollination algorithm (FPA) is investigated for the developed asymmetrical MLI. The salient features of the FPA such as less burdensome compilation and ability tos single-stage local and global search ascertain the elimination of the targeted harmonics through optimum angles computation. Moreover, the competence of the FPA is verified by comparing it with well-known SHE algorithms. Simulation analysis is carried out in MATLAB/Simulink environment, which validates the workability of the developed system. Experimental tests using fundamental and high switching frequency control techniques are further conducted under a dynamic environment to demonstrate the efficacy of the proposed methodology. [ABSTRACT FROM AUTHOR]

This article presents the design and analysis of a 12/7 (numbers of stator/rotor poles) hybridly excited asymmetric stator pole doubly salient machine (HEASPDSM) with a main focus on the special topology and operational principle by using the analytical and 2-D finite element analysis. A full comparison is conducted on the average torque, torque ripples, no-load back electromotive force and flux regulation capacity under the condition of different structural parameters, which can provide good references to the machine design. A 12/7 HEASPDSM is designed and the main performance indexes are analyzed in detail. Based on the parameters, the performance of 12/7 HEASPDSM is compared with traditional 6/7 doubly salient permanent magnet machine (DSPMM) with the same volume and thermal load. Finally, a prototype of the 12/7 HEASPDSM is manufactured and tested to validate the theoretical analysis. The results fully demonstrate that the HEASPDSM possesses the merits of strong flux regulation capability, higher torque density, and wider constant power speed range benefitted from the dc field winding than the traditional DSPMM. [ABSTRACT FROM AUTHOR]

This article presents a methodology to calculate grounding potentials in adjacent electrodes present in high-voltage substations subjected to a short-circuit current dissipated in the main grid. The contribution of the technique is the consideration of the coupling by the soil among electrodes taking into account a two-layer soil and irregular geometry of the conductors. This problem is of special concern due to the presence of passers-by near metallic fences, not directly connected to the grounding grid, whose potentials usually have not been evaluated. In this context, the article presents a general analytical formulation aiming to estimate the potential in multiple electrodes, leading to a possible risk to human beings close to the substation. Sensitivity studies are performed in order to evaluate the effect of the soil resistivity and the distance from the faulted grid and the coupled electrode. A practical application in a substation grounding system is discussed. Finally, a huge grounding system is evaluated in order to verify the robustness of the proposed formulation. [ABSTRACT FROM AUTHOR]

Bond-wire liftoff caused by mechanical stress due to thermal cycling is one of the major failures in power electronic systems. Condition monitoring concepts which allow prediction of these failures are often based on voltage-drop detection and thermal monitoring. However, solutions to determine the junction temperature and semiconductor voltage drop during operation often require additional effort and lead to increased cost. In this article, a direct semiconductor temperature detection method is proposed which is based on instantaneous semiconductor voltage-drop monitoring. A mosfet inverter system, equipped with a digital integration-based instantaneous output voltage measuring circuit, is extended by software to enable instantaneous semiconductor voltage-drop detection. Experimental results demonstrate that the proposed method is feasible for online temperature measurement and detection of increased resistance due to bond-wire faults. The voltage measurement resolution is sufficient for dynamic temperature monitoring, including fundamental frequency temperature cycles at very low frequency. [ABSTRACT FROM AUTHOR]

The performance of a two-stage electrohydrodynamic (EHD) gas pump in a circular tube has been investigated for operating conditions in which each stage is charged at a different voltage. The main objective of the study is to examine the characteristics of resulting flow as well as the efficient use of energy in sustaining and improving the volume flow rate produced by a single-stage pump over a greater distance. To this end, two different sizes of the tube are employed (61.8 and 127.8 mm in diameter). Each stage uses eight emitting electrodes flush mounted on the tube wall. In addition, two electrode configurations, aligned and offset, with fixed electrode spacing have been considered. The electrodes at both stages are charged at voltages in positive polarity from 18 to 22 kV. The velocity profile and volume flow rate delivered are compared with those produced by the same pump operating at even voltages to provide additional insight into the problem. The results, thus, obtained have important implications for practical use of the EHD gas pump. [ABSTRACT FROM AUTHOR]

Out-of-step protection has been widely studied, and it remains an important topic in the field. Given the crucial modernization of the power systems and the evolution of protective relaying, it is crucial to merge from traditionally fixed parameters to novel approaches that allow flexibility and possible time-domain protection. This article presents a new methodology to implement an out-of-step protection algorithm through the geometrical understanding of a power system oscillation using Clarke's transformation. The article is an extension of a virtual relay solution previously developed and improves the swing center voltage solution in the $\alpha$ $\beta$ plane with enhanced selectivity. The result brings a functional virtual relay capable of detecting and reacting under stable and unstable power swing events through playback techniques. The contribution of this article relies on the application of the time-domain approach to improving the function ANSI 78 as an extension of ongoing research on virtualization of power system protection and real-time prototyping. [ABSTRACT FROM AUTHOR]

A new approach is proposed for designing coils free of partial discharges (PDs) for compact machines operating at high altitudes. The proposed method consists in using an enameled wire made with a thin additional resistive layer on the outer surface, which strongly reduces the electrical field in the voids between the wires of random coils. With such a wire, PDs occur only in specific zones situated near the wire connections and a local reinforcement of the insulation can strongly increase the partial discharge inception voltage. The article proposes a theoretical method for determining the properties of the resistive layer. The local reinforcement of the insulation is analyzed with an electrostatic simulation and Paschen's law. Measurements confirm the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

An array of proportional-resonant regulators is often used in shunt active power filters to control the grid currents and reduce the harmonic distortion caused by a distorting load. The voltage that is necessary to compensate for the current harmonics must be consistent with the available dc-link voltage. In this article, three adaptive algorithms for the exploitation of the dc-link voltage are developed and compared. These algorithms adaptively change the voltage saturation of each regulator to preserve the control capability of the fundamental component of the current when the available voltage is not enough to control the filter current. Simultaneously, they try to improve the quality of the grid current because the dc-link voltage of the active power filter is allocated to the regulators to compensate only the most significant harmonics. Some experimental results are shown to demonstrate the feasibility of the three algorithms. [ABSTRACT FROM AUTHOR]

About 10 kV integrated gate-commutated thyristor (IGCT) has the potential to push wind turbine systems to higher power and voltage ratings. Converters employing IGCTs need snubber and overvoltage protection circuit to limit the rate of current rise and peak overvoltage across IGCT during turn on and turn off state, respectively. The conventional resistor-capacitor-diode (RCD) snubber, which is used in such power converters, dissipates a significant amount of power. This article proposes an enhanced scheme of the flyback clamp snubber comprising a flyback transformer with multiwinding secondary wound on a magnetic core. The flyback snubber not only meets all of the IGCTs requirements during on and off-state but also significantly saves power. Unlike the basic concept of flyback clamp snubber, the new scheme has equal voltage stress across the clamp diodes which recover the stored energy of the di/dt snubber into dc-link capacitor. Simulation and experimental results of 10 kV IGCT with conventional RCD and flyback clamp snubbers turn out the benefit of the system. [ABSTRACT FROM AUTHOR]

In this article, a combination of a two- and three-phase switching method to reduce switching loss is presented. In the conduction region, the conventional two-phase switching topology is used to reduce switching loss. On the other hand, in the short commutation region, the proposed modified three-phase switching strategy that incorporates a voltage compensation method is used to reduce torque ripple. The design of the proposed torque compensation method is based on the back electromotive force (EMF). The goal is to optimize the phase current slope by using the phase voltage and back EMF at the start and end point of the commutation region. Assuming that the slope of the back EMF in the commutation region is almost the same as a sinusoidal waveform, a proper pulsewidth modulation duty ratio can be determined to control the current slope. Experiments with a practical brushless dc motor and drive were performed to verify the performance of the proposed method. [ABSTRACT FROM AUTHOR]

Voltage feedback flux-weakening control has the advantages of simplicity and robustness against parameter variation. However, due to less voltage control margin in the flux-weakening region, the increased feedback voltage ripple could deteriorate the system performance in the flux-weakening region and may even cause oscillation. In this article, based on a nonsalient permanent magnet synchronous machine, the steady-state feedback voltage ripple in the flux-weakening region are analyzed first. It shows that the feedback voltage ripple caused by the current command ripple could dominate in some flux-weakening regions. Consequently, the speed bandwidth based on the conventional speed proportional-integral (PI) controller in the flux-weakening region can be hardly increased, which leads to poor dynamic performance. In order to obtain both fast speed dynamics and less steady-state ripple, especially in the flux-weakening region, an adaptive fuzzy logic (FLC) speed controller is designed and compared with the conventional speed PI controller. With the adaptive FLC, the dc-link voltage utilization can be increased and better flux-weakening capability can be obtained. Finally, the improved performances are verified by the experimental results. [ABSTRACT FROM AUTHOR]

Hybrid modular multilevel converter (Hyb-MMC), which consists of both half-bridge (HB) and full-bridge (FB) submodules (SMs), has the capability to withstand wide variations in dc-link voltage ranging from nominal to dc short circuit conditions. With around 50% FBSMs, the Hyb-MMC can block the dc short-circuit current while exchanging reactive power with its ac grid. Other than faults, often, the high voltage direct current system may have to operate at reduced dc voltage levels with rated dc-link current, which results in arm currents becoming unipolar. This phenomenon affects the cyclic charge/discharge of the HBSM capacitors. To overcome this problem, it is proposed to inject second harmonic circulating current (SHCC) for making the arm currents bipolar and, hence, ensuring capacitor voltage balance. However, the choice of suitable amplitude and phase angle of the SHCCs is crucial to avoid increase of losses in the converter. Hence, a method to optimize the amplitude and phase angle of the SHCCs is also presented. The proposed method is verified through simulations performed on PSCAD/EMTDC platform followed by experiments on laboratory scale prototype. [ABSTRACT FROM AUTHOR]

The induced voltage on underground pipelines is a critical parameter to consider for equipment and personnel safety in the field. However, in the real life, such induced voltage estimation on pipelines is difficult especially at the transmission line planning and routing stage. In this article, several factors affecting the induced voltage on underground pipelines due to inductive coupling with nearby transmission lines are investigated. These factors include the angle and separation distance between transmission lines and pipelines, the length of transmission lines and pipelines, and the soil model. A peak induced voltage calculation formula as the function of the angle and separation distance is derived through surface fitting of simulation data. It is proved in the article that other factors, such as the length of the transmission line and the soil model types, do not have significant influence on the peak induced voltage values on underground pipelines. [ABSTRACT FROM AUTHOR]

Grid-forming converters enable an asynchronous connection of grids, which opens new opportunities for the power system management. This includes the potential to control the amplitude and the frequency of the grid voltage to vary the power consumption of the loads and the generation in the grid. Depending on the load sensitivity to voltage and frequency, the power transfer of the grid-forming converter changes. Remarkably, this has an impact on the power semiconductors by means of thermal stress, which is limiting the lifetime of the devices. This article aims to investigate and mitigate the thermal stress in grid-forming converters by applying a load voltage-sensitivity control. Depending on the nature of the loads, their power consumption varies with the voltage. This response is dependent on the connected loads and can be characterized by constant power (independent from the voltage), constant current (linearly dependent on the voltage), and constant impedance behavior (squared-dependent on the voltage). The sensitivity to voltage is exploited to control the load power consumption, reducing the junction temperature fluctuations and, thus, the power semiconductors stress. [ABSTRACT FROM AUTHOR]

Heating and losses of induction motor (IM) grow with the supply voltage unbalance and harmonic distortion. To avoid thermal overload, the IEEE 141-1993, the IEEE 3004.8, NEMA MG1-2014, and the IEC 60034-26 standards establish derating factors for IMs operating under those conditions. In this article, we show that while the derating factors proposed by these standards adequately protect standard-efficiency IMs, they are only marginally adequate to protect modern higher-efficiency IMs. To this end, we compare the derating factors provided by the standards with the derating factors required to maintain the losses at rated values in a standard-efficiency IM, in a premium-efficiency IM, and in a super-premium-efficiency IM. To extrapolate the results from these IM, we compared the nameplate data of 548 IMs of different efficiency classes and found that higher efficiency classes correlate to higher IM starting currents and lower impedances to the negative sequence and harmonic voltages. These lower impedances in turn may lead to higher losses for unbalanced and harmonic voltages conditions. [ABSTRACT FROM AUTHOR]

A cascaded H-bridge multilevel inverter is an indispensable part of high-power industrial drives. The multilevel inverters have an increased chance of switch fault as a consequence of a considerably large number of semiconductor switches associated in the power conversion. A quick and precise fault detection–isolation strategy improves the system reliability as well as reduces the shutdown time of the drive. This article presents a novel generalized open-switch fault-diagnostic approach for an $N$ -level cascaded H-bridge multilevel inverter. In this detection technique, half-cycle mean values of bridge voltages, which are calculated for positive and negative half cycles individually, are used as fault identification features. These means under open-switch fault are predicted from the reference half-cycle means and compared with those measured values to locate the open-switch fault. This quick detection scheme can identify the faulty switch within one fundamental period of output voltage for the cascaded inverters having different number of voltage levels. The computation requirement is minimum, since this approach does not need complex calculations or domain transformations. This strategy can efficiently locate the faulty switch of the cascaded inverter working with various level-shifted pulsewidth modulation schemes, different loading conditions, modulation indexes, and switching frequencies. The potency of the fault classification algorithm is verified through simulation and experimentation. [ABSTRACT FROM AUTHOR]

This article investigates the nonlinear behavior of the conventional voltage feedback flux-weakening control, i.e., the voltage magnitude feedback control on the nonsalient permanent magnet synchronous machine, and proposes an adaptive control parameter tuning method for the voltage feedback controller. Due to less voltage margin in the flux-weakening region, the current dynamic performance is degraded. This issue is more serious when the system operates in the overmodulation region and could affect the system's stability. Based on the designed voltage feedback controller, the system performance in the flux-weakening and overmodulation regions is further improved by utilizing the current and voltage reference modifiers. Consequently, the system can operate well in both linear and overmodulation regions with the specified scaling factor, which is beneficial to general-purpose applications. The viability of the proposed method is demonstrated by the experimental results. [ABSTRACT FROM AUTHOR]

Homopolar inductor machine (HIM) has a wide range of applications in the field of flywheel energy storage system and ship propulsion due to its merits of simple structure, brushless exciting, and low idling losses. However, the three-dimensional finite element method (3-D FEM) is mainly used to investigate the electromagnetic performance indexes of HIM due to its intrinsic 3-D flux density distribution, which is time-consuming. To facilitate the analysis of HIM, an analytical method (AM) is necessary, especially in the initial design stage. Hence, this article presents an AM for analyzing the electromagnetic performance of HIM. First, the structure and operation principle of HIM are illustrated. Second, the magnetic equivalent circuit of HIM is built considering the saturation of stator and rotor core. Third, the air-gap permeance function is obtained considering the affection of stator and rotor slots. Finally, the magnetomotive force, air-gap flux density, back electromotive force, inductances and electromagnetic torque of HIM are calculated, then validated by 3-D FEM and corresponding experiments. The results indicate that the proposed AM can provide reasonable results to estimate the electromagnetic performance of HIM, which would be helpful for the analysis of HIM. [ABSTRACT FROM AUTHOR]

This article proposes a coordinated optimal feedback control approach to mitigate the induction motor starting voltage sag and support the transient restoration in distribution networks. The proposed technique is expected to reduce the starting high current to maintain the network voltage using neighboring voltage supporting distributed generation. An optimal feedback-based coordinated controller (CC) has been designed to estimate the reactive power to be injected at different locations of the network based on the motor loads. The CC on top of the existing local controller (LC) uses motor voltage feedback signals, thereby adjusting the reactive power support based on the voltage sag. The proposed voltage sag mitigation strategy is tested in both 12.4 kV network and 123 bus larger distribution networks containing single and multiple motor and distributed generation units. From simulation results, it is revealed that the proposed coordinated optimal feedback control of VSDGs can provide a fast restoration of the motor starting transient voltage dip. [ABSTRACT FROM AUTHOR]

In order to reduce the chattering and phase shift, this article proposes an enhanced sliding mode observer (SMO) for the sensorless control of permanent magnet synchronous motor (PMSM). In the conventional SMO, a low-pass filter (LPF) is commonly employed to extract the back electromotive forces (EMFs) from the sliding mode switching function, which brings the phase shift and degrades the precision of position and speed estimations. In this article, a frequency-adaptive complex-coefficient filter (FACCF) is adopted to replace the LPF. Since the FACCF has no phase shift and amplitude attenuation at the central frequency, it can be used to extract the EMFs without distortion while the chattering can also be suppressed. For an easy parameter design, the normalized phase-locked loop is used to obtain accurately the position and speed estimations. The experiments are carried out on a 3-kW PMSM drive, and the results verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Active damping is a popular approach to suppress the resonance in LCL-filtered grid-connected inverter owing to lossless damping and efficient system design. In capacitor voltage (CV) damping methods, a differential compensator is essentially needed in feedback path, where the damping effectiveness depends on emulated derivative characteristics of the compensator. Such CV feedback compensation methods face design limitation at the critical resonance frequency and may require additional delay reduction to ensure stability. In this article, an alternative parallel feedforward compensation method is proposed to synthesize an almost strictly positive real plant and achieved damping with modified stability characteristics. A second-order bandpass section is employed as a compensator in damping loop based on the proposed control scheme. The main features of the proposed method are effective damping without critical resonance frequency damping limit, extended stable damping region, improved control performance, and good robustness under filter parameters and grid inductance variation conditions. The simulation and experimental results are presented to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This article presents an ac voltage controller that can operate under a wide range of loads, thanks to its high robustness to plant-model variations. A robust voltage controller is required in a droop-controlled inverter that operates connected to a grid or in island mode with other generators. In such modes of operation, the voltage source converter can experience large load-impedance variations depending on the number of parallel generators or the grid impedance value. Concerning the controller performance, the transient response is improved by selectively minimizing the output impedance of the system at the frequencies that typically contain the largest components of the output current. Complete harmonic control is achieved due to its zero output impedance at a set of design-selected frequencies. The proposed controller only measures the output voltage, and it contains a single-loop structure that uses all available bandwidth. In addition, a fast converter-current estimator provides protection against faults and inrush output currents. The design process only requires, as input parameters, the LC filter values, the sampling frequency, and a set of harmonics where load-current circulation is expected. [ABSTRACT FROM AUTHOR]

This article presents a family of 1-φ transformerless switched-capacitor based five-level inverter (TSC5LI) topologies for photovoltaic (PV) applications. The proposed family comprises four inverter topologies: H8, H8-UPF, H10, and H10-UPF capable of mitigating the leakage current by having continuous grid frequency voltage at PV parasitic capacitor in spite of considering switch terminal capacitances. A distinctive attribute of the TSC5LI is that 100% dc-bus utilization, symmetrical operation, and constant total common-mode voltage (TCMV) are achieved together. H8 variant of the proposed inverter family is studied extensively. The control strategy used is a simple level-shifted sine-triangle pulsewidth modulation followed by the synthesis of the gate pulses utilizing logical functions. Switching function based TCMV analysis, switched capacitor design, and loss analysis are presented. Simulation and experimental results of H8 variant are presented to validate the theoretical claims. Proposed topology is also compared with the existing five-level transformerless inverters to prove its various advantages. [ABSTRACT FROM AUTHOR]

Flux-weakening (F-W) based on feedback voltage regulation is commonly adopted in interior permanent magnet synchronous motor drives. Voltage space vector magnitude is controlled in a closed loop, modifying the current reference, following a value related to the inverter limitations. A stable and fast voltage control allows to operate with lower voltage margin, leading to higher torque versus speed capability. Theoretical analysis and gain adaptation of the F-W regulation loop was reported by Bolognani et al. partially overcoming the difficulties due to the strong nonlinearity of the plant. An approximated closed-form design method was proposed and refined by Bedetti et al. This allowed the application of the algorithm to drives where autotuning is needed, ensuring stability and dynamical performances. A fundamental enhancement is introduced in this article, namely the use of a speed regulator with explicit torque reference output. An advantage of this technique is that the speed loop becomes linear in the whole operating range and an accurate control of machine torque is possible. Thanks to a novel gain adaptation for the voltage regulator, the F-W behavior is decoupled from the speed control response at speed steady-state (at constant or slowly changing torque), improving performance of the overall drive control. Adoption of this novel method allows smooth operation with invariant dynamical behavior of both the speed and F-W control loops. Extensive simulations and experimental tests are reported to prove the validity of the proposal. A sensorless operation of the drive system has also been considered in the tests to further validate the proposed solution. [ABSTRACT FROM AUTHOR]

Electrical drive systems without dedicated speed transducer require precise information about the terminal phase voltage to achieve an acceptable low-speed performance. Recently, voltage-sensing techniques have gained in importance as they improve stability at low-speeds compared to the conventional estimation based on reference values. However, the additional sensors increase the sensitivity to sensor offset drift, which can cause self-sensing control algorithms to fail at very low speeds. In this article, a novel offset adaption method is introduced that compensates sensor offsets during operation while being fully decoupled from the control algorithm. Using a pair of phase current and voltage sensors per phase, the dead-time-related inverter voltage-distortion curve is monitored continuously. Its point-symmetrical nature is utilized for the sensor offset detection. This way, both sensor offsets can be calibrated continuously during operation and for each phase individually. This article gives a step-by-step description of the calibration algorithm and addresses implementation aspects to ensure deterministic calibration dynamics. The method is evaluated through measurements performed on a test bench for an electric-vehicle traction drive. [ABSTRACT FROM AUTHOR]

The aim of this article is to prevent back corona discharge using asymmetrical rectangular ac voltage. The experimental electrostatic precipitator (ESP) consisted of a high-voltage application wire electrode and a grounded plate electrode with a gap in between. Calcium carbonate dust was placed on the surface of the grounded plate electrode. Dc, symmetric, or asymmetric rectangular ac voltage was applied to the wire electrode. The voltage waveform and the current waveform were measured, and a photograph of discharge luminescence on the surface of the dust layer was taken by a digital camera. When dc high voltage was applied, the discharge current increased, and the discharge luminescence was observed on the surface of the dust layer due to back corona discharge. On the other hand, the discharge current did not increase and discharge luminescence was not observed, when the symmetrical ac high voltage at the period of 4 ms was applied. However, the application time of the positive polarity was equal to the negative polarity, and the period was short. Accordingly, it is expected that the collection efficiency is not high in the symmetrically energized ESP. Thus, the effect of an asymmetrical ac energization was investigated. The result showed that the back corona discharge was avoided in the ESP energized by an asymmetrical rectangular ac high voltage with a period of 9 ms including a positive period of 7 ms and negative period of 2 ms. [ABSTRACT FROM AUTHOR]

This article is focused on the design of a high-voltage (800 V) bidirectional boost converter with high efficiency at medium-low power levels. Triangular current mode (TCM) enhances the efficiency of the converter at low power, thanks to soft-switching operation, but it requires variable switching frequency and large current ripple through the inductor. The former can be implemented by using silicon carbide (SiC) mosfets and the latter can be minimized by using interleaved modules. At low power, TCM requires high switching frequency, a minimum negative inductor current, and a minimum deadtime to obtain zero voltage switching. These values vary for different input/output voltage ratios and must be properly selected to reduce deadtime losses, normally neglected in the literature since it is assumed that they have low impact. However, it can be relevant at high frequencies (especially for devices with high reverse conduction voltage drop, such as SiC mosfets). In this article, deadtime losses are included in the proposed losses models and the selection of optimum values of deadtime and minimum inductor current to minimize these deadtime losses are analytically evaluated and experimentally validated. [ABSTRACT FROM AUTHOR]

The reported fifth-order boost topologies exhibiting gain (1 + D1)/(1 − D1) find limited utility in point-of-load applications due to lack of common ground, inverted load voltage polarity, highly pulsating source current, and more switching devices. This article evolves a fifth-order boost converter that successfully overcomes the enlisted limitations. The basis for the evolution of this topology is the addition of a charge-pump capacitor with a diode to the SEPIC converter. This modification alleviates the shortcomings of the existing higher order boost topologies with identical voltage gain. A remarkable feature of this topology is reduced voltage stress on all of its intermediate capacitors. After performing extensive steady-state and state-space analysis, a detailed comparison highlighting significant features is brought out. To demonstrate the proposed converter's utility, a complex proportional–integral lead compensator (PILC) is designed by placing the closed-loop dominant poles satisfying the predefined time-domain specifications, including phase margin, to ensure sufficient stability. PILC gives the flexibility to choose the complex conjugate zeros of the lead portion making the closed-loop system exhibit better disturbance rejection features. The robustness of the designed controller is verified through performance metric computation of the contoured robust controller bode plot. The converter's salient features, the developed controller design, and its robustness against the structured uncertainties are validated experimentally on a 100–150-W prototype module. [ABSTRACT FROM AUTHOR]

This article proposes a space-vector modeling formalism and a harmonic balance control strategy for the voltage equalization of a double-star modular multilevel converter employed as an active interface between a three-phase ac grid and an HVdc grid. The balancing procedure is based on the control of the power flow through the converter legs, with the aim to stabilize the energy stored in each switching module to the same value. By properly exploiting both the space-vector/zero-component and the common/differential mode decompositions, the proposed approach is able to highlight all the viable interactions between the system voltages and currents. The harmonic balance control is then formulated in its most general form in order to effectively increase the degrees of freedom available to the voltage equalization while guaranteeing the hardware constraints and functional requirements of the converter. The resulting control algorithm, based on a subset of the harmonic control variables, has been implemented on a controller board and experimentally validated on a 1.5-kW test bench. [ABSTRACT FROM AUTHOR]

Solid-state transformers (SSTs) have diverse designs and constructions that make them suitable for various industrial applications, including distributions systems. This new breed of transformers has been developed to support the typical functionalities of core-type distribution transformers, along with new functionalities, such as controlling power flows, integrating dc distribution systems, utilizing distributed generation and storage units, supporting load-side voltage/frequency control, and improving the power quality. As SSTs become candidates for distribution systems, their deployment can pose challenges for distribution systems. Such challenges include the cost, protection, size and weight, efficiency, and adequate grounding designs. This article discusses some of the challenges that face the deployment of SSTs in distribution systems. In addition, this article provides a comparison between core-type and SST transformers for applications in distribution systems. The comparison between the transformers is made in terms of their efficiency, cost, and weight. Finally, this article makes several recommendations for future works that can further facilitate the deployment of SSTs in distribution systems. [ABSTRACT FROM AUTHOR]

A slotless, lightweight permanent-magnet (PM) motor with high pole count is designed and analyzed for a drone system that requires four motors of 0.5 kW each for a 2-kW propulsion power to attain the required torque–speed profile. The design optimization was carried out using finite-element analysis that lead to a slotless stator with outer rotor Halbach PM configuration achieving high power density, zero cogging torque, low torque ripple, sinusoidal back electromotive force, and good system efficiency. The Halbach configuration is found to have superior power density and torque ripple over the conventional concepts for the aerial applications. The power density and efficiency of the slotless motor can be enhanced through the use of nonconventional thermoplastic material and Halbach segmentation. The resulting low inductance of the slotless machine introduces a controls challenge, but it can be overcome with today's enabling technology of wide bandgap devices. A comprehensive analysis and comparison of the slotless design with an equivalent slotted-radial version showed the superiority of the former. An optimum slotless design has been prototyped and test results along with analysis are presented. [ABSTRACT FROM AUTHOR]

In this article, a condition monitoring system for the degradation assessment of power semiconductor modules under switching conditions is presented. The proposed monitoring system is based on the online measurement of two damage indicators: the on-state voltage of the semiconductor and the voltage drop in the bond wires. The on-state voltage of a semiconductor can be employed for temperature estimation, in order to anticipate failures in the solder joints that increase the thermal resistance of the cooling path. Moreover, by measuring the voltage drop in the bond wires, the degradation of the bond wires can be detected. The described monitoring system has been implemented in an inverter prototype, and tests have been performed in different scenarios to verify its capabilities in healthy and degraded states. Furthermore, a monitoring routine has been proposed in order to perform the required measurements in high switching frequency applications. [ABSTRACT FROM AUTHOR]

This article presents the possibility of decreasing the inverter output voltage distortions that are caused by the typical distortions in the output voltage pulses of an impedance network using the qZ-source as an example. DC sources, such as photovoltaic cells with the qZ-source, increase the dc voltage; an impedance network operates in the continuous current mode and the discontinuous current mode (DCM). Both of these, but particularly DCM, implement the characteristic distortions to the impedance network output pulses, which results in the distortions in the inverter output voltage. It is possible to decrease these distortions in a passive way (increasing the capacitors of the network) or by using an efficient instantaneous controller of the inverter output voltage. Two controllers—a single-input single-output PID controller and a multi-input single-output improved passivity-based controller—were compared using the experimental model voltage source inverter with the input qZ-source. [ABSTRACT FROM AUTHOR]

Due to superior multi-dimensional features (e.g., large torque to inertia ratio, fast response, high power density, negligible maintenance requirement, etc.) the axial-field pancake permanent magnet dc (PMDC) motors are popularly used for many control applications. When driven by pulsewidth modulation (PWM) controllers, due to their negligible electrical time constant, the armature current tends to be discontinuous. When the current disappears the measured armature voltage [i.e., back electromotive force (EMF)] is linearly related to its speed. In this article, the armature voltage at zero current is sampled to be used as feedback for speed control of axial field PMDC motors for wide range applications. Negligible prospect of demagnetization makes these motors ideal candidate to be controlled sensorless. When PWM frequency is large the armature time-constant poses as constraint for the back EMF to be available for sampling. The choice of PWM frequency is an important design parameter for the proposed concept. Further, this article explores, in practical domain, the usability of different control functions for robust speed control of pancake PMDC motors. It also details product design for sensorless PMDC motor speed controller using modified second-order sliding mode control function. [ABSTRACT FROM AUTHOR]

In this paper, a slip speed/position estimator for sensorless control of rotor-tied doubly-fed induction generator (DFIG) systems is presented. The proposed slip speed/position estimator is based on the association of the phase locked loop and the sliding mode observer. The proposed sliding mode observer uses the three-phase stator currents and the back electromotive force as state variables. This allows for the estimation of the slip speed/position before the rotor-tied DFIG is connected to the grid or to a load. The proposed phase locked loop helps in tracking the slip speed/position. The performance of the proposed slip speed/position estimation for sensorless operations are validated through experiments using a 5.5-kW custom-designed rotor-tied DFIG in grid-connected mode. [ABSTRACT FROM AUTHOR]

The operating principle of the clamp circuits like clamping diodes and flying capacitor in three-level LLC converter is different from other three-level converters, because the mean value of the resonant tank current is always zero and pulse-frequency modulation control is generally used instead of pulsewidth modulation control. And the converter with only the clamping diodes or flying capacitor is difficult to realize voltage balance. In this paper, the characteristics of the three-level LLC converter with single clamp circuit are first analyzed. Then, the operation principle of the hybrid-clamped circuit under the unbalanced voltages on input capacitors is described with the mode analysis, based on which the mechanism for voltage autobalance is elaborated and the effects of two clamp circuits are derived. Then, the design of the clamping diodes and the flying capacitor is also involved. Finally, a three-level LLC converter prototype is built and the experimental results verify the validity of the theoretical analysis and design. [ABSTRACT FROM AUTHOR]

This work proposes a microgrid (μ-grid) integrating wind and solar photovoltaic (PV) resources, along with the battery energy storage (BES) to the three-phase grid feeding the nonlinear load. The μ-grid disconcerted by probabilistic nonlinear time dependent parameters and their effects are compensated by cohesive controllers used for utility grid side voltage source converter (GVSC) and machine side voltage source converter (MVSC). The switching controls and the reconfigurability of the μ-grid are addressed on imperative aspects of improving power quality (PQ), power reliability, nonlinear load compensation, and economic utilization of resources. The nonlinear load compensation and PQ enhancement are achieved by executing modified version of the adaptive filtering technique including “momentum”-based least mean square (MLMS) control technique, utilized for providing the switching control signals to the GVSC. It utilizes two preceding gradient weights for obtaining updated weight thereby improving the convergence rate and overcoming the limitation of conventional control of the same family. The MVSC acquires its switching signals from conventional vector control scheme and the encoderless estimation of speed and rotor position of the synchronous generator driven by wind turbine through back electromotive force control technique. The external environmental disturbances are overcome by utilizing perturb and observe (P&O) maximum power point (MPP) for wind optimal power extraction and adaptive P&O with variable perturbation step size for solar MPP estimation. Test results are obtained from the laboratory prototype under steady-state and dynamic conditions, including altering wind speed, intermittent solar insolation, and variable load conditions. The PQ issues are addressed and investigated successfully. [ABSTRACT FROM AUTHOR]

In this paper, a dual-fed (DF) common dc-link topology open-end winding permanent magnet synchronous motor for aircraft high-speed starter–generator application is considered. While on one hand the common dc bus configuration significantly simplifies and reduces the costs of the topology, on the other hand it allows the zero-sequence current (ZSC) to flow freely in the system. High-speed machines are characterized by low phase inductance, which implies low zero-sequence impedance. A small time constant of the zero-sequence circuit produces a high-frequency, high-intensity ZSC ripple with the risk of harming the switching devices. This paper presents a novel hybrid space vector pulsewidth modulation that allows to instantaneously eliminate the zero-sequence voltage (ZSV) produced by the two voltage source converters (VSCs) by square wave modulating one of the two VSCs. The non-sinusoidal machine back electromotive force (EMF) has been considered and the effect of the converters’ dead time on the ZSV has been analyzed. The square-wave-modulated VSC uses insulated-gate bipolar transistor (IGBT) devices, whereas the other uses Silicon Carbide (SiC) technology. The proposed topology is tested through both simulations and experiments. [ABSTRACT FROM AUTHOR]

In a common dc-link dual-fed open-end winding permanent magnet synchronous motor (OEW-PMSM) topology, it is well known how the additional flow of a zero-sequence current (ZSC) is permitted. The low zero-sequence impedance characteristic of high-speed machines leads to high-intensity and high-frequency ripple of the ZSC. Therefore, there is a necessity to eliminate the zero-sequence-voltage (ZSV) produced by the two voltage source converters that feed the machine. Furthermore, the non-sinusoidal back electromagnetic force (back EMF) causes the circulation of a third harmonic ZSC. An OEW-PMSM high-speed starter-generator fed by a dual-inverter with a single dc-link is considered. Part I of this paper proposes a modulation for the considered topology able to eliminate instantaneously the ZSV produced. In this paper, a detailed analysis of the deadtime (DT) effect on the ZSV has been carried out and a novel hysteresis control for the ZSC using the DT as a control action is presented. The DT produces a ZSV distortion on the zero-axis that can be used to control the third harmonic ZSC flowing due to the non-sinusoidal machine back EMF. [ABSTRACT FROM AUTHOR]

A gate driving for power devices is a key technology to further improve switching characteristics. With the help of digital gate driver IC, the switching behavior of power devices can be enhanced even under high-speed switching. In this paper, an evaluation platform for determining the optimal switching pattern of an active gate drive control is proposed for an inverter circuit. A high speed optimization system is built up to search for an advantageous switching pattern that reduces total switching loss of two power devices in an inverter circuit and constrains surge voltage simultaneously. The proposed online optimization demonstrates its feasibility for the full-bridge inverter circuit, which is rated at 500 V with digital active gate drive control. Experimental results show that the proposed optimization system is able to obtain optimal switching pattern from $64^{60}$ possible combinations of switching patterns within 15 min, which is 6 times faster than the previous study. Optimizations can also conducted under different load current conditions. Eventually, the obtained optimal pattern yields up to 42% reduction in the total switching loss when it constrains surge voltage to minimum compared with the conventional driving pattern. [ABSTRACT FROM AUTHOR]

One-axis actively positioned bearingless motors are studied for industry applications such as pumps and cooling fans. In particular, single-drive bearingless motors have a great advantage of having a simple regulation system. Only one three-phase inverter is required to generate both torque and a magnetic suspension force by the q- and d-axis currents, respectively. Therefore, their voltage equation is unique. In addition to the rotational speed induced voltage in the q-axis, the translation speed voltage is generated in the d-axis. Therefore, both the current–force factor and the torque constant can be identified from the back electromotive force (EMF). In this paper, a novel simplified identification method of the current–force factor is proposed that does not require the measurement of the active axial force and current. Furthermore, it is experimentally verified that this method is effective in the identification of machine parameters. [ABSTRACT FROM AUTHOR]

The resonant grounding is one of the possible methods of the system neutral grounding for the medium voltage distribution. IEEE standards do define this grounding configuration, but important advantages and drawbacks of the resonant grounding might not be fully known, due to its rather uncommon application in North America. On the other hand, resonant grounding in Europe is imposed by the increased requirements for power quality, especially for medium-voltage (MV) industrial users, imposed to electric utilities by regulatory authorities, with the purpose to protect the interests of users and consumers. Level of the continuity of the service, magnitude and phase of ground-fault currents, magnitude of touch voltages, all depend on how the neutral is connected to ground. In this paper, the authors will discuss electrical safety features of the resonant ground, and analyze issues when a substation, originally operated with different methods of system neutral grounding, is reconfigured with a resonant ground. In particular, a conservative approach for preserving safety during high-voltage (HV)-MV substations’ reconfiguration is herein proposed; the cases of the substation reconfiguration from resonant grounding to isolated-from-ground and vice versa shall be analyzed. Finally, the analysis of the impact of the use of Petersen coil on the global grounding systems will be provided. [ABSTRACT FROM AUTHOR]