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Nowadays, the three-level T-type inverters (3LT2Is) are widely employed in applications with high-performance requirements. The 3LT2Is commonly suffer from neutral point voltage (NPV) unbalance and common-mode voltage (CMV) variation. The medium vector pulse width modulation (MVPWM), which generates the reference voltage using medium and V0[OOO] zero voltage vectors, eliminates the CMV variation in 3LT2Is. However, it cannot keep the NPV balance, negatively affecting power quality. This article proposes a hybrid method to simultaneously eliminate CMV variation and guarantee the NPV balance without topological change or extra hardware. The proposed method uses MVPWM when NPV is balanced, eliminating CMV variation. If NPV goes unbalanced, it utilizes novel high/low triangle PWM (H/LPWM) and MVPWM in a hybrid manner to balance the NPV. The H/LPWM, similar to MVPWM, synthesizes voltage using medium and V0[OOO] voltage vectors to maintain the CMV elimination advantage during the NPV balancing process. However, the difference between H/LPWMs and MVPWM switching patterns adjusts the average neutral point current to balance the NPV. Noteworthy that the proposed method provides NPV balancing ability for the entire power factor range. As a result, it is usable for various applications of 3LT2I, such as photovoltaic inverters and motor drives. The proposed method is carrier-based, which reduces the execution time and simplifies the practical implementation. The simulation study and experimental evaluation have been accomplished, and their results demonstrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Modular multilevel converters (MMC) are increasingly gaining its importance in HVDC, drive applications due to several attributes such as modularity, scalability, low device stress, excellent output voltage waveform. For MMC operations, it is important to accurately measure the voltages across the individual capacitors of submodules (SMs). These voltage sensors, while upgrading for high voltage applications, may cause a few concerns in terms of cost, complexity, and data acquisition system. To avoid all these, a discrete time adaptive observer (DTAO) is proposed in this article to observe the voltages across the capacitors of the SMs and use the observed values for closed-loop operation of the MMC. The proposed observer is designed by considering the parametric uncertainty in the MMC and its convergence is proved mathematically. Moreover, the DTAO is compared with existing observation techniques for MMC SM capacitor voltages. The efficacy of the proposed observer is shown through simulation and validated using an experimental setup. [ABSTRACT FROM AUTHOR]

The dc transformer based on CLLC resonant converter is widely researched in the dc microgrid due to its excellent bidirectional power transfer capacity. Many resonant network design methods assume that the resonant current is constant during the deadtime. It may lead to hard switching or large conduction loss. Besides, the effects of deadtime on soft switching have not been closely analyzed. This article proposes an optimized design method to minimize conduction losses while achieving zero voltage switching, and it can easily obtain the optimal region and deadtime selection range. Parametric design and deadtime selection principles are derived based on the time-domain models, and then the design method and corresponding procedure are developed. Finally, a 4-kW 500-kHz CLLC resonant converter prototype is built to verify the feasibility of the proposed optimal design method. [ABSTRACT FROM AUTHOR]

An overmodulation method is proposed for an in-wheel system where two motors are coupled to a sum gear. In the dual-motor dual-inverter single shaft systems, the output voltage magnitudes of two inverters are not the same in the overmodulation range due to the angle offset between two motors. In this article, to maintain torque balance in the overmodulation region, holding vectors are defined between adjacent vertices of two voltage hexagons. Around these vectors, the holding region is also defined by the holding angle. If a reference voltage vector is in the holding region, it is modulated to the holding vector; otherwise, it is modulated to the vector on the arc of inscribed circle. For a given the modulation index (MI), the holding angle is obtained based on the Fourier series expansion. The proposed method keeps the output voltages of two inverters the same even if two motors have the angle offset. Further, it has the characteristic of maintaining the linearity between the reference and output MI to the maximum MI. The proposed overmodulation method is demonstrated by simulation and experimental results. [ABSTRACT FROM AUTHOR]

A synchronous condenser (SC) can provide the dynamic reactive power for the ultra-high-voltage direct current converter station during the system voltage drop caused by the single-phase short-circuit fault, which is one of the prevalent faults. However, the single-phase short-circuit fault can also result in the increase of the rotor loss and temperature and thus restrict the transient operating ability of the SC. A key factor that affects the rotor loss and temperature rise is the material of the rotor slot wedges. For a 300-MVar SC with the rotor slot wedges made of the aluminum, beryllium bronze, and stainless steel, the rotor loss and temperature distribution under the single-phase short-circuit are calculated by coupling the electromagnetic and temperature field models of the SC with the models of the power grid. The variations of the rotor losses along with the rotor slot wedge conductivity are revealed. The rotor regions, where the highest temperature rise appears, are obtained. According to the maximum permissible temperature of the rotor material, the transient operating ability of the SC withstanding the single-phase short-circuit fault is obtained. This article can provide the theoretic basis for improving the transient operating ability of the SC. [ABSTRACT FROM AUTHOR]

Solid oxide fuel cell (SOFC) becomes increasingly popular in dc microgrid applications. Controlling SOFC is challenging because the dynamics of SOFC are difficult to maintain under complex internal reactions and changing operating conditions. To solve these problems, this article proposes a novel adaptive model predictive control (AMPC) algorithm, which adopts a parameter estimator to update the system parameters online. The robustness of the proposed AMPC is investigated under different microgrid scenarios, including the overload, underload, short-circuit, and significant dc bus voltage drop situations. The proposed AMPC algorithm produces superior SOFC control performance over the conventional model predictive control (MPC), Wiener MPC, and PI and fuzzy PI controllers. Furthermore, it significantly reduces the system model dependence that is shared by nearly all the model-based SOFC control methods. The convergence of parameter estimation in the proposed AMPC is rigorously proved. The effectiveness of the proposed algorithm is validated through hardware-in-the-loop experiments under various operating conditions and system parameter variations. [ABSTRACT FROM AUTHOR]

This article studies the sharing control scheme for a hybrid 48 V/375 V/400Vac ac/dc microgrid, based on classical droop control and a novel approach for secondary control. In this article, both the dc and ac grids are controlled by a $P/V$ droop strategy. At the ac grid, this assumes a main resistive component in the distribution line impedance. The droop control voltage error in steady state is compensated by a novel and simple secondary control approach. The proposed control strategy is based on the calculation of the optimum power flow in each operating point and the real-time modification of the droop characteristics of the converters involved in the power flow calculation. The proposed control is also capable of eliminating the induced voltage drop when using virtual impedance and incorporating any power sharing criteria for the converters contributing to the power production, being this flexibility one of its more important characteristics. [ABSTRACT FROM AUTHOR]

The dc voltage and frequency $ (PVF)$ or modified dc voltage and frequency $ (PV^{2}F)$ double droop control is commended for its ability to regulate both the dc voltage and the frequency in a decentralized approach. However, a convincing response is not achieved due to an interaction between the droop characteristics of dc voltage and frequency. This interaction affects the dc voltage and frequency support of the ac-system-surrounded multiterminal HVdc (AC-MTdc) grid. To overcome this effect, a Duo control strategy is proposed in this article, which takes advantage of a bipolar voltage-source converter topology in the MTdc grid. The virtue of the proposed control technique is emphasized by comparing it with the existing $ PV^{2}F$ double droop control along with three case studies and two test systems. The validation of the interactionless Duo control strategy is carried out on a five-terminal CIGRE dc grid benchmark model integrated into a two-area power system (AC-MTdc grid-1) and a New England IEEE 39-bus system (AC-MTdc grid-2). These test systems are simulated in PSCAD/EMTdc software. [ABSTRACT FROM AUTHOR]

Thermal stress of the power semiconductor is one of the most important indicators for the reliability assessment of power electronics-based power systems. The mapping of the Insulated-Gate Bipolar Transistor (IGBT) junction temperature is usually required to analyze the thermal stress and loss dissipation. However, it is difficult to identify inherent mechanisms of the bond-wire and solder layer failure modes in IGBT power modules. In order to solve the problem, an online method to identify inherent mechanisms of the bond-wire and solder layer failure modes in IGBT power modules is proposed. This method can separate the root causes of the bond-wire lift-off and solder layer fatigue by measuring the on-state voltage drop through a sinusoidal loading current based on an H-bridge circuit, together with its corresponding control and measurement. By comparing the on-state voltage drop at the intersection current and the peak current of the converter, the wear-out conditions of the IGBT power modules can be monitored in real-time with the determination of different failure modes. Finally, experimental results are presented in order to verify the effectiveness and feasibility of the proposed method. [ABSTRACT FROM AUTHOR]

Applying 0.3–1.25 kV/cm electric potential gradients to cooled water vapor triggers the copious formation of electrified ice needles, as long as 36 mm. This is completely different from the meager ice formation in the same setup but in the absence of the external field. Needle excess electric charge is evidenced by its attraction toward the electrodes and by its shape change, when the field is withdrawn. These observations are explained considering the effect of the electric potential on ice surface tension, thus decreasing or eliminating the energy barrier to ice nucleation; and the elongated ice habit that allows the accumulation of charge sufficient to create fields higher than those initially applied. Applying this information to other crystallization phenomena in various systems can contribute to improve industrial processes while preventing the consequences of undesired electrification, in industrial plants and products. [ABSTRACT FROM AUTHOR]

Junction temperature monitoring and bond wire detection are crucial for the condition monitoring and protection of insulated gate bipolar transistor (IGBT) and freewheeling diode (FWD). on-state voltage drop is one of the most popular parameters for junction temperature estimation and bond wire detection. However, there is still a lack of cost-effective on-state voltage drop measuring techniques for both IGBT and FWD with a fast response. This article proposes an in situ junction temperature monitoring and bond wire detecting method based on IGBT and FWD on-state voltage drops. The proposed technique can measure the on-state voltage drops of IGBT and FWD online with high accuracy and fast response. The on-state voltage drops of IGBT and FWD under low load current are linearly dependent on their junction temperatures. Besides, the on-state voltage drops under high load current are closely related to the bond wire degradation. Therefore, the junction temperatures and bond wire conditions of both IGBT and FWD can be monitored based on the on-state voltage drops during a period of alternating current. The experiment results validate the feasibility of the proposed on-state voltage drop-based method for junction temperature monitoring and bond wire detecting. The proposed method has characteristics of high response speed, noninvasiveness for normal converter operating, and simple structure. [ABSTRACT FROM AUTHOR]

Previous studies have shown that the distribution of electric charges at the surface of dielectrics exposed to the corona discharge is controlled by several factors, such as the geometry of the electrodes, the level and polarity of the applied voltage, and the environmental conditions. It also depends on the nature of the exposed material and, more specifically, on the chemical and physical composition of its surface. This article aims at evaluating and maximizing the uniformity of the distribution of electric charges on several types of dielectric materials after their exposure to a corona discharge generated by a tri-needle-type electrode system. Two different methods of charging are investigated: “static” for polyvinyl chloride (PVC) plates and “dynamic” for polypropylene (PP) films and particles. In order to estimate the uniformity of the deposited charge on these dielectric materials, two characterization methods were employed: 1) surface potential mappings on PVC plates and PP films, using an electrostatic voltmeter and 2) direct measurement of the charge deposited on PP particles after their passage under the electrode system, using a Faraday cage connected to an electrometer. By modifying the geometrical parameters of the electrode system (height and distance between the needles) and the applied voltage, satisfying nonuniformity rates were recorded: less than 5% for PVC plates and PP films and less than 15% for PP particles. Exposure times longer than 2 s practically affected neither the charge level nor its uniformity. [ABSTRACT FROM AUTHOR]

The Alpine ski-resorts are conventionally powered by the electrical distribution network to perform the snow-making operations throughout the ski slopes. On one hand, these grids can present a low capacity, and on the other, the line lengths are not negligible due to natural obstacles and altitude changes. As a consequence, the voltage drops are remarkable when several power loads are fed by the low voltage section. Based on this aspect, a novel evolution of ski-resorts power grids toward microgrids is pursued to improve the power system quality of service and to foster the implementation of distributed energy resources (DERs). The article examines the ac electrical distribution system installed in the ski-resort of San Vito di Cadore, Italy. A preliminary power flow analysis identifies bottlenecks on voltage profiles and weights effective solutions to evolve the power grid. Four system configurations are contrasted in terms of voltage drop in order to establish the most convenient redesign. A proper voltage profile along the entire ski-resort is ensured by the last solution, which redistributes the loads powering among the five resort's substations. Finally, a techno-economical-environmental analysis explores the possibility of installing DER and storage to feed the resort loads. The study demonstrates the capability of hydropower plant in enhancing microgrid sustainability and environmental friendliness. [ABSTRACT FROM AUTHOR]

This article presents an analytical method to derive an optimum converter topology for a specified voltage conversion ratio (G). An optimum topology for any given G can be identified after obtaining the comprehensive pool of converter topologies. This gain-oriented converter synthesis is formulated as an inverse problem around the principle of inductor flux balance. A step-by-step method is proposed to solve the inverse problem and obtain a comprehensive set of non-redundant converter topologies for any given voltage conversion ratio. Consequently, the number of possible converter topologies for a specified voltage conversion ratio is also identified. The optimum converter topology is chosen from the comprehensive set based on three selection criteria, viz., ground-referenced output, a minimum number of switches, and minimum peak inductor current. The proposed solution methodology is illustrated with quadratic boost and quadratic buck gains as case studies. A comprehensive set of non-redundant topologies is identified in both cases. The steady-state operations of all the topologies are studied with PLECS simulation. Based on the selection criteria, an optimum topology is selected in each case, and their steady-state operation is verified experimentally using lab-developed prototypes. [ABSTRACT FROM AUTHOR]

Square plates of polypropylene (PP), dimensions 100 mm × 100 mm × 4.5 mm, were treated by atmospheric dielectric barrier discharge (DBD) generated between two disk-type electrodes (Ø 75 mm), energized from an ac amplifier 30 kV, 20 mA. The study aimed at evaluating the factors that affect the roughness and the triboelectric behavior of the plasma-treated samples. The alteration of surface aspect after each treatment was clearly visible with the naked eye and the changes were confirmed by measurements carried out with a portable roughness meter (Surftest SJ-210) and a digital microscope (Keyence VHX-7000). The roughness of the PP samples increased from an initial arithmetic mean Ra = 0.06 μm (±0.01 μm) and standard deviation Rq = 0.08 μm (±0.01 μm) to Ra = 0.22 μm (±0.03 μm) and Rq = 0.25 μm (±0.03 μm), respectively. These increases were highly dependent on the air gap distance (10.5–13.5 mm), the treatment time (5–20 min), and the configuration of the DBD cell, i.e., the number (one or two) and the thickness (4–5 mm) of the glass dielectric barriers. Untreated and DBD-treated samples were tribocharged in a linear tribometer, to evaluate the effect of the cold plasma treatment on the electric potential generated on the polymer surface by the triboelectric effect. The electric potential measured by a noncontact electrostatic voltmeter (Trek, 341B) was higher and better distributed over the surface of the plasma-treated samples. [ABSTRACT FROM AUTHOR]

This article presents the implementation and performance evaluation of a model predictive control (MPC) for three-phase (3σ) transformerless interconnected five-level power electronic converters (PECs). The proposed MPC employs a discrete-time model of five-level PECs to predict future values of the grid-injected currents and ground potential. Predicted values of the grid-injected currents and ground potential are used to set the reference signals to minimize a cost function, which is formulated in terms of the command and actual values of grid-injected current and ground potential. The proposed MPC is implemented for transformerless interconnected diode-clamped and flying-capacitor five-level PECs under different conditions. Test results show that the developed MPC can operate transformerless interconnected PECs to ensure accurate, dynamic, and fast responses to changes in the power delivered to the host grid. Furthermore, the MPC demonstrates a good ability to minimize ground potentials during steady state and step changes in the power delivered to the host grid. [ABSTRACT FROM AUTHOR]

To provide a safer work area for electrical workers, a novel design concept of portable equipotential zone mats is presented in this article. The proposed mats can create a safe work area by enabling bonding with energized equipment, and thus, creating an equipotential zone for electrical workers who may be exposed to electrical potential differences. The proposed mats are portable; they can be conveniently transported to remote areas and set up at worksites. In this article, we have designed, built, and tested two sizes of mats. To evaluate their performance, the two mats have passed type tests according to the latest revision of American Society for Testing and Materials standard F2715. The testing results of the proposed equipotential zone mats are demonstrated in the article. [ABSTRACT FROM AUTHOR]

This article proposes a common-mode (CM) voltage reduction method using an active power filter (APF) and common-mode transformer (CMT) for a grid-connected three-phase three-level neutral-point-clamped (NPC) AC-DC pulsewidth modulation (PWM) converter. The CM voltage can be caused by switching operations of converters and the CM voltage should be reduced because it is one of the main causes of electromagnetic interference (EMI) noises. In this article, the CM voltage of the three-phase converter with the proposed APF is analyzed to explain the CM voltage reduction using the proposed APF. Based on this analysis, the application of a specific PWM method to the three-phase converter for an optimal reduction of the CM voltage is described. Besides, the APF circuit design and its switching method are proposed considering practical problems such as the self-resonance of inductors and the effect of the dead-time on the CM voltage. To prove the effectiveness of the proposed APF on the CM voltage reduction, experimental results for the CM voltage and current are presented in this article. Furthermore, EMI noise measurement results are shown to verify the performance of the noise reduction capability of the proposed APF. [ABSTRACT FROM AUTHOR]

A fractal-based approach is presented for the direct-stroke shielding analysis of high-voltage substations. The proposed method considers the effect of lightning polarity and the stochastic nature of the lightning attachment phenomenon. An application to a typical 69 kV substation reveals that shielding failures may occur even if the shielding design is realized with IEEE Std 998-2012 methods. This can be explained by the fact that the shielding design methods adopted by IEEE Std 998 do not consider the effects of lightning polarity and object height on striking distance. In addition, IEEE Std 998 methods adopt a deterministic approach on shielding failure analysis neglecting the branched and tortuous behavior of lightning discharges. Fractal-based simulation results show a considerable dispersion of striking distance and a significantly higher shielding failure probability for downward positive lightning than negative lightning. This work forms a discussion framework on shielding failure analysis following a stochastic approach; this approach may explain unexpected shielding failures, such as those reported in IEEE surveys, and can be used for the direct-stroke shielding design of mission-critical high-voltage substations. [ABSTRACT FROM AUTHOR]

Many software are available to analyze the design of electrical power systems. Therefore, it becomes relevant to know the rules of thumb to be able to diagnose in an elementary and intuitive way the computerized results. For the short-circuit analysis, in most practical cases, it is sufficient to adopt simplified and standard-based calculation methods. This article introduces the parameter of the countercurrents and illustrates the approach of the short-circuit models of power system components based on the “characteristic” currents method. This article, at first, presents a short overview of the IEC Std 60909, assumed as a reference for the proposed approach. [ABSTRACT FROM AUTHOR]

Plasma application systems can be classified as an inductive-coupled plasma (ICP) system and a capacitive coupled plasma (CCP) system. Generally, a voltage-source-type pulse generator (VST-PG) is utilized in ICP systems. The VST-PG has the intrinsic problem of spike currents and voltage ringing in CCP systems. A filter inductor and damping circuit have been employed to mitigate this problem. However, this solution degrades the dynamic performance and increases the system cost, particularly for a CCP system with a large power rating. This article proposes a current-source-type pulse generator (CST-PG) to solve the problem of current spike and voltage ringing in a CCP system. The proposed circuit structure provides the output voltage and current waveform of the enhanced waveform fidelity. In the proposed system, two current sources of different scales are connected in parallel to generate the output current with high precision. The entire system consists of four major functional blocks: a bias current generator, a bias current modulator, a slope current generator, and a slope current modulator. The proposed solution also employs a SiC mosfet-type power semiconductor switch of 1200 V/90 A to meet the fast transient requirement. The proposed converter system successfully satisfies the specification of an output voltage of 1.6 kV and an output current of 35 A with a fundamental frequency of 100 kHz. The experimental validation result confirms the superior performance of CST-PG with a reduced crest factor of 1.12 for a laboratory prototype. [ABSTRACT FROM AUTHOR]

A high-frequency isolated multilevel cascaded-type bipolar direct PWM ac–ac converter is proposed. By cascading N-unit cells, the converter can produce symmetric bipolar voltage gain of ±ND. It does not require a separate ac source for each unit cell, and can provide higher ac output voltages with multiple levels using low-voltage rating devices, decreasing output voltage harmonics and filtering requirements. Moreover, phase-shift PWM switching is employed, increasing the effective frequency of the output filter, further reducing its requirements. The converter can be utilized as a dynamic voltage restorer (DVR) for grid voltage regulation, with the following features: No need for an external dc source, separate ac sources, and a line-frequency voltage injection transformer. Injection of higher voltage magnitudes than the line voltage, mitigating deep voltage sags. Injection of a negative series voltage to provide compensation for voltage swells. The detailed circuit operation is explained together with component design guidelines and application as DVR. Finally, experimental results are provided using an 800-W scale-down laboratory prototype. [ABSTRACT FROM AUTHOR]

Insulated gate bipolar transistor (IGBT) module is the most widely used power electronic device in converters. Condition monitoring of IGBT is critical for avoiding sudden failures. Health management of converters based on accurate IGBT junction temperature is of great importance to reliable operation. However, the existing monitoring methods have some drawbacks, including low feasibility of online implementation, intrusiveness, and slow response. IGBT junction temperature has a strong influence on IGBT on-state voltage drop. A novel online IGBT junction temperature measurement method based on the on-state voltage drop is proposed in this article. This technique can monitor the on-state voltage drop of IGBT and extract IGBT junction temperature online. Besides, the influences of the measurement circuit temperature variations and IGBT load current variations are considered and compensated based on the off-state stage of the IGBT. Simulation and experimental results validate the feasibility of the proposed technique. The proposed method has advantages of fast response, low cost, and simple circuit structure for noninvasive online IGBT junction temperature monitoring. [ABSTRACT FROM AUTHOR]

The submodule capacitor voltage sensing and balancing is necessary for proper operation of modular multilevel converters (MMC). Voltage controlled oscillator is used for capacitor voltage measurement in the reported literature where voltage sensor is required to be calibrated. In this article, a voltage sensing method that does not need calibration of individual voltage sensors is used for capacitor voltage measurement. Moreover, a simplified sorting algorithm is employed for capacitor voltage balancing. A method of sorting the capacitor voltages that selects the submodules to be inserted directly based on logic equations is used as compared to the conventional methods of arranging them in ascending or descending order. This facilitates to simplifying the sorting technique and the scheme is easy to implement using any controller. Furthermore, to simplify the overall MMC control, the decentralized control arrangement is developed. Fairly good capacitor voltage balancing is obtained. The proposed balancing and sensing schemes of submodule capacitors are validated on a three-phase seven-level MMC hardware prototype with six submodules per arm. The prototype is tested for different operating conditions such as precharging, circulating current control, and grid connected operation of MMC. [ABSTRACT FROM AUTHOR]

This article is aimed to propose an isolated current-fed bidirectional dc–dc converter (ICFBD2 C) in reconfigurable split battery (RSB) charging for electric vehicle applications. The proposed CFBD2 C is capable to counter potential issues of high-frequency CFBD2 C, such as high voltage spikes across switches, high initial input current, higher switch rating, hard-switched operation, narrow operating range, additional auxiliary circuitry, low charging current, and limited voltage gain. In this article, a CFBD2 C is proposed to charge RSB voltage sources. The proposed CFBD2 C comprises three stage gain circuit (synchronous boost converter, voltage doubler, and high frequency transformer) to match two dc voltage level. It operates in two distinguished modes of discharging and charging. In discharging mode, CFBD2 C offers an 8X voltage gain, and allows discharging of batteries to the grid. Furthermore, in charging mode, RSB is opted to the parallel configuration to inject high current due to high potential difference. In both operating modes, the proposed CFBD $^{2}$ C ensures zero voltage switching turn on and zero current switching turn on/off for all the switches and diodes, respectively, during entire battery charging/discharging operation range. The theoretical analysis of the proposed converter is initially validated by SIMULINK9.0, and later on verified by a laboratory prototype of 250 W, validate 145 kHz for charging and 100 kHz for discharging with 94%. [ABSTRACT FROM AUTHOR]

Transformerless grid-connected power electronic converters (PECs) are used in photovoltaic systems, motor drives, and solid-state power transformers. In these applications, transformerless grid-connected multilevel PECs can reduce harmonic distortions, increase power, and voltage ratings. This article aims to develop models for the ground potentials in these PECs, and to design grounding circuits for them. The models for ground potentials are developed using the common-mode voltages across each leg of the multilevel PEC. Grounding circuits for transformerless grid-connected multilevel PECs are designed using frequency selective circuits to limit ground potentials, and block ground currents from flowing through grounding of the host grid. The developed models, and grounding circuits are evaluated for transformerless grid connected, diode clamped, flying capacitor, and cascaded H-bridge multilevel PECs under different operating conditions. Test results demonstrate the significant advantages of the frequency-selective grounding for transformerless grid-connected PECs. Observed advantages include reduced harmonic distortion, minimized ground potentials, and improved efficiency. [ABSTRACT FROM AUTHOR]

In this article, we evaluate the noise and vibration in a permanent-magnet synchronous motor (PMSM) with distributed winding driven by voltage source pulsewidth modulation (PWM) inverters. Although the PMSM is a widely used device in a variety of fields, it tends to generate electromagnetic noise and vibration due to the PWM inverters. We describe the frequency of the electromagnetic vibration to estimate the worst point of the carrier electromagnetic vibration of dc voltage fluctuation. The PWM voltage harmonics and the modulation degree of dc voltage fluctuation were investigated through a theoretical analysis of the PWM voltage harmonics. It was found that a modulation degree near 0.56 was the maximum point of the doubled component of the carrier frequency $2f_{c}$. Compared with the dc voltage fluctuation at this point, the dominant component of the PWM voltage harmonics was near frequency $f_{c}$ at a lower voltage and near frequency $2f_{c}$ at a higher voltage. These tendencies of the carrier electromagnetic vibration of dc voltage fluctuation are also verified in an experiment. [ABSTRACT FROM AUTHOR]

A seven-level packed U-cell inverter is presented in this article. The converter uses a single dc source and two floating capacitors, whose voltages are balanced in open loop, to produce multilevel output voltage. Peak magnitude of the output phase voltage is equal to the magnitude of dc source. Voltages across floating capacitors add intermediate voltage-levels by establishing an asymmetric ratio (with respect to the available dc voltage in the circuit). The average energy exchange (when the network is in steady state) of the capacitors with the rest of the inverter circuit will be zero. This helps the capacitors to maintain desired voltages and thus create intermediate levels of steady dc voltages. Performance of the converter is validated in simulation by MATLAB/Simulink and testing of the converter is done for resistive as well as inductive loads. Experimental verification of the converter is carried out on a laboratory prototype and the obtained results match well with the simulation. [ABSTRACT FROM AUTHOR]

This article proposes a mathematical model for a switched reluctance (SR) generator feeding a dc link through a power electronic converter. SR machines are operated in single-pulse mode at close to and above base speed. The SR generator is modeled as a current source, controllable with dc-link voltage $V_{\text{dc}}$ , prime mover speed $\omega _m$ , and switching angles ($\alpha _{\text{on}}$ and $\alpha _{\text{off}}$) of the converter. This current source model is used to predict the dc-link dynamics for constant resistance, constant current, and constant power loads. This is further utilized to derive the voltage build-up condition for an SR generator. The generator model, dc-link dynamics and voltage build-up conditions are validated through simulations and experiments. [ABSTRACT FROM AUTHOR]

The purpose of this work is to design a power allocation method (PAM) for multistack fuel cell system (MFCS). Due to the limitations of technology, large-scale application of proton exchange membrane fuel cell (PEMFC) in the field of rail transportation has not been implemented. Therefore, this study presents an MFCS to promote the use of PEMFCs in the high-power energy market. During the operation of the MFCS, since the output power of the FC varies dynamically with different operation conditions, the performance of each stack is usually inconsistent. A method for evaluating the degree of performance degradation (DOPD) of stacks is presented in this study. In addition, a fuel cell (FC) semiempirical model is also adopted to simulate the effects of aging on the stacks’ performance. In order to maintain the uniform performance of stacks and enhance the lifespan of the MFCS, a PAM that considers the DOPD of each stack is presented. Besides, in order to facilitate system expansion, this article proposes a virtual droop control method to realize power splitting among the stacks. Also, a voltage control strategy is presented to compensate for the bus voltage drop caused by the droop control. The effectiveness and practicability of the presented PAM and MFCS are verified on the hardware-in-the-loop test bench constructed by RT-LAB. [ABSTRACT FROM AUTHOR]

In roll-to-roll manufacturing of products, such as thin films, fibers, textiles, or membranes, the generation and accumulation of electric charges by the triboelectric effect represents a major source of electrostatic hazards. The best solution to this problem is to eliminate these charges. The aim of this article is to pave the way to the use of a triode-type corona electrode system at an industrial frequency (50 Hz) for active neutralization of electrically charged insulating films. The experimental study was carried out on dc corona charged polypropylene films that were neutralized by a sinusoidal corona discharge. The neutralization efficiency was evaluated by noncontact measurement of the electric potential at the surface of charged and neutralized polypropylene film samples. The response surface methodology was used for quantifying the effects of the various influential factors (i.e., voltage amplitude, duration of exposure to the discharge, and relative position of the neutralizer with respect to the sample) and optimizing the neutralization process. [ABSTRACT FROM AUTHOR]

The growing adoption of electric vehicles has recently attracted increasing attention of scientists and brought about pioneering research studies from various fields. Safety concerns particularly those regarding ground faults detection and protection, have extensively been addressed. Ground faults occur quite frequently in electric vehicles and they may be due to severe operation conditions, such as vibrations, twists or even crashes. Generally, the first ground fault is not dangerous, since the powertrain systems, namely, the dc bus where the batteries are connected, the power inverter and one or more ac machines, are generally ungrounded. The second ground fault, however, can produce malfunction in some systems, power loss or even serious damages. Locating the fault has often proved hard and time consuming. For this reason, the present study focuses on developing a ground-fault detection method for electric vehicles capable of determining on which side, the dc or the ac, the ground fault is located. The method is based on the analysis of the voltage in a grounding resistor connected between the midpoint of the battery pack and ground. Based on the polarity and harmonics, it is possible to locate the ground fault. This method has been verified excellent results have been achieved using computer simulations and experimental tests in a 140-kW electronic power inverter fed by a 480 Vdc battery. [ABSTRACT FROM AUTHOR]

This article presents an analysis of conventional single-phase cascaded H-bridge multilevel inverters composed of two and three cells. The dc-link can be a dc source or a floating capacitor. Two methods are given to regulate the floating capacitor voltage. In this way, according to the capacitor voltage balancing method used, operating regions and power distribution on the floating capacitor are presented for different dc-link voltage ratios and several ranges of modulation index and load power factor. A mathematical analysis is done in order to demonstrate the influence of the modulation index and load power factor over the power distribution. Finally, simulation and experimental results are provided to validate the theoretical considerations. [ABSTRACT FROM AUTHOR]

In the application of electric railway traction, induction machines may suffer momentary power interruptions. Restarting control while machine running is a critical part of such applications, but residual flux in the free-running rotor deteriorates conventional controller performances, leading to inrush current and torque impact. Thus, this article proposes an improved feed-forward current controller that compensates voltage variations in the restart process. The residual rotor flux, as well as the induced back electromotive force, is estimated only with the measured speed in the free-running stage. The exact electromotive force is compensated at the restart moment, and the following current re-establishing stage. Based on the feed-forward compensation, the restart impact is eliminated and the restart current is controlled accurately in the predefined trajectories. Verified by experiments, the restart controller provides flexible restart manipulations. [ABSTRACT FROM AUTHOR]

Transformerless inverters (TLIs) are competently accepted for photovoltaic (PV) applications because of their high efficiency, reduced size, and lower cost. But in the absence of a transformer, there exists a galvanic connection between the PV array to ground and it results in the flow of hazardous leakage current. Several TLI topologies have been proposed in the literature with decoupling circuits to reduce the leakage current. Among those H5, Heric, and H6 topologies are the most popular and widely accepted TLIs. Nevertheless, the effect of switch junction capacitances was not considered in the common-mode voltage analysis, which inevitably causes excess leakage current. Also, reactive power capability cannot be accomplished with traditional pulsewidth modulation (PWM) schemes due to the absence of a bidirectional current path during the freewheeling period. Therefore, in this article, a bidirectional clamping (BDC) based H5, Heric, and H6 TLI topologies are proposed with improved PWM schemes. BDC branch reduces the leakage current by clamping the inverter terminal voltages to half of the dc-link voltage during the freewheeling period and the improved PWM schemes ensure the bidirectional current path while operating in negative power region. The performance of both traditional and proposed topologies is tested with MATLAB simulations and further justified with experimental results. [ABSTRACT FROM AUTHOR]

Silicon-carbide (SiC) mosfets have shown superior characteristics to Si IGBTs, bringing in significant performance improvement such as enabling more compact, higher efficiency converters that are not feasible with conventional Si IGBTs. Currently, there is a lack of systematic and conclusive investigation into soft-switching inverters using SiC mosfets in comparison to Si IGBTs. This article, therefore, presents a comparative evaluation of a soft-switching inverter, i.e., the auxiliary resonant commutated pole inverter (ARCPI) using SiC mosfets or Si IGBTs. The switching transition, switching device current stress, neutral point ripple current, electromagnetic interference (EMI), efficiency, and cost are compared on identical ARCPI setups, i.e., with the same printed circuit boards and under identical driving conditions (gate drivers). Experimental results show that the ARCPI using SiC mosfets has better performance than that using Si IGBTs due to its faster switching speed. First, the ARCPI using SiC mosfets performs full zero-voltage switching and the switching transition behavior is more predictable. Unlike Si IGBTs, SiC mosfets have no turn-off tail current and forward voltage drop during switching transitions. Second, the ARCPI using SiC mosfets endures less current stress and smaller ripple current in dc-link capacitors. Third, the ARCPI using SiC mosfets exhibits better EMI performance and higher efficiency. Specifically, a maximum 20 dBμV harmonic reduction can be achieved around 800 kHz and a 3.1% improvement in efficiency can be achieved at 6 kW. [ABSTRACT FROM AUTHOR]

Voltage multipliers (VMs) are widely used in applications with the high-voltage-gain rectifiers and dc/dc converters with the capability of increasing voltage conversion ratio. Currently, all the existing VM circuits are designed with two input terminals, while the optimal design on the voltage conversion ratio and voltage stress on the semiconductor devices of the converters with VMs can be achieved by varying the number of basic VM units. However, as the number of its input terminals is fixed and, thus, the current stress on the semiconductor devices are not adjustable at the design stage, such circuits have limited applications in today's high-power energy conversion systems. In order to address such drawbacks of the conventional VMs, a multiple input-terminal VM (MIVM) circuit is proposed in this article. The analysis of the operation principles and the performance characteristics of the proposed MIVM circuit are presented in detail. As an example, the application of the MIVM with the traditional boost converters is presented and discussed, and the efficacy of the theoretical analysis is validated experimentally. [ABSTRACT FROM AUTHOR]

In this article, a new postfault control algorithm for cascaded H-bridge (CHB) multilevel inverter is proposed to increase the maximum available output voltage under semiconductor fault conditions. Once a semiconductor switch in an H-bridge power cell fails, instead of bypassing the faulty cell, it can be utilized to generate a voltage. However, one of the three levels (positive, negative, or zero) of the faulty cell output voltage is not available, reducing the available output voltage of the cell to half. In the proposed method, the faulty cells being utilized and combined with the neutral shift (NS) method to achieve a higher output voltage of the CHB in faulty conditions. The output voltage obtained by the proposed method is analyzed for different faulty conditions and compared with the conventional NS method. Experimental results are presented confirming the effectiveness of the proposed methods in increasing the maximum output voltage at different faulty conditions. [ABSTRACT FROM AUTHOR]

With the explosion of on-road electric vehicles (EVs), private EVs become the most majority of the EV population, and also turn out to have the most flexible dispatching potential for power system. Accurate potential analysis of the flexibility has great significance for charging infrastructure upgrade, power system operation, and market mechanism design. A probabilistic evaluation method of household EVs dispatching potential is proposed here considering users’ multiple travel needs. Based on a realistic investigation on driving pattern of domestic cars, the probability distributions of multiple trip parameters are fitted with a proposed least square estimation based parameter optimization method. Sequentially, the sampling of random trip parameters is conducted considering the plug-in rate and coupling characteristics of trip parameters with a copula-based sampling method. Based on evaluating the shifting potential of EV charging load, the influence on the shifted load, brought by the implementation of time-of-use (TOU) price mechanism, is quantified by taking residential energy consumption behavior into account. Numerical result shows the accuracy and rationality to simulate the charging load considering multiple daily travel needs and the effectiveness of TOU price on EV load shifting based on the dispatching potential evaluation. [ABSTRACT FROM AUTHOR]

The effective pricing of electric vehicle (EV) charging by aggregators constitutes a key problem toward the realization of the significant EV flexibility potential in deregulated electricity systems and has been addressed by previous work through bi-level optimization formulations. However, the solution approach adopted in previous work cannot capture the discrete nature of the EV charging/discharging levels. Although reinforcement learning (RL) can tackle this challenge, state-of-the-art RL methods require discretization of state and/or action spaces and thus exhibit limitations in terms of solution optimality and computational requirements. This article proposes a novel deep reinforcement learning (DRL) method to solve the examined EV pricing problem, combining deep deterministic policy gradient (DDPG) principles with a prioritized experience replay (PER) strategy and setting up the problem in multi-dimensional continuous state and action spaces. Case studies demonstrate that the proposed method outperforms state-of-the-art RL methods in terms of both solution optimality and computational requirements and comprehensively analyze the economic impacts of smart-charging and vehicle-to-grid (V2G) flexibility on both aggregators and EV owners. [ABSTRACT FROM AUTHOR]

A conventional input-voltage sensor-based vector-controlled PWM rectifier is used in wide range of applications due to its well-known control structure, simple design, and good dynamic performance. Many existing input voltage sensorless methods have a control structure significantly different from that of conventional vector control, involving additional computational and design efforts. This article proposes a simplified input voltage sensorless control which has the same control structure as that of vector control and can utilize similar controller design procedure. The input voltage required for a phase-locked loop (PLL) is estimated from the current controller output using a simple algebraic equation. The sensorless PLL, so obtained, is mathematically modeled, and its frequency response is shown to be similar to that of a sensor-based PLL. The performance of the proposed method is compared with those of existing methods in terms of input power factor, response to distorted input voltage, sensitivity to system parameter, and computation time requirement through simulations and experiments. Apart from having the lowest computation requirement, the proposed method is shown to achieve the sensorless operation without any performance degradation, compared to the sensor-based operation, and with robustness to parameter variation. The proposed method includes a start-up procedure, which ensures low starting transient current. [ABSTRACT FROM AUTHOR]

Among the various supply voltage abnormalities, unbalance and distortion are some of the major threats to the dc bus capacitor of adjustable speed drives. The effect of supply voltage unbalance on the dc bus capacitor changes in the presence of supply voltage harmonics. Further, the value of grid impedance and the load on the drive influences the response of these supply voltage abnormalities on the dc bus capacitor. This article analyzes the impact of unbalance, distortion, and simultaneous presence of unbalance and distortion in the supply voltage, on the dc bus capacitor, along with the effect of grid impedance and the load on the drive. As a result of the analysis, the article proposes the derating of load required to keep the capacitor current within the safe value irrespective of the level of abnormalities and grid impedance. The effects are analyzed by simulations and validated by the hardware test setup. [ABSTRACT FROM AUTHOR]

Common-mode-voltage (CMV) is a well-known source of bearing currents and electromagnetic interference (EMI) in industrial applications. In industrial environments with impedance-earthed IT earthing system, such as underground mining, CMV is additionally associated with potentially undetectable fault currents, due to their diversion away from a protection circuit. This article proposes a variable speed drive (VSD) solution that generates practically zero CMV and removes alternative paths for the fault currents. The VSD topology utilized in this article is a standard two-level inverter with active front end. The article develops a control strategy such that it eliminates CMV, minimizes EMI, and optimizes harmonic distortion at the drive input and output. Experiments conducted in physically emulated industrial environment have confirmed that CMV and EMI are practically eliminated, and the earth fault protection is effective. [ABSTRACT FROM AUTHOR]

The coupled inductor single-input dual-output (CI-SIDO) dc–dc converter is an alternative to multiple parallel dc–dc converters for applications requiring multiple regulated supplies. CI-SIDO exhibits the merits of reduced ripple, small volume, and high efficiency. However, the coupling of inductor currents results in coupled outputs leading to cross-coupling and cross-regulation problems. Due to cross-coupling of the output voltages, the compensator design becomes complex. This article proposes a decoupled voltage-mode control to address the issue of cross-coupling of output voltages. It also demonstrates the stability boundary for controller design. The proposed controller is designed using simple analog Type-II compensator. A systematic compensator design procedure is also developed. The proposed controller decouples the output voltages, ensures good stability margin as well as good load regulations and audio-susceptibility. The design is verified through simulation and experiments. The experimental results shows that the decoupled control significantly suppresses the cross-regulation with fast transient response speed for the load, input, and reference variation. A transient performance comparison of proposed decoupled voltage-mode control for the CI-SIDO buck converter with state-of-art control methods for the single-inductor SIDO buck converter is also presented. [ABSTRACT FROM AUTHOR]

Conventional reduced common-mode voltage discontinuous pulsewidth modulation method for a three-level inverter can reduce the common-mode voltage and switching transitions compared with continuous modulation. However, it suffers from poor output current quality and cannot provide additional performance enhancements when applied directly on parallel three-level inverters. Based on the interactions between the parallel inverters, this article reveals that dual parallel three-level inverters could be analyzed and controlled as a single five-level inverter. Based on this idea, a novel five-level discontinuous modulation method is therefore proposed to further reduce the common-mode voltage of the system by half, in addition to dramatically improving the output current quality compared with conventional three-level method. The specific implementation process is explained in detail, and a unique switching sequence design is developed considering keeping zero average circulating current, which is crucial to the proper function of parallel operation. Furthermore, a neutral point voltage balancing strategy through alternatively applying charging and discharging switching sequences is proposed for the five-level modulation process, which can effectively restore the neutral point balance in case imbalance occurs. The effectiveness and advantages of the proposed method are verified by both simulation and experimental results. [ABSTRACT FROM AUTHOR]

A lad-used servo permanent magnet synchronous motor has been accidentally damaged due to overcurrent. On the one hand, the mechanical damage, in the end, bearing and break part generates acoustic noise even when rotating the shaft by hand. On the other hand, the back electromotive force of the motor becomes unbalanced and exceedingly high torque ripple is produced. Such torque ripple results in intolerable speed ripple and will increase the acoustic noise. This article aims to reuse this damaged motor by adding a repetitive observer (RO) to the existing speed loop, both the speed control performance and the acoustic noise of the damaged motor can become comparable with its healthy version. The RO is functionally the same as a repetitive controller (RC), but the stability of the RO is independent of the feedback loop, while the stability of the RC will affect and be affected by the rest of the system. Therefore, RO can be applied for both the healthy motor and the damaged motor. This work opens the possibility of further enhancing the fault tolerance ability of a healthy motor or even reusing a damaged motor and still achieve high performance. [ABSTRACT FROM AUTHOR]

In this article, current source converter (CSC)-fed permanent magnet synchronous motor (PMSM) drives are investigated for electrical submersible pump (ESP) applications. The CSC features motor-friendly waveform with low dv/dt, which is very suitable for long cable application. High-speed ESP by adopting a PMSM has higher efficiency and shorter length and diameter compared with the counterpart adopting induction motor. Sensorless control instead of mechanical sensor can further reduce the system size/cost and improve reliability due to the harsh downhole environment. However, low switching frequency and an inverter-side output filter cause great challenge in controller and observer design. These kinds of influence become more serious under a higher speed region due to the limited updates per fundamental cycle. To overcome these challenges, the dynamic capacitor voltage control is employed in a field-oriented control scheme to enhance the system dynamic response. Moreover, a discrete-time sliding mode observer based rotor position estimation method is proposed to reduce estimation error and improve parameter uncertainty robustness. The effectiveness of the proposed method is verified on a CSC-fed PMSM with simulation and experimental results. [ABSTRACT FROM AUTHOR]

This article provides a closer look at a high resistance grounded (HRG) power system using symmetrical components. It addresses the industry confusion, “how system charging current direction reverses during phase-ground fault condition without reversal of system voltage that causes fault current flow.” It presents fault current phasor diagram that caused industry confusion which lead IEEE Std P3003.1 published without the phasor diagram with the consensus of working group members including the author of this article. In this article, the theory of symmetrical components has been used for analysis of phase-ground fault to illustrate ground fault current flow directions and its phasor diagram. The industry concept, “phase-ground fault current flows from the faulted location to ground before it returns to the power source” has been used in the analysis. This concept has not been used in the IEEE Std. 142 -2007, causing ground fault protection confusion for HRG power systems. The fault current flow direction clarification will help in the application of a sensitive voltage polarized ground fault protection relay for HRG. During phase-ground faults with very low arcing fault currents which pose a sensitivity issue on ground fault protection relays, some relevant technical papers providing techniques of fault detection are referenced in this article. Clarification on the limitation of HRG grounding contained in IEEE Std. 142-2007 for phase-ground fault current not to exceed 10 A and power system voltage not to exceed 4.16 kV (for delayed clearing of first phase-ground fault) is also included in this article. [ABSTRACT FROM AUTHOR]

This article proposes an analytical algorithm to detect and classify voltage sag events in terms of voltage sag inception and recovery angles, which are commonly known as point-on-wave (POW). Our research results have identified that there are only three possible voltage recovery angles in each phase for all possible voltage sag inception angles. Based on these three voltage recovery points, the voltage sag waveforms can be clustered into three groups each separated by $180^\circ $. Depending on the voltage sag inception POW, the actual voltage sag duration may increase by a certain amount from the expected fault clearing time. The possible increment of the sag duration can be predicted using the proposed method. The proposed method is validated using the voltage sag waveforms obtained from the simulation of two different radial distribution networks with different types of symmetrical and asymmetrical faults. From the simulation results, it is observed that for some starting angles the actual voltage sag duration may increase significantly, which can be harmful to some sensitive equipment even if the sag is shallow in magnitude. This analysis also shows that the magnitude of the current transient also depends on the voltage sag starting angle. A large current transient can cause disruption of some sensitive equipment. The impact of the load harmonics on the proposed method has also been investigated. From the simulated and recorded voltage sag waveforms it is concluded that the load harmonics have a negligible impact on the proposed method. [ABSTRACT FROM AUTHOR]

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]