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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excess electric charge is evidenced by its attraction toward the electrodes and by its shape change, when the field is withdrawn.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]

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]

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]

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]

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]