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Geothermal energy with abundance and large quantity can partially cover building heating/cooling loads and promote the carbon-neutrality transitions. Shallow geothermal ventilation (SGV) system, with a little initial investment cost, is one of promising technologies to partly replace the conventional air-conditioning system for air pre-cooling/pre-heating. This paper reviews applications of SGV system for improving thermal performance over latest two decades, which mainly includes the reclassification of SGV system, coupling with other advanced energy-saving technologies, application potentials for building cooling/heating under various weather conditions. Heat transfer mechanism and mathematical modelling techniques have been reviewed, together with in-depth analysis on current research trends, existing limitations, and recommendations of SGV system. Phase change materials, with considerable latent energy density, can stabilize the thermal performance with high reliability. The review identifies that optimization designs and advanced approaches need to be investigated to address the existing urgent issues of SGV system (e.g., large land occupation, difficulty in centralized collection of condensate water timely for horizontal buried pipe, bacteria growth, polluted supply air, and high construction cost for vertical buried pipe). A plenty of studies show that the SGV system could greatly expand the application scope and improve system energy efficiency by combining with other energy-saving technologies. This paper will provide some guidelines for the scientific researchers and engineers to keep track on recent advancements and research trends of SGV system for the building thermal performance enhancement and pave path for future research works.

Energy piles have attracted increasing interest for application in ground source heat pumps, because it is environment-friendly, energy-efficient, and without additional drilling cost. However, when there is a large difference between the heating and cooling loads, the system will suffer from a soil thermal imbalance which may further decline the system performance and even cause a system failure. A hybrid ground source heat pump system that integrates auxiliary equipment can solve the problem, however, it needs additional investment and a complicated control strategy. In this paper, the zoning operation of energy piles can effectively improve the temperature recovery ability of soil in the energy pile group and thus alleviate the soil thermal imbalance. Specifically, a heating-dominated residential building in Beijing is selected for a case study, with 144 energy piles arranged in a 12 × 12 layout. An analytical model of the spiral-coil energy pile group with seepage will be adopted, which can consider the groundwater flow, the geometry of spiral coils, and the thermal interaction among different energy piles, achieving high calculation accuracy and fast calculation speed. Based on this analytical energy pile model, a system model will be built to investigate the system performance influenced by different zoning operation strategies. Results show that intensive heat injection into the center of the pile group (Strategy 2 and Strategy 3) or heat extraction from the outer layer of the pile group (Strategy 4) can relieve the cold accumulation. Strategy 2 can relieve the outlet temperature decline from 5.54 °C to 4.46 °C and improve the heating COP from 3.297 to 3.423 compared to the conventional full operation strategy. Although the annual heat pump COP of Strategy 2 is a little lower than that of conventional full operation strategy, Strategy 2 has the shortest unmet heating or cooling time. Therefore, the proposed zoning operation strategy can achieve good system efficiency and excellent system reliability compared to the conventional strategy.

As the technology is scaled-down and with a decrease in oxide thickness, the effect of NBTI is a major reliability issue in semiconductor industries. NBTI is an aging phenomenon in which the PMOS transistor degraded over time. Deviation in the threshold voltage of PMOS transistor results from NBTI with stress time which affects various parameter of SRAM memory such as degradation in drain current, RSNM, HSNM and access time. NBTI induced aging effect on 6 T and 8 T SRAM cell have been analyzed in this paper for the stress time of 10 years. The reliability parameters of 6 T SRAM cell obtained from simulation result shows there is 6.53%, 23.86%, 3.36% and 13.42% change in Hold SNM (HSNM), Read SNM (RSNM), Write margin and standby leakage current respectively after 10 years. Similarly in 8 T SRAM cell HSNM, RSNM, Write margin and leakage current changes by 5.81%, 5.01%, 3.11%, and 13.24% respectively. This paper also presents the leakage current sensing technique based NBTI monitoring sensor using NMOS transistors only. The sensitivity of the sensor is 40 µV/nA and the linearity of the sensor is upto the practical leakage current range of SRAM cell. Thus we can conclude that the proposed sensor works fine with greater linearity and sensitivity.

SnO2 has been extensively used in the detection of various gases. As a gas sensing material, SnO2 has excellent physical-chemical properties, high reliability, and short adsorption-desorption time. The application of the traditional SnO2 gas sensor is limited due to its higher work-temperature, low gas response, and poor selectivity. Nanomaterials can significantly impact gas-sensitive properties due to the quantum size, surface, and small size effects of nanomaterials. By applying nanotechnology to the preparation of SnO2, the SnO2 nanomaterial-based sensors could show better performance, which greatly expands the application of SnO2 gas sensors. In this review, the preparation method of the SnO2 nanostructure, the types of gas detected, and the improvements of SnO2 gas-sensing performances via elemental modification are introduced as well as the future development of SnO2 is discussed.

Recently, model-based predictive current control (MB-PCC) has been presented as a good alternative to classical control algorithms in terms of simplicity and performance reliability. However, MB-PCC suffers from the high dependence on system parameters, which may deteriorate its performance under parameters variations. On the other hand, Synchronous Reluctance Motors (SynRMs) are susceptible to suffer from inductances variations due to the magnetic saturation. Accordingly, in this paper a new model-free predictive current control of SynRMs based on a recurrent neural network (RNN-PCC) is developed and proposed. The proposed RNN-PCC relies on the identification of the SynRM currents without considering any parameters. Simulation and experimental results show that both RNN-PCC and MB-PCC have similarly excellent dynamics, while better control performance and tracking errors can be achieved thanks to the proposed RNN-PCC.

Space missions have become diversified in recent years, where connection and separation devices play a crucial role as key components of various spacecraft. Traditional pyrotechnic devices have the advantages of large carrying capacity, rapid motion and functional reliability. However, their shortcomings such as great release shock, poor safety, unrepeatability and other prominent defects make them unsuitable for new generation spacecraft such as microsatellites to separate at low shock or lock repeatedly, etc. Therefore, it is necessary to develop space non-pyrotechnic low-shock connection and separation devices (SNLD) which are required for advanced aerospace missions. In this paper, the progress of the research on space non-pyrotechnic low-shock connection and separation technology (SNLT) is summarized and reviewed. Proceed from the principle of reducing shock for non-pyrotechnic devices, present studies are classified from the perspective of actuating technology and systematic designing methods. For non-pyrotechnic actuating techniques, according to different driving sources, the separation devices are classified into several main categories: electric, magnetic, gas and thermal actuating devices. The actuation principle and application prospect of separation techniques are introduced and the working process, dimension and mechanical properties of typical devices are compared and evaluated. For the systematic designing method, the common mechanism types of SNLDs are summarized according to the designing concept of reducing shock. Then connection configurations are classified according to the structural forms of connection devices, of which the principles, bearing capacities and general applications are discussed. This paper systematically summarizes the key problems, puts forward the future development trend of SNLT, and points out the breakthrough direction for related scholars.

Online condition monitoring of winding insulation has been proved to be an effective means to improve the reliability of an inverter-fed machine, but little work has been done on the insulation of line-end coil subjected to much higher transient voltage stress with a higher risk of premature insulation break down. In this paper, the inverter self-excited high-frequency switching oscillations are utilized for the line-end coil insulation condition monitoring. To improve the condition monitoring sensitivity and its robustness to dynamic operating conditions, a switching oscillation mode decomposition (SOMD) method is proposed. Firstly, the condition-sensitive mode, i.e. high-frequency common-mode (HFCM) current is selected and separated by the variation mode decomposition (VMD) algorithm among three dominant modes in switching oscillation current. Then, the amplitude-frequency features of HFCM current are extracted for condition monitoring. Finally, the overall insulation condition of three-phase line-end coils and the degree of asymmetric degradation are quantitatively evaluated by the frequency and amplitude features respectively. Experimental work was carried out and the results demonstrate the good performance of high sensitivity, good robustness, and non-contract safety.

As an essential component of ammunition, pyrotechnics can control ignition with high reliability. However, due to limits of fabrication technology, traditional pyrotechnics are bulky. To achieve both functionality and miniaturization, MEMS pyrotechnics integrate initiator, safety-and-arming (S&A) device and lead charge and keep all components within a small size. MEMS S&A devices, as the core component to ensure system safety, are difficult to achieve active and rapid response to control signals with high safety and reliability. In order to overcome the difficulty, we propose the design and characterization of a MEMS pyrotechnic with a double-layer barrier S&A device. The MEMS pyrotechnic is a high-integrated device with an overall size of 13.4 × 8.5 × 5.2 mm3. The initiator is a NiCr bridge foil covered with an Al/CuO energetic film, which can generate flame when ignited by an excitation voltage. To match the flame energy, lead styphnate is chosen in this study as the lead charge. The S&A device contains four semi-circular barriers, which are directly driven by V-shape electro-thermal actuators to gain active control of the pyrotechnics' ignition condition with rapid response. To improve the system's reliability, the four barriers are axisymmetrically placed in two layers, two barriers for each layer, to constitute a double-layer structure with a thickness of 100 μm. The ignition test results show that the S&A device can prevent the initiator from detonating the lead charge in safety condition. In arming condition, the lead charge will be detonated.

In this paper, a novel single switch high voltage gain DC-DC converter is presented. The proposed converter operates with continuous input current and the voltage stress across the power switch is lower compared to the competitive high voltage gain topologies. Hence, a lower rating active switch can be selected for the proposed configuration to achieve reduced conduction losses due to its low on-state resistance of the switch. The leakage energy of coupled inductor is effectively recycled to the load through the voltage multiplier used in the topology. The voltage stress across the power diode at the output side is less and hence there is an improvement in the output side reverse recovery performance. Moreover, the proposed topology has reduced aggregate diode voltage stress. A detailed comparative study is presented consisting of the steady-state analysis, working principle, efficiency and reliability evaluation of the proposed converter for continuous conduction mode. The proposed concept is verified through extensive simulation studies and from the measured results from the experimental prototypes.

The reduction in the cost of PV energy is still required to be competitive as an alternative energy source. The efficiency and reliability of PV inverters are important aspects to be enhanced to reduce the cost of PV energy since it is closely related not only to the annual energy production but also to the reduction of operational and maintenance costs of PV systems. In this paper, a single-phase IT-type NPC inverter with one-leg clamping pulse width modulation (OLC-PWM) is proposed for efficiency and reliability improvements. The proposed IT-type NPC inverter with OLC-PWM can improve the efficiency by taking the advantages of I-type and T-type NPC inverters regarding the power loss. Furthermore, its reliability has been improved compared with conventional I-type and T-type NPC inverters. The IT-type NPC inverter also has an ability to balance the neutral-point voltage. The superiorities of the proposed IT-type NPC inverter in terms of reliability and efficiency are validated through the simulations and experiments by comparing the reliabilities and efficiencies of the conventional I-type and T-type, asymmetric I-type and T-type and IT-type NPC inverters.

Although excellent reliability has been reported for sintered silver as a die-attach material under both thermal and power cycling loads in power electronics applications, the promise of this material as a large-area attachment at temperatures beyond 200 °C needs to be investigated. This paper presents insights into the thermomechanical behavior and reliability of sintered silver under extreme thermal cycling conditions. In this study, we bonded sintered silver samples and subjected it to a thermal cycling profile of -40 °C to 200 °C with high ramp rates. We periodically monitored samples under thermal cycling to detect the presence of any failure mechanisms using a scanning acoustic microscope. We also included 95Pb5Sn solder in the study to obtain reference data. Results show the occurrence of cracks in sintered silver followed by a rapid rate of crack growth that exceeded the failure criterion in just 50 cycles. The predominant failure mechanism we observed was adhesive failure. As a large-area attachment, solder exhibited a higher reliability than sintered silver but failed within 100 cycles. Finally, we performed thermomechanical modeling to compute strain energy density values and correlated these with the experimentally observed crack growth rates to formulate a lifetime prediction model for sintered silver.

The goal of this paper is to advance the understanding of the impact of hard switching on the dynamic performance of GaN-based HEMTs. To this aim, we developed a fast (10 V/ns) on-wafer system for testing devices in hard switching. The system has been used to study the reliability of several WG = 2 mm p-type GaN HEMTs with different LGD or buffer properties. First, we show that by optimizing the drain node capacitance, we can speed-up the hard-switching transition to a few ns, even on-wafer level. Second, repeating the experiment by using multiple frequencies, from 1 kHz to 100 kHz, we demonstrate that, in real-world applications, cumulative turn-on stress has a much stronger effect on RON compared to off-state stress. Third, by comparing the results on identical devices having shorter LGD, we pinpoint hot electrons as the main mechanism in the device degradation, ruling out the contribution of self-heating. Finally, by comparing three wafers with different processing conditions (different passivation, different buffer) we suggest that trapping phenomena related to hot electrons happen in ns time scale and that the properties of the buffer can significantly impact the dynamic performance of the devices in hard switching.

The electrical contact status between metal layers in a Press Pack Injection Enhanced Gate Transistor (PP-IEGT) is essential information for the reliability of the whole device. This paper employs the numerical method, microscopic detection, and power cycle test (PCT) to qualify the contact degradations and performance in PP-IEGT. Firstly, the contact status of metal pair aluminum-molybdenum in a single-chip module is described through the finite element method (FEM). Then, the contact fatigue of the single-chip module is estimated by the micro-detection of chip surface and the monitor of contact resistance during PCT. Finally, PCTs are conducted on parallel branches to explore the contact degradation under different contact statuses. The results show that the chip is subjected to fretting wear and cracks due to the periodic expansion and shrink. In the aging process, the contact resistances display a linear growth trend and have a significant impact on the electrical parameter shift. Moreover, the degradation of the branch with insufficient contact is more serious, especially under smaller clamping force and longer heating duration.

SiC MOSFET power modules are becoming global solutions in systems operating in harsh environment, and due to large economic implications, achieving reliability of such systems is of utmost importance. Thereby, this paper is focused on improving the reliability of the SiC MOSFETS, accomplished by generating intelligence on the gate-driver (GD) with providing insight on real-time behavior of relevant switch information. The device switch-current Id, apart from being used for short-circuit detection assessing the short-term reliability, in the combination with the on-state drain-to-source voltage Vds,on enables the possibility of online junction temperature (TJ) estimation. The knowledge of TJ can enable active thermal control as well as condition monitoring of the SiC MOSFET device such as state-of-health, remaining useful life, maintenance scheduling, etc., tackling the long-term reliability aspects. With the aid of a Field Programmable Gate Array (FPGA) on GD, a look-up table (stored in the FLASH memory on GD) containing device output characteristics is assessed, enabling real-time TJ monitoring for both devices in the commercial SiC MOSFET half-bridge module configuration. Following the developed gate-driver prototype, the TJ is verified in pulsed operation with maximum error less than 5 °C having excellent repeatability of ±1.2 °C and is furthermore verified in continuous operation showing promising results. Additionally, degradation monitoring and aging compensation scheme are discussed, with the goal of maintaining the accuracy of the Tj estimation throughout device’s lifetime.

The superior electrical and thermal characteristics of SiC MOSFETs bring major challenges to its short-circuit reliability. To fully understand its short-circuit mechanism, estimate its safe operating area, and provide guidance for circuit design, it is crucial to establish a theoretical model to quantize the relationship between circuit parameters and short-circuit behavior of SiC MOSFETs. A temperature-dependent analytical model considering the parasitic inductances, nonlinear junction capacitances, and temperature dependence of the channel current is proposed in this paper, which only uses the parameters in the datasheet or provided by manufacturers. The proposed model is established based on the analysis for each short-circuit stage in both single-device configuration and half-bridge configuration, and the quantitatively analytical results of the transient short-circuit waveforms, energy loss, and junction temperature rise can be calculated by solving the model. The accuracy of the analytical model is verified by comparing the analytical results with the experimental results. Furthermore, the effects of varied parameters on the short-circuit behavior are evaluated by the proposed analytical model. And the corresponding circuit design guidance for higher short-circuit reliability is given.

Spin transfer torque magneto-resistive random-access memory (STT-MRAM) has many advantages, such as scalability, persistence, practically infinite endurance, and fast access speed, that make it a promising and emerging technology for memory. However, this technology has multiple reliability issues such as read and write reliability, higher write power, and long write latency, etc. At elevated temperatures, these issues exacerbate further. As the temperature increases massively in the latest compute nodes, we need to study and understand the effect of temperature on STT-MRAM memory writes and reliability. In this paper, we propose temperature-aware memory controller and device architecture techniques specific to STT-MRAM technology, that can improve write reliability, retention reliability, and memory power without sacrificing the performance. Our simulation results show that the proposed techniques cumulatively improve write BER on an average by 603X, increase retention reliability by 65%, along with 27% power reduction and 5.8% improved system performance over the baseline STT-MRAM based memory subsystem.

Micro-Electro-Mechanical Systems (MEMS) micro-mirrors have shown great potential in consumer applications, such as Light Detection and Ranging (LiDAR) devices and portable laser projectors. The LiDAR based on electromagnetic MEMS micro-mirror is usually exposed to vibration loads for autonomous vehicles, which results in the necessity for the destructive reliability assessment of micromirrors under vibration environment, but such studies are rarely reported. This paper explores the destructive reliability of electromagnetic MEMS micromirror under vibration environment according to the JESD22-B103B standard. The reliability evaluation is conducted by experimental tests, finite element stress analysis and theoretical dynamic response analysis. Micromirrors are tested under sweep excitation, and they are failed with the vibration level of around 33 g. The failure and stress analysis demonstrate that the crack fracture is located at the root of the slow axis. The nonlinear relationship between the peak displacement of the balance frame and acceleration levels is investigated through theoretical analysis. The nonlinearity of stiffness hardening is induced by the axial tensile strain of the beam, which contributes to the displacement-reduction of the gimbal. This work provides some valuable suggestions for the optimization design of MEMS micromirrors to improve the acceleration tolerance level in vibration environment.

DC circuit breakers (DCCBs) play a significant role in obtaining the reliability and stability of DC power systems. Selective and fast isolating of faults minimizes the power supply outages to end electricity users and protects the power converters implemented in the DC system. During the last decades, DCCBs have been deeply investigated in industry and academia. There has been impressive progress in terms of efficiency, response time, power-density, lifetime, and electrical operating ratings. Introducing wide bandgap (WBG) devices further has motivated researchers to propose more efficient and novel topologies. This paper provides a point of reference and a background review for DCCBs from novel aspects, fulfilling absent parts in the literature. The elaborated subjects include current commutation circuitry, DCCBs trip-curves developments, newly added functions to DCCBs, as well as marketing analysis. The advancements of DCCBs are surveyed and development needs are recognized. This paper aims to identify the future research needs of DCCBs for emerging DC power systems.

This paper presents a combined control scheme that consists of two complementary control strategies, namely hierarchical control and autonomous control to handle contingencies in a multi-terminal high voltage direct current (MTDC) system. The proposed hierarchical control considers three optimal targets, i.e., equal or proportional power sharing, minimizations of transmission loss and total DC voltage variation. The primary control layer implements the droop control for voltage source converters (VSCs). While in the secondary control layer, voltage reference setpoints of the VSCs in droop control scheme are calculated by the proposed optimal power flow method with the equal or proportional power sharing as equality constraints. As the hierarchical control relies on communication system, the autonomous control for power sharing can be activated during communication system malfunctioning or rapid power variation caused by renewable energy sources. The combined control strategy can greatly increase the reliability of the MTDC system. The simulation results of a five-terminal MTDC network conducted in the MATLAB/Simulink software verify the performance of the proposed combined control strategy.

A circulating-current-excited switched reluctance generator system using a standard diode rectifier is proposed and examined in this paper. It features a DC power source connected in series with the ring-connected windings, which provides the DC-bias current as the excitation current in the windings. Using a series-connected DC power source, a DC-bias current is easily realized in the AC winding. Compared to the existing machine having DC-bias in the AC winding, the proposed generator can provide DC power with a standard diode rectifier. Less active legs and no rotor position sensor are needed for the control of the circulating current of the proposed generator, which increases the reliability of the generation system. The system configuration and the operation principle are introduced in detail. Then, the electromagnetic performance of the proposed generation system is analyzed at both open-circuit and load conditions. The asymmetric current distributions are deduced and verified by the simulations. At last, the prototype is tested under varied operation conditions and the experiments agree well with the analysis.

Solid-state transformers can be applied in the AC/DC hybrid distribution network. The reliability and power density of a solid-state transformer is significantly influenced by the insulation design of the isolated DC-DC converter and, in particular, its medium-voltage medium-frequency transformer. This paper proposes an insulation design method for the medium-voltage medium-frequency transformer. A novel insulation structure is adopted to reduce the volume and improve the heat dissipation performance. Optimization of insulation distance parameters is performed based on finite element method simulations. The proposed method is applied to a 60 kVA/10 kHz transformer, and the simulation results verify the improved performances with the proposed insulation design method. A prototype is developed according to the proposed scheme, and the experimental results of a DC-DC converter and the partial discharge and applied voltage tests are presented.

Dc collection and transmission is one of the main developing directions of the large-scale offshore wind power system. This work proposes a multi-functional dc collector to construct a low-cost, high reliability, and high flexibility all-dc offshore wind power system. By introducing the multi-functional dc collector to achieve energy collection and cascade boost, not only the system cost, size, and intermediate links of power conversion are reduced but also the coupling among wind turbines (WTs) is greatly weakened. Accordingly, the maximum power point tracking operation can be achieved independently for each WT unit. Furthermore, a constant voltage ratio control with first harmonic elimination iterative algorithm is proposed for dc collector to link the HVDC bus voltage and discretized dc voltage for triggering the energy consumption operation and suppressing the inductor current ripple, and the detailed control parameter design is provided. Meanwhile, the various operating modes are considered for multi-functional dc collector, including practical engineering configuration, fault isolation, dynamic cut-in/out, and energy consumption operation, which provides a practical solution for the construction of a long-distance and large-capacity offshore system. Finally, the comprehensive experimental results are given to illustrate the effectiveness of multi-functional dc collector.

With the wave energy conversion system (WECS) integrated to grid, the lack of satisfactory ability to ride through transient voltage faults will reduce the stability and reliability of the grid. In this paper, in order to enhance the low-voltage-ride-through (LVRT) capability of the WECS, the structure and the mathematical model of a magnetic-gear permanent magnet synchronous generator (MG_PMSG) and a float-type wave energy converter (WEC) are introduced firstly. The output power characteristic of the WECS is analyzed. Then, a novel coordinative LVRT control scheme based on supercapacitor energy storage system (SC_ESS) is proposed. The control scheme includes four modes which are determined by the severity of voltage sags and active power deviation of the WECS. Machine-side converter (MSC) control, grid-side converter (GSC) control and SC_ESS control are used coordinately in the four operation modes. The results of simulation and experiment have verified the effectiveness of the proposed control scheme in normal running conditions.

Insulated Gate Bipolar Transistor (IGBT) module is one of the most prone-to-fail components in the wind power converter. The reduction of the junction temperature swing by thermal management can improve the reliability of a wind power converter. Due to the lack of an applicable selection criterion, not many studies on the control target of junction temperature swing were reported. This paper proposes a thermal management strategy to find the control target of junction temperature swing. The proposed strategy considers the return on investment (ROI) of thermal management as a quantitative indicator to guide the control target selection. The selected control target enables optimal benefit of the thermal management. Results show that a 1%-increase in the total harmonic distortion would extend the lifetime of IGBT module by 0.144 years. Success of the proposed scheme lies in the efficient regulation of the junction temperature swing. Case studies with different mission profiles and experimental tests on a three-phase two-level inverter are presented to validate the proposed method.

Solar-plus-storage systems could effectively mitigate uncertainties of the photovoltaic (PV) generation and improve system reliability by adding an integrated battery energy storage system. As a three-port bidirectional isolated dc-dc converter with soft-switching capability, the triple-active-bridge (TAB) converter inherently match the requirements of the solar-plus-storage system. However, challenges still remain in the TAB converter design to further improve the system efficiency. In this paper, the detailed design, implementation, and demonstration for a silicon carbide (SiC) 150-kW TAB converter are presented. Starting from a brief review of the TAB converter, the modulation scheme, power characteristics, and soft-switching region are analyzed. Then, the detailed design of the H-bridge converter building block is given. To improve the system efficiency, a comprehensive characterization of the SiC gate driver with various external gate resistances is performed to address tradeoffs between switching loss and voltage overshoot during transients, as well as the thermal performance of the H-bridge building block. In addition, the design and characterization for the 20-kHz three-port transformer are also given. Comprehensive experimental studies are conducted on a full-power prototype to verify the proposed design. With a measured 99.1% peak efficiency, the proposed TAB converter can fulfill the requirements for solar-plus-storage applications.

This paper proposes a new dc solid-state circuit breaker (SSCB) based on silicon carbide (SiC) MOSFETs. There are two main contributions. First, a transient current commutation (TCC) is obtained in the main switch during current interruption. To achieve this, a compact and fast active injection circuit (AIC) is employed. TCC brings two main benefits: 1) it eliminates the effects of parasitic inductances in circuit connections and removes voltage oscillations on the gate of the main switch, which prevents spurious turn-on; 2) it eliminates the transient power shock on the switch during turn-off, which extends the life-time of SSCB and increases its reliability. Second, the voltage on the employed metal oxide varistor (MOV) is reduced to zero during the off-state. This extends the maximum allowable dc bus voltage on the SSCB and solves the MOV reliability issue in the SSCBs. The presented SSCB employs a time-sequence control and needs no real-time detections of the dc current, which simplify the design. LTspice simulations of 380 V/80 A and 600 V/80 A are presented, and the results are compared with MOV based SSCBs and MOV resistor-capacitor-diode (MOV-RCD) based SSCBs. Also, experiments of a 380 V/80 A prototype validate the effectiveness of the proposed SSCB in practice where the voltage on the SSCB is clamped to 721 V with a fixed response time of 9.4 μs.

This paper proposes a single-phase five-level current source inverter with an inductor cell based on the switching-cell structure. Compared to the conventional inverter, the proposed structure has no open-circuit problem; thus, its reliability is greatly enhanced. The overlap-time inserted in the driving signals can also be minimized to improve the output waveform quality. The proposed inverters operation is analyzed herein, and the design guideline of switching-cell capacitors is discussed. In addition, the switching-cell extension for the n-level topology is provided. A 1 kW prototype is built and tested to validate the effectiveness of the proposed structure.

Magnetic bearing is an important part of modern high-speed rotating machinery. The performance of power electronic converter highly determines the quality of magnetic bearing drive. In this paper, a fault-tolerant converter with series-winding topology is introduced. Compared with the traditional topology, the current stress of the phase leg is reduced while the utilization of DC voltage is guaranteed, and fault-tolerant operation can be realized in the case of open circuit fault of the switching device. This paper introduces the characteristics of the series-winding topology and the current control method. Open circuit fault detection methods and countermeasures are also analyzed. Experimental results show the effectiveness of the proposed topology. Fault-tolerant experiments under static suspension and rotation of the rotor demonstrate the performance of the topology. This kind of series-winding topology provides a new scheme with good performance and high reliability for the design of magnetic bearing controllers.

To construct the bipolar low-voltage dc distribution system, a dual-active-bridge (DAB) converter and a voltage balancer are needed. However, this conventional two-stage circuit is bulky and shows low efficiency. Besides, when a short circuit fault occurs at one of the bipolar dc poles, the conventional topology cannot balance the other normal dc pole voltage due to its single closed circuit, which eventually loses the high reliability of the bipolar system. To mitigate those issues, a modified three-port DAB converter is proposed. The proposed converter is an enhanced topology of the three-port DAB converter, which can balance the bipolar voltage levels without additional voltage balancers. In addition, each bipolar output has an independent closed circuit to balance the normal dc pole under the short circuit fault at one of the dc poles, thereby improving the system reliability. Moreover, constant duty-cycle modulation and magnetizing inductance design are proposed to obtain full-range ZVS of all switches. Since the proposed ZVS modulation uses a constant duty-cycle value, its control can be easily implemented in a digital signal processor. Finally, a 2-kW prototype is developed to validate the effectiveness of the proposed converter.

Hardware security modules have become quintessential as the digital systems continue evolving. Physical Unclonable Function (PUF) is a hardware security module that exploits the intrinsic variations in manufacturability of integrated circuits. Proposed Quasi-adiabatic Tristate PUF is a weak PUF which makes use of the inherent mismatches found in the threshold voltage values of PMOS transistors, which inadvertently is introduced due to manufacturing process variations of ICs. The proposed design demonstrates lower energy consumption than those configured using comparable quasi-adiabatic logic counterparts, under varying temperature and peak voltage conditions. The design is compared using SRAM PUF design based on adiabatic logic and it is shown that the proposed one is having better uniqueness and reliability at different environmental conditions. The proposed PUF can generate 128 CRPs which can be well suited for IoT and RFID applications that require less energy to operate.

Aiming at delivering power to sensitive loads with an enhanced level of reliability and quality, a compact multilevel battery-based electric spring (ES2) topology founded on the Packed E-Cell (PEC) inverter and an artificial neural network (ANN) based control strategy are introduced. This multilevel ES2 overcomes the limitations of the two-level ES2s and offers key features in the area of electric spring that have not been considered before. From the reliability point of view, the PEC-based ES2 (PEC-ES2) has the capability of instant nine to five-level operation under its bidirectional switch faulty condition. Regarding the power quality, in comparison with the half or full bridge ES2 topologies, PEC-ES2 has switches with halved voltage rating, lower harmonic content in its output current and voltage, considerably lower switching frequency, higher power applications, etc. The proposed intelligent ANN-based controller can also tune and stabilize both the grid voltage and responsive load setup power factor independently with improved dynamic performance. The operation and viability of the proposed ES2 configuration and controller, have been also tested extensively.

This paper proposes an adaptive maximum torque per ampere (MTPA) control algorithm for interior permanent magnet synchronous motor (IPMSM) drives. This algorithm is insensitive to motor parameters variation due to operating conditions that is important for systems, which prioritizes reliability and efficiency. The proposed algorithm is designed to improve conventional control schemes, where the output of the speed controller is the commanded quadrature current and direct current is calculated using an MTPA equation. However, in distinction from the conventional MTPA approach, the proposed algorithm does not use any motor parameters. It implements a seeking technique and continuously varies the stator current phase angle while trying to minimize the magnitude of the current. The main contribution of this paper is the development of the method to overcome the main disadvantage of seeking algorithms – the necessity of stable disturbances at the consecutive measurement intervals. This paper adopts the seeking technique for the operation with the load torque varying over mechanical revolution, which is typical for many applications such as compressors, washing machines, robots, mechanical manipulators, servodrives, etc., The feasibility of the proposed algorithm is proven with experimental results shown and described in the corresponding section.

The snappy reverse recovery (SRR) and failure of high-voltage non-punch-through (NPT)-PIN diodes under extreme working conditions is of great significance to the reliability evaluation of operating diodes in actual power electronic devices. In this paper, the analysis of the physical mechanism of the diode SRR and the restrictions of the traditional PT-PIN diode model are made. Then, the traditional model for soft recovery is improved in order to accurately describe the diode SRR characteristics. Simulations of key dynamic performances of the established model agree well with the testing results. Furthermore, a suppression method for diode SRR based on the optimal RC snubber circuit is proposed. A high-voltage NPT-PIN diode used in the DC-DC converter with different RC snubber circuits is simulated using the proposed diode snappy model and tested. The comparison results show good consistency between the simulated and measured voltage and current peaks and the diode SRR can be suppressed effectively. The model developed and the results are of much importance to the prediction of the safe operation area of the diode and to the reliability improvement of power electronic device.

Toughened glass insulators installed in overhead lines play a key role in maintaining the reliability and safety of power systems. The singular properties of toughened glass make this material particularly suitable for this application on account of its excellent dielectric properties, high mechanical strength and easiness of inspection. If the glass was damaged, it would shatter completely leaving the remaining part of the insulator, called stub, still providing mechanical connection and being easily detectable from the ground by a visual inspection. In this paper, the mechanical reliability of toughened glass insulators is investigated through the analyses of experimental data obtained from laboratory tests. First, the mechanical strength of the toughened glass in insulators and the relationship between its failing load and the geometry of the insulator are investigated by means of a novel analytical approach. Afterwards, the risk of mechanical failure of glass insulators and stubs, with the shell broken off, is analysed. The results show the mechanical reliability of glass insulators for different string configurations and for large and complex systems deployed in 220 kV and 400 kV transmission lines. Finally, the effect of the shattering rate on the reliability is studied under the most adverse conditions.

V/F control has been widely applied for induction motor drive systems because of its simplicity and reliability. However, sustained oscillation often occurs under light load, which leads to undesirable faults. This paper focuses on the causes of oscillation and proposes an oscillation suppression solution. Based on the small-signal model, an open-loop transfer function of induction motor is derived. The resonant peak, which is related to system parameters such as frequency and inertia, is obtained from the transfer function and leads to the unstable regions. The oscillation effects are discussed in detail. Then, the current feedback compensation method without any motor parameter is proposed to suppress the oscillation by decreasing the resonant peak. The feedback gain is optimized and designed. Finally, three current feedback paths are tested and compared in simulation and experiment. Simulation and experimental results have demonstra-ted the correctness of theoretical analysis and the effectiveness of the proposed methods. And the feedback path from current to voltage in d-axis is the best suppression solution for its wider gain range and higher stability in application.

Inductive power transfer (IPT) systems are appropriate for electric vehicles charging applications because of the advantages of safety and convenience. However, due to the considerable influence of pad misalignment, improving misalignment tolerance is important for IPT systems. Besides, constant current (CC) and constant voltage (CV) output characteristics are usually required for electric vehicles battery charging. Therefore, to fulfill both features, a hybrid IPT system implementing high misalignment tolerance with inherent CC-CV output is proposed for electric vehicles charging applications in this paper. Two coils connected reversely in series are applied in transmitter side while two coils respectively compensated by a capacitor and an inductor-capacitor-capacitor are applied in receiver side. Hence, without extra DC-DC converter or complicated control strategy and corresponding circuits, CC-CV output can be naturally achieved with high misalignment tolerance which obviously increase the system reliability. Besides, zero-voltage switching and zero phase angle condition can be easily achieved. A 1kW experimental prototype is built. The experimental results show that the fluctuations of the constant charging current and the constant charging voltage are less than 5% when the proposed system operates within the predetermined misalignment range.

In this article, the fault-tolerant control (FTC) strategy based on current redistribution is compared for three types of triple redundant 3×3-phase motor: surface-mounted permanent magnet synchronous motor (SPMSM), synchronous reluctance motor (SynRM), and permanent magnet assisted synchronous reluctance motor (PMa-SynRM), under a single-phase open-circuit fault. The output torque of SPMSM and SynRM is produced by permanent magnet (PM) torque and reluctance torque, respectively. Nevertheless, for PMa-SynRM, it is necessary to determine the distribution ratio of PM torque and reluctance torque in the proposed FTC strategy. By comparing the FTC performance of motors, the conclusions are as follows: (1) Torque ripple of the SPMSM can be completely suppressed. (2) Torque ripple minimization for the SynRM and PMa-SynRM can be realized. (3) Optimal solution obtained in SynRM can also be applied to the PMa-SynRM when the load is heavy. In addition, to reduce the complexity and improve the reliability of the control system, a mono-inverter driven triple paralleled control system is constructed in healthy and postfault operations. The comparison results of the FTC strategy for three types of motor are obtained by simulation. And the experimental results based on a 3×3-phase PMa-SynRM are accomplished to verify the feasibility of the theory.

The neutral grounding method is one of the crucial technologies used to ensure the safe and stable operation of distribution networks. With the development of power electronics-based devices, the application of highly controllable inverters to grounding systems has become a new research direction. In this review paper, based on the summary and analysis for the research status, a flexible grounding system is systematically classified according to its control strategy and structure. And then, the following core technologies are summarized: faulted line selection, current component detection, high-resistance ground identification, ground parameter measurement, neutral point voltage control, and fault location. Subsequently, deficiencies of flexible grounding systems are summarized from the following four perspectives: reliability, accuracy, speed, and stability. Finally, some discussions and recommendations for future development and research direction are presented. Especially, the reliability-enhanced hybrid grounding system that combines active inverters and low resistance for high-resistance ground faults is recommended. This paper provides a systematic literature review of the crucial technologies for flexible grounding systems and can be used as a technical reference for future research.

In this paper, a new AC line pilot protection scheme for AC/DC hybrid system based on composite-mode model is proposed. First, taking commutation failure into consideration, 1-mode and 2-mode equivalent instantaneous models of inverter in different operating conditions are built. Second, according to the equivalent instantaneous inductances of inverter in different combinations of operating conditions, the equivalent models of inverter are summarized into 4 operation states. Then, the 1-mode and 2-mode equivalent models are combined to establish the composite-mode model of AC/DC hybrid system. And then, Using multi-time section information, the instantaneous inductances of backside composite-mode model are calculated. Thus, protection criterion is constructed on the difference between composite-mode models of in-zone faults and that of out-of-zone faults for fault locating. Finally, RT-LAB simulation tests show that, the proposed method offers high sensitivity and reliability, unaffected by commutation failure.

In more electrical aircraft, most flight control wing surface actuators are either electro-hydrostatic or electro-mechanical, whether in manual or autopilot mode. Their reliability is essential for flight safety; failure of even one actuator can have catastrophic consequences. According to ARP4761 guidelines for the development and certification of critical aircraft systems, the probability of failure of flight-control actuator components must be less than 10-9 per hour of flight. In this paper, we compare the probability of failure per hour (PFH) of conventional two-level power converters and three-level NPC and ANPC converter topologies designed in our laboratory. In accordance with ARP procedures, PFH was calculated using an approach that includes qualitative analysis based on failure mode and effect analysis (FMEA) methodology as well as quantitative analysis based on truth tables. ANPC converter met all the requirements of the functional hazard assessment in all cases of defects. Finally, we discuss factors that determine the feasibility of implementing power converters in flight control systems.

As the load steadily rises in a distribution system (DS), electrical power generation is improved. Inserting Distributed Generation (DG) unit in a DS has benefits such as enhancement in voltage profile and decreased power losses. In combination with optimal size, these advantages can be obtained to inject DG in the optimal location. Reconfiguration is another framework for optimizing the voltage profile and reduction of energy loss. Furthermore, reconfiguring the distribution network and installing the DG would ultimately improve system efficiency, which is undoubtedly challenging task. In this paper, equilibrium optimizer (EO) is explored to find out how to reconfigure the distribution network and how best DG can be positioned. For the IEEE-33 bus. Reliability Analysis is also done. The suggested method is implemented in MATLAB R2020A platform software. Outcomes of the suggested Technique based on the EO is compared with the existing techniques. There is Substantial improvement in voltage profile in addition to the decline in loss of power and reliability indexes (EENS, SAIFI, and SAIDI) for different cases of System with DG placement and System.

Marine current energy attracts much attention as a source of inexhaustible green energy. However, marine current turbines operate in a very harsh underwater environment, making it difficult to operate and maintain mechanical sensors. Therefore, the application of a sensorless control strategy is fully justified to improve the reliability of system electrical energy production. In this paper, an active disturbance rejection sensorless control strategy based on compensation sliding mode observer is proposed for the marine current turbine system. The proposed control method consists of two parts. The first part is to design an active disturbance rejection controller for the marine current turbine that will improve the system's anti-interference abilities. The second part proposes a time-delay compensation sliding mode observer based on the Smith predictor to conduct real-time delay compensation of the system. The entire system is ensured to be globally stable through the Lyapunov approach analysis. The proposed control strategy is verified by simulation, which can not only effectively suppress the lumped disturbance and eliminate the system time-delay, but also improve the power extraction capability of the system.

FeFET is a promising technology for non-volatile on-chip memories. It is rapidly attracting an ever-increasing attention from industry. The advantage of FeFETs is full compatibility with the existing CMOS process beside their low power consumption. To enable ultra-dense memories, 1-FeFET AND arrays were proposed in which a memory cell is formed from a single FeFET. All access transistors, which are traditionally needed to operate memory cells, are removed. This imposes a new reliability challenge due to indirect write disturbances. In this work, we are the first to investigate the reliability of FeFET memories from device to system level. We develop a unified model capturing the impact of both indirect disturbances and direct writes on the reliability of FeFET cells. We then investigate different array sizes, write voltages, write methods under the effect of a wide range of workloads using CPU cache as an example of on-chip memory. We demonstrate that indirect write disturbances are the dominate effect degrading the reliability of FeFET memories. For most cells, it contributes over 90% to the overall induced degradation. This provides guidelines for researchers at both device and circuit levels to optimize the FeFET reliability further, while considering the hidden impact of workloads.

The cascaded H-bridge low-capacitance static com- pensator (LC-StatCom) uses relatively small capacitors subjected to large voltage oscillations. When a capacitor degrades, its capacitance differs from the nominal value, and this deteriorates the StatCom operation and safety. This is an important reason to monitor the capacitors condition in StatComs. This letter presents a detailed analysis of the capacitor voltage oscillations and their dependence on the capacitance values. The analysis allows monitoring the condition of the capacitors using a closed- loop approach that feedbacks the error in voltage oscillations. The proposed method is a hardware-free online solution for ca- pacitor condition monitoring (CCM) in LC-StatComs. The letter presents simulation and experimental results that corroborate the effectiveness of the proposed CCM loop.

Accurate measurement of electrical currents cannot be done when the core of current transformers (CTs) is saturated. One of the reasons that causes saturation of a CT is the activation of the auto-reclose function for the circuit breaker. When the circuit breaker is switched off, a residual flux will remain in the CT core, and when the circuit breaker is reconnected, this residual flux may cause saturation of the CT core. It is necessary to remove the residual flux in an auto-reclosing scheme. In the auto-reclosing scheme, due to the short time interval between each reclosing shot of the circuit breaker, only methods that have a high-speed operation should be used to mitigate the residual flux to prevent CT core saturation. This paper introduces a fast and complete demagnetization method based on Jiles-Atherton magnetic modeling to mitigate the residual flux in the CT core. The advantages of this method are high-speed performance, independent of the CT characteristics, high accuracy and high reliability against the secondary open circuit. To evaluate the efficacy of the proposed method, software simulations and laboratory experiments are performed on a 63kV, 300A/5A CT. The results are presented and analyzed.

With the increase of urban power grid scale, the requirement of power supply reliability has been improved, and the active intervention type arc extinguishing device (AIT-AED) has been paid more and more attention to. As one of the effective means of grounding fault arc extinguishing, the AIT-AED has a high demand on the operation reliability, but the operation experience of AIT-AED is insufficient. Hence, the pilot application of this device was carried out and its operation situations were investigated in this paper. It is found that the setting value, control logic, accessories quality and artificial operation are the main influencing factors of operation reliability and the corresponding improved measures were proposed, which could provide references for the operation and maintenance of AIT-AED.

The reliability of the insulation of commercially used high voltage insulated gate bipolar transistor (IGBT) subjected to untimely initiation of partial discharge (PD) at low pressures and high temperatures is investigated and discussed in this letter. To date, no research has addressed the vulnerability of the high voltage IGBTs to the PDs at harsh environmental conditions for aerospace applications. This letter aims to fill this gap and illustrate the PD characteristics initiated between the electronic components inside the silicone gel. To this end, five commercial 3.3kV IGBT modules and four 4.5kV IGBT modules were tested at AC voltage under low pressures (20kPa, 15kPa, and 10kPa) and high temperatures up to 120C. An efficient PD test method and an anti-series connection configuration are suggested which emulate a realistic operational scenario for IGBTs together with the one suggested by the current standard. Experimental results reveal the occurrence of inconsistent PDs initiating from possible dynamic PD source inside the gel at low pressures, and more intense and consistent PDs when the temperature increases. It is expected the findings highlight the importance of PD tests on IGBTs at the abovementioned operation conditions and provide a selection and modification guidelines of PD-free IGBTs for manufacturers and engineers in the aerospace industry.

Wide voltage gain range applications are challenging for dc/dc converters, the system efficiency would be degraded in order to satisfy the voltage gain requirement. LLC resonant converters have gained popularity owning to its high efficiency feature. However, wide voltage gain range applications also challenge the LLC converters from the following three aspects: 1) large switching frequency operating range is required to meet the voltage gain requirement, which degrades the converter electro-magnetic interference (EMI) performance and challenges the optimization of magnetic components; 2) small inductor ratio is required to boost the voltage gain, which increases the resonant tank root-mean-square (RMS) current and conduction loss; 3) control instability issues may occur at both maximum voltage gain and minimum voltage gain, which reduces the converter reliability. To address these issues, in this article, a novel LLC converter with topology morphing control is proposed for wide voltage gain range applications. Three operation modes, dual full-bridge (DFB), hybrid full-bridge and half-bridge (HFBHB), and dual half-bridge (DHB), can be achieved by adopting the topology morphing control, which can cover a wide voltage gain operation range. Operational principles, design considerations, and experimental validations of the proposed converter are presented.

In the work reported in this paper, the converter-level lifetime evaluation of power devices in a railway propulsion inverter is performed to assess and compare operating strategies of a railway vehicle in terms of reliability. Two groups of velocity profiles are considered for the lifetime evaluation, wherein all the velocity profiles have the same running distance and time. The first group consists of three operation velocity profiles with the same acceleration at starting and stopping, but with different cruising ranges. In the second group, three operation velocity profiles with different coasting times and acceleration values are considered. A strategy to improve the lifetimes of power devices in propulsion inverters is proposed for vehicles on a busy railway line.