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To address the most commonly seen single IGBT open-circuit fault problems in cascaded H-bridge (CHB) converter based STATCOM, a simple online fault diagnosis method and the corresponding ride-through operation approach are proposed. The method can quickly determine the exact location of the open-circuit IGBT through three steps, via analyzing the relationships between the dc bias in the three-phase output current of CHB converter, the transient dc rail voltage variations with respect to the averaged dc rail voltage, and the response of dc rail voltage and output current when the modulation approach of the faulty power module is adjusted. Afterwards, a fault ride-through approach is adopted to seamlessly transfer the modulation approach of faulty H-bridge module and it behaves as a half-bridge to provide a half of the rated output AC voltage. Meanwhile, the corresponding dc offset voltage form this faulty module is compensated by producing the same dc voltage in the healthy phase legs to avoid the dc bias in the three-phase output current. It has been demonstrated that the proposed fault diagnosis approach and the fault ride-through approach are effective in various adverse situations including grid voltage sudden disturbances and the load power sudden changes.

This paper proposes an enhanced time delay based current component identification method for single-phase systems to overcome the absence of filtering and poor grid frequency response of conventional method. The proposed technique integrates a delayed signal cancellation (DSC) with a time delay unit, to incorporate a dc offset rejection feature, while maintaining speedy and precise extraction of orthogonal current components. The frequency adaption is also developed through the incorporation of linear interpolation. The dynamic and steady-state performance of the proposed method is analysed and compared with two advanced second-order generalised integrator (SOGI) based methods, namely, modified SOGI and cascaded SOGI under different operating scenarios. The simulation and experimental results substantiate the advantage of zero steady-state error and lower settling time of the proposed solution while exhibiting comparable overshoot with advanced SOGI based methods.

This manuscript proposes a zero-current-prediction (ZCP) based digital control scheme to achieve the seamless dynamic transition of dual-active-bridge (DAB) converters. Compared with existing methods, only an extra variable between the master PWM and the sawtooth carrier is added. This extra variable is only determined by the voltage conversion ratio and the change of the existing phase shifts between master and slave legs. It accurately predicts the zero crossings of the inductor current and tunes it with the end of the carrier period. When the output power varies, the controller updates the digital registers at the beginning of the new carrier period, when the inductor current is zero. Thus, a seamless dynamic transition is achieved with zero dc bias current. This proposed digital control scheme is universally valid for the mainstream modulation methods of DAB converter. Moreover, it is adaptive to any load conditions, regardless of the zero-voltage-switching (ZVS) conditions and power flow directions. A hardware prototype is designed, tested, and compared with the conventional control method. The experimental results well validate the advantages of the proposed concept.

There is a clear trend in the aircraft industry to use more electrical systems in propulsion and electromechanical and electrohydraulic actuators to comply with environmental sustainability and to improve reliability and maintenance processes. The increase of electrical consumption requires an increase of the rated voltages to supply power to these so called More Electrical Aircraft (MEA). Unfortunately, this voltage rise, currently up to 540 Vdc, can lead to ionization processes within the electric wiring due to the lower air density at high altitudes. As a consequence, a degraded insulation can create extremely hazardous events in flight such as arcs between wires (serial) or between wires and fuselage (parallel). Serial arcs in DC bus circuits are specially dangerous for the aircraft operation, so its detection within fractions of seconds is required to ensure a reliable operation. However, during a sustained serial arc the rated current can be passing through air deceiving the protections and avoiding their tripping. In this work, it has been found that arcing introduces high frequency current pulses superimposed to the DC component that can be identified to detect the occurrence of an arc. The frequency components of these pulses depend on the line characteristics and can be detected with inductive sensors. This manuscript also designs and tests a light and inexpensive sensor for arc detection in aircraft applications.

Due to the motor parameter mismatches, the errors of current sampling circuit, converter nonlinearities and noise, DC bias and high order harmonics exist in flux model, which make the traditional flux observer estimation inaccurate. In this paper, an interior permanent magnet synchronous motors (IPMSM) sensorless drive method based on a five order flux observer is proposed to suppress DC bias and high order harmonics. The proposed five order flux observer can completely remove DC bias and has strong filtering ability for high order harmonics. Additionally, the parameters of the five order flux observer are set through s-domain analysis. Then, the discrete five order flux observer is obtained to better implementation in digital systems, and the discrete five order flux observer is easy to implement. The proposed five order flux observer is verified by experiments on a 2.0-kW IPMSM drive platform.

The fundamental current component at the secondary side of current transformer (CT) is often accompanied with decaying direct current (DC) component produced by the system and the CT. The Discrete Fourier transform (DFT) is known as a powerful tool in digital protection for estimation of the fundamental component in the presence of harmonics. The decaying DC component, unlike harmonics, is not limited to a distinct frequency but include a wide range of low frequencies affecting the DFT output by undesirable oscillations. This paper proposes a method based on two selective interval integration for accurate estimation and elimination of the decaying DC component from the fundamental component of fault current. The two data intervals are separated by half a cycle minus one interval. The proposed algorithm is first tested using data derived by mathematical formulation under different conditions such as sampling frequency, noise, and characteristics of the DC component. The algorithm is also tested by simulation study using PSCAD/EMTDC for different fault conditions in a typical transmission system. In order to test the algorithm performance for practical applications, a Mho distance relay is simulated in the Matlab/Simulink environment. All the test cases verify efficiency, accuracy and speed of the proposed algorithm.

In the situations where multiple motors operate at the same speed, this paper designs a dual-parallel induction motor (IM) system supplied by three-phase four-leg inverter (FLI) for cost reduction and fault tolerance of normal system. The dc offset and ac fluctuation of capacitor voltages exist in this system due to the motor phases connected to bus capacitors' mid-point. It seriously affects voltage utilization and stable operational range. A novel synchronous control scheme with the ability of ac voltage fluctuation minimization (AVFM) and dc voltage offset elimination (DVOE) is proposed. The unified model of dual IMs is used to design the speed regulator, and the model predictive flux control (MPFC) method is combined with space vector modulation (SVM) to realize torque and flux control of dual IMs. AVFM is realized by controlling the electrical angle difference of dual IMs as, which is first presented in this scheme. An angle regulator is proposed to control the electrical angle by adjusting stator flux amplitude. DVOE is realized by injecting a compensatory voltage vector, which is simplified in this scheme to avoid the voltage filter or additional coordinate transformation in conventional method. Experiment results verify the effectiveness of proposed scheme.

A concern with the isolation transformer in a dual active bridge (DAB) dc–dc converter is the dc bias in magnetization. This article proposes a fluxgate-based current sensor to measure the dc component mixed with a large, high-frequency ac current. Compared with a commercial Hall effect current sensor, the proposed sensor significantly reduces measurement error. This article presents the working principle and design considerations. A prototype is demonstrated for dc bias elimination control in a DAB converter.\ud

Rapid grid integration of inverter-interfaced distributed generators (DGs) and low-voltage ride-through capability of the smart inverter, as per IEEE 1547 standard, has made unintentional islanding detection (UID) cumbersome. Also, the feeder reconfiguration capability in meshed microgrids with multiple DGs has made the existing UID techniques ineffective. The methods have limitations in UID for small power mismatch conditions characterizing nondetection zone (NDZ). In hybrid methods for UID, a disturbance injection is continuous or for an extended period, which degrades the power quality (PQ) and creates stability issues. Hence, a decentralized closed-loop hybrid islanding detection method (HIDM) based on the indices extracted from the subcycle phaselet (passive) technique with limited-time (only for two cycles) $q$ -axis dc offset voltage injection (active) is proposed for UID of DGs. The proposed HIDM mitigates the NDZ due to the closed-loop scheme. Subcycle estimations from the phaselet technique result in quick UID and fault detection and classification process. Furthermore, the PQ issue is reduced due to the limited-time voltage injection (based only on the command from phaselet technique) in the proposed HIDM. Simulation results from the real-time digital simulator on a meshed microgrid and performance comparison with other existing methods prove the efficacy of the proposed HIDM.

A 6 Gb/s 9.8 pJ/b rotatable non-contact connector applicable to industrial robot arms is developed. The proposed non-contact connector enables a high-speed and highly reliable wireless data connection between three-dimensional (3-D) cameras and an edge computer in an autonomously controlled robot. A rotatable transmission line coupler (RTLC) is proposed to accommodate the rotational operation of the robot arm. Since the proposed doughnut-shaped RTLC has a constant overlapped area at any rotation angle, the RTLC has a constant coupling gain at all rotation angles. To remove inter-symbol interference (ISI) occurring at a specific rotation angle, a pulse-equalizing receiver is also developed. An interface bridge IC is proposed to transfer a wide range of interface signals from a slow-control signal such as the control area network (CAN) to a high-speed video interface signal. A signal protocol conversion technique applying on-off keying (OOK) modulation is also developed in order to transfer slow legacy interfaces used in the robot arms that include a dc component. Experiments with a test chip fabricated in a 40 nm CMOS process confirmed that bit error rate (BER) was lower than 10⁻¹² at any rotation angle in a communication distance of 3 mm. The proposed system improves energy efficiency by a factor of 3.7, area efficiency by a factor of 1.8.

This article proposes a dual-inverter pulsewidth modulation (PWM) scheme for dc-biased vernier reluctance machines (dc-biased-VRMs) with reduced switching frequency capable of zero-sequence current regulation. The dc-biased-VRM utilizes the additional dc bias current in armature winding to construct the rotor flux. To regulate the dc bias current, two sets of three-phase inverters with common dc bus are used to provide dc current flow path. In each switching cycle, the number of switching actions is doubled compared with the conventional three-phase inverter. There is still a certain optimization space for adjusting the dc bias current and reducing the switching loss. The proposed scheme reconfigures the zero voltage vector based on the discontinuous PWM (DPWM) scheme, it effectively reduces the switching actions, thus reducing the switching frequency and ensuring the low switching loss of the inverter. In addition, an inserted zero voltage vector regulation method is associated with the proposed DPWM scheme, and it assures the zero-sequence current regulation ability. Besides, by adopting complementary zero voltage vector distribution in odd and even sectors, the balanced voltage stress of upper and lower switching devices in each bridge arm is realized. The proposed dual-inverter PWM scheme does not require any additional devices, and it provides an effective solution to improve the efficiency of the dc-biased-VRM drive system. Finally, the effectiveness of the proposed scheme is verified experimentally.

In this study, impedance spectroscopy with direct current (DC) bias was used to analyze the electric property and oxygen vacancies of flash–sintered 3 mol% Y2O3 doped tetragonal zirconia polycrystalline (3Y–TZP) ceramics at anode, middle, cathode and no field vicinity, respectively. The electric property was obtained using modified–Debye circuit model and the oxygen vacancies concentration was calculated using double Schottky barrier model. Interestingly, a phenomenon of position–sensitive electric property and oxygen vacancies concentration was observed. It means after flashing the tested samples become ununiform electrically at anode, middle and cathode vicinity. The neutral oxygen vacancies generated at cathode vicinity are responsible for this unique phenomenon fundamentally. The finding here is useful to explore the mechanism of flash sintering and tune the electric property of ZrO2 ceramics electrolyte.

Unbalanced grid voltages, appearing at stator terminals of a doubly fed induction generator (DFIG) based wind energy conversion system (WECS) deteriorate its performance, by instigating unwanted oscillations and distortions in output grid power and rotor currents, respectively, as well as by introducing unbalanced currents in the stator and the grid. This paper aims to address these challenges using a coordinated control strategy based on an improved reduced order generalized integrator (IROGI) for positive and negative sequence estimation (PNSE). The IROGIPNSE further enhances the control performance, by eliminating the effects of any DC component or unbalance in sensed voltages, on grid synchronization. The coordinated control strategy uses hysteresis scheme for current control. The hysteresis based current control requires fewer rotational transformations, and eliminates the need for PI/PIR regulators and notch filters for inner current control loops. This renders the control, computationally efficient. Moreover, the presented system is equipped to exhibit wind power levelling functionality, through a battery energy storage (BES). An approach, employing the region-specific wind speed frequency distribution graph, is utilized to constitute the power levelling operation modes. The effectiveness of the control scheme is demonstrated through test results on a prototype developed in the laboratory.

In this paper, a novel Multi-loop Moving Coil Large Output Volume Linear Compressors (M-MC-L-LC, Max 381.3cc) is proposed. A Co-core Bilateral Reverse Coil(CBRC) and a new Halbach permanent magnet ring array structure are proposed for the first time and applied to the development of prototype. The M-MC-L-LC electromagnetic force calculation equation is derived, the moving offset characteristics under different pressure ratios are studied, and a mathematical model that can reflect the moving offset law is established. Introduction the DC offset control method to solve the moving offset problem. Development the M-MC-L-LC prototype and construction a dynamic test rig for compressors. Experimental results show that increasing DC voltage countervails the moving offset and significantly increases the discharge pressure. The theoretical error of moving offset is within 8% and the mechanical efficiency of prototype is approximately 11.4% higher than that of the conventional compressor. The results of study have theoretical and practical implications for other linear compression moving offset analysis and accurate regulation of refrigeration capacity.

This article proposes a new partitioned stator hybrid excited (PS-HE) machine with dc-biased sinusoidal current. On the inner stator, the consequent pole permanent magnets (PMs) are employed as the PM excitation. On the outer stator, a set of integrated dual three-phase winding is adopted to produce the wound and armature fields at the same time by injecting the sinusoidal current with dc bias. So, the flexible flux regulation can be realized by controlling the dc bias component. The rotor composed of segmented iron cores is sandwiched between two stators. By employing the air-gap field modulation theory, the air-gap magnetic field harmonics are analyzed to explain the operating and flux regulation principle. Furthermore, a design optimization and the electromagnetic performances of the proposed machine are investigated by finite element analysis. When compared with the existing series and parallel PS-HE machines, the proposed machine can avoid the disadvantage of low torque density of PARALLEL HE machine, and it can solve the problem of the poor flux regulation ability of series HE machine as well, which is mainly contributed by the reasonable space allocation of PMs and field winding excitations. Finally, a prototype is built and tested to verify the theoretical analyses.

In this paper, a resilient ESOGI-FLL-WIF (Enhanced Second Order Generalized Integrator with Frequency Locked Loop and Inner Loop Filter) control algorithm is implemented to enhance the power quality and to regulate the voltage/frequency of a microgrid. This control has a simple structure, fast convergence, and excellent dynamic and steady-state response. The ESOGI-FLL-WIF control algorithm is used for assessing the fundamental constituent from harmonics and DC bias infected current. ESOGI-FLL-WIF control strategy tracks the frequency and tunes to the frequency fluctuations in transient situations. To have a fair comparison, the performance of ESOGI-FLL-WIF control algorithm is compared with already existing controls. This three-phase four-wire islanded system consists of a solar PV (Photovoltaic) array and pico-hydro turbine-driven SyRG (Synchronous Reluctance Generator). As an alternative to conventional generators, SyRG is used because its economical (no permanent magnets in the rotor) and has high efficiency (no electrical losses in the rotor). The four-leg converter compensates neutral current and controls the reactive power injection under unbalance load condition. Whereas, for active power management, BES (Battery Energy Storage) is incorporated in the system. A prototype of the system is developed and tested under different situations of load unbalancing and solar insolation change to confirm the effectiveness and viability of the control strategy.

Mathematically secure cryptographic algorithms leak meaningful side-channel information in the form of correlated power and electromagnetic (EM) signals, leading to physical side-channel analysis (SCA) attacks. Circuit-level countermeasures against power/EM SCA include a current equalizer, IVR, non-linear LDOs, enhancing protection up to 10M traces, and current-domain signature attenuation (CDSA), and randomized NL-LDO cascaded with arithmetic countermeasures achieved protection up to >1B. This work embraces the concept of analog CDSA but makes it easily scalable over technology nodes with digital-friendly current sources, digital control loop, and digital bleed path to increase the MTD from 10M to 250M (25x improvement, using a single digital countermeasure). Ring oscillator (RO) used as the bleed path to bypass encryption-dependent leakage acts as local negative feedback (LNFB). Besides, based on RO oscillation frequency, AES node voltage can be tuned at startup, PVT, or frequency variation. Thus, RO acts as integrated LNFB and global feedback for the digital signature attenuation circuit (DSAC). Another circuit technique, namely, the time-varying transfer function (TVTF), removes the requirement of dc bias in the current-domain equalizer (best switch capacitor-based countermeasure till date) to make it digital and utilizes switch cap-based circuit for time-domain obfuscation to achieve enhanced security. This work, namely, Syn-STELLAR: SYNthesis-friendly Signature aTtenuation Embedded crypto with Low-Level metAl Routing, combines both DSAC and TVTF techniques to achieve an MTD>1.25B for both EM and power SCA, which is 25% higher than the existing state of the art. The 65-nm CMOS test chip contains unprotected and both the protected (DSAC and DSAC-TVTF) parallel AES-256 implementation. This implementation is the first synthesis-friendly countermeasure, which converges two analog-type strong protections (signature attenuation and switched cap current equalizer) in a digital-friendly solution and achieves >1.25B MTD with power and area overheads comparable to previous circuit-level countermeasures.

This letter proposes a method for fast and accurate estimation of three-phase grid frequency under unbalanced and distorted conditions. It includes a recursive discrete Fourier transform-based frequency adaptive bandpass filter for α – β signals generated by the Clarke transform and a two-point-based algorithm for frequency estimation. The proposed method is relatively simple to implement and can eliminate adverse influences created by the imbalances, dc offset and both odd and even harmonics. It can also provide fast estimation with a response time of almost one fundamental cycle under grid disturbances. Moreover, it can present improved performance when compared to several methods reported in the technical literature. The advantages of the proposed method are confirmed by both simulated and real-time experimental results.

Introduces the definition of electric power quality, its causes and classification: transients, short-duration voltage variations, interruptions, sags, swells, long-duration voltage variations, sustained interruption, under- and over-voltage, voltage imbalance, waveform distortion, DC offset, harmonics, inter-harmonics, non-integer harmonics, triplen harmonics, sub-harmonics, time and space harmonics, characteristic and uncharacteristic harmonics, positive-negative- and zero-sequence harmonics, notching, electric noise, voltage fluctuation and flicker, and power-frequency variations. The formulations and measures used for power quality; impacts of poor power quality on power system and end-use devices; most important IEEE and IEC guidelines/recommendations/standards referring to power quality; modelling, mitigation and elimination techniques for power quality phenomena are presented. 9 application examples with solutions and 15 application-oriented problems are listed.

A mmWave antenna with beam steering capability and a single feed is introduced. 5G systems with a single feed or a single RF chain can provide inexpensive and energy efficient solutions in applications such as the Internet of Things. The antenna consists of a half-wavelength dipole with a balun structure printed on both sides of a substrate and a parasitic pixel surface in front of the dipole. The antenna achieves beam-steering in the azimuth plane by controlling two diodes that alter the connections in the parasitic surface. Phase shifters or multiple feeds are not required to control the beam angle and therefore the antenna can support single-RF 5G operation. By introducing proper objective functions, the connections of the parasitic surface and locations of the two diodes can be optimized with the genetic algorithm. The ground plane and DC bias lines are printed on the backside of the substrate. Simulation and experimental results show that the proposed single port pattern reconfigurable antenna can operate in 26-30 GHz mmWave bands. The realized gain of 7.96 dBi and two radiation patterns with peak gains directed to 75 and 110 are verified by experiment demonstrating the feasibility of the proposed design concept.

Big offset drift with the change of the temperature was found for the magnetic sensor with (Fe0.06Co0.94)72.5Si2.5B15 amorphous wire. To reduce the temperature coefficient of the magnetic sensor, a bias reversal technology was developed. Instead of the static dc bias current, a square wave current, which was switched between +IB and -IB, was used to bias the magnetic sensor with amorphous wire. The switching frequency of the square wave was about 1 kHz. Using the bias reversal technology, the temperature coefficient of the magnetic sensor was significantly reduced. This magnetic sensor with bias reversal technology will be suitable for wide temperature operation and longtime magnetic field measurement.

Tip-enhanced Raman spectroscopy (TERS) has gained great attentions for sensitive characterization and super-resolution chemical imaging of various materials. The performance of TERS is mainly affected by the probe geometry, such as the diameter of the tip apex, surface roughness, etc. In this regard, the fabrication of a sharp apex from metal wire is the one of the most important factor for TERS experiments. Conventionally, the electrochemical etching is commonly used technique for fabricating those metallic probes. To avoid the surface defects, the pulsed bias was commonly employed in the electrochemical etching process. However, it would make the fabrication system to be complex and sophisticated. Here, we report an simple automated electrochemical etching systems using DC bias for the efficient fabrication of TERS probes. With our optimized condition for DC electrochemical etching, gold probes with a clean surface and a radius of curvature below 200 nm can be obtained with yield of 85%. The fabricated metallic probe is used to detect the brilliant cresyl blue (BCB) molecules on the gold film, and it is confirmed that the enhancement factor is about 3,400.

Earth current generated by the operation of urban rail transit can enter into the neutral point of grounding transformer, which will result in the deterioration of transformer operation performance and cause electrical safety problems. In this article, the neutral current for 220 kV transformers has been measured in the real power system, the characteristics of dc and harmonic current are analyzed, and a novel suppression method for the dc and harmonic current simultaneously combining an active converter with a dc blocking capacitor is proposed, which solves not only the traditional dc bias problem but also the intrusion of the harmonic current from urban rail transit. The active converter is designed to compensate harmonic voltage to suppress harmonic current, and the capacitor provides blocking for the dc current. The protection scheme in case of the high fault current of the neutral point is presented. The improved control method is designed to control the neutral current and adjust the fundamental impedance for the requirements of relay protection. The effectiveness of the proposed method is verified by the digital simulations and the laboratory experiments based on the field working conditions, and the results demonstrate the satisfying performances.

The brushless doubly-fed machine (BDFM) has two stator windings with different pole numbers, supplied with different frequencies. Therefore, the distribution of magnetic fields in stator and rotor iron is complex. In addition, the stator flux density distribution is non-sinusoidal and has a DC offset at the natural speed. This makes the use of conventional hysteresis models utilised for sinusoidal fields impractical for the BDFM. In this paper a new hysteresis model is proposed for the BDFM stator iron based on the scalar Preisach model. The rotational characteristics of the magnetic fields in the BDFM are also considered and their effects in generating iron losses are assessed. 2-D time-stepping finite element (FE) models are developed for a prototype D160 BDFM to estimate iron losses and are validated by experiments.

It has been proposed that the main battery voltage of electric vehicles should be increased to increase the driving distance and decrease the charging time. Thus, a low-voltage dc/dc converter (LDC) with high and wide input voltage range is required for electronic loads. This article proposes a two-mode LDC and the entire input range is divided into two low and high input voltage ranges. The converter has two operating modes corresponding to these input voltage ranges. In the low input voltage range, it operates as a three-switch double-ended active clamp forward converter. In the high input voltage range, it operates as an asymmetric half-bridge converter. Changing the operating mode according to the input voltage, the proposed converter can have low-voltage stresses on the switches and a low dc offset current of the transformer resulting in high efficiency for the entire input voltage range. In order to confirm the validity of the proposed converter, a 600 W prototype is implemented and experimented.

Electric utilities are looking for novel methods to increase the transmission capacity of existing transmission lines. The conversion of conventional AC towers to hybrid AC/DC lines allows for significantly more power and reduces the need for new rights of way. Still, due to the fixed geometry, there will be coupling effects between the AC and DC systems. Corona effects, such as audible noise, which are crucial for public acceptance, will change consequentially. An outdoor test setup is used to investigate the corona audible noise and partial discharges of parallel AC and DC bundles. The effect of a DC bias on the AC corona as well as an AC ripple on DC corona are studied for varying surface gradients and weather conditions. The AC and DC audible noise clearly increased for most cases of a DC bias or AC ripple, respectively. The relative increase was found higher if the conductor was only slightly above corona as it happens in dry conditions with light pollution. Still, the highest level of AC audible noise was observed during wet weather and for DC during dry conditions.

The mission profile emulator (MPE) proves to be an effective and cost-efficient approach to validate the design and reliability of the submodule (SM) in a modular multilevel converter (MMC). This article established the detailed models for the capacitor voltages of SM in the MMC system. The factors that can determine the dc component of capacitor voltages in SM of MMC are analytically solved. The difference between the capacitor voltage of SM in a complete MMC system and that of SM in MPE is discovered, explained, and verified. In order to improve the emulating accuracy for the capacitor voltage in SMs of the MPE, a novel voltage control method, which is more adaptive to the operating conditions of MMC, is proposed. The simulation models and experimental setup are built to verify the validity of the proposed methods.

A model for the peak frequency in the imaginary part of ${Y}_{{22}}$ (Im( ${Y}_{{22}}{))}$ based on the bias for gallium nitride (GaN) high electron mobility transistors (HEMTs) is investigated while considering both self-heating (SH) and Poole–Frenkel (PF) (electric field) effects. The peak frequency of Im( ${Y}_{{22}}{)}$ corresponds to the emission time constant of the trap in the GaN layer. In this study, ${Y}_{{22}}$ for GaN HEMTs were measured for low frequencies at which the traps respond by significantly changing not only drain voltage ( ${V}_{\text {DS}}{)}$ but also gate voltage ( ${V}_{\text {GS}}{)}$ . Because the vector network analyzer used ac with an extremely small power of −20 dBm as a signal for sensing the trap, the trap properties can be measured at a fixed dc bias. In this model, the SH effect is introduced to replace the ambient temperature in the conventional Arrhenius equation by simulating the lattice temperature. The PF effect introduces the apparent activation energy, based on the simulated electric field at the channel under the gate field edge of the drain side. The electric field is related to the voltage between the gate and drain. This model is consistent with the experimental data for a wide range of transistor biases, i.e., from the ${V}_{\text {GS}}$ near the pinch-off voltage to the ON-state condition, and the ${V}_{\text {DS}}$ in the saturation region at ambient temperatures between 23 °C and 160 °C. Furthermore, using this model, we confirmed that the PF effect dominates at a low ${V}_{\text {GS}}$ of −2 V near the pinch-off.

In order to accurately analyze the effect of combined magnetic shielding on stray load losses of converter transformer, a three-dimensional (3D) finite-element analysis (FEA) model is established. The total losses can be gotten by summing the simulated losses of each harmonic. The effectiveness of the presented simulation method is verified by comparing the simulated and tested stray load losses of the converter transformer in the case of rated operation without lobe-type magnetic shielding structure. Afterwards, the installation position of lobe-type magnetic shielding is optimized by considering its effect on stray load losses. Finally, the stray load losses under different DC bias currents are simulated and analyzed.

Accurate simulation of the hysteresis loop is challeng-ing, especially using manufacturer data. Traditional parameter extraction methods (e.g., using optimization algorithm and solving transcendental equation) can extract the static Jiles-Atherton (JA) hysteresis model parameters under an arbitrary condition, but it requires fitting parameters because the model parameters vary with flux density. To reduce the dependence on measurement data, this paper proposes a simple but effective parameter extraction method. Firstly, an identification procedure of minor loop is presented using only static B - P loss curves by investigating the influence of model parameters on hysteresis loop, where the average root-mean-square error of the hysteresis loop is decreased by 4. To estimate the dynamic loss coefficients under DC bias, a calculation method based on the Statistical Theory of Losses (STL) is established by investigating the law of influence of DC bias on hysteresis loss and dynamic loss. The effectiveness of the proposed method is verified.

In order to obtain DC bias characteristics of controlled shunt reactors (CSRs) of thyristor controlled transformer (TCT) type in the thyristor abnormal operation state, a DC bias characteristics analysis model for the CSR based on Jiles-Atherton(J-A) theory is proposed. A single-phase prototype for the CSR is developed and tested. The coil currents and magnetic flux densities of the iron core are calculated in time domain and frequency domain based on the model. The experimental results agree well with the calculated results. The DC bias characteristics of the CSR are analyzed.

Underwater wireless optical communication (UWOC) has attracted considerable attention as a technology with high data rates and low time delays. However, the light scattering in water spreads beam pulse temporally, thereby resulting in time-varying underwater optical channels with inter-symbol interference (ISI) especially when the data rate is very high. To overcome this problem, in this letter, a multi-carrier autoencoder (AE) is proposed to incorporate the direct current optical orthogonal frequency-division multiplexing (DCO-OFDM) scheme into the AE network. In this way, proper constellation mapping and demapping schemes can be learned to cooperate with the DCO-OFDM modulation and the DC bias can be adaptively adjusted, efficiently dealing with the time-varying diffuse channel. The simulation results indicate that the proposed multi-carrier AE can achieve superior performance compared with other state-of-the-art techniques.

The magnetic property measurementfor grain oriented (GO) silicon steel sheet under non-sinusoidal excitations (DC bias and harmonic) were conducted based on the experimental platform. Based on the Preisach model, the static hysteresis and loss properties were accurately simulated. Furthermore, an improved loss model was proposed by adjusting the statistical parameter of abnormal loss, which depends on the characteristic quantities of DC bias or harmonic excitations. The simulated dynamic hysteresis loops and iron losses under different non-sinusoidal conditions were compared with the measured ones, and thus the accuracy and generality of the improved model proposed in this paper were verified. In addition, the influences of the harmonic and DC-biasing quantities upon the total losses is investigated.

A hybrid stator pole memory machine (HSP-MM) with direct current (DC) bias magnetization is developed in this paper. By introducing the concept of zero-sequence current magnetization, the DC magnetizing winding used in the traditional DC magnetizing MM is eliminated, which improves the utilization rate of internal machine space and the overall torque density. The re/demagnetization of low coercion force (LCF) permanent magnet by DC bias pulse enables HSP-MM to obtain the flexibility of flux regulation. The topology and adjustment flux principle of HSP-MM are depicted and addressed. The electromagnetic characteristics of the HSP-MM at different magnetization levels are analyzed and investigated, which demonstrates that the proposed machine has the good ability of flux regulation.

A multiphase continuous-wave (MPCW) Doppler radar with a multiarc circle fitting (MACF) algorithm is proposed for improving the accuracy of small periodic displacement measurements. In the proposed radar, local oscillator (LO) signals with different phases are incident to multiple I/Q mixers, to simultaneously generate multiarcs for small periodic motions. The multiarcs obtained from the synchronized data are used in the circle fitting method to provide dc offset compensation, for accurate phase demodulation. The proposed MACF algorithm, based on the Levenberg–Marquardt method, can more precisely compensate for the dc offset by combining multiarcs generated from the proposed radar. A 5.8-GHz MPCW Doppler radar module with four-phased LO signals is implemented as a demonstration. The small periodic displacement of a metal plate on a single-axis linear stage is measured using the proposed radar module and algorithm. Compared with conventional CW Doppler radar using a single arc, measurement results using the proposed radar show that the root-mean-square error (RMSE) can be effectively decreased in the periodic motion from 1 to 2 mm, at distances from 30 to 60 cm. The RMSE is reduced by more than 33% for a peak-to-peak displacement of 1 mm at a distance of 60 cm.

It is recognized that in very-high-frequency capacitively coupled plasma (VHF CCP) reactors, the standing wave effects can be enhanced by the presence of nonlinear higher harmonics self-excited by the plasma series resonance (PSR). In this work, we investigated the influence of the dc bias on the excitation of the nonlinear standing waves in a parallel-plate capacitively coupled dc/VHF (60 MHz) hybrid discharge sustained in argon, with both the dc source and the VHF source applied to the top electrode. A hairpin probe was employed to determine the axial/radial distribution of the electron density, while a high-frequency B-dot probe was used to measure the radial distributions of the harmonic magnetic field and the harmonic current density. With no dc bias applied, the nonlinear standing wave excitation was observed to be predominant; the high-order harmonic current density exhibited a main peak at the electrode center and one or more minor peaks between the electrode center and the edge, leading to a center-high electron density profile. With the addition of the dc source, the harmonic excitations and the corresponding nonlinear standing wave effect tend to be suppressed with the increase of dc bias, resulting in improved plasma uniformities. Underlying mechanisms of the suppression effect of the dc bias on the nonlinear standing wave excitation were analyzed.

Transient dc bias current will appear in dual-active-bridge (DAB) dc–dc converter when power changes, resulting in transformer core saturation. Traditionally, a transitional period with extra calculation is added in the transient process to keep the voltage-second balance and eliminate the dc bias current for the DAB converter. In this article, the modulation process rather than the phase-shift control is concerned, and the transient dc bias current can be reduced or even eliminated by staggering the load time of the primary bridge and secondary bridge compare values. The modulation scheme with this modification does not need any transitional period or extra calculation, and the time delay in the closed-loop control is constant and smaller than the previous schemes. Besides, as only the load time is modified, the modulation scheme can be implemented in all the phase-shift control methods and the whole operation range. The experimental results verify the theoretical analysis and show the practical feasibility of the modified modulation schemes.

The development of technology also affects human health, including body posture due to poor human position when using gadgets, both smartphones, and laptops. This study is design a tool that can measure the elevation of a person's neck angle equipped with electromyography, to help health workers, medical rehabilitation doctors to diagnose and provide treatment to patients with a bent head posture or forward head posture. In this research, an electromyography module is designed which consists of a series of instruments, a pre-amplifier circuit, a high pass filter, a low pass filter, and a dc offset regulator to be converted to digital so that it can be displayed on a laptop. In this study, the tapped muscle was the upper trapezius muscle using disposable electrodes. Meanwhile, to measure the angular elevation, the MPU 6050 sensor is used to measure the movement of the head forward. The frequency of the electromyography signal is 20-500 Hz. For software or display readings from this tool is Delphy. Meanwhile, the microcontroller used for ADC communication is Arduino Uno. From the research, it was found that the neck angle elevation gauge has a 0,597% error rate, for conditioning conducted on respondents, all respondents experienced a decrease in amplitude on the same frequency spectrum in the last ten minutes. Meanwhile, a drastic decrease occurred at the neck angle of 60°. Thus, it can be concluded that the forward position of the head affects the frequency spectrum of the neck muscles.

OBJECT. When developing DC test voltage sources to assess the insulation quality of high-voltage equipment, the task is to measure the leakage current flowing through the test object. METHODS. When solving the problem the authors proposed a technical solution for measuring the current flowing through the test when testing insulation with rectified voltage, which uses a precision resistor, an isolating amplifier, a 2-channel operational amplifier with a unipolar power supply, zero voltage drift, and an ADC of a microcontroller.RESULTS. The article in the course of the study of the stand of the circuit for measuring the leakage current flowing through the tested object when testing the insulation with rectified voltage, an experimental industrial sample was created, which makes it possible to measure the leakage current value in the range from 10 μA to 1000 μA. The use of the developed circuit for measuring the current flowing through the test object when testing the insulation with rectified voltage makes it possible to calculate the DC component of the voltage signal from the alternating signal and in real time, and, therefore, to quickly monitor the current in high-voltage circuits for continuous monitoring. CONCLUSION. So the introduction of this sample will make it possible, on its basis, to create a number of digital measuring microammeters that make it possible to measure the leak-age current in high-voltage test installations for testing the insulation of objects from 15 nF to 200 nF, in the leakage current measurement range from 10 μA to 1000 μA. The results obtained can be used in high voltage technology to study circuits for measuring the leakage current flowing through the test object when testing insulation with rectified voltage.

The presence of dc offsets results in fundamental frequency oscillations in the frequency estimation and it is a challenging problem in single-phase grids. In this article, a four consecutive samples (4CSs) based method is proposed to estimate grid frequency with strong dc offset rejection capability. In details, a 4CS model is established based on the relationship among the fundamental grid voltage, dc offsets, and their consecutive sample signals. Different from the traditional 3CS model, the proposed 4CS model can reject the negative effects of dc offsets completely. Based on the obtained model, a frequency estimation is proposed and stability analysis is provided according to the adaptive control theory. Unlike the traditional 3CSs relying on prefilters, the proposed method is filter-free and it still has strong suppression capability against dc offsets. The theoretical sound and experimental results indicate that the proposed method achieves accurate frequency estimation with good dc offset rejection capability.

In this article, a four-phase current-fed push–pull dual active bridge converter is proposed for applications requiring high power and a wide-voltage range. In addition to the conventional advantages of a small filter inductor, a small clamp capacitor, and low current stress in the primary switches due to the effect of four-phase interleaving, the proposed converter has a low total rms current of switches when operating at a wide-voltage range compared with the existing two- and three-phase converters. Also, the proposed converter was shown to be capable of the complete ZVS turn -on of all switches under a wide duty cycle range of 0.25–0.75 in both power-flow directions when small auxiliary inductors were added. A balanced four-phase transformer structure is proposed not only to cancel the dc-flux offset caused by the dc component of the primary winding current but also to reduce the core volume, footprint, and height of the transformer compared with the separated-core transformer. The experimental results from a 15-kW prototype are provided to validate the proposed concepts. The converter achieved a peak efficiency of 98% and maintained high efficiency when operated at a wide-voltage range.

The control of a single-phase grid-connected energy storage system (ESS) requires a very fast and accurate estimation of grid voltage frequency and phase angle. A phase-locked loop (PLL) based synchronization algorithm usually extracts this information. The operation and control of the entire system are directly affected by the performance of PLL. In this article, a novel advanced single-phase PLL (ASϕPLL) technique with reduced complexity is proposed for the fast and accurate extraction of grid information in an ESS under distorted and abnormal grid conditions, including harmonics, interharmonics, dc offset, and grid faults. The proposed method provides a faster dynamic response, lower frequency overshoot, and accurate estimation under off-nominal grid frequencies with reduced computational complexity in comparison with the existing method. The advanced performance of the proposed ASϕPLL is verified through the simulation and experimental results.

This letter presents a planar endfire Yagi-Uda antenna phased array fed by a corporate network. The phase of each radiating element is controlled by a loaded line phase shifter based on liquid crystal technology. The phase shifters are meandered to minimize the dimension of the array and are measured to provide maximum differential phase shift of 400 ${^\circ }$ with a figure-of-merit of ${54}{{^\circ }\rm {dB}^{-1}}$ at 28.4 GHz. Each phase shifter is tuned individually by applying bias voltage through high impedance chromium line together with dc blocks. The array is designed for full-range scanning in E -plane with $>\!{360}{^\circ }$ phase shifters. Measurements show that it can be steered from −40 ${^\circ }$ to 40 ${^\circ }$ by applying dc bias in the range of 0–5 V and from −50 ${^\circ }$ to 60 ${^\circ }$ with degraded patterns. The maximum gain of the phased array antennas is measured to be 4.5 dBi. The array beam is able to be fast steered within approximately 1 s.

During the dynamic operation of the dc metro system, excessive neutral direct current (NDC) of the grounding transformer appears in the ac power system, which has not been clarified until now. Seriously, the high-level NDC has led the transformer under dc bias, which affects the lifespan and safety of transformers and systems. To analyze the NDC of the grounding transformer with the dynamic metro train, the synchronous monitor schemes of the traction current and rail potential of the dc metro system and the NDC of the nearby transformer are proposed. The relationship between the metro rail potential and NDC is analyzed and presented. Based on the monitor data analysis, the negative correlations are found in the directions and magnitudes of the RSP and the NDC. To explain the reasons for the relationship, the numerical simulation is proposed based on the structure of the monitored metro line and substation. Moreover, the universality of the relationship is verified through the coupled simulated model. Results show that the NDC is commonly flowing into the transformer as the rail potential is positive. Moreover, the NDC may exceed the allowable threshold of transformers in acceleration and brake conditions of the dynamic train.

This letter reports a digital signal processing based frequency estimation technique that relies on the storage of fundamental three-phase grid voltage samples. Unlike phase-locked loop algorithms, the proposed algorithm does not require the phase error information when estimating the grid frequency. Moreover, only four consecutive samples of the fundamental orthogonal components are required in order to estimate the deviation in the grid frequency. The proposed scheme is facilitated with an inherent nonadaptive comb filtering behavior in order to reject the dc offset and harmonics while attaining a good immunity to voltage sag and the fundamental negative sequence component. Additionally, the off-nominal harmonic rejection capability of the proposed frequency estimator is enhanced by using a postfiltering method. The experimental validations reported in this study demonstrate that the proposed frequency estimator is suitable for three-phase grid applications.

Single-phase ac to three-phase ac converters are needed in numerous applications, including motor drives used for residential applications. These converters, however, suffer from an inherent problem of mismatch between instantaneous input and output powers. Specifically, the instantaneous input power has a dc component along with an alternating component with double-line frequency, while the three-phase instantaneous output power is only dc. Conventional single-phase ac to three-phase ac converters use large electrolytic capacitors to handle this mismatch of power. However, these electrolytic capacitors may have high failure rates, which contribute to reduced lifetime of the converters. Moreover, these capacitors can be bulky and heavy. This article introduces a new single-phase ac to three-phase ac converter that uses a small film capacitor instead of large electrolytic capacitors. Despite using a small film capacitor, the double-line frequency harmonic does not appear at the input or output currents/voltages. The principles of the operation of the proposed topology are presented in this article, and its performance is evaluated through both simulations and experiments.