Using Jensen's inequality and integration by parts, we derive some tight upper bounds on the Gaussian Q-function. The tightness of the bounds obtained by Jensen's inequality can be improved by increasing the number of exponential terms, and one of them is invertible. We obtain a piece-wise upper bound and show its application in the analysis of the symbol error probability of various modulation schemes in different channel models.

The commutation failure is the most prevalent fault in line-commutated converter based HVDC systems, which may result in transient overvoltage on the sending-side system. Overvoltage level evaluation has become a crucial task for power industries to assess the tripping risk of large-scale wind turbines and implement effective stability control measures. In this paper, decision tree (DT) model is adopted to extract the mapping relationship between transient overvoltage and massive electrical quantities of power grids. The common DT algorithm is transformed by modifying the error weight assignment, which reflects the error tolerances for different actual overvoltage regions. To compensate for potential inaccuracies in the data-driven method, a derivation of the mathematical relationship between the reactive power consumed by the rectifier and AC voltage is presented, along with an analytical expression for the peak value of transient overvoltage. On this basis, an overvoltage analysis method integrating the model-driven and data-driven techniques is proposed, and the improved DT algorithm is ap-plied to fast error correction, enhancing the interpretability of regression prediction results. Case studies were performed in the actual Northwest China local region hybrid AC/DC power grid with transient overvoltage problems, and the simulation results verified the effectiveness of the proposed method.

Adequacy is a crucial consideration in the planning and operation dispatching of the power system, especially in the power system with high penetration of renewable energy sources. Considering the multi-time scale characteristics of renewable energy power and the response characteristics of flexible regulation resources, a multi-time scale adequacy evaluation method based on empirical mode decomposition is proposed. In this method, a net load curve is decomposed into multiple component curves at a multi-time scale by the empirical mode decomposition (EMD) algorithm. As a result, the adequacy demand of the system at each time scale is obtained by waveform recognition. Moreover, the available adequacy resources of the system at different time scales are obtained according to the regulation models of flexible regulation resources. By analyzing the adequacy demand and available adequacy resources of the system at the same time scale, the adequacy evaluation indices at each time scale can be calculated and weighted to form the comprehensive indices. At last, taking a practical power system as a case, the adequacy evaluation indices at each time scale with different capacities of renewable energy sources and energy storage systems are compared and analyzed. Simulation results indicate the validity of the method.

A broadband heterogeneous circularly polarized (CP) dipole antenna with a backed cavity is presented in this letter. The proposed antenna consists of a pair of rotational symmetric short-circuited heterogeneous branches and a Γ-shaped feed structure. Each branch is designed to be axe-shaped so that the antenna can achieve a broad 3dB axial ratio (AR) bandwidth. The coupled feeding method assures the antenna is wideband, and the shorting-to-the-ground technique miniaturizes the lateral dimensions of the antenna. The profile of the proposed antenna is around 0.16λL (λL denotes the wavelength of the lower bound frequency). The introduction of a back cavity effectively enhances the boresight gain and improves the isolation level if the antenna is used to form an array. Finally, the design is prototyped, and the measurement results agree well with the simulation. The fractal -10 dB S11 bandwidth and 3dB AR bandwidths are 54.3% (2.74-4.78 GHz) and 45.9% (3.15-5.03 GHz), respectively. The antenna’s efficiency exceeds 91.5% over the target frequency band.

Solar storms impact electrical power grids by causing DC neutral point currents in transformers. These currents lead to half-cycle saturation as well as other related and unwanted effects in the grid. To reduce the effect of these currents on the grid, DC-blocking devices can be installed or changes in the grid topology can be made. However, these counter measures often have unwanted side effects or cannot be applied to the grid due to operational restrictions. In this work, a novel mitigation approach, based on the distribution of currents on more transformers, is presented. The number and location of grounded transformer neutral points is optimized, taking grid related constraints such as the minimal number of transformer connections into account. It is shown that the algorithm can effectively reduce the stress on transformers without any additional assets and thus increase system security.

The social economy is growing rapidly, and the power grid load demand is increasing. To maintain the stability of the power grid, it is crucial to achieve accurate and rapid power system stability assessment. In the actual operation of the power network, data loss is an unavoidable situation. However, most of the data-driven models currently used assume that the input data is complete, which has obvious limitations in real-world applications. This paper suggests an IVS-GAN model to assess power system stability using incomplete PMU measurement data with random loss. The proposed method combines the super-resolution perception technology based on Generative Adversarial Network (GAN) with a time-series signal classification model. The generator adopts a one-dimensional U-Net network and uses convolutional layers to complete and recover missing data. The discriminator adopts a new GRU-Attention architecture proposed in this paper to better extract voltage temporal variation features on key buses. The result of this paper is that the stability evaluation method outperforms other algorithms in high voltage data loss rates on the New England 10-machine 39-bus system.

Radar forward-looking imaging is gaining significance due to its convenience in various applications like battlefield reconnaissance, target surveillance and precision guidance. Although synthetic aperture radar (SAR) techniques are commonly used to achieve high azimuth resolution, they suffer from limitations in forward-looking area due to the poor Doppler resolution and the “left-right” ambiguity problem. In recent years, generative adversarial networks (GANs), a common deep learning approach that produces excellent results in image motion blur removal, has been extensively used. This letter proposes building an end-to-end forward-looking imaging network using GAN to produce high-resolution images, which increases the efficiency and quality of imaging. Compared to conventional forward-looking imaging methods such as the deconvolution-based methods, this algorithm eliminates the design and iterative processes of the observation matrix. Simulated and real radar data verified that this approach offers robust recovery and better performance.

The multi-scale flexibility coordination of multiple storages is a key technology to enhance the diversified regulation ability of the power system.This paper first considered the interaction mechanism of multi-type storage peak regulation time sequences based on the Euclidian distance, Dynamic time warping distance, and storage correlation distance. A matching index was proposed to consider the temporal correlation, overall distribution characteristics, and dynamic characteristics of the net load and energy storage. The multitype storage coordination mode, including battery storage, pumped storage, and electric vehicles, was formulated, and a collaborative optimal scheduling system architecture of source-grid-load-storage (SGLS) was constructed. To attain a low-carbon economy, a collaborative optimal scheduling model of SGLS considering the dynamic time-series complementarity of multiple energy storage systems was constructed. The Nash equilibrium theory was used to achieve friendly interaction among the source, grid, load, and storage. Then, an improved transfer reinforcement learning algorithm for SGLS was proposed, which used reinforcement learning and transfer learning algorithms combined with K-means clustering and dual-structure experience pool technology. The test results of actual regional power grid data indicated that the proposed strategy can effectively reduce the economic and carbon treatment costs of the system and improve the absorption capacity of renewable energy.

We propose criteria for recess etching to fabricate T-gate used in InGaAs HEMTs. By patterning additional rectangular pads on the source and drain metals in the e-beam lithography step, it is possible to measure the drain-to-source resistance (Rds) and current (Ids). the ratio (Γ) of before and after etching for each Rds and Ids can be used as criteria to determine the point in time to stop etching. By performing recess etching with Γ= 1.97 for Rds and Γ= 0.38 for Ids on an epiwafer having cap doping concentration of 2= 1019 cm−3 and channel indium content of 0.7, we have fabricated InGaAs mHEMT device showing gm,max= 1603 mS/mm and ft= 290 GHz at Lg= 124 nm. The criteria presented can be applied to InGaAs HEMTs with various epitaxial structures.

This letter proposes an instantaneous frequency tracking method to extend the dynamic range for heterodyne fiber optic hydrophones (FOHs). They are used directly to compensate for large signal amplitudes. The working principle is discussed, and simulations are conducted. The simulations achieve at least 20 dB dynamic range improvement.

This letter proposes a cross-domain WiFi-based gesture recognition system (WiCross) based on a dynamically weighted multi-label generative adversarial network. Most existing WiFi-based gesture recognition systems are user, orientation, and environment sensitive, which limits the application of WiFi sensing. Compared with the influence of users and environments on WiFi sensing systems, the influence of orientation on WiFi sensing systems is more difficult to remove. To alleviate the confusion caused by the orientation more effectively, we arrange the transmitting and receiving antennas according to the characteristics of the Fresnel region. We propose to dynamically weight different links according to users’ orientations and use a multi-label generative adversarial network to obtain domain-independent features. More importantly, WiCross can use domain-independent features to classify some unknown gestures without modifying any code or data set. Lightweight computing resource consumption allows WiCross to respond in real-time. The experimental results show that WiCross can achieve an in-domain recognition accuracy of 93.54% and a cross-domain recognition accuracy of 93.11%

Today’s healthcare system relies on MRI (medical resonance imaging) for early diagnosis and treatment planning. For open MRI systems to achieve resolutions of about a hundred microns, a high voltage is required, as well as a specialized power supply. NP0 (Negative-Positive-Zero) ceramic is selected for the fabrication of adjustable capacitors. Specifically, it stands for which is a classification based on the temperature coefficient of capacitance (TCC) of the ceramic material used in the capacitor. NP0 capacitors have a TCC of 0 ±30 ppm/°C, which means that their capacitance value does not change significantly with temperature and frequency. They are known for their stability and low losses, making them ideal for applications that require high accuracy and reliability, such as timing circuits for RF applications. In this paper, MgTiO-CaTiO ceramic is used to make an adjustable capacitor with desired properties for MRI systems. To enhance the dielectric properties of MgTiO3 ceramics,CaTiO3 was added in varying concentrations. After pressing and sintering, the resulting samples were tested using a vector network analyzer in the frequency range of 10 MHz to 130 MHz.The adjustable capacitor fabricated using high co-fired NP0 ceramic may have been used for MRI applications such as tuning circuits and matching networks, where precise capacitance values and low loss are critical[1]. MRI systems with resonance frequencies of 128 MHz require trimmers with ceramic cores.

The voltage endurance coefficient n of cross-linked polyethylene (XLPE) insulation is an important indicator for the analysis of insulation failure mechanism. Accurately obtaining the value of n can provide technical support for the reliability evaluation of cable operation. The constant stress method and the step stress method are used to obtain the values of n, but the test parameters can influence the accuracy of the obtained n values. Two methods for selecting test parameters are proposed. The equivalence between the two methods is established, providing theoretical support for the accurate evaluation of the n value of solid insulation materials by using the step stress method. The accuracy of the evaluation results is verified by analyzing the test data. The test results show that the nstep=13.04 evaluated by the step stress test with the proposed parameter selection method is consistent with the test result of constant stress nconstant=12.83.

A novel 3-bit frequency-reconfigurable antenna (FRA) with miniaturized dimensions is realized with a meander line. The frequency reconfiguration of the antenna is achieved by introducing N RF p-i-n diodes into the meander line. The related parts of the meander line with different lengths are bypassed or included into the antenna by switching on or off the diodes, resulting in 2N switchable size lengths of the antenna and equally spaced operating frequencies. A 3-bit meander-line reconfigurable antenna (N=3) is designed, and the simulated and measured results agree well. The antenna provides 23=8 independent switchable states, with the operating frequencies covering a wide switchable frequency range from 1.04 GHz to 1.51 GHz and the working bandwidths varying from 80 MHz to 150 MHz. The number of working states is optimally large, considering the number of switches used. Besides, this work has an acceptable peak gain of 1.59 dBi regarding the miniaturized total dimension of 0.17 λ × 0.07 λ (λ is the wavelength of the lowest working frequency), which is more compact than many published FRAs.

A power line carrier (PLC) communication characteristics-based method is proposed for single-phase-to-ground fault location in neutral isolated medium voltage (MV) meshed distribution networks in this paper. The carrier signals with a time-varying frequency and constant amplitude are processed by a set of PLC transmitters and receivers, whose placement is optimized by regarding the power network as an undirected graph. Two signal encoding and decoding algorithms for the PLC terminals are proposed to avoid using expensive timing systems between the terminals. The fault location technique is implemented by comparing the cosine similarity of amplitude attenuation (AA) and phase offset (PO) between the fault and a library. The node corresponding to the maximum cosine similarity of the characteristics between the present fault and the library is selected as the location of the current fault. Only one set of low-cost PLC communication terminals and the widely available power lines are needed in the fault location system, making this approach highly practical. Numerical simulations using MATLAB/Simulink have been performed to verify the technique’s feasibility. The results show that the method can accurately locate faults in neutral isolated MV meshed distribution networks. Besides, the presented approach achieves high accuracy in estimating transition resistance values.

This paper proposes a novel primary frequency regulation (PFR) scheme for Multi infeed HVDC (MIDC) system. First, a dynamic model for frequency response (FR) in MIDC system is carried out to involve LCC-HVDCs in frequency regulation. Then, a disturbance observer (DO) is proposed to estimate both the power imbalance and the full order states of the system. By combining a Kalman filter (KF), this DO gets an accurate estimation quickly with local frequency measurement. On the basis of the estimated disturbance and state variables, feedforward control schemes can be concluded to fully utilize the fast adjustability of LCC-HVDCs. In this paper, an model predictive control (MPC) based scheme is designed to coordinate LCC-HVDCs under constraints of HVDC capacity and frequency boundaries. As a result, the optimal power-sharing property of LCC-HVDCs is achieved to enhance the PFR dynamic performance of the AC main system. Further, the stability of the proposed method is analyzed using Lyapunov method. Finally, numerical simulations are concluded to verify the effectiveness and the merits of the proposed method, by comparing it to typical droop controls.

This paper presents an energy-efficient digital-to-analog converter (DAC) switching method with low common-mode variations for high resolution successive approximation register (SAR) analog-to-digital converters (ADCs), while enabling to implement resolutions such as 14-bit as compared to the typical 10-bit. The proposed switching method enables high resolution by having a nearly constant common-mode voltage and employing input-swapping to use the reference voltage (Vref) only in the sampling phase. This method eliminates the need for the third reference voltage during the entire DAC switching steps, which reduces the required number of switches even compared to the state-of-the-art methods that use low number of switches. The use of lower number of switches not only lowers the DAC control logic complexity, but also results in a faster operation, lower power, and smaller area. When compared to conventional 10-bit SAR ADCs, the proposed switching method in a 10-bit implementation reduces the average switching energy and area by 93.7 % and 75 %, respectively, while offering high resolution implementation options such as 14 bits.

An explosion accident in an enclosed cable trench caused by the discharge of 10 kV three-phase cable joints is discussed. Combined with the disassembly analysis, the fault recording data analysis, and the validation of experiment, the evolution of the cable joint fault is deduced and discussed. The results show that the trigger of the cable joint fault is the creepage discharge at the XLPE-SiR insulation interface. This results in the partial breakdown and the grounding failure of three-phase cable joints. Under the long-term floating potential and current thermal effect, the insulations are gradually ablated and decomposed into a large amount of combustible gas. Finally, the accumulated combustible gas is ignited by the arc caused by a three-phase short circuit at the moment of the reclosing operation. The analytical method and conclusions proposed in this paper can provide suggestions and guidance for the analysis of similar fault accidents in the future.