Frequency Stability Research Articles

Introduction of Bi(Zn2/3Sb1/3)O3 to BaTiO3-based ceramics for high energy storage performance

In this study, (1-x)BaTiO3-xBi(Zn2/3Sb1/3)O3 ((1-x)BT-xBZS) ceramics were designed and tested. With the introduction of BZS, it was found that the grain size of the ceramics was increased, which increased the breakdown field strength (Eb) of the ceramics and further improved the energy storage density. The 0.84BT-0.16BZS ceramic achieved both high recoverable energy density (Wrec = 2.32 J/cm3) and energy efficiency (η = 89.7 %) at 620 kV/cm. In addition, excellent temperature stability (20-160 °C) and frequency stability (1–200 Hz) of recoverable energy density have been obtained under 300 kV/cm. A high power density of 28.93 MW/cm3 and transient discharge time (t0.9 = 1.07 μs) were achieved for 0.84BT-0.16BZS ceramic under 200 kV/cm.

High Energy Storage Performance in Pb1−xLax(Hf0.45Sn0.55)0.995O3 Antiferroelectric Ceramics

Energy storage efficiency (η) and large recoverable energy density (Wre) are necessary for antiferroelectric materials in order to develop antiferroelectric-based dielectric capacitors with exceptional energy storage capacity. In the present paper, the effect of doping La3+ on the energy storage capacity of Pb1−xLax(Hf0.45Sn0.55)0.995O3 antiferroelectric ceramics was studied. Adjusting the content of La and changing the phase structure of PLHS from antiferroelectric to relaxor ferroelectric gradually, which narrowed its hysteresis loop, yielded a high energy storage efficiency of 81.9% and the maximum breakdown field strength of 200 kV/cm when x = 2 mol%. In addition, the recoverable energy density and energy storage efficiency both showed excellent temperature stability and frequency stability in the temperature range of 10–110 °C and the frequency range of 10–100 Hz, suggesting that Pb0.98La0.02(Hf0.45Sn0.55)0.995O3 are favorable materials candidates for the preparation of pulsed-power capacitors that can be used in a wide range of conditions.

Advanced AI and renewable energy sources for unified rotor angle stability control

Maintaining a reliable electricity supply amidst the integration of diverse energy sources necessitates optimizing the stability of power systems. This paper introduces a groundbreaking method to enhance the efficiency and resilience of power grids. The increasing dependence on renewable energy sources poses significant challenges to traditional power networks, thereby demanding innovative solutions to uphold their stability and security. To address these challenges, we propose an architecture that seamlessly unifies dynamic, transient, and static rotor angle stability (RAS) controls into a single, streamlined system. Utilizing reinforcement learning and real-time decision-making, we present Lazy Deep Q Networks (LDQNs) as a novel approach to RAS control. LDQNs provide real-time rotor angle instructions to RAS devices, enabling precise and efficient stability management. The incorporation of mass-distributed energy storage further augments the system's responsiveness and flexibility, mitigating fluctuations and promoting overall stability. This study advances the application of AI methods to RAS control, building on prior research in frequency and voltage stability frameworks. The proposed system outperforms conventional RAS control methods by integrating LDQNs with mass-distributed energy storage, offering superior performance and adaptability. Case studies validate the effectiveness of the unified RAS framework, demonstrating its advantages over traditional approaches across various power system configurations.

Frequency stabilization via interference between transmitted and reflected lights from a reference cavity

Frequency stabilization via interference between transmitted and reflected lights from a reference cavity

Coarse frequency offset estimation and compensation based on short-time spectrum analysis in FSO communication system

Due to the high-speed movement of low-orbit satellites, the Doppler frequency offset in 1550-nm wavelength satellite-to-ground coherent laser communication is as high as ±4.5 GHz, which greatly increases the difficulty of carrier frequency acquisition. Low complexity, short capture time, and stable coarse frequency offset estimation and compensation algorithms are technical bottlenecks that must be addressed. In this work, a coarse frequency offset estimation and compensation algorithm based on short-time spectrum analysis is proposed. In the proof-of-principle system, the feasibility of the coarse frequency offset capture is verified based on a 2.5-GBaud data rate PM-QPSK modulation FPGA-based coherent receiver. The results show that the frequency offsets capture range is extended to ±4.5 GHz, covering the Doppler frequency offset range. Moreover, the standard deviation of the residual frequency offset after coarse frequency offset compensation is less than 140 MHz, which is smaller than the accurate frequency offset compensation range of 312.5 MHz.

АНАЛІЗ НАЛАШТУВАННЯ ПРИСТРОЇВ АВТОМАТИЧНОГО ЧАСТОТНОГО РОЗВАНТАЖЕННЯ З УРАХУВАННЯМ ЄВРОПЕЙСЬКИХ ВИМОГ

The paper deals with the structure of under-frequency load shedding (UFLS) relays in the interconnected power system (IPS) of Ukraine. The equivalent power system model to study the UFLS operation is developed, and UFLS configuration scenarios considering the requirements of ENTSO-E, are configured. The frequency stability for different scenarios of UFLS settings considering planned and emergency active power imbalances are studied. The plots illustrating the frequency change in the power system under these conditions are presented. References 4, table 1, figures 5.

The Coordination Control Strategy for Improving Systems Frequency Stability Based on HVDC Quota Power Support

This paper aims to improve the recovery characteristics of the receiving grid during DC blocking failures through DC emergency power support, revealing the mechanism of improving the power angle stability of the receiving grid through timely DC power increase and decrease. Based on the transmission pattern of “north-to-south power transmission” in a certain provincial power grid, the actual maximum long-term overload capacity of multiple DC lines is calculated, considering multiple constraints such as the strength of the receiving grid, the stability limit of AC evacuation channels, and DC overload capacity. A multi-DC emergency power support strategy after DC blocking is developed, avoiding the risk of AC transmission channel overload caused by power flow transfer, reducing the impact of large-capacity DC blocking and inappropriate DC power increases on the receiving grid, and achieving coordination between AC and DC systems. The effectiveness of the proposed strategy is verified through simulation.

Dynamic optimisation of virtual synchronous generator to enhance stability of power system

AbstractVirtual synchronous generators (VSGs) are essential for the high penetration of renewable energy sources. VSGs have virtual rotating inertia, a damping effect, and synchronising power such as actual SGs. Such features of VSGs offer a promising structure to improve the stability of power systems. VSGs are required to suppress power and system frequency oscillations. In addition, VSGs must operate within a current limit since they are vulnerable to the overcurrent, unlike actual SGs. The authors propose a novel dynamic and optimal VSG to enhance the frequency stability in power systems while guaranteeing the current limit. The proposed approach determines an optimal tuple of inertia and damping of VSG online and guarantees the current limit with the use of a circuit model. The effectiveness of the proposed method is demonstrated via experiments, comparing it with the conventional methods.

Readout circuit for a ZnO bulk-acoustic-wave X-ray dose rate detector

Bulk Acoustic Wave (BAW) resonators based on piezoelectric semiconductors are radio frequency devices that can convert X-ray dose rate into resonant frequency offset, which exhibit strong anti-interference capabilities and low power consumption and are suitable for wireless sensing systems. In this study, we designed a readout circuit for a ZnO BAW X-ray dose rate detector. (0001)-oriented ZnO single crystals were used to fabricate the high-quality BAW X-ray detector. Under dark field and X-ray irradiation conditions, the resonant frequency offset of the detector was recorded via the readout circuit. The readout circuit consists of an oscillator circuit based on a Pierce oscillator circuit structure, a frequency mixing circuit, and an STM32 microcontroller. This design offers higher frequency stability and lower phase noise. In practical applications, it can replace the expensive and bulky vector network analyzer for detecting and storing the resonant frequency of BAW resonators with the advantages of fast readout speed and portability.

Enhancing Energy Storage Performance of 0.85Bi0.5Na0.5TiO3-0.15LaFeO3 Lead-Free Ferroelectric Ceramics via Buried Sintering.

Bismuth sodium titanate (Bi0.5Na0.5TiO3, BNT) ceramics are expected to replace traditional lead-based materials because of their excellent ferroelectric and piezoelectric characteristics, and they are widely used in the industrial, military, and medical fields. However, BNT ceramics have a low breakdown field strength, which leads to unsatisfactory energy storage performance. In this work, 0.85Bi0.5Na0.5TiO3-0.15LaFeO3 ceramics are prepared by the traditional high-temperature solid-phase reaction method, and their energy storage performance is greatly enhanced by improving the process of buried sintering. The results show that the buried sintering method can inhibit the formation of oxygen vacancy, reduce the volatilization of Bi2O3, and greatly improve the breakdown field strength of the ceramics so that the energy storage performance can be significantly enhanced. The breakdown field strength increases from 210 kV/cm to 310 kV/cm, and the energy storage density increases from 1.759 J/cm3 to 4.923 J/cm3. In addition, the energy storage density and energy storage efficiency of these ceramics have good frequency stability and temperature stability. In this study, the excellent energy storage performance of the ceramics prepared by the buried sintering method provides an effective idea for the design of lead-free ferroelectric ceramics with high energy storage performance and greatly expands its application field.

A Redundant Secondary Control Scheme to Resist FDI Attacks in AC Microgrids

Hierarchical control of AC microgrids, despite providing stable voltage, frequency, and optimal power distribution, is susceptible to false data injection (FDI) attacks on its secondary control. Electric power systems in countries such as the United States and Venezuela have suffered cyberattacks. This paper proposes a redundant secondary control method to resist FDI attacks. This method uses distributed generators (DGs) online as redundant units on standby, generating dynamic corrections to the attacked DGs, thus eliminating the attack impact. It effectively addresses the numerical tampering and addition brought by FDI to the frequency and voltage setting values of the secondary control, ensuring the microgrid can still output stable frequency and voltage. The principle of this control method is direct and practical; it doesn't require complex controllers and can respond quickly to FDI attacks. Then, focusing on a microgrid system containing six DGs, the setting values of the microgrid system are tampered by multiple values in different time periods, the simulation results confirm that the proposed method can effectively resist FDI attacks under various scenarios. Finally, FPGA-in-the-loop experiments further verify the effectiveness of the proposed method.

Development and Validation of a Mathematical Model for Pyroelectric Temperature Measurement Sensors for Application in Mobile Robotic Systems

A pyroelectric temperature sensor for measuring human body temperature with increased accuracy and speed for application in mobile robotic systems has been developed. This pyroelectric temperature sensor for measuring human body temperature is intended for use in various educational institutions. Its usage will allow for identifying sick or potentially ill people and providing them with preliminary advice and avoid infecting other people. This is particularly important considering the seasonality of dangerous infectious diseases and the emergence of new ones (e.g., COVID-19). It is also advisable to use this pyroelectric sensor in hospitals, where temperature measurement is very crucial for monitoring the course of various diseases. The proposed pyroelectric temperature sensor is based on a nonlinear oscillatory system, which provides high sensitivity and allows for solving the problem of increasing the accuracy of measuring the human body temperature in a non-contact way. Measurement error is ±0.1% in the operating range (32–43) °C, measurement time—1 s, and the frequency instability is 3·10−4.

Experimental Investigation of a Distributed Architecture for EV Chargers Performing Frequency Control

The demand for electric vehicle supply equipment (EVSE) is increasing because of the rapid shift toward electric transport. Introducing EVSE on a large scale into the power grid can increase power demand volatility, negatively affecting frequency stability. A viable solution to this challenge is the development of smart charging technologies capable of performing frequency regulation. This paper presents an experimental proof of concept for a new frequency regulation method for EVSE utilizing a distributed control architecture. The architecture dynamically adjusts the contribution of electric vehicles (EVs) to frequency regulation response based on the charging urgency assigned by the EV users. The method is demonstrated with two Renault ZOEs responding to frequency fluctuation with a combined power range of 6 kW in the frequency range of 50.1 to 49.9 Hz. The results confirm consistent power sharing and effective frequency regulation, with the system controlling the engagement of the EVs in frequency regulation based on priority. The delay and accuracy analyses reveal a fast and accurate response, with the cross-correlation indicating an 8.48 s delay and an average undershoot of 0.17 kW. In the conclusions, the paper discusses prospective improvements and outlines future research directions for integrating EVs as service providers.

Ultra-low frequency discharge instability of a barium tungsten hollow cathode at lower self-sustaining margin

Development of low-orbiting constellations stimulated the demand for low-power Hall thrusters, as well as their accompanying low-current hollow cathodes. In this paper, such cathodes were tested on quite low currents to search their self-sustaining limit, and were found to exhibit an ultra-low frequency instability at lower current limit. The instability would grow fast when the cathode current was below 0.3A, and oscillate on 0.1Hz to a few Hz with a visibly blinking plume. At the same time, the emitter temperature was fluctuating with a 15 °C peak-to-peak amplitude. The instability was confirmed to originate from the cathode interior, as a result of depleted plasma heating. Then the thermionic cathode had to rely mainly on neutral gas to heat the emitter. Because thermionic emission was in exponential relation with emitter temperature, the temperature fluctuation was then amplified to cause larger fluctuation in total current as well as in total discharge power, which led to deeper fluctuation in temperature. Regarding the heating of both neutral gas and emitter, an instability model showed that multiple unnoticed factors could determine the onset of instability, including the thermal inertia of neutral gas and emitter, the heat transfer from discharging plasma to neutral gas, the heat loss of cathode and the response time of power supply. As a result of this instability, the plume ion energy was elevated from <50eV to 30∼120eV due to the fluctuating density on cathode exit and fluctuating discharge voltage. It was estimated that the increased ion energy could accelerate the keeper erosion by 4∼22 times.

Enhancing Load Frequency Control of Interconnected Power System Using Hybrid PSO-AHA Optimizer

The integration of nonconventional energy sources such as solar, wind, and fuel cells into electrical power networks introduces significant challenges in maintaining frequency stability and consistent tie-line power flows. These fluctuations can adversely affect the quality and reliability of power supplied to consumers. This paper addresses this issue by proposing a Proportional–Integral–Derivative (PID) controller optimized through a hybrid Particle Swarm Optimization–Artificial Hummingbird Algorithm (PSO-AHA) approach. The PID controller is tuned using the Integral Time Absolute Error (ITAE) as a fitness function to enhance control performance. The PSO-AHA-PID controller’s effectiveness is evaluated in two networks: a two-area thermal tie-line interconnected power system (IPS) and a one-area multi-source power network incorporating thermal, solar, wind, and fuel cell sources. Comparative analyses under various operational conditions, including parameter variations and load changes, demonstrate the superior performance of the PSO-AHA-PID controller over the conventional PSO-PID controller. Statistical results indicate that in the one-area multi-source network, the PSO-AHA-PID controller achieves a 76.6% reduction in overshoot, an 88.9% reduction in undershoot, and a 97.5% reduction in settling time compared to the PSO-PID controller. In the dual-area system, the PSO-AHA-PID controller reduces the overshoot by 75.2%, reduces the undershoot by 85.7%, and improves the fall time by 71.6%. These improvements provide a robust and reliable solution for enhancing the stability of interconnected power systems in the presence of diverse and variable energy sources.

Ultra‐Stable Phonon Laser Through Closed‐Loop Feedback Control for Optomechanical Sensing

AbstractThe resonant amplification of the optical and mechanical components in cavity optomechanical systems enhances the performance of sensing applications, which rely on precise frequency control and narrowed mechanical linewidth. This study proposes a direct closed‐loop feedback technique for a narrow linewidth phonon laser based on optomechanical self‐oscillation. By continuously pumping a mechanical resonator with a laser, a phonon laser is achieved with an oscillation frequency of 17.58 MHz, exhibiting a narrow linewidth of just 0.44 mHz and an effective mechanical Q of 4 × 1010, while preserving the linear frequency response. The oscillator phase is fed back to the pump laser, yielding a mechanical frequency stability of 7.2 × 10−11 and providing a real‐time output of direct current voltage corresponding to the oscillator frequency changes. The system's real‐time sensing capability is tested using fiber probes and polystyrene particles, demonstrating a performance approach to the theoretical resolution limit. This work opens new avenues for real‐time precision measurement technology and can be extended to different optomechanical systems.

Ratchet loading and multi-ensemble operation in an optical lattice clock

We demonstrate programmable control over the spatial distribution of ultra-cold atoms confined in an optical lattice. The control is facilitated through a combination of spatial manipulation of the magneto-optical trap and atomic population shelving to a metastable state. We first employ the technique to load an extended (5 mm) atomic sample with uniform density in an optical lattice clock (OLC), reducing atomic interactions and realizing remarkable frequency homogeneity across the atomic cloud. We also prepare multiple spatially separated atomic ensembles, and realize multi-ensemble clock operation within the standard one-dimensional (1D) OLC architecture. Leveraging this technique, we prepare two oppositely spin-polarized ensembles that are independently addressable, offering a platform for implementing spectroscopic protocols for enhanced tracking of local oscillator phase. Finally, we demonstrate a relative fractional frequency instability at one second of 2.4(1)×10−17 between two ensembles, useful for characterization of intra-lattice differential systematics.

Development of Xanthoangelol-Derived Compounds with Membrane-Disrupting Effects against Gram-Positive Bacteria.

Infections caused by multidrug-resistant pathogens have emerged as a serious threat to public health. To develop new antibacterial agents to combat such drug-resistant bacteria, a class of novel amphiphilic xanthoangelol-derived compounds were designed and synthesized by mimicking the structure and function of antimicrobial peptides (AMPs). Among them, compound 9h displayed excellent antimicrobial activity against the Gram-positive strains tested (MICs = 0.5-2 μg/mL), comparable to vancomycin, and with low hemolytic toxicity and good membrane selectivity. Additionally, compound 9h demonstrated rapid bactericidal effects, low resistance frequency, low cytotoxicity, and good plasma stability. Mechanistic studies further revealed that compound 9h had good membrane-targeting ability and was able to destroy the integrity of bacterial cell membranes, causing an increase in intracellular ROS and the leakage of DNA and proteins, thus accelerating bacterial death. These results make 9h a promising antimicrobial candidate to combat bacterial infection.

Optimization of Fuzzy Control Parameters for Wind Farms and Battery Energy Storage Systems Based on an Enhanced Artificial Bee Colony Algorithm under Multi-Source Sensor Data.

With the rapid development of sensors and other devices, precise control for the generation of new energy, especially in the context of highly stochastic wind power generation, has been strongly supported. However, large-scale wind farm grid connection can cause the power system to enter a low inertia state, leading to frequency instability. Battery energy storage systems (BESSs) have the advantages of a fast response speed and high flexibility, and can be applied to wind farm systems to improve the frequency fluctuation problem in the process of grid connection. To address the frequency fluctuation problem caused by the parameter error of the fuzzy membership function in the fuzzy control of a doubly fed induction generator (DFIG) and a BESS, this paper proposes an improved Artificial Bee Colony (ABC) algorithm based on multi-source sensor data for optimizing the fuzzy controller to improve the frequency control ability of BESSs and DFIGs. A Gaussian wandering mechanism was introduced to improve the ABC algorithm and enhance the convergence speed of the algorithm, and the improved ABC algorithm was optimized for the selection of fuzzy control affiliation function parameters to improve the frequency response performance. The effectiveness of the proposed control strategy was verified on the MATLAB/Simulink simulation platform. After optimization using the proposed control strategy, the oscillation amplitude was reduced by 0.15 Hz, the precision was increased by 40%, and the steady-state frequency deviation was reduced by 26%. The results show that the method proposed in this paper provides a great improvement in the frequency stability of coordinated systems of wind farms and BESSs.

Design of Universal Control Structure for Regulation of Voltage and Frequency in Hybrid Microgrid

Hybrid microgrid (HMG) control strategies reveal several critical research gaps that must be addressed. Current approaches often fall short in efficiency and reliability due to the inherent complexities of transitioning between grid-connected mode (GCM) and islanded mode (IM), resulting in increased losses and operational difficulties. Additionally, managing overloads, especially in IM, poses significant challenges for maintaining stable voltage and frequency regulation. This paper seeks to address these issues by introducing a novel universal control structure (UCS) for HMGs, which includes a frequency compensation unit (FCU) and a three-stage bidirectional AC/DC droop. It presents a streamlined yet robust solution for handling overloads, maintaining power balance, and ensuring precise voltage and frequency regulation while promising smooth maneuver in both GCM and IM. The proposed UCS provides flexible and reliable operation, allowing for the versatile placement of DC and AC sources and loads. This will reduce power transformation stages thereby lowering cost and increasing efficiency of system. Through experimental validation, this study demonstrates the effectiveness of the proposed control in addressing these critical research gaps and advancing the field of HMG control strategies.