Effect Of Frequency Deviation Research Articles

Self-Frequency Tracking for Fixed-Ratio Switch-Capacitors in Data Center Application without Extra Sensors

As research into data centers progresses, the importance of resonant switched-capacitor converters in power supply design becomes more evident. Practical applications reveal that the values of resonant capacitors and inductors may deviate from their nominal values due to various factors, leading to resonant frequency instability. This instability poses a challenge to power electronics technology, affecting system reliability and performance. This paper analyzes the effect of frequency deviation on system functionality, identifies the relationship between output voltage and switching frequency, and proposes a self-tracking frequency strategy to address this issue. Through experimental validation, this approach shows that it maintains synchronization between switching and resonant frequencies, reducing losses associated with frequency misalignment. Simulation and experimental results validate the converter’s stable operation and its ability to achieve zero-voltage and zero-current switching.

An Inductance Online Identification-Based Model Predictive Control Method for Grid-Connected Inverters With an Improved Phase-Locked Loop

To simplify the tuning process and enhance the parameter robustness of the model predictive control (MPC) for grid-connected inverters, an improved phase-locked loop (PLL) and a new inductance online identification method are proposed in this article. First, an improved finite control set-based PLL is presented, which removes the PI controller, simplifying the tuning process. Next, a new inductance online identification method based on a model reference adaptive system is presented, which takes the actual grid voltage and the estimated one as the reference model and adjustable model, respectively. Here, a sliding mode observer (SMO) is proposed to estimate the grid voltage, and the inductance adaptive law is deduced by exploring the effects of the inductance on the estimated grid voltage. Furthermore, the sensitivity of the proposed SMO to frequency deviation is also analyzed, which shows that a proper sliding mode gain can be selected to reduce the effects of frequency deviation. Thus, a fixed grid frequency of 50 Hz can be used in the proposed SMO, indicating that it is not required to calculate the actual grid frequency using differential operation any more. Finally, experimental studies verify the validity of the proposed strategies.

Impact Assessment of the Asynchronous Clocks Between Reference and User Receivers in Differential Pseudolite Navigation System

Compared with the Global Navigation Satellite System (GNSS), the asynchronous pseudolite (PL) navigation system does not provide corrections for the frequency deviation between PL signals. To realize precise positioning, a reference receiver is utilized to reduce the effect of frequency deviation between PLs via the differential method using carrier phase measurements. However, there exists time deviation between the user and reference receivers due to their asynchronous clocks. With this time deviation, the effect of frequency deviation between PLs cannot be removed thoroughly. Theoretical derivation and experimental verification indicate that the residual error in double difference of carrier phase measurements is proportional to the frequency deviation between PLs and the time deviation between receivers. To solve this problem, two approaches, refer to hardware and software methods, are proposed, which are experimentally proven to be feasible.

Generalized Integrator-Extended State Observer With Applications to Grid-Connected Converters in the Presence of Disturbances

Large-scale fast-varying sinusoidal disturbances (FVSDs) strongly impact the operation of Grid-connected Converters (GcCs). A conventional extended state observer (ESO) is not sufficiently capable to deal with these rapid disturbances. This critical weakness has limited ESO's applications to GcCs. Therefore, a generalized integrator-ESO (GI-ESO) is developed from ESO to address such issues. Knowing that grid common disturbances can be expressed as a phase, frequency, or magnitude disturbed sinusoidal signal, multi-GIs of selective resonant frequencies are, hence, applied into the disturbance estimation loop, which enables FVSD to be observed with relatively low bandwidth. Besides, a frequency-adaptive mechanism is introduced in order to mitigate the effects of frequency deviations. The proposed GI-ESO resolves the tradeoff between the observer's bandwidth and noise filtering. A case of the three-phase phase-locked loop control system of disturbed regimes is, in particular, studied to assess the performance of GI-ESO and the stability of the resulting controlled system. Theoretical analysis and experimental results have proven its effectiveness in applications to GcCs in the presence of various disturbances.

Long-Term Frequency Stability Assessment Based on Extended Frequency Response Model

Large frequency deviation degrades the operation performance of the boiler and its auxiliaries. It affects the output of thermal power units. A significant change in power generation leads to a great frequency deviation. An extended frequency response model for long-term frequency stability assessment is constructed to consider the effects of frequency deviations on boiler auxiliaries. The static power-frequency characteristic of the thermal power unit within an extensive frequency variation range is analyzed. It reveals that the active power output of the generating unit is not monotonically increasing with frequency dropping. An inflection point is observed on the static power-frequency characteristic curve when considering boiler auxiliary frequency characteristics. In the range of greater frequency deviation, the output power decreases rapidly with frequency declination, and an unstable equilibrium point (UEP) of frequency stability is identified. A quantitative index is proposed for frequency stability assessment based on UEP. The stability characteristic and the frequency stability quantitative index based on UEP are analyzed. The frequency dynamic behaviors of the extended model are demonstrated to analyze frequency stability characteristics within an extensive frequency variation range by a single machine system and the IEEE 39-bus system with considering boilers and its auxiliaries.

PID Controller Adjustment using Particle Swarm Optimization for Multi-Area Load Frequency Control Said A. Kotb Magdy M. Z. Abdelaal Ahmed R. Adly ETRR-2,Nuclear Research Center, Atomic Energy Authority, Egypt

This paper present particle swarm optimization based study of multi area power network. Particle swarm optimization and Fuzzy system inferences have been employed to effectively obtain the optimized gains of PID controller. Any change in the load demand causes generator’s shaft speed lower than the pre-set value and the system frequency deviates from the standard value results in malfunctioning of frequency relays. A three area load frequency model is constructed in Matlab/Simulink by implementing the PID controllers to control the frequency deviation on the three areas together and each area to illustrate the effect of frequency deviation on the integrated model. One of these areas is a nuclear power plant. Performance of the proposed controller is compared with fuzzy system based PID controller and conventional PID controller to indicate the excellence of the proposed algorithm for PID parameters regulation. Simulations performed show the effectiveness of the current approach over simple fuzzy inferences in terms of performance as well as execution efficiency.

Adaptive phasor estimation technique during off-nominal frequency for numerical relays

ABSTRACTThe use of digital multifunction protection relays and their proper integration on the power system and smart grid is an important element. However, the performance of digital relays depends on many factors and needs to be carefully evaluated. These factors may be caused by correct operations with less performance or completely incorrect operations. Frequency deviation is one of those factors which results from unbalanced demand load and generation levels. Load characteristics and generation control response to demand load changes will effect on amount and duration of frequency deviations. Frequency decreases when demand load is higher than generation, whereas it increases when load is less than generation. Protection relays are provided with frequency tracking to reduce the effects of frequency deviations on accuracy of relay decisions. In this paper, traditional frequency tracking technique used on protection relays is modified to give a better performance (less Total Vector Error, TVE) during off-nominal frequency variations. The performance of the proposed algorithm is compared with traditional tracking using Least Square Error (LSQ), and Discrete Fourier transform (DFT) algorithm without any tracking, which are investigated in MATLAB environment.

A Modified Differential Coherent Bit Synchronization Algorithm for BeiDou Weak Signals with Large Frequency Deviation

BeiDou system navigation messages are modulated with a secondary NH (Neumann-Hoffman) code of 1 kbps, where frequent bit transitions limit the coherent integration time to 1 millisecond. Therefore, a bit synchronization algorithm is necessary to obtain bit edges and NH code phases. In order to realize bit synchronization for BeiDou weak signals with large frequency deviation, a bit synchronization algorithm based on differential coherent and maximum likelihood is proposed. Firstly, a differential coherent approach is used to remove the effect of frequency deviation, and the differential delay time is set to be a multiple of bit cycle to remove the influence of NH code. Secondly, the maximum likelihood function detection is used to improve the detection probability of weak signals. Finally, Monte Carlo simulations are conducted to analyze the detection performance of the proposed algorithm compared with a traditional algorithm under the CN0s of 20~40 dB-Hz and different frequency deviations. The results show that the proposed algorithm outperforms the traditional method with a frequency deviation of 50 Hz. This algorithm can remove the effect of BeiDou NH code effectively and weaken the influence of frequency deviation. To confirm the feasibility of the proposed algorithm, real data tests are conducted. The proposed algorithm is suitable for BeiDou weak signal bit synchronization with large frequency deviation.

A review on frequency tuning methods for piezoelectric energy harvesting systems

Piezoelectric energy harvesting technologies have received a great attention during the last decade to design self-powered microelectronic devices such as wireless sensor nodes. Piezoelectric energy harvester is a resonant system that produces maximum power output when its resonant frequency matches the ambient vibration frequency. The deviation from the resonance causes significant decrease in the power output. There are two possible solutions to compensate the effect of frequency deviation: widening the operating frequency bandwidth and tuning the resonant frequency. Tuning the resonant frequency is a more efficient technique for applications with single time varying dominant frequency. This paper presents a comprehensive review of frequency tuning methods for piezoelectric energy harvesting systems. Two categories generally investigated in the literature include manual and autonomous tuning methods. The recent developments of many tuning strategies are discussed and summarized.

Revisit of series-SSHI with comparisons to other interfacing circuits in piezoelectric energyharvesting

SSHI (synchronized switch harvesting on inductor) techniques have been demonstrated tobe capable of boosting power in vibration-based piezoelectric energy harvesters. However,the effect of frequency deviation from resonance on the electrical response of an SSHIsystem has not been taken into account from the original analysis. Here an improvedanalysis accounting for such an effect is proposed to investigate the electrical behavior of aseries-SSHI system. The analytic expression of harvested power is proposed and validatednumerically. Its performance evaluation is carried out and compared with the piezoelectricsystems using either the standard or parallel-SSHI electronic interfaces. The result showsthat the electrical response of an ideal series-SSHI system is in sharp contrast to thatof an ideal parallel-SSHI system. The former is similar to a strongly coupledelectromechanical standard system operated at the open circuit resonance, while the latteris analogous to that operated at the short circuit resonance with different magnitudes ofmatching impedance. In addition, the performance degradation due to non-idealvoltage inversion is also discussed. It shows that a series-SSHI system avails againstthe standard technique in the case of medium coupling, since its peak power isclose to the ideal optimal power and the reduction in power is less sensitive tofrequency deviation. However, the consideration of inevitable diode loss in practicaldevices favors the parallel-SSHI technique, since the frequency-insensitive feature ismuch more pronounced in parallel-SSHI systems than in series-SSHI systems.

A Frequency Control Method by Wind Farm & Battery using Load Estimation in Isolated Power System

Currently, there are several published reports on wind farms (WFs) for controlling output power by using pitch angle control. In addition, to reduce the adverse effects of frequency deviations, battery energy storage systems (BESSs) are introduced to small power systems. In this context, this paper presents a frequency control method by the WF and the BESS using load estimation. The load is estimated by a disturbance observer. The frequency deviations in low and high frequency domain are reduced by the WF using pitch angle control and battery charge/discharge, respectively. By using the proposed method, the reduction of the rated capacity of the BESS is possible. Furthermore, for the pitch angle control system of each WTG in the WF, generalized predictive control (GPC) is applied to achieve robust control performance. The effectiveness of the proposed method is verified by numerical simulation.

Interaction of pulse ultrasonic signals with reflectors of different types

The results of experimental studies of the processes of interaction of pulse ultrasonic signals with artificial reflectors of different types are presented. To estimate nonstationary frequency characteristics of echo signals, it is proposed to use an algorithm for determining the instantaneous frequency that is based on the use of a wavelet transform characterized by increased noise immunity. It is shown that the instantaneous frequency of the reflected pulse signal may substantially differ from the rated frequency of a piezoelectric transducer for different types of reflectors. The frequency difference has a minimum value at a minimum curvature of the reflected-wave front. The obtained results must be considered during implementation of conventional methods of ultrasonic nondestructive testing because disregarding the effect of frequency deviation from the rated value may lead to a violation of the requirements of the acting standards for the tolerance for the operating frequency of a piezoelectric transducer. The difference of the instantaneous frequency from the rated frequency depends on the reflector type and can be used as an informative indicator of a flaw’s shape.

New techniques for enhancing accuracy of EMTP/TSP hybrid simulation

This paper proposes a new hybrid approach, which integrates the simulation of electromagnetic transient program (EMTP) for waveform solutions to concerned electrical components, such as FACTS devices and HVDC etc. and the simulation of transient stability program (TSP) for phasor solutions to the rest of power systems. In the interface between the two simulations, new techniques considering the effect of frequency deviation due to disturbances are proposed for improving accuracy of the hybrid simulation. A case study is performed on the IEEE 10-generator New England systems. The results show that simulation accuracy of conventional EMTP/TSP hybrid methods has been evidently improved. The proposed new method would thus provide an efficient tool in the design and analysis of behaviors of FACTS devices in power system dynamics.

Consideration of Figure of Merit of Piezoelectric Vibratory Gyroscope Using Charge Sensitivity

In this paper, charge sensitivity has been considered as a figure of merit of piezoelectric vibratory gyroscope. First, an approximate equation for charge sensitivity is derived based on an equivalent circuit of the gyroscope. Second, the charge sensitivity characteristics have been discussed in terms of the effects of frequency deviation and load capacitance. The difference between charge sensitivity and voltage sensitivity is quantitatively clarified. Charge sensitivity is effective as a figure of merit for applying a piezoelectric single crystal to the gyroscope.

A fast load flow model for a dispatcher training simulator considering frequency deviation effects

This article presents a fast load flow algorithm considering the effect of frequency deviation on loads and generator outputs. The model was developed for and applied to a dispatcher training simulator (DTS) in the People's Republic of China. In order to meet the real time requirements of DTS, new solution techniques have been suggested to handle non-symmetric nature of the load flow Jacobian matrices resulting from the presence of the frequency deviation forms. The suggested methods reduce the memory requirement and provide faster solution. Results have been obtained on a 220 kV, 67 bus and another 22 bus provincial power system networks in China.