Large Frequency Deviations Research Articles

Improvement of Transient Response in Microgrids Using Virtual Inertia

Generation is shifting from a centralized power generating facility having large synchronous generators to distributed generation involving sources of smaller capacity. Most of these sources require inverters on the front end while being connected to the grid. Lower available kinetic energy, coupled with less short-circuit current ratio compared to large synchronous generators, compromises the transient stability of the microgrid when isolated from the main grid. Sources in the microgrid use droop control to share power according to their capacity without any form of communication. This paper proposes a novel controller for inverters to improve the frequency response of microgrid under disturbances involving large frequency deviations. It also discusses design of various parameters defined for the proposed control. The microgrid, which has two inverters and two synchronous generators, is simulated using Simulink/MATLAB software to test the proposed control strategy.

Resistive switching effect on Al2O3/InGaAs stacks

Display Omitted HighlightsWe examine the post breakdown characteristics of metal gate/Al2O3/InGaAs.It is observed resistive switching (RS) effect.The oxide-substrate interface is studied by X-ray photoelectron spectroscopy spectra.The As-O bonds are responsible for large frequency deviations and the RS effect. The resistive switching (RS) phenomenon is currently attracting a lot of attention due to its potential applicability for nonvolatile memory devices. Among all the systems currently under consideration, the analysis of MG/Al2O3/InGaAs is very relevant since this stack is a strong candidate for the new generation of CMOS devices with high mobility channels.

A Robust Baseband Demodulator for ISO 18000-6C RFID Reader Systems

One key challenge for ultra-high frequency (UHF) radio-frequency identification (RFID) reader design is to demodulate the weak tag response signal which tends to be easily distorted and has considerable frequency deviations. In this paper, a baseband demodulator based on a matched filter (MF) is proposed to enhance the reliability of signal processing for the EPCglobal Class-1 Generation-2 (Gen2) RFID reader systems. The proposed demodulator is very robust against strong signal distortions and large frequency deviations happening on the received backscattered signal from a passive RFID tag. The validity and usefulness is demonstrated by both computer simulations and implementation experiments.

A three phase PLL with a dynamic feed forward frequency estimator for synchronization of grid connected converters under wide frequency variations

This paper presents a synchronization technique to accurately track the phase and frequency of the input signal under large frequency deviations. The hybrid FPLL structure consists of a conventional SRF PLL feedback loop along with a feed forward frequency estimator loop. The advantage of this technique is that the feedback controller has to reduce only the phase error and the frequency error is eliminated by the feed forward controller. This increases the dynamic response of the system under frequency deviations. The performance of the hybrid structure is compared with the conventional SRF PLL and the former shows improved performance over the SRF PLL in terms of filtering characteristics and transient response for wide range of frequency deviations. The steady state error analysis is carried out and the necessary condition for stability is also derived. Simulations are carried out in MATLAB/Simulink and implemented in real time using an ALTERA cyclone II FPGA board. The results obtained for various grid conditions such as unbalance, harmonics, phase jump and frequency deviation demonstrate the phase-tracking ability of the technique.

Impact of Mechanical Vibrations on Laser Stability and Carrier Phase Estimation in Coherent Receivers

Coherent communication systems are largely limited by the laser linewidth of the local oscillator. In addition to phase noise, large frequency deviations can occur if the laser is mechanically vibrated. The detrimental effect of the frequency instability is measured for coherent optical receivers on a typical laser and numerically analyzed for quadrature phase-shift keying and 16-quadrature amplitude modulation using common feed-forward carrier phase recovery algorithms.

Generation of frequency-modulated sub-terahertz signal using microwave photonic technique

We present a photonic technique for generating a frequency- modulated sub-terahertz signal for non-destructive or noninvasive sensing and imaging applications. Large frequency deviation was achieved by using optical phase modulation and heterodyne photomixing with an uni-travelling photodetector. The operation principle is theoretically derived and explained. In addition, the generation of 350-GHz frequency- modulated sub-terahertz signal with 6.7-GHz frequency deviation is experimentally demonstrated, and the possibility of frequencies up to 1 THz and wider frequency deviations is discussed.

Maximum Frequency Deviation Calculation in Small Isolated Power Systems

Large frequency deviations due to a number of disturbances are frequent in small isolated power systems. The maximum frequency deviation in the system is limited to prevent other generator tripping. It is important to have an accurate model to calculate it, both for system planning and operation. A new simplified model to calculate the maximum frequency deviation when either a generator or load-related disturbance occurs in these systems is presented. This model takes into account the response of governor-prime mover even when different technologies are present in the power system. Model parameters can be easily obtained from either more complex models or from test records. Simulation results for an actual power system aimed at checking the model accuracy are presented. High accuracy is obtained while computation time is reduced due to the simplicity of the model.

Improvement of the Performance of Scheduled Stepwise Power Programme Changes within the European Power System

Since the deregulation of the electrical energy market, the technical realisation of power transactions based on energy market contracts often effects large stepwise power programme changes – especially at the change of the hour. Originating from mainly economic reasons, these stepwise power programme changes lead to remarkable power imbalances within the European Power System causing large unintended frequency deviations with a negative impact on the control performance of power plants and power system. Within the framework of this paper, possible causes for the resulting poor control performance are analysed. Subsequently, measures for an improvement of the performance of scheduled stepwise power programme changes are proposed.

The effect of converter configurations of HVDC links on sub- and super-synchronous disturbances to turbine units

In this paper, the rotor torque disturbances to turbine–generator units arising from harmonic interactions between converters of a HVDC system are studied. It is shown that a distinct-pulse converter configuration will be a better choice for avoiding sub- or super-synchronous resonance. For an asynchronous HVDC link, the risk of electromechanical resonance could be completely got rid of on either side of the link, no matter what directions the powers flow, if an 18-pulse converter were used on the 60 Hz side and a 12-pulse converter on the 50 Hz side. Such a configuration could still perform well even under the large frequency deviations. Furthermore, it shows that power system type plays a significant role on the possible excitation of resonance and on the probably damaging sections of a turbine–generator unit. Good match of the converter configuration and power system type is significant for a HVDC link to exempt from sub- and super-synchronous resonance.

Generalized Energy Demodulation for Large Frequency Deviations and Wideband Signals

The Teager-Kaiser energy operator and the related energy separation algorithm (ESA) find numerous applications in various problems related to monocomponent AM-FM demodulation. This energy-operator-based approach, however, applies only to signals with narrowband frequency content, i.e., the information bandwidth and frequency deviation about the carrier are small relative to the carrier frequency. For signals with large frequency deviation, modulation indices, this approximation fails, and the ESA incurs large frequency/amplitude demodulation errors. In this letter, we develop a generalized energy-operator-based approach that uses frequency transformations derived from multirate operations such as decimation/interpolation and heterodyning. This generalized approach is shown to produce significant reduction of the demodulation error over the conventional ESA, particularly where the modulation index or frequency deviation is large.

Optical FSK/IM Signal Generation Using an Integrated Optical FSK Modulator

We demonstrate simultaneous optical modulation by frequency shift keying (FSK) and intensity modulation (IM) using a newly developed high-speed FSK modulator, for optical packet systems where payload and label signals are, respectively, in IM and FSK format. The modulator consists of four optical phase modulators, with traveling-wave electrodes to obtain high-speed frequency switching and large frequency deviation in FSK modulation.

An induction motor parameter estimation method

The auxiliary systems of large thermal power plants are mainly driven by large induction motors. Their accurate modeling is essential for the analysis of black or emergency start procedures during power system restoration, where auxiliaries are started from relatively small diesel, hydro, or gas turbines, and where large voltage and frequency deviations occur. This paper proposes a new parameter estimation method for induction motors which allows to build induction motor models from manufacturer data such as nameplate data, and motor performance characteristics. The models can be used for black and emergency start studies with the Electromagnetic Transients Program (EMTP) or with stability programs. The method is based on a non-linear optimization routine. Its objective function, boundaries, and constraints are described in this paper. The method is first formulated neglecting saturation and then extended to allow for the saturation of the motor leakage reactances. It is tested to ensure that it is sufficiently robust and that its application gives the best agreement between model and manufacturer data. The effectiveness of the method is demonstrated for a 600-HP pump motor, such as typically used in large thermal power plants, and by a practical emergency start case study.

Theoretical analysis of phase diversity optical homodyne receiver with FSK demodulation

A detailed analysis of optical coherent phase diversity single-filtered and dual-filtered frequency-shift keying (FSK) receivers corrupted by shot and phase noise is presented. With delay and cross-product detection, the effect of various parameters, including bandwidths of filters, delay time, frequency deviation and noises, are investigated. The tolerance of phase noise is quite large, when small time delay in the demodulator and appropriately large frequency deviation is selected. It is also shown that there exists an optimal bandwidth for the first filter in the dual-filtered FSK receiver. For a total linewidth equal to half of the bit rate, the power penalty incurred (at BER=10/sup -9/) is 1.92 dB when the modulation index is 4, provided that an optimal filter bandwidth and a frequency deviation-delay product of 0.25 are used.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Improved Unit Dynamic Response using Condensate Stoppage

Large frequency deviations can cause users to be automatically disconnected (load shedding) from the primary electrical grid. Such disconnections can have serious consequences for the users of the electrical power grid.All power plant units involved in the grid frequency control must provide as fast as possible power to the grid in case of disturbances to the grid frequency. The activation of the necessary power is normally provided by fast opening of the turbine control valves. However the valves must be throttled in normal operation in order to be able to supply power in case of frequency disturbances. This causes a loss in efficiency.The use of the condensate stoppage technique in keeping the turbine control valve throttling to a minimum has proved to be successfull.In this paper an expanded control concept is proposed, whereby not only in cases of frequency support but also in cases of large load changes the condensate stoppage technique is used. As a result the fuel over firing can be reduced, this in turn producing a smoother und more optimal firing.The testing of the new control concept was carried out on a nonlinear power plant model. The concept has been included in the control design of a coal fired power plant, which is scheduled for commissioning in 1992.

PLL synchronized time-varying constrained notch filter for retrieving a weak multiple sine signal jammed by FM interference

A method of retrieval of a multitone corrupted by a strong wideband FM interference is presented. The input mixture is transformed into a new time domain, resulting in a concentration of the FM interference around a chosen frequency; this inference is then rejected by a constrained notch filter with a fixed notch point. The time warping is implemented through nonequally spaced sampling. The method provides results superior to those of conventional adaptive processing, which fails to track the parameters of an FM interference with significantly large frequency deviations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

System design and long-span transmission experiments on an optical FSK heterodyne single filter detection system

The influence of LD phase noise on a heterodyne noncoherent detection system was evaluated. Based on the evaluation, an optical FSK heterodyne single filter detection system with large frequency deviation and wide-band IF filter has been developed to allow use of stand-alone DFB LD's. In the system, a phase tunable DFB LD was used as an FSK transmitter light source to improve the FSK modulation characteristics. An IF filter with appropriate bandwidth evaded the influence of LD phase noise. With these configurations, long-span (243 km at 140 Mbit/s and 204 km at 280 Mhit/s) transmission experiments have been successfully carried out on this single filter detection system. To the contrary, influence of LD phase noise appeared in a limited IF bandwidth case, which agrees well with the theoretical evaluation.

Discriminator with partial response detection of nrz. fsk signals

AbstractIn the TDMA subscriber loop radio communication system, large carrier frequency deviation exists in burst signals from subscribers to a base station. A modulation/demodulation technique, which is suitable for the burst transmission with large frequency variation, is studied in this paper. First, problems in the terrestrial TDMA system and clarified and it is shown that the use of conventional FSK‐discriminator detection causes large CNR degradation due to the variation. Next, differential FSK‐Partial Response Detection (DFSK), which can cope with the frequency variation and has a simple structure, is proposed and its principle and structure are described. Furthermore, the intersymbol interference and adjacent channel interference characteristics are evaluated theoretically and the bit error rate (BER) characteristics are evaluated experimentally. As a result, the optimum modulation index and IF‐band reception band path filter are obtained. Finally, the optimum transmission system of DFSK designed for wide‐band Digital Radio Subscriber Loop System using 26‐GHz band is described. DFSK is shown to be a practical and promising modulation/demodulation system for a terrestrial TDMA communication system, on which a large demand is expected in the future.

An Advanced Dispatcher Training Simulator

This paper describes a dispatcher training simulator which provides a realistic environment for system dispatchers to practice operating tasks and experience emergency operating situations. The dispatcher interacts with the digital computer based simulator through a flexible CRT display system. Normal operating activities, such as load following, interchange scheduling, supervisory control, voltage control, and transmission dispatch can all be practiced. However, the simulator is especially advanced in the degree of realism with which it allows the operator to observe and practice procedures for abnormal conditions, including voltage degredation, line overloads, cascading outages, system islanding with large frequency deviations, load interruption, and system restoration.

An inherited blood group A variant in the Finnish population. II. Population studies.

Abstract. A rare variant of blood group A, Afinn, is used as a marker when studying the Finnish population structure. Slow immigration is probably the main cause of the primary enrichment of this gene that has not yet been described outside Finland. Practically all the 98 propositi originated from the areas in the south‐west and south‐east that were first settled in prehistoric times. This indicates that both were inhabited by the same settlers, probably immigrating over the Gulf of Finland rather than using two different routes.The frequency of Afinn in the first settled areas was estimated at approximately 1:1,000, showing large local differences at community level, with estimated peaks as high as more than 1%. The frequency distribution was analysed in a computer simulation programme; the similarities with the observed distribution of Afinn were compatible with the effect of sampling and drift, causing substantial loss and large frequency deviations in the isolated subpopulations.

An Inherited Blood Group A Variant in the Finnish Population

A rare variant of blood group A, A(finn), is used as a marker when studying the Finnish population structure. Slow immigration is probably the main cause of the primary enrichment of this gene that has not yet been described outside Finland.Practically all the 98 propositi originated from the areas in the south-west and south-east that were first settled in prehistoric times. This indicates that both were inhabited by the same settlers, probably immigrating over the Gulf of Finland rather than using two different routes. The frequency of A(finn) in the first settled areas was estimated at approximately 1:1,000, showing large local differences at community level, with estimated peaks as high as more than 1%. The frequency distribution was analysed in a computer simulation programme; the similarities with the observed distribution of A(finn) were compatible with the effect of sampling and drift, causing substantial loss and large frequency deviations in the isolated subpopulations.