Automatic Frequency Control Research Articles

A Low-Power NB-IoT Transceiver With Digital-Polar Transmitter in 180-nm CMOS

A fully integrated 750~960 MHz wireless transceiver (TRX) is presented for single-tone NB-IoT applications. Effective design methodologies and techniques, from the system level to circuit level, are proposed to address various design challenges while achieving low-power consumption. The TRX consists of a low-IF receiver with 180-kHz signal bandwidth, a digital polar transmitter with 3.75-kHz signal bandwidth, and a fractional-N frequency synthesizer. Passive current mixer is employed in the receiver to improve the linearity and avoid the sensitivity degradation due to 1/ ${f}$ noise. Automatic I/Q imbalance calibration is integrated to improve image rejection ratio (IRR) with the aid of external FPGA. The transmitter is implemented in the digital polar architecture to improve the narrow-band spectrum purity, integrated with an inverse Class-D digital power amplifier (DPA) to achieve high output power and efficiency. A Class-C voltage-controlled oscillator with automatic frequency control assisted the dynamic gate biasing technique is used in the fractional-N PLL frequency synthesizer. Two prototypes are implemented in 180-nm CMOS. By optimizing analog baseband configuration in the receiver and utilizing the revised thermometer-coding and binary-coding-based array placement in the DPA, the receiver achieves 4.0-dB noise figure, 48-dB IRR, and 60-dB PGA dynamic range, and the DPA outputs 23.2dBm maximum saturation power with 44.5% PAE. Furthermore, the transmitter system verifications demonstrate 3.87% error-vector magnitude (EVM) for 891 MHz $\pi $ /4-DQPSK signals at 18.87-dBm output power with −40-dBc out-of-band rejection. The transmitter achieves a dynamic range from −35 to 20 dBm when the demodulation EVM threshold of the system is set to 10%.

A 6.6 mW 1.25–2.25 GHz low phase noise PLL frequency synthesizer based on wide tuning range Class-C VCO

A wide tuning range low phase noise phase-locked loop (PLL) frequency synthesizer based on Class-C voltage-controlled oscillator (VCO) for IEEE 802.11ah is presented. Feedback loop technique is adopted to provide dynamic gate bias to the core transistors of the Class-C VCO, guaranteeing robust start-up against process, voltage and temperature (PVT) variations. Automatic frequency control (AFC) algorithm with tail bias switching scheme is proposed to guarantee start-up condition and maintain optimum oscillation amplitude across the whole tuning range, avoiding the deterioration of figure-of-merit (FoM). Implemented in 65-nm CMOS, the presented frequency synthesizer prototype achieves a tuning range of 57%, from 1.25GHz to 2.25GHz. Drawing 5.5mA current from a 1.2-V power supply, the prototype demonstrates −127.8 dBc/Hz phase noise at 1-MHz offset and −94.6 dBc/Hz in-band phase noise from a carrier of 1.536GHz. With the proposed dynamic gate bias technique and AFC-assisted tail bias switching scheme, the wide tuning range Class-C VCO exhibits a peak FoM of 187.5 dBc/Hz, with only 2.5dB variation across the whole tuning range.

Combined control of voltage and frequency of multi‐area multisource system incorporating solar thermal power plant using LSA optimised classical controllers

This study presents the combined model of automatic load frequency control (ALFC) and automatic voltage regulator (AVR) of a multisource multi-area system for control of voltage, frequency and tie-line power. Each area comprises of a solar thermal, thermal and diesel plant. A more realistic system is studied by considering generation rate constraint and governor dead band (GDB) for the thermal plant. Integral (I)-double derivative (DD) controller with derivative (D) filter (IDDF) is proposed for the combined ALFC and AVR model by considering 1% step load perturbation in area1. The controller parameters are optimised using lightning search algorithm (LSA). The performance of proposed controller is compared with other conventional controllers such as proportional–I (PI), I–D and PI–D. The analysis reveals that the proposed controller outperforms the others in terms of settling time and peak deviations. The comparative performance of various performance indices shows that integral squared error is better than others. Analysis of the effect of GDB with IDDF controller and LSA indicates that the presence of GDB leads to more oscillations in the system dynamics. The sensitivity analysis against the change in magnitude and position of disturbance derived the robustness of the IDDF controller parameters obtained at nominal condition.

Seeing is believing: a demonstration of critical fusion frequency and its multidimensional nature.

critical fusion frequency (CFF), or the flicker fusion threshold, is defined as the critical frequency above which a flickering light source appears steady to the observer (see [Fig. 1][1]). It is known to depend on a number of parameters, namely, intensity of the light source ([5][2], [15][3]),

Broadband W-band Rapid Frequency Sweep Considerations for Fourier Transform EPR.

A multi-arm W-band (94 GHz) electron paramagnetic resonance spectrometer that incorporates a loop-gap resonator with high bandwidth is described. A goal of the instrumental development is detection of free induction decay following rapid sweep of the microwave frequency across the spectrum of a nitroxide radical at physiological temperature, which is expected to lead to a capability for Fourier transform electron paramagnetic resonance. Progress toward this goal is a theme of the paper. Because of the low Q-value of the loop-gap resonator, it was found necessary to develop a new type of automatic frequency control, which is described in an appendix. Path-length equalization, which is accomplished at the intermediate frequency of 59 GHz, is analyzed. A directional coupler is favored for separation of incident and reflected power between the bridge and the loop-gap resonator. Microwave leakage of this coupler is analyzed. An oversize waveguide with hyperbolic-cosine tapers couples the bridge to the loop-gap resonator, which results in reduced microwave power and signal loss. Benchmark sensitivity data are provided. The most extensive application of the instrument to date has been the measurement of T1 values using pulse saturation recovery. An overview of that work is provided.

Development of an automatic frequency control system for an X-band (=9300 MHz) RF electron linear accelerator

KAERI is developing a 6MeV X-band radio frequency (RF) electron linear accelerator for medical purposes. The proposed X-band accelerator consists of an e-gun, an accelerating structure, two solenoid magnets, two steering magnets, a magnetron, a modulator, and an automatic frequency control (AFC) system. The accelerating structure of the component consists of oxygen-free high-conductivity copper (OFHC). Therefore, the ambient temperature changes the volume, and the resonance frequency of the accelerating structure also changes. If the RF frequency of a 9300MHz magnetron and the resonance frequency of the accelerating structure do not match, it can degrade the performance. That is, it will decrease the output power, lower the beam current, decrease the X-ray dose rate, increase the reflection power, and result in unstable operation of the accelerator. Accelerator operation should be possible at any time during all four seasons. To prevent humans from being exposed to radiation when it is operated, the accelerator should also be operable through remote monitoring and remote control. Therefore, the AFC system is designed to meet these requirements; it is configured based on the concept of a phase-locked loop (PLL) model, which includes an RF section, an intermediate frequency (IF) [1-3] section, and a local oscillator (LO) section. Some resonance frequency controllers use a DC motor, chain, and potentiometer to store the position and tune the frequency [4,5]. Our AFC system uses a step motor to tune the RF frequency of the magnetron. The maximum tuning turn number of our magnetron frequency tuning shaft is ten. Since the RF frequency of our magnetron is 9300±25MHz, it gives 5MHz (∵±25MHz/10 turns → 50MHz/10 turns =5MHz/turn) frequency tuning per turn. The rotation angle of our step motor is 0.72° per step and the total step number per one rotation is 360°/0.72°=500 steps. Therefore, the tuning range per step is 10kHz/step (=5MHz per turn/500 steps per turn). The developed system is a more compact new resonance frequency control system. In addition, a frequency measuring part is included and it can measure the real-time resonance frequency from the magnetron. We have succeeded in the stable provisioning of RF power by recording the results of a 0.01% frequency deviation in the AFC during an RF test. Accordingly, in this paper, the detailed design, fabrication, and a high power test of the AFC system for the X-band linac are presented.

A fast and efficient constant loop bandwidth with proposed PFD and pulse swallow divider circuit in [formula omitted] fractional-N PLL frequency synthesizer

This work presents the design of a ΔΣ fractional-N PLL frequency synthesizer with a new loop bandwidth calibration and automatic frequency control (AFC) circuit, applicable for wide band RF communication system. This new and unique loop bandwidth calibration circuit has been implemented using logarithmic and anti-logarithmic (Base2) architecture. This architecture is an efficient design technique as well as faster operation in CMOS domain. The operating frequency range of the ΔΣ fractional-N PLL frequency synthesizer is from 2.158 to 5.133GHz. The variation of LC VCO gain (KVCO) is obvious due to wide band application and it varies from 30.65MHz/Volt to 368MHz/Volt for the frequency range of 2.158–5.133GHz. Constant loop bandwidth is maintained by controlling the charge pump current. Power consumption of the ΔΣ fractional-N PLL frequency synthesizer is 34mW from a 1.2Volt power supply and the work has been carried out in 0.13μm standard CMOS process. Also, this design includes an automatic frequency control unit for the LC VCO circuit which is coarsely tuned within 1.825μs for KVFC=10 for worst case condition and it completes the loop bandwidth (LBW) calibration within 7.84μs for KLBC=150 for worst case condition. The maximum locking time of the ΔΣ fractional-N PLL frequency synthesizer with loop bandwidth calibration and automatic frequency control circuit is 12.7μs for KVFC=10 and KLBC=150 for worst case condition. The ΔΣ fractional-N PLL is locked much faster than any work reported earlier using the proposed PFD, CP, proposed pulse swallow divider, efficient AFC circuit for LC VCO and a new loop BW calibration technique in transistor level simulation using Cadence SpectreRF. The main advantage of this loop bandwidth calibration technique is that the calibration time can be adjusted according to the PLL output frequency, loop bandwidth calibration accuracy and tuning frequency range of the LC VCO.

Effect of Rabi splitting on the low-temperature electron paramagnetic resonance signal of anthracite

Specific distortions of the EPR signal of bulk anthracite are observed at low temperatures. They are accompanied by variations in the microwave oscillator frequency and are explained by the manifestation of the Rabi splitting due to the strong coupling between electron spins and the cavity, combined with the use of an automatic frequency-control (AFC) system. EPR signals are recorded at negligible saturation in the temperature range of 4–300K with use of the AFC system to keep the oscillator frequency locked to the resonant frequency of the TM110 cylinder cavity loaded with the sample. For the sample with a mass of 3.6mg the line distortions are observed below 50K and increase with temperature lowering. The oscillator frequency variations are used to estimate the coupling strength as well as the number of spins in the sample. It is shown that the spin-cavity coupling strength is inversely proportional to temperature and can be used for the absolute determination of the number of spins in a sample. Our results indicate that at low temperatures even 1016 spins of the anthracite sample, with a mass of about 0.5mg, can distort the EPR line.

Range tracking method based on adaptive “current” statistical model with velocity prediction

This study considers the problem of range tracking of a maneuvering target by an airborne digital array radar system. In the classic “current” statistical (CS) model, the maneuvering frequency α is not adaptive, and an acceleration limit has to be set. First, a new range tracking method called “adaptive CS model with velocity prediction” (ACSMVP) is proposed. This method utilizes the velocity prediction algorithm of cross product automatic frequency control with loop filter to measure the radial acceleration between the radar and the target. With the acceleration been obtained, the maneuvering frequency is derived, which is calculated in every tracking period. Second, an improved algorithm called “Sage–Husa-based ACSMVP” (SH-ACSMVP) is also proposed. In this algorithm, an online measuring noise covariance matrix is achieved by a simplified Sage–Husa estimator. Third, a Cramér-Rao lower bound of pulse-Doppler pulse train signal for range estimation is derived to assess the range tracking performance of the proposed algorithms. Simulations highlight the superior performance of our proposed algorithms over existing techniques.

An Automatic Frequency Controller for Kotmale Hydro Power Station using Fuzzy Logic

During supply demand mismatches, the system frequency can either fall or rise compared with its previous steady state operating value. In such instances, the generator governors either increase or decrease the generation (in accordance with the governor droop setting) to restore the supply demand balance and stop the ensuing frequency change (fall or rise). However, even after the supply demand balance has been restored and the frequency has reached a new steady state value, there can be a frequency error. The governor action assists to minimize the steady state frequency error. However, zeroing the frequency error and bringing the system frequency back to the rated value need adjustment to the “speed reference” of governors. Although this is normally done by Automatic Generation Controllers (AGC) that are on secondary load-frequency control, in Sri Lanka, the frequency controlling act is performed entirely manually through operator intervention. Such manual frequency control has a number of draw backs, including possible operator errors and longer response times. One of the four power stations designated to perform the frequency control function in the Sri Lankan power system is at Kotmale. This paper presents an automatic frequency controller using Fuzzy Logic to carry out frequency controlling at Kotmale power station. The Fuzzy Logic based controller is designed to replace the action of the operator, who presently controls the frequency manually. The paper presents the modeling and the simulation of the existing frequency control system using relevant parameters of the Kotmale governor and the chronological load curve of the Sri Lankan power system. MATLAB/SimulinkTM 2013 software package is used to calculate the steady state frequency error. Subsequently, the parameters are fine-tuned and the Fuzzy Logic Controller (FLC) is introduced as a secondary loop frequency controller and the study is repeated. Mamdani type fuzzy inference system is employed here to implement this project because of its simplicity, robustness, reliability and intuitive characteristics. Finally the simulation results using the FLC are compared with the existing frequency controlling system of Kotmale power station to prove that the FLC yields improved control performance.

A fast automatic frequency and amplitude control LC-VCO circuit with noise filtering technique for a fractional-N PLL frequency synthesizer

This work presents the design of an automatic frequency and amplitude control LC VCO circuit with noise filtering technique for fractional-N PLL frequency synthesizers. The LC VCO frequency of operation is from 2.158GHz to 5.133GHz. Phase noise of the LC VCO at 1MHz offset frequency is −123.0dBc/Hz and −116.8dBc/Hz for carrier signal frequency of 2.158GHz and 5.133GHz, respectively. The power consumption of the LC VCO without buffer circuit is 5.14mW from a 1.2V power supply and the fractional-N PLL has been implemented in 0.13μm standard CMOS process. A binary search fast frequency calibration process greatly reduces the overall locking time of the fractional-N PLL frequency synthesizers along with proposed PFD and a CP switching circuit and an efficient pulse swallow based fractional divider circuits, fractional bits are controlled by the HK-MASH 111 Digital Delta Sigma Modulator (DDSM). The fractional-N PLL is coarsely tuned within the maximum time of 1.825μs and the fractional-N PLL is locked within 4μs considering the worst case coarse tuning condition.

Participation of PMSG-based wind farms to the grid ancillary services

With the increased penetration of wind energy in many utility grids throughout the world, transmission system operators (TSO) are facing further difficulties regarding power system control and stability. Therefore, modern wind farms should participate to the primary voltage and frequency control of power systems. This paper presents the design of a supervisory control strategy for grid-connected wind farms. Wind turbines within the investigated wind farm are pitch controlled and use the Direct Drive technology. It has a total installed capacity of 50MW and it includes 25 PMSG-based wind turbines with a rated power of 2M each. The proposed supervisor is developed with all features that make the wind farm able to provide active and reactive power control. It includes automatic voltage and frequency control with droop and dead band. Performances of this supervisor are evaluated in terms of compliance with the Danish TSO requirements.

Математическое моделирование процессов автоматического регулирования частоты и мощности в ОЭС с солнечными электростанциями

The unstable nature of solar power plant (SPP) power output in the network determines the need for a comprehensive study of the relevant control processes and their impact on the operation of the power system, especially from the point of view of influence of processes of generation capacity in the SPP on the frequency, and on the relevant processes of automatic frequency and power control (AFPC). The mathematical model of the generation processes on the SPP included in the AFPC model allows to investigate the processes of regulation in the AFPC systems with traditional regulators (generators), and in the AFPC systems with fast controllable loads. On the example of interconnected power system (IPS) of Ukraine presents the results of experiments with the mathematical model of the SPP given in the article. It is established that for generators-regulators is a key limitation on the speed of the power set/reset, unlike controllable loads for which key is a maximum power limitation. It is revealed that under the condition of maximum power SPP equal to the maximum power of the generator-regulator of the power plant (3 GW) speed of the power set/reset of hydroelectric power provides effective regulation for the permissible frequency deviation of 0.02 Hz. Ceteris paribus, neither coal-fired nor oil-gas thermoelectric power station is not able to hold the frequency deviation even in the range of 0.2 Hz.

Computer Aided System for Superfinishing Process Control

Abstract Superfinishing is one of the techniques ensuring a very low value of surface roughness of the most common external assets. The roughness of the obtained surfaces depends on the proper selection of the abrasive material and processing parameters. Yield in superfinish machining with oscillating tool depends largely on the kinematics of the oscillating movement trajectory. The paper presents the superfinishing control system based on frequency control strategy of the oscillating motion. System was developed to study the process of the controlled oscillation frequency of a grinding tool. Frequency control was enabled by the use of an inverter which provided input to the motor that drives the oscillating head. A system for automatic frequency control of the oscillating motion using computer was developed. The inverter was connected via an analog to digital interface to a PC. Dedicated control software in Visual Basic was made for this purpose. Therefore, a single system for controlling a two-stage superfinishing process has been created. This ensured quality implementation of the optimal well-known method for processing. The presented control system provides wide possibilities for control of the surface grinding, and creates opportunities for further research in determining optimal grinding conditions.

Assessing the Possibility of Participation of Cross-Connection Thermal Power Plants in Assigned-Reserve Primary Frequency Control

The results of tests conducted at the Tobolsk CHPP confirm that cross-connection thermal power plants can participate in assigned-reserve primary frequency control and automatic secondary frequency and power-flow control.

A class-C VCO based Σ–Δ fraction-N frequency synthesizer with AFC for 802.11ah applications

A 1.4–2 GHz phase-locked loop (PLL) Σ–Δ fraction-N frequency synthesizer with automatic frequency control (AFC) for 802.11ah applications is presented. A class-C voltage control oscillator (VCO) ranging from 1.4 to 2 GHz is integrated on-chip to save power for the sub-GHz band. A novel AFC algorithm is introduced to maintain the VCO oscillation at the start-up and automatically search for the appropriate control word of the switched-capacitor array to extend the PLL tuning range. A 20-bit third-order Σ–Δ modulator is utilized to reduce the fraction spurs while achieving a frequency resolution that is lower than 30 Hz. The measurement results show that the frequency synthesizer has achieved a phase noise of < −120 dBc/Hz at 1 MHz offset and consumes 11.1 mW from a 1.7 V supply. Moreover, compared with the traditional class-A counterparts, the phase noise in class-C mode has been improved by 5 dB under the same power consumption.

Техніко-економічні аспекти використання споживачів-регуляторів у системах автоматичного регулювання частотою і потужністю

Техніко-економічні аспекти використання споживачів-регуляторів у системах автоматичного регулювання частотою і потужністю

Control and Monitoring of Power Facilities as Per LFC Standard

The article brings closer the principle of operation of the new power distribution system, LFC, being the successor of the ARCM SOWE system. The majority of the study is concentrated on the architecture of the local LFC system node authored by IASE sp. z o.o. there have been brought closer, here, the problems of automatic unit control in accordance with the plans and commands from the central LFC controller, of the system operation monitoring via the integrated SMPP module as well as the problems connected with the new technologies employed by LFC (the protocol ICCP-TASE.2 and the standard IEC60870-6, among other things). There have been also described the most important components, SRM LFC, responsible, among others, for the exchange of data with the unit automation, archiving and making available the historical data, setting and viewing of the current automatic control values transmitted by OSP. DOI: 10.12736/issn.2300-3022.2015109 1. General information, design requirements and short description of the LFC system LFC is a currently implemented, by PSE Operator SA, standard of the automatic frequency and power control system, the objective of which is the real-time operating and monitoring of the power generating units operated in the Polish electric power network, defined by the name of the centrally disposed generating units (Jednostki Wytworcze Centralnie Dysponowane (JWCD)). The LFC system is the successor of the SOWE system; it operates in a distributed environment, integrating into the available networks, JWCD, and realising the controls of the central controller of LFC (RC LFC). Each JWCD is autonomous in the LFC network and participates in the automatic power control process when it is officially admitted, by OSP, for operation in the production environment of LFC. The global system “intelligence” is wired in the central controller component, the basic task of which is to maintain the balance between the power produced and the current demand for it within KSE. RC LFC communicates with a power plant via the local node of the LFC system (WL LFC). The local node integrates various technological solutions applied on the facility site so that it is transparent for RC LFC. It conducts the direct or indirect dialogue with the unit automation, realising the controls from RC LFC and transferring back to WC SMPP the current values and the operating parameter states of JWCD. The official specification of WL LFC defines very precisely the way of conduction of the communication in the relation OSP WL LFC (the ICCP-TASE.2 protocol), but it does not impose any specific design solutions with respect to the communication of WL LFC with the automation systems of JWCD. The diversity of the technological solutions on the facility side translate directly into the complexity of the LFC local node implementation. The integration process of SRM LFC with the existing solutions is not trivial and requires the cooperation of all enterprises involved, in order to build a reliable infrastructure interconnecting each JWCD with RC LFC. The design requirements set for the local nodes have been made more precise by PSE Operator SA in two documents entitled ”Wymogi wobec JWCD na potrzeby wdrazania systemu LFC” (The requirements for JWCD for the purposes of implementation of the LFC system) and ”Procedura odbioru wezlow lokalnych systemu LFC w elektrowniach” (The procedure of acceptance of the local nodes of the LFC system). The following may be rated among the most important design goals of OSP: • high operational reliability of action of the whole system • provision of the redundancy of the hot spare type • fast switching between the master/slave modes of the SRM server instances D, Wojtanowicz et al. | Acta Energetica 1/22 (2015) | 121–127

Development and Examination of a Relay System for Automatic Control of Emission Frequency for Submerged Hydrodynamic Generators

A relay system for automatic control of emission frequency for a submerged hydrodynamic generator has been developed and examined. This system provides hydromechanical equipment operation calibration for formation dominant frequency. Mathematical model incorporates the presence of a long hydraulic line in a form of an extended well through which an actuating signal passes. Analytical expressions for amplitude and frequency of auto oscillation occurring in the system are obtained. The increase in delay time in the hydraulic line is found out to result in the decrease of frequency and increase of auto oscillation amplitude that is undesirable for efficient realization of vibroseismic impact. Numerical simulation of control system operation has demonstrated the qualitative validity of obtained theoretical findings.

Узагальнена математична модель та характеристики адаптивних систем автоматичного регулювання частоти і потужності

Узагальнена математична модель та характеристики адаптивних систем автоматичного регулювання частоти і потужності