7,545 research outputs found
Analysis of the effect of clock drifts on frequency regulation and power sharing in inverter-based islanded microgrids
© 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.Local hardware clocks in physically distributed computation devices hardly ever agree because clocks drift apart and the drift can be different for each device. This paper analyses the effect that local clock drifts have in the parallel operation of voltage source inverters (VSIs) in islanded microgrids (MG). The state-of-the-art control policies for frequency regulation and active power sharing in VSIs-based MGs are reviewed and selected prototype policies are then re-formulated in terms of clock drifts. Next, steady-state properties for these policies are analyzed. For each of the policies, analytical expressions are developed to provide an exact quantification of the impact that drifts have on frequency and active power equilibrium points. In addition, a closed-loop model that accommodates all the policies is derived, and the stability of the equilibrium points is characterized in terms of the clock drifts. Finally, the implementation of the analyzed policies in a laboratory MG provides experimental results that confirm the theoretical analysis.Peer ReviewedPostprint (author's final draft
A Code Phase Division Multiple Access (CPDMA) technique for VSAT satellite communications
A reference concept and implementation relevant to the application of Code Phase Division Multiple Access (CPDMA) to a high capacity satellite communication system providing 16 Kbps single hop channels between Very Small Aperture Terminals (VSAT's) is described. The description includes a potential implementation of an onboard CPDMA bulk demodulator/converter utilizing programmable charge coupled device (CCD) technology projected to be available in the early 1990's. A high level description of the system architecture and operations, identification of key functional and performance requirements of the system elements, and analysis results of end-to-end system performance relative to key figures of merit such as spectral efficiency are also provided
Advanced tracking systems design and analysis
The results of an assessment of several types of high-accuracy tracking systems proposed to track the spacecraft in the National Aeronautics and Space Administration (NASA) Advanced Tracking and Data Relay Satellite System (ATDRSS) are summarized. Tracking systems based on the use of interferometry and ranging are investigated. For each system, the top-level system design and operations concept are provided. A comparative system assessment is presented in terms of orbit determination performance, ATDRSS impacts, life-cycle cost, and technological risk
Multitones’ Performance for Ultra Wideband Software Defined Radar
This chapter proposes and tests an approach for an unbiased study of radar waveforms’ performances. Through an empirical performance analysis, the performances of Chirp and Multitones are compared with both simulations and measurements. An ultra wideband software defined radar prototype was designed and the prototype has performances comparable to the state of the art in software defined radar. The study looks at peak-to-mean-envelope power ratio, spectrum efficiency, and pulse compression as independent waveform criteria. The experimental results are consistent with the simulations. The study shows that a minimum of 10 bits resolution for the AD/DA converters is required to obtain near-optimum performances
Optical sampling and metrology using a soliton-effect compression pulse source
A low jitter optical pulse source for applications including optical sampling and optical
metrology was modelled and then experimentally implemented using photonic
components. Dispersion and non-linear fibre effects were utilised to compress a periodic
optical waveform to generate pulses of the order of 10 picoseconds duration, via
soliton-effect compression. Attractive features of this pulse source include electronically
tuneable repetition rates greater than 1.5 GHz, ultra-short pulse duration (10-15 ps), and
low timing jitter as measured by both harmonic analysis and single-sideband (SSB)
phase noise measurements. The experimental implementation of the modelled
compression scheme is discussed, including the successful removal of stimulated
Brillouin scattering (SBS) through linewidth broadening by injection dithering or phase
modulation. Timing jitter analysis identifies many unwanted artefacts generated by the
SBS suppression methods, hence an experimental arrangement is devised (and was
subsequently patented) which ensures that there are no phase modulation spikes present
on the SSB phase noise spectrum over the offset range of interest for optical sampling
applications, 10Hz-Nyquist. It is believed that this is the first detailed timing jitter study
of a soliton-effect compression scheme. The soliton-effect compression pulses are then
used to perform what is believed to be the first demonstration of optical sampling using
this type of pulse source.
The pulse source was also optimised for use in a novel optical metrology (range
finding) system, which is being developed and patented under European Space Agency
funding as an enabling technology for formation flying satellite missions. This new
approach to optical metrology, known as Scanning Interferometric Pulse Overlap
Detection (SIPOD), is based on scanning the optical pulse repetition rate to find the
specific frequencies which allow the return pulses from the outlying satellite, i.e. the
measurement arm, to overlap exactly with a reference pulse set on the hub satellite. By
superimposing a low frequency phase modulation onto the optical pulse train, it is
possible to detect the pulse overlap condition using conventional heterodyne detection.
By rapidly scanning the pulse repetition rate to find two frequencies which provide the
overlapping pulse condition, high precision optical pulses can be used to provide high
resolution unambiguous range information, using only relatively simple electronic detection circuitry. SIPOD’s maximum longitudinal range measurement is limited only
by the coherence length of the laser, which can be many tens of kilometres. Range
measurements have been made to better than 10 microns resolution over extended
duration trial periods, at measurement update rates of up to 470 Hz. This system is
currently scheduled to fly on ESA’s PROBA-3 mission in 2012 to measure the intersatellite
spacing for a two satellite coronagraph instrument.
In summary, this thesis is believed to present three novel areas of research: the first
detailed jitter characterisation of a soliton-effect compression source, the first optical
sampling using such a compression source, and a novel optical metrology range finding
system, known as SIPOD, which utilises the tuneable repetition rate and highly stable
nature of the compression source pulses
Timing Signals and Radio Frequency Distribution Using Ethernet Networks for High Energy Physics Applications
Timing networks are used around the world in various applications from telecommunications systems to industrial processes, and from radio astronomy to high energy physics. Most timing networks are implemented using proprietary technologies at high operation and maintenance costs. This thesis presents a novel timing network capable of distributed timing with subnanosecond accuracy. The network, developed at CERN and codenamed “White- Rabbit”, uses a non-dedicated Ethernet link to distribute timing and data packets without infringing the sub-nanosecond timing accuracy required for high energy physics applications. The first part of this thesis proposes a new digital circuit capable of measuring time differences between two digital clock signals with sub-picosecond time resolution. The proposed digital circuit measures and compensates for the phase variations between the transmitted and received network clocks required to achieve the sub-nanosecond timing accuracy. Circuit design, implementation and performance verification are reported. The second part of this thesis investigates and proposes a new method to distribute radio frequency (RF) signals over Ethernet networks. The main goal of existing distributed RF schemes, such as Radio-Over-Fibre or Digitised Radio-Over-Fibre, is to increase the bandwidth capacity taking advantage of the higher performance of digital optical links. These schemes tend to employ dedicated and costly technologies, deemed unnecessary for applications with lower bandwidth requirements. This work proposes the distribution of RF signals over the “White-Rabbit” network, to convey phase and frequency information from a reference base node to a large numbers of remote nodes, thus achieving high performance and cost reduction of the timing network. Hence, this thesis reports the design and implementation of a new distributed RF system architecture; analysed and tested using a purpose-built simulation environment, with results used to optimise a new bespoke FPGA implementation. The performance is evaluated through phase-noise spectra, the Allan-Variance, and signalto- noise ratio measurements of the distributed signals
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