International Telemetering Conference Proceedings / October 25-28, 1999 / Riviera Hotel and Convention Center, Las Vegas, Nevada / At present, there is no means of instrument direct measurement to frequency deviation when it is up 500kHz. But the frequency deviation of high bit rate telemetry transmitter is 700kHz or more. In this paper, an indirect measurement method using spectrum analyzer and counter is put forward. It effectively solves the measurement problem of frequency deviation and frequency response of high bit rate telemetry transmitters. Measuring theory, summary of experiences and difficulties in measuring work, have been deeply studied with the viewpoint of how to avoid the limitation of different methods of measurement. Focused on the establishment of an automatic measuring system, expert system, skilled data and software of the system are studied in detail. The data for comparison is also supplied. Finally, the analysis to the measuring error and general uncertainty is given.

This thesis presents a novel approach for a power system to find a practical power flow solution when all the generators in the system have hit their real power output limits, such as some generator units shutting down or load outages. The approach assumes the frequency of the system is unable to be kept at the rated value (usually 60 or 50 Hz) and accordingly, the generator real power outputs are affected by the system frequency deviation. The modification aims to include the system frequency deviation as a new state variable in the power flow so that the power system can be described in a more precise way when the generation limits are hit and the whole system is not operated under the normal condition. A new mathematical formulation for power flow is given by modified the conventional power flow mismatch equation and Jacobian matrix. The Newton – Raphson method is particularly chose to be modified because Newton – Raphson method is most widely used and it is a fast convergent and accurate method. The Jacobian matrix will be augmented by adding a column and a row. Matlab is used as a programming tool to implement the Power Flow for Long Term Frequency Stability (PFLTFS) method for a simple 4-bus system and the IEEE 118-bus system. And PSS/E Dynamic simulation is used to verify the steady state solution from PFLTFS is reasonable. The PSS/E Dynamic Simulation plots are used to analyze the long term frequency response. The PFLTFS method provides a technique for solving an abnormal state system power flow. From the results we can conclude that the PFLTFS method is reasonable for solving power flow of a real power unbalanced system.

The ionosphere is the conducting part of the upper atmosphere that plays a significant role in trans-ionospheric high frequency (HF, 3-30 MHz) radiowave propagation. Solar activities, such as solar flares, radiation storms, coronal mass ejections (CMEs), alter the state of the ionosphere, a phenomenon known as Sudden Ionospheric Disturbance (SID), that can severely disrupt HF radio communication links by enhancing radiowave absorption and altering signal frequency and phase. The Super Dual Auroral Radar Network (SuperDARN) is an international network of low-power HF coherent scatter radars distributed across the globe to probe the ionosphere and its relation to solar activities. In this study, we used SuperDARN HF radar measurements with coordinated spacecraft and riometer observations to investigate statistical characteristics and the driving mechanisms of various manifestations of solar flare-driven SIDs in HF observations. We begin in Chapter 2 with a statistical characterization of various effects of solar flares on SuperDARN observations. Simultaneous observations from GOES spacecraft and SuperDARN radars confirmed flare-driven HF absorption depends on solar zenith angle, operating frequency, and intensity of the solar flare. The study found flare-driven SID also affects the SuperDARN backscatter signal frequency, which produces a sudden rise in Doppler velocity observation, referred to as the ``Doppler flash'', which occurs before the HF absorption effect. In Chapter 3, we further investigate the HF absorption effect during successive solar flares and those co-occurring with other geomagnetic disturbances during the 2017 solar storm. We found successive solar flares can extend the ionospheric relaxation time and the variation of HF absorption with latitude is different depending on the type of disturbance. In Chapter 4, we looked into an inertial property of the ionosphere, sluggishness, its variations with solar flare intensity, and made some inferences about D-region ion-chemistry using a simulation study. Specifically, we found solar flares alter the D-region chemistry by enhancing the electron detachment rate due to a sudden rise in molecular vibrational and rotational energy under the influence of enhanced solar radiation. In Chapter 5, we describe a model framework that reproduces HF absorption observed by riometers. This chapter compares different model formulations for estimating HF absorption and discusses different driving influences of HF absorption. In Chapter 6, we have investigated different driving mechanisms of the Doppler flash observed by SuperDARN radars. We note two particular findings: (i) the Doppler flash is predominantly driven by a change in the F-region refractive index and (ii) a combination of solar flare-driven enhancement in photoionization, and changes in the zonal electric field and(or) ionospheric conductivity reduces upward ion-drift, which produces a lowering effect in the F-region HF radiowave reflection height. Collectively, these research findings provide a statistical characterization of various solar flare effects on the ionosphere seen in the HF observations, and insights into their driving mechanisms and impacts on ionospheric dynamics. / Doctor of Philosophy / The Earth's ionosphere, extending from about 60 km to 1000 km in altitude, is an electrically charged region of the upper atmosphere that exists primarily due to ionization by solar X-ray and extreme ultraviolet radiation. The ionosphere is an effective barrier to energetic electromagnetic (EM) radiation and charged particles originating from the Sun or any other extraterrestrial sources and protect us against harmful space radiation. High frequency (HF, 3-30 MHz) radio communication, broadly used for real-time medium and long-range communication, is strongly dependent on the state of the ionosphere, which is susceptible to solar activities, such as solar flares, solar energetic particles (SEPs), and coronal mass ejections (CMEs). Specifically, we are interested in the impacts of solar flares. In this study, we use Super Dual Auroral Radar Network (SuperDARN) HF radars, ground-based riometers, and coordinated spacecraft observations to investigate the driving mechanisms of various space weather impacts on the ionosphere and radiowave propagation following solar flares. We begin in Chapter 2 with a characterization of various kinds of ionospheric disturbances manifested in SuperDARN backscattered signal following solar flares. Specifically, we characterized HF absorption effects and frequency anomalies experienced by traveling radiowaves, also known as Shortwave Fadeout (SWF) and Sudden Frequency Deviations (SFDs), respectively. In SuperDARN HF radar observations, SFDs are recorded as a sudden enhancement in Doppler velocity, which is referred to as the ``Doppler flash''. In Chapter 3, we investigate a special event study that elucidates the nonlinear physics behind HF absorption caused by multiple simultaneous solar flares and flares co-occurring with SEPs and CMEs. In Chapter 4, we explore an inertial property of the ionosphere, known as sluggishness, and its dependence on solar flares can provide important information about the chemical proprieties of the ionosphere. We found that the enhanced solar radiation during a solar flare increases the molecular vibrational and rotational energy that in turn enhances the electron detachment rate and reduces ionospheric sluggishness. In Chapter 5, we describe a framework to estimate HF absorption observed by riometers following solar flares. We analyze the influence of different physical parameters, such as collision frequency and electron temperature, on HF absorption. In Chapter 6, we delved into the physical processes that drive the Doppler flash in SuperDARN observations following solar flares. We find, (i) the Doppler flash is predominately driven by change in the F-region refractive index and (ii) a combination of solar flare-driven enhancement in photoionization, and change in zonal electric field and(or) ionospheric conductivity reduces upward ion-drift, which produces a lowering effect in the F-region HF radiowave reflection height. Taken together, these research findings provide new insights into solar flare impacts on the ionosphere and could be used to improve forecasting of ionospheric space weather disturbances following solar flares.

The rise of Renewable Energy Sources (RES) such as wind and solar power, creates new challenges for electric power systems. One of these challenges occur in Frequency Containment Reserves (FCR) on power system because of decreasing system inertia from RES. The purpose of FCR is to regulate the system frequency after a disturbance that gives rise to a Rate of Change of Frequency (RoCoF) and an Instantaneous Frequency Deviation (IFD). Conventional electricity production such as hydro and nuclear power have a contribution for the amount of inertia in the system, while RES lack this contribution of inertia.This paper studies different cases of amount of inertia to understand the impact of lower amount of inertia caused by RES on power system. A power system was simulated and the IFD and SteadyState Frequency Deviation (SSFD) of the system were examined as the nuclear powers were substituted by wind powers. The results showed that a large amount of inertia implies a small IFD and vice versa.Furthermore, this paper also studies Battery Energy Storage System (BESS) as a power support for FCR when using RES. The conclusion for the impact of the battery was to use high injected power and triggering frequency level (TLF) and vice versa to get an acceptable IFD. In other words, this means that it is possible to keep the IFD within predefined limits by using batteries and identify the appropriate range of battery control settings.

Fade and inter-fade duration data obtained from the three beacons at 12, 20, and 30 GHz aboard the OLYMPUS satellite were analyzed. The different types of signal impairments and their causes were highlighted and a literature survey conducted. Twelve months of fade and inter-fade data were analyzed and the results of these statistics are presented in the form of tables and figures. The analysis was done on both the monthly and annual data. These tables and figures show that at the higher fade levels, the number of fade events and the fade time is smaller than at the lower thresholds. For the same fade level the number of fade events and the fade time goes down as the fade duration which it exceeds is increased. Inter-fade durations also showed similar results. The fades exhibited seasonal dependencies. The number of fades (and consequently the fade time) were much higher for the months of May through August and for the months of March and December. The other months showed very little fade activity. A model was also constructed that can predict the fade time as a function of frequency, attenuation level, and fade duration interval. The predicted fade times agree well with the measured fade duration data. An alternate simplified version of the model is also presented. / Master of Science

Two algorithms for estimating the frequency and power of the carriers of 20 GHz and 30 GHz satellite signals are compared. Both algorithms operate on a prefiltered sequence generated by lowpass filtering followed by signal decimation for the purpose of sampling rate reduction. The lowpass filtering is accomplished via the overlap-add method of FIR filtering using the FFT. Carrier frequency prediction and tracking is accomplished with a Kalman predictor, for which the frequency drift process is modeled via polynomial extrapolation. The Kalman predictor operates on frequency measurements provided by one of two frequency estimators. One of the frequency estimation algorithms, a refinement of the DFT-automatic frequency control technique, uses the Chirp-Transform algorithm in its aim for the maximum likelihood estimate of frequency and power. The averaged periodogram is computed from the prefiltered sequence and is used to measure the frequency of the drifting frequency signal as well as its power. One of the disadvantages of this algorithm is the bias present in the estimation of power. The bias can be removed only with knowledge of the noise power. The algorithm has the advantage of being almost exclusively a convolution and therefore is accomplished with minimal computation via the FFT. An alternative parametric approach to frequency estimation is also investigated. In this approach the weighted least-squares modified Yule-Walker method of autoregressive model estimation is used on the prefiltered sequence to yield frequency estimates. Power estimation is accomplished next via modal decomposition of the estimated correlation sequence. The advantage of this approach is that for slowly varying frequency drift paths (24 hour cycle) the frequency estimates exhibit MSE approximately 3 dB less than the Chirp-Transform algorithm over a wide range of SNR. There are two disadvantages to the parametric algorithm. First the parametric algorithm estimates power with MSE approximately 2 dB greater than the nonparametric algorithm. Secondly the algorithm is more complicated than the nonparametric Chirp-Transform algorithm because it requires matrix inversions and the determination of the roots of a polynomial. For the digital beacon receiver problem investigated here both algorithms perform similarly in two important respects. First both algorithms can lock onto a carrier signal whose frequency is drifting at the rate of 5 Hertz per second in a noise environment corresponding to a 15 dB/Hz SNR. Secondly both algorithms can make unbiased frequency estimates of the carrier signal allowing the receiver to track the carrier at 7 dB/Hz SNR. Both algorithms attain the Cramer-Rao bound for estimation of constant frequency sinusoids. For a simulated satellite signal with maximum frequency drift of 5 Hertz per second the Kalman frequency predictor is able to reduce the problem to nearly that of the constant frequency case so that the resulting performance corresponds to the Cramer-Rao bound for estimation of constant frequency sinusoids. Where computational considerations are critical the nonparametric algorithm is preferred. In fact, unless the superior accuracy of the frequency prediction afforded by the parametric algorithm is paramount, the nonparametric algorithm is to be chosen. / Master of Science

Fundação de Amparo a Pesquisa do Estado de Minas Gerais / The purpose of this work is to present an active and reactive power flow controller applied to inverter paralelism with the stiff AC system. An additional loop is implemented into a conventional control loop based on the characteristic curves of active power versus frequency and reactive power versus voltage. This loop uses the active power variation as feedback to generate the load angle of the voltage reference of the inverter, when it is connected in parallel with the electric network. As a consequence, the active and reactive transitory power oscillations are atenuated, without producing undesirable colateral effects as significative voltage and reactive power variations presented in the utilization of PSS (Power System Stabilizer), another technique used to improve the system damping, [Martins, M. P., 2004]. A dynamic model of the system based on the small signal analysis is presented. The root locus graphics, showing the system poles under parametric variations are also presented, allowing the analysis of the system stability. The simulation results and the experimental ones using a laboratory prototype with and without the additional loop are showed, which validate the obtained small signal model. / Este trabalho apresenta um controlador de fluxos de potência ativa e reativa aplicado ao paralelismo de um inversor com a rede elétrica. Uma malha adicional de controle é inserida a um controlador convencional, o qual é baseado nas curvas características de potência ativa versus freqüência e potência reativa versus tensão. Essa malha utiliza a realimentação da própria variação da potência ativa para a geração do ângulo de carga da tensão de referência do inversor, quando o mesmo é conectado em paralelo com a rede elétrica. Como resultado as oscilações transitórias das potências ativa e reativa são melhor atenuadas, sem produzir efeitos colaterais indesejáveis tais como as variações de tensão e potência reativa presentes na utilização do PSS (Power System Stabilizer Estabilizador de Sistemas de Potência), outra técnica usada para melhorar o amortecimento do sistema, [Martins, M. P., 2004]. Um modelo dinâmico do sistema baseado na análise para pequenos sinais é apresentado. Gráficos do lugar das raízes, mostrando os pólos do sistema diante de variações paramétricas também são apresentados, permitindo a análise de estabilidade do sistema. Resultados de simulação e resultados experimentais utilizando-se um protótipo de laboratório, com e sem a malha de realimentação adicional são mostrados, os quais validam o modelo para pequenos sinais obtido. / Doutor em Ciências

Wide Area Measurements (WAMs) have been widely used in the energy management system (EMS) of power system for monitoring, operation and control. In recent years, the advent of synchronized Phasor Measurements Unit (PMU) has added another dimension to the field of wide-area measurement. However, the high cost of the PMU, which includes the manufacture and deployment fee, is a hurdle to the wide use of the PMU in power systems. Unlike traditional PMUs, the frequency monitoring network (FNET) developed by the Virginia Tech Power IT lab is an Internet—based, GPS—synchronized, wide-area frequency monitoring network deployed at the distribution level, providing a low-cost and easily deployable WAMs solution. In this dissertation, the research work can be categorized into two parts: FNET Design and Situation Awareness Algorithm Development. / Ph. D.