Generalised dq-dynamic phasor modelling of STATCOM connected to a grid for stability analysis

The synchronous dq based small-signal stability using the eigenvalue analysis and impedance methods is widely employed to assess system stability. Generally, the harmonics are ignoredin stability analysis which may lead to inaccuracies in stability predictions, particularly, when the system operates in a harmonic-richenvironment. Typically, the harmonic state-space method (HSS) facilitates stability studies of linear time-periodic (LTP) systems, which considersthe impact of harmonics. The use of the dq-dynamic phasor state space and impedance method offers significant advantages over the HSS counterpart, as it reduces system order, is more suitable for studying control systems, retains mutual coupling of harmonics, and simplifies the stability study under unbalanced conditions. This paper extends dynamic phasor modelling for studying stability of modern power systems that include power converters. It is shown that the proposed method reproduces the typical response of STATCOM at the fundamental frequency as well as at significant low-order harmonics using both eigenvalues and impedance analysis. Quantitative validations of the proposed extended models against synchronous dq small signal models confirm their validity

Robustness analysis for power systems based on the structured singular value tools and the [nu] gap metric

Modern power systems are operated more stressed than ever because of the advent of deregulation and competition. One of the important issues in the design of controllers for a stressed system is to evaluate the stability of the controlled system over a range of operating conditions.;The conventional controllers are designed to make the system stable under certain conditions of operation. The time consuming time domain simulation is then used to evaluate the controllers for a few selected operating conditions around which the controllers are designed. Such a design and evaluation procedure cannot guarantee robustness of the controller over the whole range of operating conditions.;In this dissertation, practical algorithms to perform robustness analysis based on two tools, structured singular value and the nu gap metric, are investigated. The power system stabilizer is used as the controller and small signal stability is of interest.;The robustness problem in the SSV framework is set up for the multimachine power system. In this formulation, an improved uncertainty characterization has been used to capture the effect of parameter variations in terms of the varying elements of the linearized system matries, which are derived from the component differential equations and the network algebraic equations separately. SVD decomposition is used to reduce the size of the problem. Based on the resulting framework, a branch and bound scheme is proposed to intelligently select frequency intervals on which the frequency sweep test can be performed further to find the peak of mu. Instead of blindly choosing frequency intervals to sweep, which could ignore important frequency points on the mu plots, this scheme provides searching under guidance. The analysis procedure accurately predicts the range of stable operating conditions which are verified by repeated eigenvalue analysis.;Fir the robustness in terms of nu gap metric, we set up the feedback configuration for multimachine power system. The frequency response of the nu gap metric is plotted and its relationship with that of the stability margin is used to determine the stability of the perturbed systems. A weighted nu gap metric is defined and its frequency domain interpretation is explored to further reduce the conservatism of the results.;Finally, a feedback configuration is carefully developed to carry out the McFarlane and Glover Hinfinity loop shaping design procedure. The effect of the damping controller on improving system dynamic performance is also examined.;Comparisons are made between the two major analysis tools via the results on the same test systems with the same scenarios

Passivity-Based Decentralized Criteria for Small-Signal Stability of Power Systems with Converter-Interfaced Generation

With the increasing penetration of converter-interfaced distributed generation systems, it would be advantageous to specify local compliance criteria for these devices to ensure the small-signal stability of the interconnected system. Passivity of the device admittance, which is an example of a local criterion, has been used previously to avoid resonances between these devices and the lightly damped oscillatory modes of the network. Typical active and reactive power control strategies like droop control and virtual synchronous generator control inherently violate the passivity constraints on admittance at low frequencies, although this does not necessarily mean that the interconnected system will be unstable. Therefore, passivity of the admittance is unsuitable as a stability criterion for devices that are represented by their wide-band models. To overcome this problem, this paper proposes the use of criteria based on admittance at higher frequencies and an alternative transfer function at lower frequencies. The alternative representation uses active and reactive power and the derivatives of the polar components of voltage as interface variables. To allow for the separate analysis at low and high frequencies, the device dynamics should exhibit a slow-fast separation; this is proposed as an additional constraint. Adherence to the proposed criteria is not onerous and is easily verifiable through frequency response analysis

Broadband Methods in Dynamic Analysis and Control of Battery Energy Storage Systems

Battery energy storage systems have become essential in the operation of many modern power-distribution systems, such as dc microgrids, electric ships, and electric aircraft. Energy storage systems often rely on the operation of bidirectional converters to control the power flow. In modern power systems, these bidirectional converters are typically a part of an extensive converter system, a multi-converter system that consists of several electrical converter-based sources and loads. Even though each converter in a multi-converter system is standalone stable, adverse interactions between the interconnected converters can present issues to the system’s performance and stability. Assessing the stability of multi-converter systems is usually challenging, given that the systems are complex, and the dynamics are affected by various operating modes and points. Recent studies have presented methods for assessing the stability of interconnected converters through impedance-based stability criterion. Impedance-based analysis is particularly advantageous for complex multi-converter systems as this method does not require the knowledge of intricate details of the system’s parameters. The method can also facilitate adaptive stabilizing control schemes using reliable and fast identification implementations. However, impedance identification of multi-converter systems is typically challenging due to the coupled nature of the interconnected converters and potential non-linear behavior. Moreover, the bidirectional power flow of battery energy storage systems further complicates the stability assessment. This thesis presents small-signal modeling methods, online stability assessment methods, and adaptive stabilizing control strategies for multi-converter systems that have bidirectional converters. The accuracy of traditional, small-signal-model-based converter control design is enhanced with a procedure that extends a converter’s small-signal model with given load and source dynamics. In addition, frequency response identification methods are used to assess the system stability under varying operating conditions. The presented identification methods offer reliable and quick impedance measurements and stability assessment among several converters. The design aims to minimize the interference on the system, which allows the identification during the system’s regular operation. The stability assessment provides a platform for adaptive stabilizing control methods, and two such techniques are implemented on a bidirectional converter. Several experimental results confirm the effectiveness of the proposed methods

Channel Modeling and Direction-of-Arrival Estimation in Mobile Multiple-Antenna Communication Systems

Antennas that are able to adaptively direct the transmitted (and received) energy are of great interest in future wireless communication systems. The directivity implies reduced transmit power and interference, and also a potential for increased capacity. This thesis treats some modeling and estimation problems in mobile communication systems that employ multiple antennas, primarily at the base stations. With multiple antennas at the receive side, the spatial dimension is added, and processing is performed in both the temporal and spatial domains. The potential benefits are increased range, fading diversity and spatially selective transmission. Specifically, the problems dealt in this thesis are mainly related to the uplink transmission from mobile to the base station. Two main topics are studied, channel modeling and estimation of channel parameters. This thesis first describes the modeling of the reflected power distribution due to the scatterers close to the mobile stations, in terms of the received signal azimuth at the base station with multiple-antenna. As a more realistic channel modeling, a multipath fading deterministic channel model is proposed to generate properly correlated faded waveforms with appropriate power distribution through azimuth spread of received signal. The purpose of the proposed channel model is to model fading received signal waveforms with Laplacian distribution of power through received signal azimuth spread. This thesis is divided into two parts; in the first part multipath fading by local scattering are used to derive a channel model including the spatial dimension for non frequency-selective fading. This means that the mobile is not modeled as a point source but as a cluster of a large number of independent scatterers with small time delay spread to take into account angular spreading of the signal. Properly correlated fading waveforms are obtained by taking into account the angular spread of the scattered signals from a particular distribution of scatterers. By appropriate scaling of the array response vector (ARV) based on non-equal locations for various received signal components as a function of distance from the transmitter, the reflected power from a given scatterer is no longer constant but varies as a function of the distance from the transmitter. Our proposed channel model is able to produce fading signal waveform which agrees with the results of reflected angular power dispersions measured in the field, e.g. Laplacian distribution of power in azimuth. It is also shown that the channel response can be modeled as a complex Gaussian vector. Although the channel will be frequency selective in the case of multipath propagation with considerable time spread, this can be modeled as having more than one cluster of scatterers. By employing Walsh-Hadamard codewo VdLrs)l wideband multipath fading model is achieved. It is shown that the statistical properties of proposed model such as signal waveform's correlation, autocorrelation and crosscorrelation between generated paths, are in good agreement with the theory in space and time domain. The model can be applied to evaluate smart antenna systems and beamforming algorithms in the uplink by generating uncorrelated multipaths Rayleigh fading waveforms with certain spatio-temporal correlation and spatial coordinates relative to base stations to simulate received signals from mobiles and interferers. Bit-error-rate (BER) performance analysis of uniform linear array antenna (ULA) based on correlation - matrix is also presented as an application of our proposed model for multipleantenna evaluations. Our simulated results show 5% improvement than other published related works. One problem when modeling frequency selective fading is that each cluster has to be assigned spatial parameters. Since the joint spatial and temporal characteristics are unknown, non-parametric channel estimation approaches are required in this case in order to estimate the channel parameter, which is the subject of the second part. The second part of the thesis deals with channel parameter estimation of distributed scattering sources. Because of local scattering around the transmitter the signal waveforms appears spatially distributed at the receiver. The characterization of the spatial channel, in particular mean direction of arrival and spatial spread, is of prime interest for system optimization and performance prediction. Low-complexity spectral-based estimators are used for the estimation of direction and spatial spread of the distributed source by employing the proposed channel model for simulation. Estimated parameters from recent measurements ([PMFOO]) are compared with estimated parameters from model generated waveforms as well as theoretical distribution of received signal's angular spread. Good agreement between them is observed which shows the correctness of our proposed channel model for simulating spatio-temporally correlated received signal at an antenna array. The estimated parameter error improved by 5% over the other published related works

CHARACTERIZATION AND MODELING OF III-V TRANSISTORS FOR MICROWAVE CIRCUIT DESIGN

New mobile communication technologies have given a boost to innova-tions in electronic for telecommunications and microwave electronics. It’s clear that the increasing request for mobile data availability, as proved by the growth of 69% of mobile data traffic in 2014, poses great challenges to indus-tries and researchers in this field. From this point of view a rapid diffusion of wireless mobile broadband network data standards, like LTE/4G, should be seen, which requests a state-of-the-art transceiver (i.e., transmitter/receiver) electronics. It will be mandato-ry to use higher frequencies, with wider bandwidth and excellent efficiency, to improve battery duration of mobile phones and reduce the energy consump-tion of the network infrastructures (i.e. base stations). Moreover, the microwave electronics is ubiquitous in satellite systems. As an example the GPS-GLONASS systems, developed respectively by United-States and Russian Federation for geo-spatial positioning, now are commonly used as navigation support for planes, ships, trains, automobiles, and even people. Other interesting applications are the earth-observation satellites, like the Italian system COSMO-SkyMed: a constellation of four satellites developed for the observation of the entire planet. These systems are able to produce a detailed image of the earth surface exploiting a microwave synthetic aperture radar, with the possibility to observe an area even by night or with bad weather conditions. Clearly these features are impossible for traditional opti-cal systems. Even if a lot of electronic applications are focused on the system architec-ture, in microwave electronics the single transistor still plays a key role. In-deed, the number of transistors in high-frequency circuits is low and wide ar-eas are occupied by numerous passive elements, required to optimize the sys-tem performance. There is a lot of interest in finding the optimum transistor operating condition for the application of interest, because the high-frequency electron-device technologies are relatively young and often still in develop-ment, so the transistor performance is generally poor. As a matter of fact, transistor characterization plays a very important role: various measurement systems, developed for this purpose, have been pro-posed in literature, with different approaches and application fields. Moreover, a meticulous characterization of the transistor is the basis for the identification of accurate models. These models, allowing to predict the tran-sistor response under very different operating conditions, represent a funda-mental tool for microwave circuit designers. This thesis will resume three years of research in microwave electronics, where I have collaborated in research activities on transistor characterization and modelling oriented to microwave amplifier design. As various kinds of amplifiers (i.e., low-noise amplifier, power amplifier) have been developed, various characterization techniques have been exploited. In the first chapter, after a presentation of the most common large-signal characterization systems, a low-frequency large-signal characterization setup, oriented to transistor low-frequency dispersion analysis and power amplifier design, will be described as well as the development of the control algorithm of the measurement system and its application to the design of a Gallium-Nitride class-F power-amplifier, operating at 2.4 GHz with 5.5 W of output power and 81% efficiency. Another application of the proposed setup for fast-trap characterization in III-V devices is then reported. Successively, an exten-sion of the setup to very low frequencies will be presented. In the second chapter, small-signal characterization techniques will be dealt with, focusing on noise measurement systems and their applications. Af-ter a brief introduction on the most relevant small-signal measurement system (i.e., the vector network analyzer), an innovative formulation will be intro-duced which is useful to analyze the small-signal response of Gallium-Arsenide and Gallium-Nitride transistors at very low frequencies. Successive-ly, the application of neural network to model the low-frequency small signal response of a Gallium-Arsenide HEMT will be investigated. The third and last chapter will deal with the EM-based characterization of Gallium-Nitride transistor parasitic structures and its usage, combined with small-signal and noise measurements, for developing a transistor model ori-ented to low-noise amplifiers design. In particular, the design of a three stages low-noise amplifier with more than 20 dB of gain and less than 1.8 dB of noise figure operating in Ku-band will be described

A Controller for Optimum Electrical Power Extraction from a Small Grid-Interconnected Wind Turbine

[EN] Currently, wind power is the fastest-growing means of electricity generation in the world. To obtain the maximum efficiency from the wind energy conversion system, it is important that the control strategy design is carried out in the best possible way. In fact, besides regulating the frequency and output voltage of the electrical signal, these strategies should also extract energy from wind power at the maximum level of efficiency. With advances in micro-controllers and electronic components, the design and implementation of efficient controllers are steadily improving. This paper presents a maximum power point tracking controller scheme for a small wind energy conversion system with a variable speed permanent magnet synchronous generator. With the controller, the system extracts optimum possible power from the wind speed reaching the wind turbine and feeds it to the grid at constant voltage and frequency based on the AC-DC-AC conversion system. A MATLAB/SimPowerSystems environment was used to carry out the simulations of the system. Simulation results were analyzed under variable wind speed and load conditions, exhibiting the performance of the proposed controller. It was observed that the controllers can extract maximum power and regulate the voltage and frequency under such variable conditions. Extensive results are included in the paper.This work was partially supported by the Spanish Ministry of Education, Culture and Sports-reference FPU16/04282.García-Sánchez, TM.; Mishra, AK.; Hurtado-Perez, E.; Puche-Panadero, R.; Fernández-Guillamón, A. (2020). A Controller for Optimum Electrical Power Extraction from a Small Grid-Interconnected Wind Turbine. Energies. 13(21):1-16. https://doi.org/10.3390/en13215809S1161321Fernández-Guillamón, A., Villena-Lapaz, J., Vigueras-Rodríguez, A., García-Sánchez, T., & Molina-García, Á. (2018). An Adaptive Frequency Strategy for Variable Speed Wind Turbines: Application to High Wind Integration Into Power Systems. Energies, 11(6), 1436. doi:10.3390/en11061436Fernández-Guillamón, A., Sarasúa, J. I., Chazarra, M., Vigueras-Rodríguez, A., Fernández-Muñoz, D., & Molina-García, Á. (2020). Frequency control analysis based on unit commitment schemes with high wind power integration: A Spanish isolated power system case study. International Journal of Electrical Power & Energy Systems, 121, 106044. doi:10.1016/j.ijepes.2020.106044Huber, M., Dimkova, D., & Hamacher, T. (2014). Integration of wind and solar power in Europe: Assessment of flexibility requirements. Energy, 69, 236-246. doi:10.1016/j.energy.2014.02.109Fernández-Guillamón, A., Martínez-Lucas, G., Molina-García, Á., & Sarasua, J.-I. (2020). Hybrid Wind–PV Frequency Control Strategy under Variable Weather Conditions in Isolated Power Systems. Sustainability, 12(18), 7750. doi:10.3390/su12187750Fernández‐Guillamón, A., Vigueras‐Rodríguez, A., & Molina‐García, Á. (2019). Analysis of power system inertia estimation in high wind power plant integration scenarios. IET Renewable Power Generation, 13(15), 2807-2816. doi:10.1049/iet-rpg.2019.0220Fernández-Guillamón, A., Das, K., Cutululis, N. A., & Molina-García, Á. (2019). Offshore Wind Power Integration into Future Power Systems: Overview and Trends. Journal of Marine Science and Engineering, 7(11), 399. doi:10.3390/jmse7110399Muñoz-Benavente, I., Hansen, A. D., Gómez-Lázaro, E., García-Sánchez, T., Fernández-Guillamón, A., & Molina-García, Á. (2019). Impact of Combined Demand-Response and Wind Power Plant Participation in Frequency Control for Multi-Area Power Systems. Energies, 12(9), 1687. doi:10.3390/en12091687Gil-García, I. C., García-Cascales, M. S., Fernández-Guillamón, A., & Molina-García, A. (2019). 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Influence of Intrinsic Trapping on The Performance Characteristics of ZnO-Bi 2

The lumped parameter/complex plane analysis technique reveals several contributions to the ac small-signal terminal immittance of the ZnO-Bi2O3 based varistors' grain-boundary response. The terminal capacitance constitutes multiple trapping phenomena, a barrier layer contribution, and a resonance effect in the frequency range 10-2 ≤ f ≤ 109 Hz. A trapping response near to ∼105 Hz (∼10-6 s), observed via the loss-peak and a distinct depressed semicircular relaxation in the complex capacitance plane, is common to all well-formed (exhibiting good performance for applications) devices regardless of the composition recipe and processing route. This trapping is attributed to possible formation of ionized intrinsic or native defects, and believed to be predominant within the electric field falling regions across the microstructural grain-boundary electrical barriers. The nature of rapidity of this intrinsic trapping and the corresponding degree of uniformity/non-uniformity can be utilized in conjunction with relevant information on other competing trapping phenomena to assess an overall performance of these devices. The constituting elements, responsible for the average relaxation time of the intrinsic trapping, indicate some sort of possible surge arrester (i.e., suppressor/absorber) applications criteria in the power systems' protection. The factors related to materials' history, composition recipe, and processing variables influence or modify relative magnitudes and increase or decrease the visibility of the constituting elements without distorting devices' generic dielectric behavior

Requirements to Testing of Power System Services Provided by DER Units

The present report forms the Project Deliverable ‘D 2.2’ of the DERlab NoE project, supported by the EC under Contract No. SES6-CT-518299 NoE DERlab. The present document discuss the power system services that may be provided from DER units and the related methods to test the services actually provided, both at component level and at system level