Measurement, control and protection of microgrids at low frame rates supporting security of supply

Increasing penetrations of distributed generation at low power levels within electricity networks leads to the requirement for cheap, integrated, protection and control systems. To minimise unit cost, algorithms for the measurement of AC voltage and current waveforms should be implemented on a single microcontroller, which also carries out all other protection and control tasks, including communication and data logging. This limits the frame rate of the major algorithms, although ADCs can be over-sampled using peripheral control processors on suitable microcontrollers. Measurement algorithms also have to be tolerant of poor power quality which may arise, even transiently, within a microgrid, battlefield, or disaster-relief scenario. This thesis analyses the potential magnitude of these interfering signals, and presents suitably tolerant architectures and algorithms for measurements of AC waveforms (amplitude, phase and frequency). These algorithms are shown to be robust and accurate, with harmonic content up to the level of 53% THD, and with the major algorithms executing at only 500 samples per second. This is achieved by the careful optimisation and cascaded use of exact-time averaging techniques, which prove to be useful at all stages of the measurements: from DC bias removal to low-sample-rate Fourier analysis to sub-harmonic ripple removal. Algorithms for three-phase nodal power flow analysis are benchmarked on the Infineon TC1796 microcontroller and require less than 8% of the 2000μs frame time, leaving the remainder free for other algorithms. Furthermore, to optimise security of supply in a microgrid scenario, loss-of-mains must be detected quickly even when there is an accidental or deliberate balance between local active power generation and demand. The measurement techniques are extended to the detection of loss-of-mains using a new Phase Offset relay, in combination with a novel reactive power control technique to avoid the non-detection-zone. These techniques are tested using simulation, captured network transient events, and a real hardware microgrid including a synchronous generator and inverter

Automated design synthesis of CMOS operational amplifers

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1994.Includes bibliographical references (p. 159-161).by Ognen J. Nastov.M.S

Implementation of DSP-based algorithms on USRP for mitigating non-linear distortions in the receiver

In recent years, software-defined radio (SDR) has attracted increasingly more attention in regards to modern communication systems. The concept of SDR defines a radio device that is capable of flexibly reconfiguring its radio interface by software. This opens multiple fields of application and makes SDR an enormously adjustable and versatile radio technology. However, RF impairments induced by cheap and simple RF front-ends turn out to be a significant limitation in practice. Non-linear distortions emerge from non-linear components of the direct down-conversion chain that are driven into their saturation level. This is a result of a finite linearity and limited dynamic range of the RF frontend. The focus of this thesis are non-linear distortions in wideband receivers and a mitigation of them by means of digital signal processing. The idea is to artificially regenerate the non-linear distortions in the digital domain by applying a memoryless, polynomial model. An adaptive filter adjusts these reference distortions in their magnitude and phase and subtracts them from the distorted signal. A hardware implementation of a mitigation algorithm on a typical SDR-platform is presented. No prior implementation of this pure-digital approach is known. An implementation design flow is described following a top-down approach, starting from a fixed-point high-level implementation and ending up with a low-level hardware description language implementation. Both high-level and low-level simulations help to validate and evaluate the implementation. In conclusion, the implementation of the mitigation algorithm is a sophisticated mitigation technique for cleaning a down-converted baseband spectrum of non-linear distortions in real-time. Therefore, the effective linearity of the RF front-end is increased. This may lead to a significant improvement in the bit error rate performance of cleansed modulated signals, as well as to an enhanced sensing reliability in the context of cognitive radio.Zusammenfassung: In den letzten Jahren sorgte Software-Defined Radio (SDR) in Bezug auf moderne Kommunikationssysteme für immer größere Aufmerksamkeit. Das Konzept von SDR bezeichnet ein Funkgerät, das in der Lage ist, seine Funkschnittstelle durch Software flexibel zu rekonfigurieren. Dies ermöglicht eine Vielzahl von Anwendungsmöglichkeiten und macht SDR zu einer enorm anpassungsfähigen und vielseitigen Funktechnologie. Allerdings stellen im HF-Frontend ausgelöste Störungen in der Praxis eine erhebliche Einschränkung dar. In direkt umsetzenden Empfängerstrukturen entstehen durch nichtlineare Komponenten, die in ihren Sättigungsbereich getrieben werden, nichtlineare Verzerrungen. Das ist ein Ergebnis der begrenzten Linearität und des Dynamikbereich des HF-Frontends eingeschränkt sind. Der Fokus der Arbeit liegt auf nichtlinearen Verzerrungen in breitbandigen Empfängern und deren Minderung mit Hilfe von digitaler Signalverarbeitung. Die Idee ist, die nichtlinearen Verzerrungen im digitalen Bereich auf Basis eines gedächtnislosen, Polynom-Modells zu regenerieren. Ein adaptives Filter passt dabei den Betrag der nichtlinearen Referenzverzerrungen an und subtrahiert diese vom verzerrten Signal. In der Arbeit wird eine Hardwareimplementierung eines Störungsminderungsalgorithmus auf einer typischen SDR Plattform vorgestellt. Bisher ist keine Implementierung des rein-digitalen Ansatzes bekannt. Der Implementierungsablauf beschreibt anhand eines Top-Bottom-Ansatzes, wie der Algorithmus zuerst in einer Festpunkt High-Level Realisierung und schließlich in einer Low-Level Implementierung mit einer Hardwarebeschreibungssprache umgesetzt wird. Sowohl High-Level als auch Low-Level Simulationen unterstützen dabei die Validierung und Bewertung der Implementierung. Die Implementierung des Abschwächungsalgorithmus stellt schließlich eine ausgefeilte Methode dar, um ein heruntergeschmischtes Basisbandspektrum in Echtzeit von nichtlinearen Verzerrungen zu befreien. Demzufolge wird die effektive Linearität des HF-Frontends erhöht. Dies kann zu einer erheblichen Verbesserung der Bitfehlerrate von modulierten Signalen führen sowie die Zuverlässigkeit des Sensings in Bezug auf kognitiven Funk steigern.Ilmenau, Techn. Univ., Masterarbeit, 201

Nonlinear control of an industrial robot

The precise control of a robot manipulator travelling at high speed constitutes a major research challenge. This is due to the nonlinear nature of the dynamics of the arm which make many traditional, linear control methodologies inappropriate. An alternative approach is to adopt controllers which are themselves nonlinear. Variable structure control systems provide the possibility of imposing dynamic characteristics upon a poorly modelled and time varying system by means of a discontinuous control signal. The basic algorithm overcomes some nonlinear effects but is sensitive to Coulomb friction andactuator saturation. By augmenting this controller with compensation terms, these effects may largely be eliminated.In order to investigate these ideas, a number of variable structure control systems ~re applied to a low cost industrial robot having a highly nonlinear and flexible drive system. By a combination of hardware enhancements and control system developments, an improvement in speed by a factor of approximately three was achieved while the trajectory tracking accuracy was improved by a factor of ten, compared with the manufacturer's control system.In order to achieve these improvements, it was necessary to develop a dynamic model of the arm including the effects of drive system flexibility and nonlinearities. The development of this model is reported in this thesis, as is work carried out on a comparison of numerical algorithms for the solution of differential equations with discontinuous right hand sides, required in the computer aided design of variable structure control systems

Hydrological modelling with weather radar data in urban drainage systems

The management of large scale strategic urban combined drainage systems is becoming increasingly dependent upon weather radar systems which can provide quantitative precipitation information to improve the overall efficiency of a system's operational performance. Thus, there has been an increasing requirement for a more detailed knowledge of the radar rainfall data accuracy and the development of a mathematical rainfall-runoff model that can be used to analyse and control a system in real-time. Within this context, several important factors including signal attenuation, temporal and spatial data resolutions and rainfall quantisation schemes that determine the accuracy of radar rainfall estimates were examined in this thesis. In order to facilitate real-time flow simulation and forecast, a Conceptually Parametrised Transfer Function (CPTF) model has been developed based on Dynamic Linear Reservoir theory. The model is structurally simple and operationally reliable. It can be easily identified and robustly updated following a pulse response-to-CPTF procedure in which Genetic Algorithms play a key role. Using the model, the accuracy of areal rainfall estimates obtained by the Hameldon Hill radar has been assessed, firstly by comparing the radar rainfall estimates with `ground truth', and then by comparing the simulated hydrographs with the actual flow observations. Finally, a case study was conducted using radar rainfall data to highlight the potential benefit of real-time control for the strategic urban drainage system in the Fylde Coast. The major achievements documented in this thesis are: 1) A rule for determination of an appropriate input data resolution for hydrological models; 2) A general probability density function for describing the sampled radar rainfall intensities; 3) An efficient quantising law (ß-Law) and an associated adaptive rainfall quantisation scheme; 4) Three general conceptual pulse-response functions developed based on Dynamic Linear Reservoir theory; 5) CPTF model; and 6) A case study on the potential benefit of real-time control in the Fylde urban drainage system

Towards direct frequency comb spectroscopy using quantum logic

[no abstract

Dual-axis tilting quadrotor aircraft: Dynamic modelling and control of dual-axis tilting quadrotor aircraft

This dissertation aims to apply non-zero attitude and position setpoint tracking to a quadrotor aircraft, achieved by solving the problem of a quadrotor’s inherent underactuation. The introduction of extra actuation aims to mechanically accommodate for stable tracking of non-zero state trajectories. The requirement of the project is to design, model, simulate and control a novel quadrotor platform which can articulate all six degrees of rotational and translational freedom (6-DOF) by redirecting and vectoring each propeller’s individually produced thrust. Considering the extended articulation, the proposal is to add an additional two axes (degrees) of actuation to each propeller on a traditional quadrotor frame. Each lift propeller can be independently pitched or rolled relative to the body frame. Such an adaptation, to what is an otherwise well understood aircraft, produces an over-actuated control problem. Being first and foremost a control engineering project, the focus of this work is plant model identification and control solution of the proposed aircraft design. A higher-level setpoint tracking control loop designs a generalized plant input (net forces and torques) to act on the vehicle. An allocation rule then distributes that virtual input in solving for explicit actuator servo positions and rotational propeller speeds. The dissertation is structured as follows: First a schedule of relevant existing works is reviewed in Ch:1 following an introduction to the project. Thereafter the prototype’s design is detailed in Ch:2, however only the final outcome of the design stage is presented. Following that, kinematics associated with generalized rigid body motion are derived in Ch:3 and subsequently expanded to incorporate any aerodynamic and multibody nonlinearities which may arise as a result of the aircraft’s configuration (changes). Higher-level state tracking control design is applied in Ch:4 whilst lower-level control allocation rules are then proposed in Ch:5. Next, a comprehensive simulation is constructed in Ch:6, based on the plant dynamics derived in order to test and compare the proposed controller techniques. Finally a conclusion on the design(s) proposed and results achieved is presented in Ch:7. Throughout the research, physical tests and simulations are used to corroborate proposed models or theorems. It was decided to omit flight tests of the platform due to time constraints, those aspects of the project remain open to further investigation. The subsequent embedded systems design stemming from the proposed control plant is outlined in the latter of Ch:2, Sec:2.4. Such implementations are not investigated here but design proposals are suggested. The primary outcome of the investigation is ascertaining the practicality and feasibility of such a design, most importantly whether or not the complexity of the mechanical design is an acceptable compromise for the additional degrees of control actuation introduced. Control derivations and the prototype design presented here are by no means optimal nor the most exhaustive solutions, focus is placed on the whole system and not just a single aspect of it

A superconducting bandpass delta-sigma modulator for direct analog-to-digital conversion of microwave radio

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2003.Includes bibliographical references (p. 291-305).This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Direct analog-to-digital conversion of multi-GHz radio frequency (RF) signals is the ultimate goal in software radio receiver design but remains a daunting challenge for any technology. This thesis examines the potential of superconducting technology for realizing RF analog-to-digital converters (ADCs) with improved performance. A bandpass delta-sigma (AE) modulator is an attractive architecture for digitizing narrowband signals with high linearity and a large signal-to-noise ratio (SNR). The design of a superconducting bandpass AE modulator presented here exploits several advantages of superconducting electronics: the high quality factor of resonators, the high sampling rates of comparators realized with Josephson junctions, natural quantization of voltage pulses, and high circuit sensitivity. Demonstration of a superconducting circuit operating at clock rates in the tens of GHz is often hindered by the difficulty of high speed interfacing with room-temperature test equipment. In this work, a test chip with integrated acquisition memory is used to simplify high speed testing in a cryogenic environment. The small size (256 bits) of the on-chip memory severely limits the frequency resolution of spectra based on standard fast Fourier transforms. Higher resolution spectra are obtained by "segmented correlation", a new method for testing ADCs. Two different techniques have been found for clocking the superconducting modulator at frequencies in the tens of GHz. In the first approach, an optical clocking technique was developed, in which picosecond laser pulses are delivered via optical fiber to an on-chip metal-semiconductor-metal (MSM) photodiode, whose output current pulses trigger the Josephson circuitry. In the second approach, the superconducting modulator is clocked by an on-chip Josephson oscillator.(cont.) These testing methods have been applied in the successful demonstration of a super-conducting bandpass AE modulator fabricated in a niobium integrated circuit process with 1 kA/cm2 critical current density for the Josephson junctions. At a 42.6 GHz sampling rate, the center frequency of the experimental modulator is 2.23 GHz, the measured SNR is 49 dB over a 20.8 MHz bandwidth, and a full-scale (FS) input is -17.4 dBm. At a 40.2 GHz sampling rate, the measured in-band noise is -57 dBFS over a 19.6 MHz bandwidth.by John Francis Bulzacchelli.Ph.D