Fast voltage detection method for grid-tied renewable energy generation systems under distorted grid voltage conditions

© The Institution of Engineering and Technology. A fast voltage detection method to assist with the low-voltage ride-through operation of grid-tied renewable energy generation systems is proposed in this study. It is designed to detect every phase voltage, so that it can be applied in both three-phase and single-phase applications. The whole voltage detection approach consists of two stages, the pre-filtering stage and the voltage detection stage. In the pre-filtering stage, a cascaded delayed signal cancellation (CDSC) module and a low-pass filter are connected in series to filter low-order harmonics and high-frequency noises. For eliminating the low-order harmonics of interest, different types of CDSC methods are studied in detail. Subsequently, a new orthogonal signal generator is built to calculate the voltage amplitude in the voltage detection stage. Finally, the proposed voltage detection method is verified by experimental results

Achieving synchronization and syntonization using GPS receivers

Every day, millions of people ask what time it is. Depending on the person and their reason for asking, the required accuracy and precision of an answer varies. Humans are not the only ones that care about time though, (perhaps more importantly) countless electronic devices ranging from cell phones to satellites do as well. Without accurate and precise frequency references and timekeeping systems, many of the electronics in use today would function incorrectly. The primary goal of this thesis was to achieve both synchronization and syntonization using a Global Positioning System (GPS) receiver called Namuru, which was developed at the University of New South Wales (UNSW). In the former case, this means that the pulse per second (PPS) signals output by the receiver should be aligned with the second boundaries of GPS Time (GPST). In the latter case, this means that the frequency of the voltage-controlled temperature-compensated crystal oscillator (VC-TCXO) onboard the receiver should be equal to its setpoint. The secondary goal of this thesis was to develop a clock model that accurately simulated the synchronization and syntonization performance of the receiver. The tertiary goal of this thesis was to develop supplementary features for the receiver like position-hold and holdover modes. In order to achieve these goals, several new capabilities were added to the receiver and much work was done in a number of different areas, such as field-programmable gate array (FPGA) programming, writing firmware, modifying hardware, and modeling

Retrofit Control to Prevent ASD Nuisance Tripping Due to Power Quality Problems

Since the onset of automation, industry has relied on adjustable speed drives to accurately control the speed of motors. Recent advances have increased the number of adjustable speed drives hitting the market. The proper operation of the speed drives requires electrical supply with relatively high power quality which is not the case in most industrial facilities. Power quality problems such as harmonic, sag, swell, flicker, and unbalance can trip the speed drive with a wrong message, which is referred as a premature tripping. Although the power quality problems can be mitigated by using custom power devices, they are bulky and costly. Moreover, they themselves might adversely affect the operation of the adjustable speed drive. A comprehensive study done in this thesis presents the overlooked effect of the custom power devices on the speed drive stability. It is found that the speed drive system might trip due to its interaction with custom power devices. Obviously, it is vital to increase ASD immunity to premature tripping because of poor power quality or custom power. This thesis offers fast, efficient and robust algorithms to achieve this immunity by retrofitting the ASD control unit and integrating the power conditioning function with the adjustable speed drive. Therefore, the power quality problem is mitigated and the drive system performance is significantly enhamced. Such integration requires the modification of the control unit by considering various elements such as envelope tracking, phase-locked loop, symmetrical component extraction, and the controller. Simple but robust and fast algorithms are proposed for such elements based on a newly developed energy operator algorithm. The developed energy operator and the developed algorithms overcome the drawbacks of the existing algorithms

System and circuit design for a capacitive MEMS gyroscope

In this thesis, issues related to the design and implementation of a micro-electro-mechanicalangular velocity sensor are studied. The work focuses on a system basedon a vibratory microgyroscope which operates in the low-pass mode with a moderateresonance gain and with an open-loop configuration of the secondary (sense) resonator.Both the primary (drive) and the secondary resonators are assumed to have a high qualityfactor. Furthermore, the gyroscope employs electrostatic excitation and capacitivedetection. The thesis is divided into three parts. The first part provides the background informationnecessary for the other two parts. The basic properties of a vibratory microgyroscope,together with the most fundamental non-idealities, are described, a shortintroduction to various manufacturing technologies is given, and a brief review of publishedmicrogyroscopes and of commercial microgyroscopes is provided. The second part concentrates on selected aspects of the system-level design of amicro-electro-mechanical angular velocity sensor. In this part, a detailed analysis isprovided of issues related to different non-idealities in the synchronous demodulation,the dynamics of the primary resonator excitation, the compensation of the mechanicalquadrature signal, and the zero-rate output. The use of ΣΔ modulation to improveaccuracy in both primary resonator excitation and the compensation of the mechanicalquadrature signal is studied. The third part concentrates on the design and implementation of the integratedelectronics required by the angular velocity sensor. The focus is primarily on the designof the sensor readout circuitry, comprising: a continuous-time front-end performingthe capacitance-to-voltage (C/V) conversion, filtering, and signal level normalization;a bandpass ΣΔ analog-to-digital converter, and the required digital signal processing(DSP). The other fundamental circuit blocks, which are a phase-locked loop requiredfor clock generation, a high-voltage digital-to-analog converter for the compensationof the mechanical quadrature signal, the necessary charge pumps for the generationof high voltages, an analog phase shifter, and the digital-to-analog converter used togenerate the primary resonator excitation signals, together with other DSP blocks, areintroduced on a more general level. Additionally, alternative ways to perform the C/Vconversion, such as continuous-time front ends either with or without the upconversionof the capacitive signal, various switched-capacitor front ends, and electromechanicalΣΔ modulation, are studied. In the experimental work done for the thesis, a prototype of a micro-electro-mechanicalangular velocity sensor is implemented and characterized. The analog partsof the system are implemented with a 0.7-µm high-voltage CMOS (ComplimentaryMetal-Oxide-Semiconductor) technology. The DSP part is realized with a field-programmablegate array (FPGA) chip. The ±100°/s gyroscope achieves 0.042°/s/√H̅z̅spot noise and a signal-to-noise ratio of 51.6 dB over the 40 Hz bandwidth, with a100°/s input signal. The implemented system demonstrates the use of ΣΔ modulation in both the primaryresonator excitation and the quadrature compensation. Additionally, it demonstratesphase error compensation performed using DSP. With phase error compensation,the effect of several phase delays in the analog circuitry can be eliminated, andthe additional noise caused by clock jitter can be considerably reduced

Harmonic compensation in a grid using doubly fed induction generators

Ideally, electric utilities are expected to deliver a sinusoidal voltage with a constant rated frequency, while customers are expected to draw a sinusoidal current with unity power factor. The recent widespread use of harmonic producing equipment in industrial applications, especially non-linear loads, has increased the distortion of electric currents and voltages in transmission and distribution systems. This thesis proposes a method of using multiple reference frame theory for measuring and mitigating harmonic currents of nonlinear loads using a doubly fed induction generator. The most significant low-order harmonics to be compensated are calculated using a multiple reference frame harmonic observer. This observer is simulated using Matlab® Simulink® and then implemented using the Texas Instruments TMS320F28335 digital signal processor. Experimental and simulation results are provided to verify the analysis of the observer by comparing the results with calculations from the Fourier spectrum. Along with active and reactive power generation, an algorithm is proposed to inject currents in the rotor for the mitigation of harmonics in the system. Simulation results are presented to demonstrate the performance of this proposed method. These results validate the effectiveness of the method in compensating the targeted harmonics in the system. This method of measuring and compensating harmonics discussed in this thesis is accurate, straightforward, easily implemented and effective in the mitigation of any harmonic in the system. The currents obtained in the fundamental reference frame can be further employed for the control of active and reactive power flow --Abstract, page iii

Control strategy of grid connected power converter based on virtual flux approach

A la portada consta el nom del programa interuniversitari: Joint Doctoral Programme in Electric Energy Systems [by the] Universidad de Málaga, Universidad de Sevilla, Universidad del País Vasco/Euskal Erriko Unibertsitatea i Universitat Politècnica de CatalunyaDistributed Generation (DG) provides an alternative to the Centralized Generation (CG) by means of generating electricity near to the end user of power with the employment of small-scale technologies to produce electricity, mainly using Renewable Energy Sources (RES). The prospects of renewable energy integration during the next years are still very optimistic. This PhD dissertation is made to provide an alternative control framework for the grid connected power converter by adopting the virtual flux concept in the control layer. This dissertation can be divided into three main topics. The 1st topic presents the voltage sensorless control system for the grid-connected power converter. The control system presented is done without depending on AC-voltage measurement where the grid synchronization is based on the Virtual Flux (VF) estimation. In this regard, the Frequency Locked Loop (FLL) is used in conjunction with the estimation scheme to make the system fully adaptive to the frequency changes. This voltage sensorless application is useful for reducing cost and complexity of the control hardware. It is also can be utilized in case of limited reliability or availability of voltage measurements at the intended point of synchronization to the grid. Considering that most previous studies are based on the VF estimation for the case of power converter connected to the grid through the L-filter or LC-filter, this dissertation is focused on the power converter connected to the grid through the LCL filter. The Proportional Resonant (PR) current controller is adopted in the inner loop control of the power electronics-based converter to test the performance of such system. Another control method based on VF synchronization that permits to control the active and reactive power delivery in a remote point of the grid is also presented in this dissertation. This is due to the fact that the VF is implemented that the voltage in a remote point of the line can be estimated. As it will be shown in simulations and experiments, the proposed control scheme provides a good tracking and dynamic performance under step changes in the reference power. The fast synchronization and the smooth reference tracking achieved in transient conditions have demonstrated the effectiveness of the Dual Second Order Generalized Integrator controlled as Quadrature Signal Generator (DSOGI-QSG) and also the current controller used in the proposed system. In addition to the power control itself, this study could also benefit the frequency and the voltage regulation methods in distributed generation applications as for instance in microgrid. Considering the fact that the grid connected power converter can be controlled as a virtual synchronous generator where the flux is a variable to be used for controlling its operation, this dissertation also presents a Virtual Synchronous Flux Controller (VSFC) as a new control framework of the grid connected power converter. In this regard, a new control strategy in the inner loop control of the power converter will be proposed. The main components of the outer loop control of VSFC are based on the active and reactive power control. The results presented show that the VSFC works well to control the active and reactive power without considering any synchronization system. The inner loop control is able to work as it is required, and the measurement flux is able to track the reference flux without any significant delays. All the work presented in this dissertation are supported by mathematical and simulation analysis. In order to endorse the conclusions achieved, a complete experimental validations have been conducted before wrapping this dissertation with a conclusion and recommendation for future enhancement of the control strategies that have been presented.Postprint (published version

Miniaturized Doppler radar sensor for non-contact vital sign detection

Non-contact vital sign detection based on Doppler radar systems presents several advantages in bio-medical and healthcare applications. Many research efforts have been proposed in this field to obtain accuracy and effectiveness for reliable wireless bio-signal detection. However front-end architectures, demodulation algorithms and signal processing methods can be further improved to retrieve the heartbeat and respiration spectra. In this work, based on existing millimeter wave systems, a continuous wave Doppler radar sensor operating at 60GHz was designed and implemented utilizing a low-IF receiver architecture to accurately detect heartbeat and respiration rate of a human target. In order to achieve robustness in addition to effectiveness, the sensor is integrated on a miniaturized single-board and the components power consumption is low. Potential other applications for this radar system will also be discussed

Cooperative Strategies for Management of Power Quality Problems in Voltage-Source Converter-based Microgrids

The development of cooperative control strategies for microgrids has become an area of increasing research interest in recent years, often a result of advances in other areas of control theory such as multi-agent systems and enabled by emerging wireless communications technology, machine learning techniques, and power electronics. While some possible applications of the cooperative control theory to microgrids have been described in the research literature, a comprehensive survey of this approach with respect to its limitations and wide-ranging potential applications has not yet been provided. In this regard, an important area of research into microgrids is developing intelligent cooperative operating strategies within and between microgrids which implement and allocate tasks at the local level, and do not rely on centralized command and control structures. Multi-agent techniques are one focus of this research, but have not been applied to the full range of power quality problems in microgrids. The ability for microgrid control systems to manage harmonics, unbalance, flicker, and black start capability are some examples of applications yet to be fully exploited. During islanded operation, the normal buffer against disturbances and power imbalances provided by the main grid coupling is removed, this together with the reduced inertia of the microgrid (MG), makes power quality (PQ) management a critical control function. This research will investigate new cooperative control techniques for solving power quality problems in voltage source converter (VSC)-based AC microgrids. A set of specific power quality problems have been selected for the application focus, based on a survey of relevant published literature, international standards, and electricity utility regulations. The control problems which will be addressed are voltage regulation, unbalance load sharing, and flicker mitigation. The thesis introduces novel approaches based on multi-agent consensus problems and differential games. It was decided to exclude the management of harmonics, which is a more challenging issue, and is the focus of future research. Rather than using model-based engineering design for optimization of controller parameters, the thesis describes a novel technique for controller synthesis using off-policy reinforcement learning. The thesis also addresses the topic of communication and control system co-design. In this regard, stability of secondary voltage control considering communication time-delays will be addressed, while a performance-oriented approach to rate allocation using a novel solution method is described based on convex optimization