New pulse width modulation technique to reduce losses for three-phase photovoltaic inverters

Nowadays, most three-phase, “of the shelf” inverters use electrolytic capacitors at the DC bus to provide short term energy storage. However, this has a direct impact on inverter lifetime and the total cost of the photovoltaic system. Tis article proposes a novel control strategy called a 120∘ bus clamped PWM (120BCM). Te 120BCM modulates the DC bus and uses a smaller DC bus capacitor value, which is typical for flm capacitors. Hence, the inverter lifetime can be increased up to the operational lifetime of the photovoltaic panels. Tus, the total cost of ownership of the PV system will decrease signifcantly. Furthermore, the proposed 120BCM control strategy modulates only one phase current at a time by using only one leg to perform the modulation. As a result, switching losses are signifcantly reduced. Te full system setup is designed and presented in this paper with some practical result

Distributed static series compensator in 11kV networks

PhD ThesisSeries compensation techniques can be very effective when applied in an electrical network to increase the power transfer capacity of existing power lines. Distributed Static Series Compensation (DSSC) is a power electronics based series compensation scheme in which a DSSC device comprises of a single-phase H-bridge voltage source converter, a dc link capacitor and a low pass filter suspended from the power line via a single turn transformer. The application of DSSC in the 11kV distribution network is investigated in this thesis. This is followed by a study of existing control strategies employed in DSSC and Static Synchronies Series Compensation (SSSC) schemes. Most of these controllers are based on dq transformation methods in which balanced conditions are assumed and zero sequence currents are assumed to be negligible. While this might be a reasonable assumption at transmission level voltages, but it can be argued that in the presence of unbalanced loads and currents (a common feature of lower voltage distribution networks) these strategies can be inaccurate, leading to the wrong amount of compensation being injected. In addition some of the studied controllers are based on the 90° phase shift of line current. Practically, the injection angle must be slightly different in order to compensate the internal losses of the DSSC. The need for the diversion from the 90° can change over the time and this can threaten the stability of the system. A new single-phase control strategy based on the instantaneous power exchange between the DSSC devices and each of the three phase conductors is proposed in this thesis to address this issue. The new control method does not employ a dq transformation and is immune from the probable errors resulting from the presence of unbalanced network conditions. In the same time the injection angle is not fixed and it is adjusted by the controller. The operation of DSSC can be categorized in two modes and transfer function of system is obtained based on these two modes. The transfer function is used in the design of controller. This is followed by analyzing immunity of the designed controller against change of system parameters. The proposed scheme is simulated (using PSCAD software) to examine the operation of the new control method and the resulting impact on the 11kV distribution feeder, including the ability to divert power from one line to another and the ability to improve network voltage profiles. Performance of DSSC using the proposed controller is compared with performance of DSSC when the traditional controllers are employed

Contributions on spectral control for the asymmetrical full bridge multilevel inverter

Las topologías de circuitos inversores multinivel pueden trabajar a tensiones y potencias mayores que las alcanzadas por convertidores convencionales de dos niveles. Además, la conversión multinivel reduce la distorsión armónica de las variables de salida y en algunos casos, a pesar del aumento de elementos de conmutación, también reduce las pérdidas de conversión al incrementarse el número de niveles. La reducción de distorsión alcanzada por el número de niveles puede aprovecharse para reducir las pérdidas de conmutación disminuyendo la frecuencia de las señales portadoras. Para reducir aún más esta frecuencia sin degradar el espectro, nosotros controlamos las pendientes de las portadoras triangulares. Primero se han desarrollado dos modelos analíticos para predecir el espectro del voltage de salida, dependiendo de: el índice de modulación MA, la razón de distribución de voltaje K de las fuentes de alimentación , y las cuatro pendientes de las portadoras{r1, r2, r3, r4}. El primer modelo considera el Muestreo Natural y se basa en Series Dobles de Fourier (SDF) mientras que el segundo modelo, utiliza la Serie Sencilla de Fourier (SSF) introduciendo el concepto de Muestreo Pseudo-Natural, una aproximación digital de la modulación natural. Ambos modelos son programados en Matlab, verificados con Pspice y validados con un prototipo experimental que contiene un modulador digital implementado con DSP.La concordancia entre las modulaciones natural y pseudo-natural, asi como entre sus respectivos modelos, es aprovechada por un algorítmo genético (AG) donde la THD es la función costo a reducir. Después de varios ensayos y de sintonizar el AG, se genera una matriz que contiene conjuntos de portadoras optimizadas dentro un rango específico de las variables {MA,K} y es probada con un segundo prototipo en lazo cerrado. Un lazo lento digital modifica las portadoras creadas por un dsPIC en modulaciones PWM; estas son demoduladas y sus amplitudes corregidas por un lazo de acción anticipada. Estas portadoras se comparan con una referencia sinusoidal que a su vez es modificada por variables de estado, generando finalmente la modulación multinivel en lazo cerrado. Los resultados finales demuestran la fiabilidad de la reducción de armónicos usando la programación de las pendientes de las portadoras. Palabras claves: inversor multinivel, PWM, distorsión armónica, modelo espectral, pendiente de portadora, conjunto de portadoras, distribución de niveles, Serie Doble de Fourier, Serie Simple de Fourier, muestreo natural, muestreo regular, muestreo pseudo-natural , Algoritmos Genéticos.Multilevel inverter (MI) topologies can work at higher voltage and higher power than conventional two-level converters. In addition, multilevel conversion reduces the output variables harmonic distortion and, sometimes, in spite of the devices-count increment, the conversion losses can also decrease by increasing the number of levels. The harmonic distortion reduction achieved by increasing the number of levels, can be used to further reducing the switching losses by decreasing the inverter carrier frequencies. To reduce even more the switching frequency without degrading output spectrum, we control the triangular carrier waveforms slopes. First, to achieve this target, two analytical models have been created in order to predict the inverter output voltage spectrum, depending on diverse parameters: the amplitude modulation index MA, the voltage distribution K of the inverter input sources, and the four carrier slopes {r1, r2, r3, r4}. The first model considers Natural Sampling and is based on Double Fourier Series (DFS) whereas the second model based on Simple Fourier Series (SFS), introduces the concept of Pseudo-Natural Sampling, as a digital approximation of the natural modulation. Both models are programmed in Matlab, verified with Pspice simulations and validated with a first experimental prototype with a DSP digital modulator.The good agreement between natural and pseudo-natural modulations, as well as their respective DFS and SFS models, is exploited by a Genetic Algorithm (GA) application where THD is the cost function to minimize. After testing and properly tuning the GA, a framework matrix containing the optimized carriers set for a specific range of variables {MA,K} is generated and then, tested with a second, closed-loop prototype. A slow digital loop modifies the carrier slopes created by dsPIC microcontroller as PWM modulations, whose amplitude, once demodulated, are affected by a feed-forward loop. These carriers, compared with a sinusoidal reference, state-feedback modified, generate finally the closed-loop multilevel modulation. The final results demonstrates the feasibility of harmonic reduction by means of carrier slopes programming. Keywords: multilevel inverter, PWM, harmonic distortion, spectral modeling, carrier slope, carriers set, level distribution, Double Fourier Series, Simple Fourier Series, natural sampling, regular sampling, pseudo-natural sampling, Genetic Algorithms

The development of a field-portable MEMS gravimeter

Gravimetry is a technique that has existed since the 17th and 18th century and involves the measurement of the acceleration due to gravity. The technique can be used to measure changes in density below the ground where conventional methods cannot. This is because gravity cannot be shielded, and therefore, can always be measured. It has many useful applications, particularly in surveying for oil, gas and minerals but can also be used to detect the precursors to volcanic eruptions and earthquakes, the density contrast of buried walls for archaeology and the detection of subsurface voids. Typically, however, gravimeters can cost in excess of ￡70k and weight over 8 kg. This cost and weight has prohibited some applications of gravimeters where either many of the devices would be required or if weight was prohibitive. In the winter of 2014, an important step forward to a lightweight, low-cost and portable MEMS gravimeter was made. This was the first time that a MEMS based gravimeter had measured the Earth Tides as reported by R. P. Middlemiss et al. The device, however, still required a large array of electronics and vacuum equipment which made it impossible to be able to be taken into the field. Clearly, if the device was to ever become a disruptive technology within the gravimeter industry, significant effort would be required to obtain a device with sufficient sensitivity that was also portable. This thesis highlights the work that was required to bring the MEMS that was a lab-bound device, and make successful measurements of the change in acceleration due to gravity in the field. In this thesis, a miniaturised MEMS gravimeter is presented with an RMS of 13 μGal when averaged to 1000 s, a factor three better than the original set-up from R. P. Middlemiss et al. The system went from a set-up with the approximate dimensions of a typical fridge freezer(including the array of electronic equipment) to a portable platform of dimensions 30cm wide by 30 cm deep by 15 cm high. The platform used a small steel cube as a vacuum container for the device, three micrometer legs for precision levelling, batteries and a custom electronics board. This custom electronics board was designed, tested and improved during the course of this thesis. The board was controlled by a microcontroller from Microchip (the dsPIC33EP512MU810) and is shown to be capable of a large amount of digital filtering that was required for this application, including the use of a decimator and digital based lock-in amplifier. The board measured displacements, temperatures (which were also controlled) and tilts, all of which the microcontroller digitally filtered and down sampled so that they could be sent to a computer for data logging

Flow measurement of pneumatically conveyed solids using intrusive electrostatic sensors

Particulate solids are commonly conveyed in industry by means of pneumatic pipelines. The particle flows often need to be controlled and maintained within certain bounds, but the development of instrumentation to monitor them remains a challenging area. A variety of techniques have been researched to measure various flow parameters. An overview of the existing technology is presented, along with advantages and limitations of each method. A detailed investigation is conducted into the use of electrostatic sensors with intrusive electrodes to measure the velocity of pneumatic particle flows. Previous work has been reported on the use of non-intrusive ring electrodes, but few studies of intrusive electrodes have been undertaken to date. Modelling, based on the finite element method, is used to determine the characteristics of the charge induced by solid particle flows onto intrusive electrodes. These are then compared with the properties of non-intrusive circular ring electrode elements. The effects of electrode intrusion depth are studied, and it is shown that whilst stability of the velocity measurements improves with intrusion depth, some types of flow are best measured using a particular intrusion that results in the most accurate average velocity reading. Electrode spacing, which must be close enough to allow a measurement to be taken but far enough to avoid unwanted interactive effects, is investigated, along with the effect of electrode cross sectional shape on sensor signals and the effect of common mode noise on cross correlation velocity measurement. This information is used in the development of a practical sensor system that uses embedded signal processing, which is then tested on laboratory and industrial flow rigs. The results are used to characterise the features of intrusive electrostatic sensors and their response to different flow conditions. Most significantly, intrusive electrodes are shown to be sensitive to localised flow regimes. Finally, suggestions on aspects of electrostatic sensors that would benefit from further development are discussed

An Integrated Control and Data Acquisition System for Pharmaceutical Capsule Inspection

Pharmaphil Inc. manufactures two-part gelatin capsules for the pharmaceutical industry. Their current methods of quality control of their product is by performing manual inspection of every carton of capsules prior to shipment. In today\u27s modern manufacturing world, more efficient and cost-effective means of quality control exist. It is Pharmaphil\u27s desire to develop a custom machine vision system to replace manual inspection with a potential opportunity in the capsule manufacturing quality control market. In collaboration with the Electrical and Computer Engineering Department at the University of Windsor, a novel system was developed to achieve this goal. The objective was to develop a system capable of inspecting 1000 capsules per minute with the ability to detect holes, cracks, dents, bubble, double caps and incorrect colour or size. Using an antiquated machine vision system for capsule inspection from the mid-nineties as a base, a modern inspection system was developed that performed faster and more thorough inspections. As a measure to minimize the overall system cost as well as to increase flexibility, a full custom design was undertaken. The resulting system follows a traditional machine vision system whereby the main components include an image acquisition component, a processing unit and machine control. The designed system uses custom USB2.0 cameras to acquire images, a standard desktop PC to process image data and a custom machine control board to perform machine control and timing. The system operates with four identical quadrants operating in parallel to increase throughput. The final system developed provided a proof-of-concept for the approach taken. The machine control and image acquisition component of the system yielded a maximum throughput of 1200 capsules per minute. After incorporating image inspection, the final result was a system that was capable of inspecting capsules at a rate of about 800 capsules per minute with high accuracy. With optimizations, the system throughput can be further improved. The findings throughout the development of the prototype system provide an excellent basis from which the first generation commercial unit can be designed