7 research outputs found

    Novel Offline Switched Mode Power Supplies for Solid State Lighting Applications

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    In recent years, high brightness light emitting diodes (HBLEDs) have increasingly attracted the interest of both industrial manufacturers and academic research community. Among the several aspects that make LED technology so attractive, the most appreciated characteristics are related to their robustness, high efficiency, small size, easy dimming capability, long lifetime, very short switch-on/switch-off times and mercury free manufacturing. Even if all such qualities would seem to give to solid state lighting a clear advantage over all the other kinds of competing technologies, the issues deriving from the need of LED technology improvement, on one hand, and of the development of suitable electronic ballasts to properly drive such solid state light sources, on the other, have so far hindered the expected practical applications. The latter problem, in particular, is nowadays considered the main bottleneck in view of a widespread diffusion of solid state technology in the general lighting market, as a suitable replacement of the still dominant solutions, namely halogen and fluorescent lamps. In fact, if it is true that some aspects of the devices’ technology (e.g. temperature dependent performance, light quality, efficiency droop, high price per lumen, etc…) still need further improvements, it is now generally recognized that one of the key requirements, for a large scale spread of solid state lighting, is the optimization of the driver. In particular, the most important specifications for a LED lamp ballast are: high reliability and efficiency, high power factor, output current regulation, dimming capability, low cost and volume minimization (especially in domestic general lighting applications). From this standpoint, the main goal is, therefore, to find out simple switched mode power converter topologies, characterized by reduced component count and low current/voltage stresses, that avoid the use of short lifetime devices like electrolytic capacitors. Moreover, if compactness is a major issue, also soft switching capability becomes mandatory, in order to enable volume minimization of the reactive components by increasing the switching frequency in the range of the hundreds of kHz without significantly affecting converter’s efficiency. It is worth mentioning that, in order to optimize HBLED operation, also other matters, like the lamp thermal management concern, should be properly addressed in order to minimize the stress suffered by the light emitting devices and, consequently, the deterioration of the light quality and of the expected lamp lifetime. However, being this work focused on the issues related to the research of innovative driving solutions, the aforementioned thermal management problems, as also all the topics related to the improvement of solid state devices’ technology, will be left aside. The main goal of the work presented in this thesis is, indeed, to find out, analyze and optimize new suitable topologies, capable of matching the previously described specifications and also of successfully facing the many challenges dictated by the future of general lighting. First of all, a general overview of solid state lighting features, of the state of the art of lighting market and of the main LED driving issues will be provided. After this first introduction, the offline driving concern will be extensively discussed and different ways of approaching the problem, depending on the specific application considered, will be described. The first kind of approach investigated is based on the use of a simple structure relying on a single power conversion stage, capable of concurrently ensuring: compliance with the standards limiting the input current harmonics, regulation of the load current and also galvanic isolation. The constraints deriving from the need to fulfil the EN 61000-3-2 harmonics standard requirements, when using such kind of solution for low power (<15W) LED driving purposes, will be extensively discussed. A low cost, low component count, high switching frequency converter, based on the asymmetrical half bridge flyback topology, has been studied, developed and optimized. The simplicity and high compactness, characterizing this solution, make it a very good option for CFL and bulb replacement applications, in which volume minimization is mandatory in order to reach the goal of placing the whole driving circuitry in the standard E27 sockets. The analysis performed will be presented, together with the design procedure, the simulation outcomes and the different control and optimization techniques that were studied, implemented and tested on the converter's laboratory prototype. Another interesting approach, that will be considered, is based on the use of integrated topologies in which two different power conversion stages are merged by sharing the same power switch and control circuitry. In the resulting converter, power factor correction and LED current regulation are thus performed by two combined semi-stages in which both the input power and the output current have to be managed by the same shared switch. Compared with a conventional two-stages configuration, lower circuit complexity and cost, reduced component count and higher compactness can be achieved through integration, at cost of increased stress levels on the power switch and of losing a degree of freedom in converter design. Galvanic isolation can be provided or not depending on the topologies selected for integration. If non-isolated topologies are considered for both semi-stages, the user safety has to be guaranteed by assuring mechanical isolation throughout the LED lamp case. The issue, deriving from the need of smoothing the pulsating power absorbed from the line while avoiding the use of short lifetime electrolytic capacitors, will be addressed. A set of integrated topologies, used as HBLED lamp power supplies, will be investigated and a generalized analysis will be presented. Their input line voltage ripple attenuation capability will be examined and a general design procedure will be described. Moreover, a novel integrated solution, based on the use of a double buck converter, for an about 15W rated down-lighting application will be presented. The analysis performed, together with converter design and power factor correction concerns will be carefully discussed and the main outcomes of the tests performed at simulation level will be provided. The last kind of approach to be discussed is based on a multi-stage structure that results to be a suitable option for medium power applications, like street lighting, in which compactness is not a major concern. By adopting such kind of solution it is, indeed, possible to optimize converter’s behavior both on line and on load side, thereby guaranteeing both an effective power factor correction at the input and proper current regulation and dimming capability at the output. Galvanic isolation can be provided either by the input or the output stage, resulting in a standard two stage configuration, or by an additional intermediate isolated DC-DC stage (operating in open loop with a constant input/output voltage conversion ratio) that namely turns the AC/DC converter topology into a three stage configuration. The efficiency issue, deriving from the need of multiple energy processing along the path between the utility grid and the LED load, can be effectively addressed thanks to the high flexibility guaranteed by this structure that, relaxing the design constraint, allows to easily optimize each stage. A 150W nominal power rated ballast for street solid state lighting applications, based on the latter (three stage) topology, has been investigated. The analysis performed, the design procedure and the simulations outcomes will be carefully described, as well as the experimental results of the tests made on the implemented laboratory prototype

    Nonlinear Modeling of Power Electronics-based Power Systems for Control Design and Harmonic Studies

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    The massive integration of power electronics devices in the modern electric grid marked a turning point in the concept of stability, power quality and control in power systems. The evolution of the grid toward a converter-dominated network motivates a deep renovation of the classical power system theory developed for machine-dominated networks. The high degree of controllability of power electronics converters, furthermore, paves the way to the investigation of advanced control strategies to enhance the grid stability, resiliency and sustainability. This doctoral dissertation explores four cardinal topics in the field of power electronics-based power systems: dynamic modeling, stability analysis, converters control, and power quality with particular focus on harmonic distortion. In all four research areas, a particular attention is given to the implications of the nonlinearity of the converter models on the power system

    A Flexible, Low-Power, Programmable Unsupervised Neural Network Based on Microcontrollers for Medical Applications

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    We present an implementation and laboratory tests of a winner takes all (WTA) artificial neural network (NN) on two microcontrollers (μC) with the ARM Cortex M3 and the AVR cores. The prospective application of this device is in wireless body sensor network (WBSN) in an on-line analysis of electrocardiograph (ECG) and electromyograph (EMG) biomedical signals. The proposed device will be used as a base station in the WBSN, acquiring and analysing the signals from the sensors placed on the human body. The proposed system is equiped with an analog-todigital converter (ADC), and allows for multi-channel acquisition of analog signals, preprocessing (filtering) and further analysis

    Emulation of Narrowband Powerline Data Transmission Channels and Evaluation of PLC Systems

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    This work proposes advanced emulation of the physical layer behavior of NB-PLC channels and the application of a channel emulator for the evaluation of NB-PLC systems. In addition, test procedures and reference channels are proposed to improve efficiency and accuracy in the system evaluation and classification. This work shows that the channel emulator-based solution opens new ways toward flexible, reliable and technology-independent performance assessment of PLC modems

    Design and Development of Advanced Control strategies for Power Quality Enhancement at Distribution Level

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    In recent times, power quality (PQ) issues such as current and voltage harmonics, voltage sag/swell, voltage unbalances have become the important causes for malfunctioning and degradation of the quality of power. Poor power quality severely affects on electrical equipment and finally results in significant economic losses. Hence, installation of the custom power devices to improve the power quality issues becomes an important consideration. Therefore, this thesis considers the enhancement of power quality for power distribution systems by utilizing unified power quality conditioner (UPQC). An UPQC can adequately handle several power quality problems such as load current harmonics, supply voltage distortions, voltage sags/swells and voltage unbalance. Therefore, the main focus behind this thesis is to develop advanced control strategies that improve the compensation capability of the UPQC so that power quality issues of distribution network are efficiently improved. Firstly, the current harmonics are considered and are compensated by using the shunt active power filter (SAPF). Therefore, two control strategies such as Hysteresis current control (HCC) and Sliding Mode Control (SMC) based control algorithms are implemented to compensate current harmonics in the power distribution network. Furthermore, both the current control techniques utilize the Coulon oscillator based PLL (CO-PLL) for extraction of positive sequence signal from the supply voltage and generate the three-phase reference currents by employing PI-controller based DC-link voltage regulation. The performances of both current control techniques for SAPF are evaluated under different source voltage conditions such as balanced, unbalanced and non-sinusoidal. The SAPF effectively compensates currents harmonic, however, it is unable to compensate voltage related problems. To overcome this drawback, this thesis considers the UPQC, which comprises with shunt APF and series APF, can be utilized to compensate both current and voltage related problems. The research on UPQC is carried out progressively by considering different advanced control strategies. Each progress in the research enhances the compensation capabilities of the previous UPQC control system. The simulation and realtime Opal-RT studies are carried out to verify the operating performance of each design concept of UPQC. At first, operating principle and design of UPQC is presented and then a novel control algorithm is introduced with the aid of nonlinear DC-link voltage controller such as nonlinear variable gain fuzzy (NVGF) controller and nonlinear sliding mode controller (NLSMC) with modified synchronous reference frame (SRF) control strategy for improvement of both current and voltage compensation performance of the UPQC. However, existence of large settling time in dc voltage leads to poor dynamic performance of NVGF control technique and hence current harmonics, voltage distortions and voltage disturbance such as voltage sag/swell as well as voltage unbalance compensation capability of this technique is not quite effective in comparison to the NLSMC technique. Moreover, NLSMC is very sensitive to model mismatch and noise. It is quite sluggish in rejecting long drifting grid disturbances. Hence, a suitable control strategy has to be developed in UPQC, which has improved DC-link voltage regulation as well as tracking performance through load and grid perturbations. To overcome this drawback a resistive optimization technique (ROT) incorporated with enhanced phase-locked loop (EPLL) based NVGF hysteresis control strategy and an optimum active power (OAP) technique combined with enhanced phase-locked loop (EPLL) based fuzzy sliding mode (FSM) pulse-width modulation (PWM) control strategy for UPQC have been discussed. ROT-NVGF and OAP-FSMC based UPQC control strategies are adaptive as well as robust and able to mitigate the PQ problems satisfactorily during all dynamic conditions of power system perturbation. However, performances of these controllers are not effective when there is a variation occurring either in the nonlinear load parameter or supply voltage parameter. Thus, UPQC may not be able to compensate PQ problems satisfactorily. Considering aforesaid problems, this thesis proposes a command generator tracker (CGT) based direct adaptive control (DAC) applied to a three-phase three-wire UPQC to improve the current and voltage harmonics, sag/swell and voltage unbalance in the power system distribution network. CGT is a model reference control law for a linear timeinvariant system with known coefficients and is formulated for the generation of reference signal for both shunt and series inverter. The main advantage of the proposed control algorithm is that no online extraction is needed to perceive the UPQC parameters. Moreover, IV the adaptive control law is designed to track a linear reference model to reduce the tracking error between model reference output and measured signal to be controlled. Additionally, this proposed algorithm adaptively regulates the DC-link capacitor voltage without utilizing additional controller circuit. As a result, the proposed algorithm provides more robustness, flexibility and adaptability in all operating conditions of the power system network. At last, model reference robust adaptive control (MRRAC) technique is proposed for single phase UPQC system. This control strategy is designed with the purpose of achieving high stability, high disturbance rejection and high level of harmonics cancellation. From simulation results, it is not only found to be robust against PI-controller, but also satisfactory THD results have been achieved in UPQC system. This has motivated to develop a prototype experimental set up in the Laboratory using FPGA (Field Programmable Gate Array) based NI (National Instruments) cRIO-9014. From both the simulation and experimentation, it is observed that the proposed MRRAC approach to design a UPQC system is found to be more effective as compared to the conventional PI-controller
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