Off-Grid Inverter with Regulated Output Voltage Amplitude

The paper discusses the design, simulation, and implementation of a 60W, 115VAC, 60Hz off-grid power inverter. The off-grid inverter creates a mains-level voltage from a 12V lead-acid battery input without connection to a conventional electric grid. The inverter includes a low-voltage H-Bridge circuit that is controlled with 3-level Pulse Width Modulation (PWM), and uses a low frequency step up transformer from 12V to 115V. A feedback system based on IQ sampling and a Proportional, Integral, Derivative controller (PID) is implemented to maintain a constant output voltage amplitude over an input range of 10 to 15VDC. A microcontroller is used to generate PWM and implement the feedback loop. The inverter successfully powers small household loads such as a desktop fan and laptop

Deliverable D4.1: VLC modulation schemes

This report presents the analysis of different modulation schemes D4.1 for VLC systems of the VIDAS project. Considering the final prototype design and application, the deliverable D4.1 was projected. The detail analysis of various modulation schemes are carried out and a robust technique based on direct sequence spread spectrum (DSSS) is followed. DSSS technique though necessitates use of high bandwidth while minimizing the effect of noise. Since the final application does not require very high dat a rate of transmission but robustness against the noise (external lights) becomes necessary. The analysis is followed by model development using Matlab/Simulink. The performance of both of these systems are compared and evaluated. Some of the simulation results are presented

Study of substrate noise and techniques for minimization

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2003.Includes bibliographical references (p. 155-158).This thesis presents a study of the effects of substrate noise on analog circuits in mixed-signal chips and techniques for minimizing these harmful effects on sensitive analog circuits. A microchip built in a 0.25um CMOS epitaxial process was designed, fabricated, and tested for this research. Through the use of an on-chip sampling scope, the effect of substrate noise generated by digital inverters with coupling capacitors to the substrate on analog circuits was characterized. Substrate noise coupled into a representative analog circuit, a switched capacitor delta-sigma modulator primarily through the asymmetrical parasitics of the input sampling circuit. Furthermore, since some of the parasitics are nonlinear with input voltage, substrate noise couples into the analog circuits producing an input signal dependent component and an input signal independent component. The substrate noise, with decay time constants of a few nanoseconds and ringing frequencies of few hundred megahertz, can decrease analog circuit performance. In the case of a delta-sigma modulator, substrate noise caused the signal to noise power ratio to decrease by more than 18dB, 3 bits in terms of analog-to-digital converter metrics. In addition, two techniques of minimizing the substrate noise and its effects were explored. The first used a replica delta-sigma modulator on the same chip to subtract the effects of substrate noise from the original delta-sigma modulator. This method proved useful for removing input signal independent substrate noise, but not input signal dependent substrate noise which dominates in-band noise for large input signal magnitudes. The second technique involved an active substrate noise cancellation system.(cont.) A discrete time feedback loop senses the substrate noise, processes it through a filter, and uses an array of digital inverters to cancel the substrate noise. The principal advantages of this technique are the shaping of substrate noise through a designed filter without a significant power penalty and design independence from the analog and digital components. Measured data shows that this technique is capable of over 20dB reduction in substrate noise on the substrate voltage itself. Measured data also shows over 10dB improvement in SNDR of the delta-sigma modulator in certain cases.by Mark Shane Peng.Ph.D

The control of a static var compensator and active power filter

In an AC supply system, good management of reactive power plays an important role in ensuring a good quality of supply. A solid-state static VAr compensator enables precise and continuous reactive power control to be achieved. A leading and lagging VAr can be compensated to give a system with unity power factor. This thesis describes a solid- state static VAr compensator which utilises a deadband PWM switching pattern. By using simulation as well as experimental results, a comparison is made with conventional sinusoidal PWM. The use of deadband PWM enables higher modulation indices to be achieved hence facilitating a smaller size of reactive component on the DC side. Deadbanding reduces the effective switching frequency thus minimising the switching losses and resulting stresses. Power quality is also affected by harmonic distortion which originates from the non- linear characteristics of electrical devices and loads. The use of an active power filter to provide harmonic compensation as well as power factor correction is described in this thesis. Modified delta modulation is proposed to control the switching of an active power filter. Compensation is achieved with a reduction in switching losses. The application of a variable structure control system is considered. Sliding mode switching control is used to ensure good tracking of the reference current, thus providing the required compensation

Boost Matrix Converters in Clean Energy Systems

This dissertation describes an investigation of novel power electronic converters, based on the ultra-sparse matrix topology and characterized by the minimum number of semiconductor switches. The Z-source, Quasi Z-source, Series Z-source and Switched-inductor Z-source networks were originally proposed for boosting the output voltage of power electronic inverters. These ideas were extended here on three-phase to three-phase and three-phase to single-phase indirect matrix converters. For the three-phase to three-phase matrix converters, the Z-source networks are placed between the three-switch input rectifier stage and the output six-switch inverter stage. A brief shoot-through state produces the voltage boost. An optimal pulse width modulation technique was developed to achieve high boosting capability and minimum switching losses in the converter. For the three-phase to single-phase matrix converters, those networks are placed similarly. For control purposes, a new modulation technique has been developed. As an example application, the proposed converters constitute a viable alternative to the existing solutions in residential wind-energy systems, where a low-voltage variable-speed generator feeds power to the higher-voltage fixed-frequency grid.Comprehensive analytical derivations and simulation results were carried out to investigate the operation of the proposed converters. Performance of the proposed converters was then compared between each other as well as with conventional converters. The operation of the converters was experimentally validated using a laboratory prototype

Micro combined heat and power management for a residential system

Fuel cell technology has reached commercialisation of fuel cells in application areas such as residential power systems, automobile engines and driving of industrial manufacturing processes. This thesis gives an overview of the current state of fuel cell-based technology research and development, introduces a μCHP system sizing strategy and proposes methods of improving on the implementation of residential fuel cell-based μCHP technology. The three methods of controlling residential μCHP systems discussed in this thesis project are heat-led, electricity-led and cost-minimizing control. Simulations of a typical HT PEMFC -based residential μCHP unit are conducted using these control strategies. A model of a residential μCHP system is formulated upon which these simulated tests are conducted. From these simulations, equations to model the costs of running a fuel-cell based μCHP system are proposed. Having developed equations to quantify the running costs of the proposed μCHP system a method for determining the ideal size of a μCHP system is developed. A sizing technique based on industrial CHP sizing practices is developed in which the running costs and capital costs of the residential μCHP system are utilised to determine the optimal size of the system. Residential thermal and electrical load profile data of a typical Danish household are used. Having simulated the system a practical implementation of the power electronics interface between the fuel cell and household grid is done. Two topologies are proposed for the power electronics interface a three-stage topology and a two-stage topology. The efficiencies of the overall systems of both topologies are determined. The system is connected to the grid so the output of each system is phase-shifted and DC injection, harmonic distortion, voltage range and frequency range are determined for both systems to determine compliance with grid standards. Deviations between simulated results and experimental results are recorded and discussed and relevant conclusions are drawn from these

Data-driven model-based approaches to condition monitoring and improving power output of wind turbines

The development of the wind farm has grown dramatically in worldwide over the past 20 years. In order to satisfy the reliability requirement of the power grid, the wind farm should generate sufficient active power to make the frequency stable. Consequently, many methods have been proposed to achieve optimizing wind farm active power dispatch strategy. In previous research, it assumed that each wind turbine has the same health condition in the wind farm, hence the power dispatch for healthy and sub-healthy wind turbines are treated equally. It will accelerate the sub-healthy wind turbines damage, which may leads to decrease generating efficiency and increases operating cost of the wind farm. Thus, a novel wind farm active power dispatch strategy considering the health condition of wind turbines and wind turbine health condition estimation method are the proposed. A modelbased CM approach for wind turbines based on the extreme learning machine (ELM) algorithm and analytic hierarchy process (AHP) are used to estimate health condition of the wind turbine. Essentially, the aim of the proposed method is to make the healthy wind turbines generate power as much as possible and reduce fatigue loads on the sub-healthy wind turbines. Compared with previous methods, the proposed methods is able to dramatically reduce the fatigue loads on subhealthy wind turbines under the condition of satisfying network operator active power demand and maximize the operation efficiency of those healthy turbines. Subsequently, shunt active power filters (SAPFs) are used to improve power quality of the grid by mitigating harmonics injected from nonlinear loads, which is further to increase the reliability of the wind turbine system

Analysis of the internal short-circuit conditions of the Acceleration Grid Power Supply of the MITICA experiment

Analisi della situazione di guasto interno del sistema di alimentazione delle griglie di accelerazione dell'esperimento MITICA,il quale è un prototipo di NBI, un sistema di riscaldamento ausiliario, per reattori a fusione. Viene analizzato il guasto per valutare l'utilizzo di alcuni sistemi di protezione e verificarne l'efficacia. Per fare ciò è stato sviluppato un modello circuitale del sistema e sono state effettuate le simulazioni del guastoope

New optimal PWM strategies for a VSI induction motor drive

The applications of robust squirrel-cage induction motors in variable speed inverter drive systems have increased considerably due to the availability of easily controlled semiconductor switching devices. One problem encountered in inverter drives is the non-sinusoidal nature of the supply voltage, which results in increased motor losses and harmful torque pulsations producing undesirable speed oscillations. The latter effects are negligible at high frequency operation, due to the damping effect of the rotor and load inertia. However, torque pulsations and speed ripple may be appreciable at low frequency, wore they may result in abnormal wear of gear-teeth or torsional shaft failure. Hence, in applications where constant or precise speed control is important, eg; machine tool, antenna positioning, traction drives etc., it is essential to establish a method for determining the magnitudes of these torque pulsations and speed ripple, as a first stage in minimizing or eliminating them. When a voltage source inverter is used in such applications, pulse width modulation (PWM) techniques are usually employed, whereby the quasi square waveshape is modulated so as to minimize or eliminate the low order harmonic voltage components and thereby reduce the torque pulsations. Recent investigations have shown that total elimination of low order components does not produce optimal efficiency or torque pulsations and speed ripple. minimization. This thesis describes new PWM strategies which does not rely on complete elimination of low order harmonics, but on controlling the magnitude and phase of these components to achieve a smooth rotor motion. Initially, a mathematical model for the inverter/induction motor drive was developed, based on numerical integration of the system differential equations. The changing topology of the inverter bridge was simulated using tensor techniques. Then an analytical method, based on harmonic equivalent circuit analysis was proposed for calculating the induction motor pulsating torque components under steady-state operating conditions, in terms of stator and rotor current harmonics. The accuracy of this method was verified by comparing its results with those obtained from the mathematical model developed earlier. This provided an extremely rapid, numerically stable and efficient means for evaluating harmonic current and torque components with balanced non-sinusoidal applied voltages. This method was then used to formulate the torque performance function necessary to determine the new optimal PWM switching strategies. Throughout the work, the predicted performance was extensively validated and supported by practical results obtained from an experimental rig specifically designed to drive the machine under different PWM techniques