Modelling and analysis of switching DC-to-DC converters in constant-frequency current-programmed mode

An analysis of dc-to-dc switching converters in constant-frequency current-programmed continuous conduction mode is performed, and leads to two significant results. The first is that a ramp function, used to eliminate a potential instability, can be chosen uniquely to assure both stability and the fastest possible transient response of the programmed current. The second is the development of an extension of the state-space averaging technique by means of which both the input and output small-signal properties of any such converter may be accurately represented by a linear small-signal equivalent-circuit model. The model is presented and experimentally verified for the cuk converter and for the conventional buck, boost, and buck-boost converters. All models exhibit basically a one-pole control-to-output transfer function response

IMPROVEMENTS IN INVERTER MODELING AND CONTROL

In this dissertation, the generalized averaging method models for inverters, reactive power control methods for photovoltaic inverters, and a noise immunity improvement for hybrid position observers for brushless dc motor drives are studied. Models of inverters and other converters based on averaging have been widely used in numerous simulation applications. Generalized averaging can be applied to model both average and switching behavior of converters while retaining the faster run times associated with average-value models. Herein, generalized average models for single- and three-phase pulse width modulation inverters are proposed. The modulation signal for the proposed model could be either a sinusoidal waveform without high order harmonics or a sinusoidal waveform with third-harmonic injection. And this generalized average models also can apply for modeling three-phase pulse width modulation inverters with varying modulation signal frequency in the reference frame. These models are based on a quasi-Fourier series representation of the switching functions that includes fundamental and switching frequency components as well as sideband components of the switching frequency. The proposed models are demonstrated both in simulation and experimentally and are found to accurately portray both the fundamental and the switching behavior of the inverter. In particular, the use of sideband components allows accurate representation of the variation in switching ripple magnitude that occurs in the steady state. The generalized average models are found to have simulation run times that are significantly faster than those associated with detailed models. Therefore, the proposed generalized average models are suitable for simulation applications in which both accuracy (including the switching behavior) and fast run times are required (e.g., long simulation times, systems with multiple converters, and repeated simulations). Variations in the output power of intermittent renewable sources can cause significant fluctuations of distribution system voltage magnitudes. Reactive power control methods that employ the reactive power capability of photovoltaic three-phase inverters to mitigate these fluctuations are proposed. These control methods cause the three-phase inverters to substitute reactive output power for real output power when fluctuations in the solar power are experienced, allowing the fluctuations to be controlled. Performance metrics for assessing the ability of these controllers to perform this mitigation are defined. The controllers are examined using the IEEE 123-bus feeder distribution system, and it is found that the controllers can effectively mitigate voltage magnitude fluctuations and that the appropriate choice of controller depends on the performance metrics of interest. Finally, a noise immunity improvement for hybrid position observers for brushless dc motor drives is proposed. A finite state machine is used to detect Hall-effect sensor transitions to determine if these transitions are true transitions or the result of momentary glitches. This filter causes a delay in the detection of the Hall-effect sensors that is compensated in the proposed observer. The proposed observer is compared in simulations with the original hybrid position observer under both non-noisy and noisy conditions for both constant and variable speed operation, and it has good performance even under high noise and variable speed conditions

The behaviour and analysis of a three-phase AC-DC step-down unity power factor converter

Abstract unavailable please refer to PD

From analog to digital

Analog-to-digital conversion and its reverse, digital-to-analog conversion, are ubiquitous in all modern electronics, from instrumentation and telecommunication equipment to computers and entertainment. We shall explore the consequences of converting signals between the analog and digital domains and give an overview of the internal architecture and operation of a number of converter types. The importance of analog input and clock signal integrity will be explained and methods to prevent or mitigate the effects of interference will be shown. Examples will be drawn from several manufacturers' datasheets

Dynamic calibration of current-steering DAC

The demand for high-speed communication systems has dramatically increased during the last decades. Working as an interface between the digital and analog world, Digital-to-Analog converters (DACs) are becoming more and more important because they are a key part which limits the accuracy and speed of an overall system. Consequently, the requirements for high-speed and high-accuracy DACs are increasingly demanding. It is well recognized that dynamic performance of the DACs degrades dramatically with increasing input signal frequencies and update rates. The dynamic performance is often characterized by the spurious free dynamic range (SFDR). The SFDR is determined by the spectral harmonics, which are attributable to system nonlinearities.;A new calibration approach is presented in this thesis that compensates for the dynamic errors in performance. In this approach, the nonlinear components of the input dependent and previous input code dependent errors are characterized, and correction codes that can be used to calibrate the DAC for these nonlinearities are stored in a two-dimensional error look-up table. A series of pulses is generated at run time by addressing the error look-up table with the most significant bits of the Boolean input and by using the corresponding output to drive a calibration DAC whose output is summed with the original DAC output. The approach is applied at both the behavioral level and the circuit level in current-steering DAC.;The validity of this approach is verified by simulation. These simulations show that the dynamic nonlinearities can be dramatically reduced with this calibration scheme. The simulation results also show that this calibration approach is robust to errors in both the width and height of calibration pulses.;Experimental measurement results are also provided for a special case of this dynamic calibration algorithm that show that the dynamic performance can be improved through dynamic calibration, provided the mean error values in the table are close to their real values