Effect of control method on impedance-based interactions in a buck converter

All the interconnected regulated systems are prone to impedance-based interactions making them sensitive to instability and transient-performance degradation. The applied control method affects significantly the characteristics of the converter in terms of sensitivity to different impedance interactions. This paper provides for the first time the whole set of impedance-type internal parameters and the formulas according to which the interaction sensitivity can be fully explained and analyzed. The formulation given in this paper can be utilized equally either based on measured frequency responses or on predicted analytic transfer functions. Usually, the distributed dc-dc systems are constructed by using ready-made power modules without having thorough knowledge on the actual power-stage and control-system designs. As a consequence, the interaction characterization has to be based on the frequency responses measureable via the input and output terminals. A buck converter with four different control methods is experimentally characterized in frequency domain to demonstrate the effect of control method on the interaction sensitivity. The presented analytical models are used to explain the phenomena behind the changes in the interaction sensitivity

Analysis, Design and Control of a Modular Full-Si Converter Concept for Electric Vehicle Ultra-Fast Charging

L'abstract è presente nell'allegato / the abstract is in the attachmen

Impedance-based stability and transient-performance assessment applying maximum peak criteria

The impedance-based stability-assessment method has turned out to be a very effective tool and its usage is rapidly growing in different applications ranging from the conventional interconnected dc/dc systems to the grid-connected renewable energy systems. The results are sometime given as a certain forbidden region in the complex plane out of which the impedance ratio--known as minor-loop gain--shall stay for ensuring robust stability. This letter discusses the circle-like forbidden region occupying minimum area in the complex plane, defined by applying maximum peak criteria, which is well-known theory in control engineering. The investigation shows that the circle-like forbidden region will ensure robust stability only if the impedance-based minor-loop gain is determined at the very input or output of each subsystem within the interconnected system. Experimental evidence is provided based on a small-scale dc/dc distributed system

Stability challenges and solutions in current-mode controlled power electronic converters

This dissertation focuses on stability issues in single-staged and multi-staged current controlled power electronic converters. Most current-mode control (CMC) approaches suffer from sub-harmonic oscillations. An external ramp is usually added to solve this problem. However, to guarantee stability this ramp has to be designed for the worst possible case which consequently over damps the response. Adaptive slope compensation (ASC) methods are the solution for this problem. In paper 1 of this dissertation, first three ASC methods will be investigated and analyzed through their small signal models. Then, through simulation analyses and experimental test of a variable-input voltage converter the results will be validated. Two of the methods studies in the first paper are peak CMC methods and the last one is called the projected cross point control (PCPC) approach. This method is relatively new. Therefore, a detailed discussion of the principles of operation of PCPC will be presented in paper 2. In addition, the small signal model of PCPC is developed and discussed through simulation and experimental analyses in the second paper of this dissertation. Peak, average, and hysteresis CMC schemes are used for comparison. In paper 3, the stability issues which arise in multistage converters will be addressed. A solid state transformer (SST) as an example of a multistage converter will be studied. A comprehensive small signal modeling will be conducted which helps for stability analysis of SST. Time domain simulations in Computer Aided Design software (PSCAD) are presented which validates the frequency domain analysis --Abstract, page iv

High Efficiency Power Supplies for Multi-mode RF Power Amplifiers in Cellular Handset Applications

Cellular handset evolution requires the front end transmitter to support multiple 3G/4G bands for global roaming, and also to be backward compatible with the existing 2G (quad-band GSM/EDGE) network. The cost and size would be prohibitive if one power amplifier (PA) only supports one band or if multiple supplies are required for multiple PAs. Solutions of interest are based on multi-standard multi-band PAs (e.g. 2 multi-mode PAs instead of 8+ mode-specific PAs), and an efficient power supply that supports these multi-mode PAs. The thesis starts with a study of PA supply architectures and DC-DC converters. A series architecture consisting of a boost converter followed by a buck converter has advantages of low-noise buck converter output, together with the ability to deliver full power at low battery voltages to extend the battery life. The buck converter presents a constant power load for the boost converter, which raises stability concerns. Small-signal control-to-output transfer functions are derived for peak or valley current mode controlled boost converter with a downstream regulated converter modeled as constant power load. It is shown how current mode control provides active damping to ensure stability and well-behaved dynamic response. Furthermore, it is shown how load current feedforward presents an effective way to improve power load transient response. Modeling and design approaches are validated by test circuit simulations, demonstrating stable operations using current mode control under constant power loads, and improved power step load transient response based on load current feedforward. A buck/boost and LDO series architecture is proposed as the solution to address efficiency, linearity, noise and time mask requirements for the supplies supporting multi-standard, multi-band PAs. A monolithic integrated circuit (IC) has been designed and implemented in a standard 0.5 5V CMOS process for supplying the multi-mode PAs. The buck/boost converter with wide output range delivers the peak efficiency of 92%. The power LDO has 1-4 MHz bandwidth, to support the GSM/EDGE/WCDMA time mask requirements and the polar EDGE operation. The test chip consumes the quiescent current 1.1 mA, and it delivers maximum 5 W output

Transient Mitigation of DC–DC Converters for High Output Current Slew Rate Applications

published_or_final_versio

Analysis and bifurcations of a dc-dc buck converter controlled by sine wave

Los sistemas de baja potencia se utilizan ampliamente en la robótica y en la industria, por lo tanto, el modelado y análisis de sistemas proporcionan fiabilidad y mejores diseños para tales sistemas. El convertidor buck es uno de los sistemas que ha sido ampliamente analizado durante años con el objetivo de conocer su comportamiento y mejorar el diseño de los algoritmos de control. En consecuencia, en este trabajo el convertidor buck controlado por PWM de voltaje es modelado, simulado y estudiado. Sin embargo, dado que muchos trabajos se han desarrollado en el marco del estudio del sistema controlado por rampa, esta tesis se centra principalmente en el nuevo estudio del convertidor buck controlado por onda sinusoidal (cambiando la señal rampa T-periódica no suave por la señal sinusoidal T-periódica suave) operando en modo de conducción continua y discontinua, convergiendo hacia el análisis bifurcacional de casi todos los parámetros que rigen el sistema. Además, algunos resultados obtenidos a partir de ambos sistemas son comparados. Utilizando un método para la detección de eventos, los sistemas son simulados describiendo numéricamente todos los fenómenos encontrados al computar respuestas temporales, retratos de fase, diagramas de bifurcaciones uno dimensionales, dos dimensionales y tridimensionales para diferentes parámetros. Con esto, todos los comportamientos complejos serán fácilmente reconocidos cuando un parámetro específico es variado, sin mencionar que nuevos fenómenos de la naturaleza no suave son observados y descritos. Posteriormente, ya que los diagramas de bifurcaciones son calculados variando los parámetros de forma ascendente y descendente, coexistencia de atractores, los cuales son normalmente un comportamiento no deseado en los sistemas no lineales, son observados y estudiados. No obstante, también se demuestra que estos diagramas de bifurcaciones no son el remedio suficiente para encontrar coexistencia de soluciones. Finalmente, algoritmos de control son aplicados al convertidor buck controlado por PWM de voltaje, los cuales son una técnica basada en un control adaptativo, donde se modifica la señal rampa T-periódica (V ramp) o la señal seno T-periódica (V s) de tal forma que se comporten similar a la señal de control (V co) y a los cambios en el voltaje de entrada (V in); todo a fin de ampliar aún más el rango de V in sobre el cual la órbita 1T-periódica se mantiene estable. Además, con esta técnica de control se reduce considerablemente el porcentaje de error de regulación (%e) así como también se elimina el comportamiento caótico cuando V in es variado. Al final, resultados numéricos y experimentales, los cuales concuerdan altamente, son obtenidos con el fin de validar el funcionamiento del sistema controlado por rampa adaptativa / Abstract: Low power systems are widely used in robotics and industrial areas; therefore, modeling and systems analysis provide reliable and best designs of such systems. The Buck converter is one of the systems that has been widely analyzed for years in order to understand its behavior and design better control algorithms. Accordingly, in this work the PWM voltage{controlled buck converter is modeled, simulated and studied. However, since many works have been developed under the study of the system controlled by ramp, this thesis will be mainly focused in the new study of the buck converter controlled by sine waveform (changing the non-smooth T-periodic ramp signal by the smooth T-periodic sine signal) operating in continuous and discontinuous conduction mode, converging towards the bifurcation analysis of almost all the parameters that govern the system. Additionally, some results obtained from both systems are compared. Using a method for detecting events, the systems are simulated describing numerically all the phenomenons found computing temporal responses, phase portraits, one dimensional, two dimensional and three dimensional bifurcation diagrams for different parameters. With this, every complex behavior will be easily recognized when a specific parameter is varied, not to mention new phenomenons of the non{smooth nature are observed and described. Then, as bifurcation diagrams are computed varying the parameters ascending and descending, coexisting attractors, which are normally an undesired behavior in nonlinear systems, are observed and studied. Nevertheless, it is demonstrated that these bifurcation diagrams are not the sufficient remedy to find coexistence of solutions. Finally, control algorithms are applied to the PWM voltage-controlled buck converter, which is a technique based on an adaptive control, where the T-periodic ramp signal (V ramp) or the T-periodic sine signal (V s) are modified to behave according to the control signal (V co) and the input voltage (Vin) changes; all in order to extend even more the Vin range over which the 1T-periodic orbit remains stable. Moreover, with this control technique it is greatly reduced the percentage of regulation error (%e) as well as it is eliminated the chaotic behavior when V in is varied. After all, numerical and experimental results, which show high agreement, are obtained so as to validate the performance of the system controlled by adaptive ramp.Maestrí

Design and Control of Power Converters 2019

In this book, 20 papers focused on different fields of power electronics are gathered. Approximately half of the papers are focused on different control issues and techniques, ranging from the computer-aided design of digital compensators to more specific approaches such as fuzzy or sliding control techniques. The rest of the papers are focused on the design of novel topologies. The fields in which these controls and topologies are applied are varied: MMCs, photovoltaic systems, supercapacitors and traction systems, LEDs, wireless power transfer, etc