Nonlinear control of dc/dc power converters with inherent current and power limitation

A nonlinear controller with an inherent current-limiting capability is presented in this paper for different types of dc/dc power converters (boost, buck-boost). The proposed controller is based on the idea of applying a dynamic virtual resistance in series with the inductor of the converter, which varies according to a nonlinear dynamical system. It is shown that the proposed approach acts independently from the converter parameters (inductance, capacitance) or the load and has a generic structure that can be used to achieve different regulation scenarios, e.g. voltage, current or power regulation. Based on the nonlinear model of the boost and the buck-boost converter, it is analytically proven that the inductor current remains always bounded below a given maximum value using input-to-state stability theory under a suitable choice of the controller parameters. Hence, the proposed control strategy offers an inherent protection property since the power of the converter is limited below a given value during transients or unrealistic power demands. Simulation results for both types of dc/dc converters are presented to verify the desired controller performance

Estudo de estratégias de controle para conversores CC-CC conectados em paralelo com foco numa microrrede fotovoltaica operando em modo isolado

TCC (graduação) - Universidade Federal de Santa Catarina. Centro Tecnológico. Engenharia Elétrica.Neste trabalho de conclusão de curso de engenharia elétrica da Universidade Federal de Santa Catarina (UFSC) são estudadas técnicas de controle para conversores CC-CC conectados, em paralelo, a um barramento CC. Os conversores também estão conectados a um sistema fotovoltaico de geração de energia e foram projetados para processar até 8 kW de potência por meio de 40 módulos instalados no topo do prédio do Instituto de Eletrônica de Potência (INEP) da UFSC. O estudo foi constituído considerando que a microrrede (MR) proposta possa atuar em dois modos de operação: conectado e isolado. No primeiro modo, a estratégia deve garantir que os conversores sejam controlados individualmente para funcionarem como rastreadores do ponto de máxima potência ( do inglês Maximum Power Point Tracker - MPPT), pois podemos utilizar a rede elétrica como fonte de geração ou armazenamento infinito de energia. Isso faz com que não nos preocupemos num balanço de potências entre a carga e a fonte geradora e que pensemos na máxima extração possível de potência do arranjo fotovoltaico. No segundo modo, o controle tem o objetivo de garantir que os conversores mantenham, de forma compartilhada, a tensão do barramento CC regulada, pois com a ausência da rede elétrica, o balanço de potência é necessário para regular o barramento e garantir o funcionamento adequado do sistema. É importante ressaltar que este trabalho tem como foco o estudo da microrrede operando no segundo modo e, embora técnicas do primeiro sejam apresentadas, suas discussões serão resumidas ou omitidas. Além de uma introdução e motivação ao estudo do tema, o projeto e o dimensionamento de um conversor boost também são apresentados no decorrer do texto. Finalmente, resultados provenientes de simulação teórica computacional com o software PSIM® e de experimentação prática são apresentados e discutidos, considerando a microrrede operando no modo isolado.In this undergraduate thesis of electrical engineering of the Federal University of Santa Catarina (UFSC), control techniques are studied for DC-DC converters connected, in parallel, to a common DC bus. The converters are also connected to a photovoltaic power generation system and were designed to process up to 8 kW of power through 40 modules installed at the top of the building of the Institute of Power Electronics (INEP) of the UFSC. The study was constituted considering that the proposed microgrid can act in two modes of operation: connected and isolated. In the first mode, the strategy must ensure that the converters are individually controlled to function as Maximum Power Point Trackers (MPPT), because we can use the electrical network as a source of infinite power generation or storage. This means that we do not need to worry about a balance of power between the load and the generating source and we should think on the maximum possible extraction of power of the photovoltaic arrangement. In the second mode, the control has the objective that the converters maintain, in a shared form, the voltage of the DC bus regulated, because with the absence of the electric network, the power balance is necessary to regulate the bus and ensure the proper operation of the system. It is important to emphasize that this work focuses on the study of the microgrid operating in the second mode and, although techniques of the first one are presented, their discussions will be summarized or omitted. In addition to an introduction and motivation to study of the theme, the design of a boost converter is also presented throughout the text. Finally, results from theoretical computer simulation through PSIM® software and practical experimentation are presented and discussed, considering the microgrid operating in isolated mode

Robustness and durability aspects in the design of power management circuits for IoT applications

With the increasing interest in the heterogeneous world of the “Internet of Things” (IoT), new compelling challenges arise in the field of electronic design, especially concerning the development of innovative power management solutions. Being this diffusion a consolidated reality nowadays, emerging needs like lifetime, durability and robustness are becoming the new watchwords for power management, being a common ground which can dramatically improve service life and confidence in these devices. The possibility to design nodes which do not need external power supply is a crucial point in this scenario. Moreover, the development of autonomous nodes which are substantially maintenance free, and which therefore can be placed in unreachable or harsh environments is another enabling aspect for the exploitation of this technology. In this respect, the study of energy harvesting techniques is increasingly earning interest again. Along with efficiency aspects, degradation aspects are the other main research field with respect to lifetime, durability and robustness of IoT devices, especially related to aging mechanisms which are peculiar in power management and power conversion circuits, like for example battery wear during usage or hot-carrier degradation (HCD) in power MOSFETs. In this thesis different aspects related to lifetime, durability and robustness in the field of power management circuits are studied, leading to interesting contributions. Innovative designs of DC/DC power converters are studied and developed, especially related to reliability aspects of the use of electrochemical cells as power sources. Moreover, an advanced IoT node is proposed, based on energy harvesting techniques, which features an intelligent dynamically adaptive power management circuit. As a further contribution, a novel algorithm is proposed, which is able to effectively estimate the efficiency of a DC/DC converter for photovoltaic applications at runtime. Finally, an innovative DC/DC power converter with embedded monitoring of hot-carrier degradation in power MOSFETs is designed