Reset observers and temperature control for induction hobs

Resumo

Nowadays, domestic induction heating technology is quite well consolidated in such a manner that it is difficult to find substantial differences between the induction hobs offered by different manufacturers. All of them present induction hobs with similar features: maximum power, size, shape, etc. For this reason, finding new distinguishing features between them is indispensable to the manufacturers. To this end, we consider as the main objective of this work the development of a pot temperature control for domestic induction hobs, which allows the user to directly control the temperature of the cooking pot rather than the supplied power as standard hobs do. Several advantages are obtained by a proper control of the cooking pot temperature: For the user: resultant system is safer and more reliable because dangerously high temperatures are avoided. Overall performance is higher because energy consumption is minimized. It simplifies the cooking process, due to the fact that the hob itself informs the user when the cooking pot reaches the desired temperature. For the cooking pot: by controlling its temperature, its nonstick surface cannot be damaged, which increases its durability in the long term. For the manufacturers: they obtain distinguishing features with respect to competitors. Moreover, by controlling the cooking pot temperature, the temperature of the cooking surface is under control as well. Therefore, new materials with less demanding thermal properties but considerably cheaper than glass ceramic could be used instead. Issues concerning cooking pot temperature control are addressed from two standpoints. The first, based on a theoretical perspective, will consist in the development of observation algorithms that allow an accurate estimation of the cooking pot temperature. The second, based on a more practical and experimental focus, will consist in the design of novel sensing methods that outperform the currently used temperature sensors. Inspired by the excellent features of reset systems in terms of transient response and lack of overshooting, we will explore throughout this Thesis the applicability of reset systems to the observer framework. To this end, a formal definition of a new sort of observer, the reset observer, will be proposed. The influence of the different reset conditions on the reset observer structure will be studied as well. Additionally, the reset observer formulation will be extended to different sorts of systems, including time-delay systems, non-linear systems, and systems affected by external disturbances. It is worth noting that we will consider not only stability and convergence analysis but also the observer's parameter synthesis. Before checking the applicability of reset observers in controlling the cooking pot temperature, a significant effort will be made to determine what temperature sensor is more suitable depending on the load of the cooking process. To this end, novel temperature sensors will be developed, and their performance will be compared with the existing ones in terms of robustness, time response and cost. Once this task is done, the proposed control and estimation algorithms will be implemented in actual induction hobs. Finally, exhaustive experimental and application tests will be carried out in order to show the applicability of reset observers for controlling the cooking pot temperature in induction hobs. Specifically, the main contributions of this Thesis are: The development of more efficient algorithms for the reset observer that can be used for estimating and controlling the cooking pot temperature. This new observer, the reset observer, results from the novel application of the reset theory to the observer framework, and can be applied to a wide class of systems. This work includes both, stability analysis and reset observer's parameter synthesis. The development of three novel sensing devices specially suitable for measuring the cooking pot temperature in induction hobs: the contact spots, the sensor line and the magnetic sensor. This work includes a complete comparison between these novel proposals and other existing methods so that the most suitable temperature sensor for the system under study can be determined. The application of our theoretical results (i.e. the reset observers) to a real industrial application, including the design, tuning, and testing of the proposed control-estimation algorithms. Specifically, this Thesis finally contributes with the development of a temperature cooking pot control for induction hobs that is suitable for high and low load cooking processes. Besides, this Thesis shows by exhaustive experiments the superior performance of our theoretical contributions, and their applicability to the cooking pot temperature control for induction hobs.