PH.D.DISSERTATION EXAM
Ph.D. Student: David Zambrano Prada
Thesis title: A sliding mode approach to control heatsinks and power supplies in dc-dc switching converters
Supervisors: Luis Martínez-Salamero and Abdelali El Aroudi
SUMMARY
This thesis deals with the analysis and control of power converters as power elements used in photovoltaic systems, microgrids and electric vehicles. The obtained models appear as two-terminal elements like constant power loads (CPL), or as two-port networks like a transformer, gyrator and loss free resistor. Power converters loaded with CPL are particularly difficult to control, due to their inherent open-loop instability. Different proposals to deal with the control and stabilization of power converters loaded CPL has can be found in the literature ranging from linear to nonlinear control methods. All the existing methods have a common complexity in the (i) mathematical development of the control, (ii) in experimental implementation of the control system, (iii) in the need to sense several variables of the system, or a combination of all these issues. On the other hand, the demand for constant power to the load appears as a necessity in certain applications such as electric vehicle (EV) charging. A constant power-constant voltage (CP-CV) charging protocol in ultrafast EV charging has reported relative advantages with the constant current-constant voltage (CP-CV) protocol in EV ultrafast charging has reported relative advantages with the traditional constant current-constant voltage (CC-CV) protocol. This opens the question of finding a way to deliver power to different types of loads, generalizing the concept of which is a load. Generalizable procedures are gathered in this study for the control of power converters loaded with CPLs and estimation of power and for the synthesis of one-port and two-port power sources canonical elements such as the loss-free resistor. The Sliding Mode Control (SMC) approach is used for this purpose, a method consistent with the variable structure nature of switching power converters, achieving robustness control and simplicity of implementation.
PH.D.DISSERTATION EXAM
Control of Distributed Power in Microgrids: PV Field to the Grid, Islanding Operation, and Ultra-fast Charging Station
Ph.D. Student: Seyedamin Valedsaravi
Thesis title: Control of Distributed Power in Microgrids: PV Field to the Grid, Islanding Operation, and Ultra-fast Charging Station
Supervisors: Luis Martínez-Salamero and Abdelali L'Aroudi
Examiners: Elhoussin Elbouchikhi (ISEN Incré France ), Guillem Velasco (UPC) and Robert Giral (URV)
Place: Sala de Graus (ETSE)
Date/time: November 10, 2023 / 11:00 a.m.
SUMMARY
The emergence of DC fast chargers for electric vehicle batteries (EVBs) has prompted the design of ad-hoc MGs, in which the use of a SST instead of a low-frequency service transformer can increase the efficiency and reduce the volume and weight of the MG electrical architecture. Mimicking a conventional gasoline station in terms of service duration and service simultaneity to several customers has led to the notion of ultra-fast chargers, in which the charging time is less than 10 minutes and the MG power is higher than 350 kW. This survey reviews the state-of-the-art of DC ultra-fast charging stations, SST transformers, and DC ultra-fast charging stations based on SST. Ultra-fast charging definition and its requirements are analyzed, and SST characteristics and applications together with the configuration of power electronic converters in SST-based ultra-fast charging stations are described. A new classification of topologies for DC SST-based ultra-fast charging stations is proposed considering input power, delta/wye connections, number of output ports, and power electronic converters. More than 250 published papers from the recent literatura have been reviewed to identify the common understandings, practical implementation challenges, and research opportunities in the application of DC ultra-fast charging in EVs. In particular, the works published over the last three years about SST-based DC ultra-fast charging have been reviewed.
PH.D.DISSERTATION EXAM
Self-oscillating resonant converters: general approach and applications
Ph.D. Student: Ricardo Bonache-Samaniego
Thesis title: Self-oscillating resonant converters : general approach and applications
Supervisor: Carlos Olalla and Luis Martinez-Salamero
Examiners: Francisco Javier Azcondo (Universidad de Cantabria), Abdelali El Aroudi (URV) and Luca Corradini (University of Padova)
Place: Sala de Graus (ETSE)
Date/time: February 23rd 2017 / 11h:15 am
SUMMARY
Self-oscillation in resonant converters is a simple operating mode to generate a sinusoidal signal without requiring an external reference. Scattered in the literature, this mode has been attained by means of different techniques, all having in common the change of the input voltage polarity induced by the internal state of the resonant converter. Due to this spread, the absence of a unified approach in their analysis and the inherent delay in the different processing stages of the feedback path, self-oscillating converters have been relegated to the margins of the main stream in resonant converters, which is largely dominated by a frequency modulation-based operating mode.
A general approach for self-oscillating resonant converters is presented in this dissertation for a particular class of circuits in which the change of input voltage polarity is caused by the zero-crossings of the input inductor current. The key features of the method are an analytical description in the time-domain of a spiral that eventually converges into an ellipse, and a frequency-domain analysis that explains the behavior of the ellipse as a limit cycle. On a theoretical basis, this class of circuits behaves as loss-free resistors because in steady-state the input inductor current is in phase with the first harmonic of the input voltage.
The proposed analytical procedure predicts accurately the amplitude and frequency of the limit cycle and justifies the stability of its generation. This accuracy is reflected in the close agreement between the theoretical expressions and the corresponding simulated and measured waveforms. Second, third and fourth order resonant converters are designed following simple guidelines derived from the theoretical analysis. In addition, a voltage regulation loop is inserted to fully exploit the benefits of the self-oscillation by mitigating the effect of the perturbations entering through the input voltage or the output load.
The problem of delay in the control feedback path is appropriately compensated when dealing with the practical implementation of this class of resonant converters in view of its industrial applications.