Resumen de Contributions to the Modeling of Resonant DC DC Converters: Implementation of Control in Programmable Circuits
Nowadays, the cost of different digital control circuits has decreased significantly, while the complexity and features has increased. In case of power converters (DC-DC), this allows to implement different control strategies, taking advantage of the calculation capabilities (harmonic analysis, etc).
The resonant converters are characterised by no linear behaviour; the static models usually are complex, and most of the times the design process involves complex equations that have to be represented graphically. There are different analysis methods that try to simplify somehow the process, such as First Harmonic Approach for static models and Extended Describing Function to obtain the small-signal model, for instance.
The present work deals with modelling resonant converters, in order to implement the static model in digital control circuits, such as Digital Signal Controllers (DSC) or Field Programmable Gate Arrays (FPGAs). There are many papers in the most important journals (IEEE Transactions on Power Electronics, IEEE Transactions on Industrial Electronics) that reveal the importance of this trend. Several control schemes based on either FPGAs or DSCs have been presented during last years.
In the first chapters, the thesis goals and a brief review of resonant converters are presented. Then, two topologies are selected for the modelling process, in order to validate the proposed method: the Serial Resonant Converter and the Parallel Resonant Converter. These two topologies are used in different uses: The SRC is the typical topology used in Wireless Power Transfer (WPT), typically low voltage and high power, and the Parallel Resonant Converter, intended for high output voltage/power applications. The selected topologies are being studied and the proposed method, modelling with polynomial, is applied to them. In order to do it, the following steps were followed, for both topologies: Static model for the topology, using time domain analysis.
Polynomial model obtained from the previous model.
Validation of the proposed model.
Implement the model in the DSC.
Validation by simulation.
Validation by experimental results.
Implement the model in the FPGA. The model has been implemented directly in hardware; it means that the native processor has not been used.
Validation by simulation.
Validation by experimental results.
Fuzzy logic control for the PRC, based on polynomial. Simulation results.
In order to obtain the different models as well as their implementation in the DSC, MATLAB tools were used; in this way, a simplified process is defined. The developed work demonstrates that the proposed method is suitable solution to obtain resonant converters models to be implemented in digitals circuits. Regarding the FPGA code, it was implemented in VHDL, for the SRC , avoiding the use of native processor (In case of Altera/Intel, the Nios Processor): in this way, the most optimum code is obtained, in terms of speed. The polynomials were implemented in hardware, avoiding the use of any processor. The document includes different experimental results: A PRC with high output voltage (around 5kV), has been tested and a SRC was also built. The experimental results obtained demonstrate the models validity.
The thesis proposes different research lines, based on the obtained results, which include the development of control algorithms, evaluate the fuzzy logic control (based on polynomial) in another topologies, evaluate the proposed method in different topologies (multi-resonant converters, PWM, etc), for instance.
