Design of Digitally Controlled Quadratic Boost Converter

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Dr. Stumpf Péter Pál
Department of Automation and Applied Informatics

DC-DC converters are one of the mostly applied power electronic converters. They play important role in various devices, from low power home appliances via electric cars to the utilization of renewable energies, as they enable the efficient conversion of the voltage level. Recently increasing attention has been paid to the development of novel DC-DC topologies. One of these is the Quadratic Boost converter which is presented in this study. As its name implies, the conversion ratio of the Quadratic Boost converter has a quadratic dependence on the duty-cycle. However it has the same amplification ratio as two cascade-connected Boost converters, it has the advantage of using only one semiconductor switching device. Applying an average current mode control for this type of converter the output voltage can be kept constant even when the input voltage is low and fluctuating in a wide range such as in the case of photovoltaic or fuel cells.

The aim of my final project is to model a quadratic boost converter, derive its differential equations by taking into consideration the effect of the non ideal elements and calculate from the corresponding state space model the transfer functions required to controller design. The output voltage of the converter is controlled by a PI controller with a fast inner current loop. The algorithm is tested by simulations in MATLAB/Simulink environment. With the simulations the behaviour of the converter and the control algorithm is investigated in continuous and discrete time as well. The algorithm is implemented on a microcontroller.

A printed circuit board including the converter and the analog sensing circuitry was designed in Eagle. The average current control algorithm is implemented in an external STM32F401RE ARM microcontroller. For the visualisation of the measured and computed values of the microcontroller I have designed a graphical user interface in Matlab environment. All the four state variables can be measured by the microcontroller, which makes it possible to implement further controller algorithms like full state space control. A graphical user interface was developed for visualisation of the measured and computed values of the microcontroller.

Measurements on the built converter are carried out, the efficiency of the converter was computed and measured as well. At the end the measured values are compared to the simulation results.


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