Design of a Cascade Controlled Boost-Power-Stage Converter for Photovoltaic Application
Niku, Mikko Henrik (2014)
Niku, Mikko Henrik
2014
Sähkötekniikan koulutusohjelma
Tieto- ja sähkötekniikan tiedekunta - Faculty of Computing and Electrical Engineering
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Hyväksymispäivämäärä
2014-10-08
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tty-201409301465
https://urn.fi/URN:NBN:fi:tty-201409301465
Tiivistelmä
A photovoltaic generator converts solar radiation into electrical energy. Power electronic converters are of prime importance in managing the produced energy e.g. between source and grid. Design of a photovoltaic generator interfacing converter is based on the electrical characteristics of the generator. Characteristics such as: maximum output power, short circuit current and open circuit voltage, which are dependent on the amount of insolation and the value of ambient temperature, are important to know when the converter is designed. Also, the dynamic resistance of a photovoltaic generator has a significant effect especially on the control design. Measurement data of the electrical characteristics of a Raloss SR30-36 solar panel measured in certain climate conditions was used in the design in this thesis.
In this thesis, a boost-power-stage converter with a cascaded inner inductor-current and outer input-voltage control was designed for photovoltaic generator interfacing. The main focus of this work is in obtaining a correct dynamic model for such a system, as well as, to evaluate the effect of the dynamic resistance on control. A prototype converter was built based on the design, and the control was implemented digitally. Every closed-loop frequency response of the converter and the responses to a voltage reference step-change were measured in order to verify the theoretical findings. The idea for testing this type of control was obtained from recent publications.
The measurement results confirmed that the obtained system model was correct, however, if the control is implemented digitally, the sampling delay should be taken into account in the design. Two PI-controllers were sufficient for providing a stable system. Control performance was significantly affected by the dynamic resistance. The control was much slower when the operation point was in the constant voltage region. The dynamic resistance had no effect on the system output impedance. More research is needed in order to determine the feasibility of the proposed control, for which this thesis gives a good foundation.
In this thesis, a boost-power-stage converter with a cascaded inner inductor-current and outer input-voltage control was designed for photovoltaic generator interfacing. The main focus of this work is in obtaining a correct dynamic model for such a system, as well as, to evaluate the effect of the dynamic resistance on control. A prototype converter was built based on the design, and the control was implemented digitally. Every closed-loop frequency response of the converter and the responses to a voltage reference step-change were measured in order to verify the theoretical findings. The idea for testing this type of control was obtained from recent publications.
The measurement results confirmed that the obtained system model was correct, however, if the control is implemented digitally, the sampling delay should be taken into account in the design. Two PI-controllers were sufficient for providing a stable system. Control performance was significantly affected by the dynamic resistance. The control was much slower when the operation point was in the constant voltage region. The dynamic resistance had no effect on the system output impedance. More research is needed in order to determine the feasibility of the proposed control, for which this thesis gives a good foundation.