Grid-connected converters in hybrid wind-hydrogen systems
Withana, Nishan (2024)
Withana, Nishan
2024
Master's Programme in Electrical Engineering
Informaatioteknologian ja viestinnän tiedekunta - Faculty of Information Technology and Communication Sciences
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Hyväksymispäivämäärä
2024-03-20
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-202403182947
https://urn.fi/URN:NBN:fi:tuni-202403182947
Tiivistelmä
The production of hydrogen, facilitated by wind-generated energy, is currently a topic of significant interest among scientists and engineers. One of the arrangements is to connect an electrolyzer to the DC-link of the two converters, which are in a back-to-back configuration between the generator and the grid. The grid-connected converter of this system plays a pivotal role in system operation since it has to handle the dynamical effects of the wind generator, the hydrogen electrolyzer and the grid. This thesis has proposed a suitable control strategy that can be employed in the grid-connected converter of a hybrid wind-hydrogen system.
The work commenced with the development of small-signal dynamic models for the wind generator, the hydrogen electrolyzer system and the grid-connected converter. This was followed by the integration of closed-loop dynamics of the wind generator and the hydrogen electrolyzer system into the grid-connected converter model. Next, a control strategy was developed for the grid-connected converter model using linear PI controllers, which was later validated through both software and hardware implementations. Finally, the real test system was presented, and its components, capabilities and limitations were discussed.
The incorporation of wind generator and hydrogen electrolyzer dynamics was carried out by obtaining the closed-loop admittance transfer functions of each system model. The operation of the grid-connected converter is dependent on the dynamics of its subsystems due to their interactions. Hence, the DC input current, which the grid-connected converter receives, is dependent on the admittances of the other two subsystems. In this way, the source-affected open-loop transfer functions for the grid-connected converter model could be developed, which can be used for the loop-shaping technique to tune the PI controllers by setting the required stability margins. DC-link voltage regulation and converter current control are among the major objectives of the designed control scheme. The system performance was evaluated under four scenarios in both software and hardware implementations, and the results were observed. The results in all four scenarios depicted that the developed controller can accurately maintain the steady-state operation at both rated and under-rated operating conditions. Furthermore, the converter demonstrated its ability to deal with dynamical impacts caused by sudden changes in the input current by returning to steady-state operation quickly and smoothly.
The real test system which is present at the Power Electronics Laboratory of Tampere University, consists of components to emulate wind generation to an extent that is sufficient for most research. However, it lacks the ability to create various grid conditions and reflect the dynamic behavior of wind gusts, turbine blades and the turbine tower.
The work commenced with the development of small-signal dynamic models for the wind generator, the hydrogen electrolyzer system and the grid-connected converter. This was followed by the integration of closed-loop dynamics of the wind generator and the hydrogen electrolyzer system into the grid-connected converter model. Next, a control strategy was developed for the grid-connected converter model using linear PI controllers, which was later validated through both software and hardware implementations. Finally, the real test system was presented, and its components, capabilities and limitations were discussed.
The incorporation of wind generator and hydrogen electrolyzer dynamics was carried out by obtaining the closed-loop admittance transfer functions of each system model. The operation of the grid-connected converter is dependent on the dynamics of its subsystems due to their interactions. Hence, the DC input current, which the grid-connected converter receives, is dependent on the admittances of the other two subsystems. In this way, the source-affected open-loop transfer functions for the grid-connected converter model could be developed, which can be used for the loop-shaping technique to tune the PI controllers by setting the required stability margins. DC-link voltage regulation and converter current control are among the major objectives of the designed control scheme. The system performance was evaluated under four scenarios in both software and hardware implementations, and the results were observed. The results in all four scenarios depicted that the developed controller can accurately maintain the steady-state operation at both rated and under-rated operating conditions. Furthermore, the converter demonstrated its ability to deal with dynamical impacts caused by sudden changes in the input current by returning to steady-state operation quickly and smoothly.
The real test system which is present at the Power Electronics Laboratory of Tampere University, consists of components to emulate wind generation to an extent that is sufficient for most research. However, it lacks the ability to create various grid conditions and reflect the dynamic behavior of wind gusts, turbine blades and the turbine tower.