Adjustable Speed of Synchronous Machine for Hydro Power Application
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- Institutt for elkraftteknikk 
When Europe is transitioning from fossil fuels to renewables, hydropower plants will have an important role in the integration of large quantities of fluctuating sources in the power system, such as wind and solar. With the development of variable speed of hydrogenerators, the objective is to further improve the flexibility and efficiency of the plants. If applying this technology in hydropower plants, Norway can be a green battery in the European power system. This thesis focuses on the development and preparation of a lab set-up with a converter fed synchronous machine, for research on variable speed of hydrogenerators. This includes testing and documentation of the synchronous machine, modelling and simulation of the lab set-up, development and simulations of possible operating scenarios which later can be tested in lab. A large part of the work covers determination of parameter values of the 8kVA synchronous machine. Several tests have been conducted in lab, to determine its most important parameter values, while other parameters were estimated based on typical values. Those were needed for modelling of the machine, and tuning of the control system. A simulation model has been developed to simulate variable speed control of the lab machine,where the machine is fed by a two-level voltage source converter. The objective has been to make the simulation model representative to the lab set-up so that it can be relevant for further lab research. The simulations show that the converter set-up is suitable for adjustable speed control of the synchronous machine. Synthetic inertia contribution by a converter fed synchronous machine has been simulated, by implementing a control loop that deaccelerates the machine in case of a frequency drop in the grid. This was done by letting the frequency signal pass through a derivative controller, which either affects the torque or the speed reference in case of a frequency drop. Highest impact was achieved by letting the derivative controller affect the speed reference, where the power boost lasted 0.7s and peaked at 18\% increase in the presented simulation. A significant impact was also achieved by affecting the torque reference for the inner control loop. However, this impact only lasted 0.1s, since the speed controller quickly compensated for the injection from the derivative controller. For further work, these operating scenarios can be tested in the lab set-up.