Optimal operation of Francis Small Hydro turbines with variabiable flow

In this paper is presented a solution for optimal operation of the Francis turbine, the most used hydro energy converter in small hydro plants. As the efficiency of this turbine is highly dependent from the water flow, which generally has a large variation, variable speed operation was chosen. Due to the fact that all hydro generators are AC machines, the connection to the 50 Hz power grid can be done only using as interface the AC/DC DC/AC static converters. For higher than 1 MW power generators, front end three level inverters are recommended. In addition, for higher than 1 kV voltage, double three level inverters shall be used, as these are allowing their connection directly to the medium voltage grid, eliminating in this way the need of separation transformers. The converter control is done by a single chip DSP controller TM3202028, which takes care of all system functions.