I have come across some variable frequency motor controllers that have regenerative braking. In regenerative braking mode they can act as variable torque inverters to connect to the electrical grid (400V, 50Hz). The challenge is programming the motor controllers to vary the torque on the generator and thus on the hydro turbine to optimize the power output. Does anyone have experience of programming a 200 kW motor controller in regenerative braking mode ? What is the best control algorithm ? I was thinking of continually changing the torque up and down very slightly to try to find the top of the power curve for a given water flow (wicket gate setting) through th hydro turbine. Does this correspond to the point of optimal turbin efficiency for a Kaplan turbine ?