I had spent a lot of time building up two insula PV systems for emergeny power. This kept me occupied and away from the project. Now I have some time during my holidays and I am tackling the task of keeping the tracker on track on average, i.e. after a tracking step it should be ahead for some time and then fall behing. Right now, it is usually behind. You can set the parameters such that a step takes the tracker "beyond" the sun position. However, this makes oscillations more likely. I tried a scheme where there is a correction value added to the the sensor readings. This worked well for some time, but then it again led to oscillations. 

One issue is noon time when the elevation "speed" reaches zero and then reverses. Apparently this is a problem, because without movements the correction values cannot readjust.

Another issue is the dependence of the tracker sensitivity on the sky conditions. For some reason, the sensor sensitivity becomes higher when the amount of direct sunlight is low. This again can generate oscillations when the tracker is overshooting too much. 

My next idea would be to measure the change of e.g. azimuth sensor readings during an azimuth step. The trigger level could adjust to half of this step size. A hysteresis is already available to suppress reverses.