It's not synchronous according to that data sheet. I would look into the slip settings as well, that data sheet actually has the info to calculate slip. At 50 Hz, unloaded a 4-pole motor will run at 1500 Hz. Slip is just 1500 - the rated speed. So should be somewhere between 34 and 48 if it's similar to those motors. I'd try changing the torque saturation back and try putting in a value of 30 or so for slip and work up from there.