Simple! In that EMU, every 3rd coach is a motor coach with a net power output of 1600 HP.
In addition, these EMUs have a high gear ratio too (GR is 97:17 for Siemens EMU), because of which their torque output is excellent in low to medium speed ranges. This, in addition to distributed traction improves the starting ability on gradients.
BTW, here's a reading material :
click here