(a) Explain in details the working principle of the doubly fed induction generator (DFIG) used in wind power generation. [5 marks] (i) Draw a grid connected DFIG wind generator and name all the system components. Develop the rotor frequency equation. (iii) Develop the stator frequency equation. [5 marks] [2.5 marks] [2.5 marks] (b) A doubly-fed induction generator having 4 magnetic poles. The generator supplies power to a 50 Hz ac power network. Considering that an external source makes the generator rotate at a speed of 1980 rev/min, calculate the frequency of the ac currents that need to be fed into the generator rotor windings. [5 marks]