Answer Happy

Q3. (a) Discuss what would happen if the torque loop is slower to respond than the speed loop in the cascade control structure of a drive. [4 marks] (b) An elevator on a cruise ship is driven by a permanent magnet DC motor. You are required to diagnose a fault and you disconnect it from the supply. For testing, you draw power from the auxiliary battery, which outputs 225 V DC. You connect the motor and measure its rotational speed, which is 1,800 rpm. You want to run the test for a while, and the battery has a total capacity of 11.25 kWh. After running the motor on the battery for an hour at the above conditions, the battery state of charge has dropped by 4.35%. The battery cannot supply more than 105 A and the motor is coupled to a load with a counter-torque of 110 Nm. The motor's electrical constant is stated on the nameplate as ke = 0.5 V/(rad/s), but you don't trust the nameplate. Verify if the above electrical constant is correct or not. If not, determine if the torque provided by the motor would actually be enough to supply the load. [8 marks] (c) You are asked to select the type of generator for a wind turbine. The wind turbine has a variable speed, within a certain range. Your boss proposes a Doubly-Fed Induction Generator (DFIG). Discuss the operation and advantages of the DFIG, with regards to variable speed operation. [4 marks] (d) An engineering apprentice designed a three-phase machine so that the space vector of the magneto-motive force is Fs = 89520 A turns. The machine has 6 poles and Ns = 49 conductors. You perform some tests and measure the stator currents at time t as follows: ia = 64 A, i = -32 A, le = -32 A. Determine if the design is correct or not. [4 marks]