E4102- DC MOTOR CONTROL( ANSWER) – TEST2

 E4102- DC MOTOR CONTROL( ANSWER)
 TEST2  (20 marks)

1.  Draw the circuit diagram of regenerative braking.                                                                   (5 marks)

                            

Explain the method.                                                                                                                      (5 marks)

Chopper is used to increase and decrease the voltage. Referring to diagram above: When the chopper Ch1 is ON, the machine  will function as a motor and when the chopper Ch1 OFF, the stored energy in the motor will exposed through D1 diode and then the current will be decreased.  When the chopper Ch2 is ON, the voltage in the motor will be generated. The reverse current will flow through the chopper and the energy will be stored in the motor. When the chopper Ch2 is OFF, this energy will exposed through D2 to the supply (the energy is in current form).

2. DC series motor, cupply voltage 600V, Ra=0.02 and Rf=0.03, 15.27mV/A-rad/s. Average Ia = 250A and duty cycle = 60%. calculate:

a.                   Vch average= (1-k) Vs = 0.4x600=240V                              (1  mark)

b.                   Pg = IaVs(1 –k)  = 250Ax600x0.4=6000W                           (2 marks)

c.                    Rm = Ra +Rf = 0.02W+0.03W = 0.05W.                               (1  mark)

d.                   w_min = Rm/Kv = 0.05W/15.27mV/A-rad/sec = 3.27rad/sec  (2 marks)

e.                   w_max =(Vch+IaRm)/IaKv = 252.5V/(250Ax15.27mV/A-rad/sec)

                         =66.14rad/sec                                                            (2 marks)

f.                     w      =(Vch-IaRm)/IaKv =227.5V/(250Ax15.27mV/A-rad/sec)

                          =59.59rad/sec                                                           (2 marks)