Operation of Type B Chopper (Regenerative Chopper)

Type B Chopper [Regenerative Chopper]

• Figure (a) shows the type B single quadrant chopper. The positions of the switch and the diode are interchanged as compared to Type A chopper.
• Due to this position interchanging, the output current i_o can only be negative but v_o will be positive. The direction of power flow now reverses and it is from load to source. Figure (b) shows type B chopper with motor load. E_b is the back emf of the dc motor whereas L and R are inductance and resistance of the motor winding.
• To discuss the operation of type B chopper it is assumed that the dc motor is already running and the back emf E_b is already developed with the polarity as shown.

  

  Figure (a)

  

  Figure (b)

Operation of Type B chopper

• When SCR S₂ is closed, the back voltage E_b drives current through inductor L and the output voltage becomes zero (see Figure (c)). The inductor L will store the energy. The current through the inductor will rise.

  

  Figure (c)

  

  Figure (d)

• When the SCR S₂ is open circuited, the stored energy in the inductance will induce a voltage across it as shown in Figure (c).
• Thus the total voltage of E_b plus inductor voltage is greater than V. This will forward bias diode D₂ and the stored energy is returned back to the source. The load voltage is +V but the load current is negative and decreasing.

  

  Figure (e)

• The dc motor in this case acts for a short duration as a generator and the kinetic energy stored in the system is returned to the input dc source. Due to the electrical loading the speed of the dc machine (now acting as generator), decreases.
• Higher the current drawn from it, faster will be the reduction in speed. This is known as the regenerative braking of the motor.
• The load voltage and load current waveforms for type B chopper are as shown in Figure (d) The type B chopper works in the second quadrant as shown in Figure (e).
• This chopper is also known as regenerative chopper. The other applications of type B chopper are transfer of energy stored in larger inductors or stepping up battery voltage to higher values.

  

  Figure (f)

  
  

Type A Chopper