Power Control

A chopper converts  fixed  de input voltage to a controllable dc output voltage. It is  the single  stage dc to dc conversion device. It is a high  speed  on/ off  semiconductor switch. The  control of a dc series motor. When  the chopper is ON ( this is  ON period it means chopper  switch  is closed) for the  period T_on  output voltage V_o ( which  is then applied to dc series motor) is equal  to source  voltages.

Vs in this  period  the inductance of armature winding  will store the energy. When the chopper is OFF for period T_off ( it  means chopper  switch  is Opened)  output  voltage  will be zero  but armature current will be  flowing  through  freewheeling  diode FD series fields  and armature.

                                       Figure voltage and current waveforms of a chopper controlled dc series motor

Therefore  the output  voltage  can be controlled  by varying duty  cycle α hence the speed  of dc  series motor  can be  controlled.