I have heard that the motor can work as generator when the supply is stopped because back EMF flows from stator coils & charges the battery. Now, even when the motor is running & we supply the voltage to stator, the rotor magnetic field is still cutting the stator coils & generating a back EMF which will oppose the voltage currently being applied to the stator. So what is the role of this back EMF generated & how it affects the motor performance & stator current & voltage ? If conceptually wrong, correct me.
When working as a motor, a electrical machine "uses" its back EMF to regulate the current through the machine. When there is no mechanical load, the angular speed rises until the back EMF perfectly balances the supply voltage, so no current flows and no work is done by the electrical supply on the electrical machine.
When a load is imposed on the machine, the rotation speed slows and the back EMF no longer balances the supply. Current thus flows through the machine, and it is this current which feels the Lorentz force and does work. The higher the load, the lower the back EMF and the greater the current, so that the rate of electrical working on the motor by the supply equals the rate of mechanical work output. When a DC motor is stopped and the supply is switched on, the current and torque can be enormous; a DC motor's torque is typically maximal at zero angular speed. This is an ideal torque speed characteristic for getting heavy loads moving, which is why the DC motor is heavily used in industry and transportation.