In regenerative braking as the name suggests the energy recovered from the rotating masses is fed back into the d.c. power source. Thus this type of braking improves the energy efficiency of the machine.

The armature current can be made to reverse for a constant voltage operation by increase in speed/excitation only.

Increase in speed does not result in braking and the increase in excitation is feasible only over a small range, which may be of the order of 10 to 15%.Hence the best method for obtaining the regenerative braking is to operate, the machine on a variable voltage supply.

As the voltage is continuously pulled below the value of the induced emf the speed steadily comes down. The field current is held constant by means of separate excitation.

The variable d.c. supply voltage can be obtained by Ward-Leonard arrangement, shown schematically in Fig. 51. Braking torque can be obtained right up to zero speed.

In modern times static Ward-Leonard scheme is used for getting the variable d.c. voltage. This has many advantages over its rotating machine counterpart. Static set is compact, has higher efficiency, requires lesser space, and silent in operation

However it suffers from drawbacks like large ripple at low voltage levels, unidirectional power flow and low over load capacity.

Bidirectional power flow capacity is a must if regenerative braking is required. Series motors cannot be regenerative braked as the characteristics do not extend to the second quadrant.