Q4Electric Drives
Question
Q.4. What is regenerative braking and how does it work?
Answer
Regenerative braking recovers the kinetic energy of a decelerating motor/load by operating the motor as a generator, feeding the recovered electrical energy back into the supply or storage system, rather than dissipating it as heat, thereby improving overall system efficiency.
Regenerative braking works by reversing the normal power-flow direction of a motor drive during deceleration: instead of the motor converting electrical energy into mechanical energy to drive the load, the load's stored kinetic energy (or, in a descending elevator/vehicle, its potential energy) drives the motor to rotate faster than its synchronous/no-load speed reference, causing the machine to operate as a generator instead — the induced back-EMF now exceeds the supply voltage, reversing the direction of armature current and hence power flow, feeding electrical energy back into the DC bus/supply (or into an energy storage device such as a battery or capacitor bank) rather than dissipating this braking energy as wasted heat in a resistor, as in simple dynamic (rheostatic) braking. This requires the drive's power-electronic converter to be capable of bidirectional power flow (e.g., a four-quadrant chopper or a regenerative-capable inverter/rectifier), and is widely used in electric vehicles, elevators, and electric traction systems to significantly improve overall energy efficiency.