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Robotics

Regenerative Braking

ActivePublished: 21 October 2026Updated: 21 October 2026Published
Key innovation
Instead of dissipating braking kinetic energy as friction heat, it recovers it by running the motor as a generator and returning the energy to storage (a battery, supercapacitor, or traction grid).
Category
Robotics
Abstraction level
Pattern
Operation level
Robot control
Use cases
Electric and hybrid vehicles (EV/HEV)Electric railways and rail vehiclesRobot joint drives and actuatorsElevators and cranesIndustrial variable-speed drives (inverters)Electric bicycles and scooters

How it works

During braking the drive controller switches the motor into generator mode. The spinning rotor induces a back-EMF; a bidirectional, four-quadrant inverter (a MOSFET/IGBT bridge) controls the current so that the machine's torque opposes the direction of motion, producing a braking torque. The recovered energy is routed by the same inverter back to the DC bus and on to storage (battery, supercapacitor) or the traction grid. The magnitude of braking torque and the recovered power flow are regulated by the controller (e.g. via PWM and current control, often within field-oriented control). As speed falls, the generator voltage drops and regeneration becomes less effective; when the storage is full or the DC-bus voltage exceeds a safe level, the surplus energy must be dissipated in a braking resistor (chopper) or taken over by the friction brake.

Problem solved

Conventional friction braking irreversibly turns kinetic energy into heat, wasting it and wearing brake linings. Regenerative braking addresses this by recovering part of that energy and returning it to the power system, raising energy efficiency and reducing brake wear.

Components

Motor operating as generatorConverts the mechanical braking energy into electrical energy

The drive machine (typically BLDC or PMSM) reverses its function: instead of drawing current it generates it via back-EMF, producing a braking torque.

Bidirectional (four-quadrant) inverterControls bidirectional energy flow between the motor and the storage

A transistor bridge (MOSFET/IGBT) allowing current to flow both to the motor (driving) and from the motor to the DC bus (regeneration), with torque regulated by PWM.

Energy storageAbsorbs and stores the recovered energy for reuse

A battery, a supercapacitor bank, or a flywheel; in railways the traction grid itself absorbs the returned energy.

Braking and blending controllerSplits the braking demand between regeneration and the friction brake

Control logic sets the regenerative torque based on speed, state of charge, and DC-bus voltage, and when regeneration is not possible hands braking over to a braking resistor or the friction brake.

Implementation

Implementation pitfalls
Full or cold storage cannot absorb energyHigh

When the battery is fully charged or too cold it cannot accept the return current; without energy management the DC-bus voltage rises.

Fix:Throttle regenerative torque based on state of charge and temperature, and use a braking resistor (chopper) to bleed off surplus energy.
Loss of effectiveness at low speedsMedium

At low speed the back-EMF is small, so regeneration cannot produce enough torque and will not bring the vehicle fully to a stop.

Fix:Smoothly hand braking over to the friction brake below a speed threshold (brake blending).
DC-bus overvoltageHigh

A sudden, strong regeneration can push the DC-bus voltage above its rated limit, risking damage to transistors and capacitors.

Fix:Use voltage monitoring, a braking chopper, and rate-limiting of the return current.

Hyperparameters (configurable axes)

Maximum regenerative torqueHigh

Upper bound on the braking torque obtained from regeneration; a higher value recovers more energy but loads the storage and power stage more.

SoC / DC-bus voltage cutoffHigh

The state of charge or DC-bus voltage above which regeneration is throttled to avoid overcharging the storage or exceeding a safe voltage.

Brake blending ratioMedium

The split of the braking demand between regeneration and the friction brake, dependent on speed and conditions, ensuring predictable deceleration.