A power resistor bank connected to the DC bus of a VVVF drive to dissipate regenerative braking energy as heat when the elevator is unable to feed energy back to the supply grid.
Full Definition
During regenerative braking — when a loaded car descends or an empty car ascends — the traction motor acts as a generator, returning energy to the drive's DC bus. If the drive does not have a regenerative (active front-end) converter, DC bus voltage rises. The brake chopper (IGBT switch) monitors bus voltage and connects the brake resistor when the threshold (typically 800–900 V DC for 400 V AC input) is exceeded, dissipating the excess energy thermally. Resistor sizing requires calculation of peak power (kW) and continuous power (kW), determined by duty cycle analysis for the specific installation. Resistors are mounted externally to the drive in ventilated enclosures; thermal switches protect against overtemperature. Energy recovery drives (regenerative units) eliminate the brake resistor by returning energy to the grid, improving building energy performance. IEC 61800-5-1 governs drive component safety.
