Aug 20, 2026
Elevator systems frequently accelerate, decelerate, and change direction during daily operation. During braking, the elevator motor can operate as a generator and return electrical energy to the drive system. If this regenerative energy is not properly handled, the DC bus voltage of the elevator drive may rise excessively. U-shaped braking resistors provide an effective way to dissipate this excess energy as heat, helping maintain stable operation and reliable braking performance.
A U-shaped braking resistor is a high-power resistor designed to absorb and dissipate electrical energy generated during motor deceleration. Its resistance element is formed into a U-shaped configuration, allowing the resistor to provide the required resistance and power rating while maintaining a compact and practical installation structure.
In elevator applications, the resistor is generally connected to the braking circuit of a VFD (Variable Frequency Drive). When regenerative energy causes the DC bus voltage to rise above a certain level, the braking circuit activates the resistor and converts the excess electrical energy into heat.
Elevator deceleration → Motor generates regenerative energy → DC bus voltage increases → Braking resistor activates → Electrical energy converts into heat
This process helps prevent excessive DC bus voltage and allows the elevator to decelerate in a controlled manner.
During elevator braking, especially when a heavily loaded elevator is moving downward, the motor can generate significant regenerative energy.
The elevator braking resistor provides a controlled path for this excess energy. By converting electrical energy into heat, it helps prevent the energy from causing an excessive increase in DC bus voltage.
This is particularly important for elevators that operate frequently and perform repeated acceleration and deceleration cycles.
Excessive regenerative energy can increase the voltage of the VFD's DC bus. If the voltage becomes too high, the drive may trigger an overvoltage fault and stop the elevator.
A properly selected U-shaped braking resistor for elevator VFD systems helps dissipate the excess energy before the DC bus voltage reaches a dangerous level.
As a result, it can help:
Elevators may start and stop hundreds of times during daily operation. Unlike many industrial machines, elevator drives can experience frequent changes between motor and generator operation.
A high-power braking resistor designed for repetitive duty can withstand repeated energy absorption and heat generation.
Therefore, resistor selection should consider not only the resistance value but also:
The U-shaped structure can provide a practical configuration for high-power resistance elements. By using an appropriate resistor material and mounting structure, heat can be effectively transferred to the surrounding air or an external heat-dissipating structure.
For elevator equipment installed in relatively compact spaces, the physical design of the resistor is important.
A suitable U-shaped resistor can provide a balance between:
High power capacity + Compact installation + Effective heat dissipation
In a typical elevator drive system, the braking resistor works together with the VFD and braking unit.
A simplified configuration is:
Elevator Motor → VFD → Braking Unit → U-Shaped Braking Resistor
When the elevator decelerates and regenerative energy increases the DC bus voltage, the braking unit switches the resistor into the circuit. The resistor then converts the excess electrical energy into heat.
This allows the VFD to maintain a more stable operating voltage during braking.
U-shaped resistance elements can be customized according to the required resistance and power rating, making them suitable for different elevator drive systems.
Key advantages include:
The actual braking performance, however, depends on the complete braking system rather than the U-shaped design alone. Correct matching between the VFD, braking unit, and braking resistor is essential.
U-shaped braking resistors help elevator systems manage regenerative energy generated during deceleration. By dissipating excess electrical energy and helping control DC bus voltage, they support stable VFD operation and reliable elevator braking.
For elevator manufacturers and drive-system suppliers, selecting a braking resistor with the correct resistance, power rating, duty cycle, and thermal design is essential for achieving reliable long-term performance.
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