What is the role of a braking chopper or resistor in VFD applications for induction motors?
1 Answer
In Variable Frequency Drive (VFD) applications for induction motors, a braking chopper or resistor is used to dissipate excess energy that is generated during the deceleration or braking of the motor. This is especially important when the motor is connected to a mechanical load that needs to be slowed down or stopped quickly.
When an induction motor is decelerating or being braked, its mechanical energy is converted back into electrical energy. This electrical energy needs to be absorbed or dissipated somewhere, otherwise it can cause issues such as overvoltage within the VFD's DC bus. A braking chopper or resistor provides a path for this excess energy to be safely released as heat.
Here's how it works:
Motor Deceleration or Braking: When the VFD reduces the frequency of the voltage supplied to the motor, the motor's speed starts to decrease, and it starts acting as a generator. This generates electrical energy that flows back into the VFD.
DC Bus Voltage Rise: The generated electrical energy increases the DC bus voltage of the VFD. If this voltage rise is not controlled, it can exceed the safe operating limits of the VFD, potentially damaging its components.
Braking Chopper/Resistor: To prevent the DC bus voltage from rising too high, a braking chopper or resistor is used.
Braking Chopper: A braking chopper is an electronic circuit that connects to the DC bus of the VFD. It regulates the voltage by periodically switching on and off, effectively dissipating excess energy as heat. The energy is absorbed by the chopper's power electronics and transferred to a heatsink.
Braking Resistor: A braking resistor is a physical resistor that is connected to the DC bus. When excess energy needs to be dissipated, the VFD redirects the energy through the resistor, causing it to heat up and dissipate the energy as heat.
By using a braking chopper or resistor, the excess energy generated during deceleration or braking is managed and prevented from causing voltage spikes that could damage the VFD. The choice between a chopper and a resistor depends on factors such as the amount of braking energy, the control strategy, and the specific requirements of the application.
When an induction motor is decelerating or being braked, its mechanical energy is converted back into electrical energy. This electrical energy needs to be absorbed or dissipated somewhere, otherwise it can cause issues such as overvoltage within the VFD's DC bus. A braking chopper or resistor provides a path for this excess energy to be safely released as heat.
Here's how it works:
Motor Deceleration or Braking: When the VFD reduces the frequency of the voltage supplied to the motor, the motor's speed starts to decrease, and it starts acting as a generator. This generates electrical energy that flows back into the VFD.
DC Bus Voltage Rise: The generated electrical energy increases the DC bus voltage of the VFD. If this voltage rise is not controlled, it can exceed the safe operating limits of the VFD, potentially damaging its components.
Braking Chopper/Resistor: To prevent the DC bus voltage from rising too high, a braking chopper or resistor is used.
Braking Chopper: A braking chopper is an electronic circuit that connects to the DC bus of the VFD. It regulates the voltage by periodically switching on and off, effectively dissipating excess energy as heat. The energy is absorbed by the chopper's power electronics and transferred to a heatsink.
Braking Resistor: A braking resistor is a physical resistor that is connected to the DC bus. When excess energy needs to be dissipated, the VFD redirects the energy through the resistor, causing it to heat up and dissipate the energy as heat.
By using a braking chopper or resistor, the excess energy generated during deceleration or braking is managed and prevented from causing voltage spikes that could damage the VFD. The choice between a chopper and a resistor depends on factors such as the amount of braking energy, the control strategy, and the specific requirements of the application.