Dufew provides the Braking Chopper as an external dynamic braking solution for variable frequency drives (VFDs), helping control DC bus voltage when motors operate as generators during rapid deceleration or overhauling loads. Designed for 220V, 380V, and 690V drive systems, the CBU Series can be configured according to braking power, duty cycle, DC bus voltage, resistor specifications, and installation requirements.
A braking chopper is a key switching component in a dynamic braking system. When a motor decelerates, regenerative energy can flow back into the VFD's DC bus and cause its voltage to rise. If this energy is not properly controlled, the drive may experience overvoltage protection or an uncontrolled shutdown. A braking chopper monitors the DC bus voltage and rapidly switches an IGBT circuit to transfer excess energy to a braking resistor, where it is converted into heat. This article explains how braking choppers work, their main technical parameters, selection criteria, applications, protection functions, and installation considerations.
Table of Contents
- What Is a Braking Chopper?
- How Does a Braking Chopper Work?
- What Technical Parameters Matter?
- How Should You Select a Braking Chopper?
- Where Are Braking Choppers Used?
- Braking Chopper vs. Braking Resistor
- What Protection Functions Are Important?
- Installation and Commissioning Considerations
- Manufacturing and Quality Considerations
- Frequently Asked Questions
What Is a Braking Chopper?
A braking chopper is an electronic switching device used in the DC intermediate circuit of a variable frequency drive. Its primary purpose is to control the rise of DC bus voltage caused by regenerative energy.
During normal motor operation, electrical energy is converted into mechanical energy. However, when a high-inertia load decelerates, the motor can temporarily operate as a generator. Mechanical energy is then converted back into electrical energy and transferred to the DC bus. This regenerative energy increases the DC link voltage.
A braking chopper provides a controlled path for this excess energy. When the DC bus voltage reaches its preset braking threshold, the chopper's IGBT switching circuit turns on and directs energy toward an external braking resistor. The resistor converts the electrical energy into heat, helping keep the DC bus within an appropriate operating range.
Therefore, a braking chopper does not independently dissipate energy. Instead, it controls when and how the braking resistor is connected to the DC bus.
How Does a Braking Chopper Work?
The operating principle is based on automatic DC bus voltage monitoring and rapid electronic switching. The complete process can be summarized as follows:
- Motor deceleration: The VFD commands the motor to reduce speed.
- Regenerative operation: The motor temporarily acts as a generator.
- DC bus voltage rises: Regenerative electrical energy returns to the drive's DC link.
- Threshold detection: The braking chopper detects that the DC bus voltage has reached its configured operating level.
- IGBT switching: The switching circuit conducts and provides a path to the braking resistor.
- Energy dissipation: The braking resistor converts the excess electrical energy into heat.
- Switch-off: When the DC bus voltage falls below the release threshold, the chopper turns off.
This switching cycle can repeat rapidly during braking. The result is controlled dissipation of regenerative energy without requiring a separate external controller for basic voltage monitoring.
For applications with frequent braking or high regenerative energy, an external braking chopper can be particularly useful when the internal braking capacity of a VFD is insufficient.
What Technical Parameters Matter?
Choosing a braking chopper based only on motor power can lead to an unsuitable braking system. The actual regenerative conditions, DC bus voltage, braking frequency, resistor characteristics, and duty cycle should all be evaluated.
| Parameter | Dufew CBU Series Reference | Engineering Significance |
|---|---|---|
| System Voltage | 220VAC / 380VAC / 690VAC | Determines the applicable drive and DC bus voltage class |
| 220V Braking Voltage | DC340 / 360 / 380 / 400 / 420V ±10V | Provides selectable braking thresholds for compatible systems |
| 380V Braking Voltage | DC630 / 660 / 690 / 730 / 760V ±10V | Matches different 380V-class drive configurations |
| 690V Braking Voltage | DC1140V ±10V | Designed for compatible 690V-class drive systems |
| Control Method | Automatic DC bus voltage monitoring | Allows the chopper to respond automatically to regenerative conditions |
| Parallel Response | ≤1ms | Supports coordinated switching in parallel configurations |
| Fan Start Temperature | Approx. 45°C | Helps manage heat during higher braking loads |
| Overtemperature Protection | Approx. 85°C | Provides thermal protection for the braking circuit |
| Protection Rating | IP20 or higher | Indicates the enclosure protection level of the applicable configuration |
| Applicable Standard | GB/T 12668 | Supports technical compliance for applicable drive-related equipment |
Final voltage, model, electrical configuration, and braking capacity should always be confirmed against the specific VFD and application requirements.
How Should You Select a Braking Chopper?
Professional selection starts with the braking conditions rather than simply matching the chopper to the motor's rated power. A system that stops a small motor very frequently can generate more demanding thermal conditions than a larger motor that brakes only occasionally.
Key selection factors include:
- Drive system voltage: Confirm that the chopper's voltage class corresponds to the VFD system.
- Motor power: Use motor rating as a reference for overall system sizing.
- Load inertia: High-inertia loads generally generate more regenerative energy during rapid deceleration.
- Deceleration time: Shorter stopping times can increase instantaneous braking power.
- Braking frequency: Repeated braking cycles increase thermal stress.
- Braking resistor: Resistance value, power rating, and duty cycle must be compatible with the chopper.
- Ambient temperature: Higher ambient temperatures can reduce available thermal capacity.
- Cabinet ventilation: Adequate airflow and installation clearance are essential for heat dissipation.
- Parallel operation: Multiple choppers may be considered when the braking requirement exceeds the capacity of one unit.
For engineering evaluation, useful information includes the VFD model, motor rating, load type, required deceleration time, braking frequency, existing resistor specifications, and expected duty cycle.
Where Are Braking Choppers Used?
Braking choppers are widely applicable to industrial drive systems where rapid deceleration, high inertia, or overhauling loads can return significant energy to the DC bus.
| Application | Typical Braking Requirement |
|---|---|
| Elevators | Controls regenerative energy during downward travel and rapid deceleration |
| Hoisting Equipment | Handles regenerative energy produced while lowering loads |
| Cranes | Supports dynamic braking of lifting and high-inertia loads |
| Centrifuges | Manages energy generated during rapid stopping |
| Conveyors | Controls DC bus voltage when moving loads generate regenerative energy |
| Textile Machinery | Supports frequent acceleration and deceleration cycles |
| Paper Machinery | Helps manage dynamic braking requirements in continuous production |
| Machine Tools | Supports rapid stopping and controlled deceleration |
| Industrial Washing Machines | Handles repeated braking cycles |
Braking Chopper vs. Braking Resistor
A common misconception is that the braking chopper and braking resistor perform the same function. In reality, they are complementary components within a dynamic braking system.
| Component | Main Function |
|---|---|
| DC Bus | Provides the electrical connection between the VFD and braking circuit |
| Braking Chopper | Controls when regenerative energy is transferred from the DC bus |
| Braking Resistor | Converts transferred electrical energy into heat |
The chopper therefore acts as the switching controller, while the resistor acts as the energy-dissipation element. Both components must be correctly matched to the drive system and braking duty cycle.
What Protection Functions Are Important?
Because braking circuits can handle substantial electrical and thermal energy, protection functions are important for reliable industrial operation. Depending on the selected configuration, the Dufew CBU Series can incorporate several protection functions.
- DC bus overvoltage protection
- Braking circuit short-circuit protection
- Overtemperature protection
- Cooling fan fault protection
- Fault relay output
The fault relay can provide a signal to an external control system when a defined fault condition occurs. This can help integrate the braking circuit into a broader industrial automation and protection strategy.
Installation and Commissioning Considerations
Correct installation is essential for both electrical safety and braking performance. Before commissioning a braking chopper, engineers should verify the complete braking circuit rather than checking the chopper in isolation.
- Confirm that the chopper voltage class matches the drive system.
- Verify the DC bus polarity before connection.
- Check the braking resistor's resistance and power rating.
- Ensure all terminals are correctly connected and securely tightened.
- Provide sufficient ventilation and installation clearance.
- Separate power wiring from sensitive control and signal wiring where appropriate.
- Connect the fault relay circuit when required by the control architecture.
- Perform electrical inspections before energizing the system.
Forced-air cooling can be important for applications involving high braking frequency or substantial braking power. Actual thermal performance depends on braking power, duty cycle, ambient temperature, cabinet ventilation, installation clearance, and operating frequency.
Installation and commissioning should be completed by qualified electrical personnel according to the applicable product documentation and electrical requirements.
Manufacturing and Quality Considerations
For industrial customers purchasing a braking chopper from a China manufacturer or supplier, product performance should be evaluated together with manufacturing capability, testing procedures, documentation, and technical support.
Dufew Electric manufactures power electronics components for industrial drive and power control applications, including braking choppers, braking resistors, braking units, reactors, filters, transformers, and industrial resistors.
Depending on the product configuration, quality control may include:
- Incoming material inspection
- Electrical connection inspection
- Insulation resistance testing
- Dielectric strength testing
- Switching function verification
- Protection function verification
- Cooling fan inspection
- Terminal and dimensional inspection
- Final product inspection and packaging
The CBU Series is manufactured according to applicable requirements of GB/T 12668, while Dufew Electric maintains relevant ISO and CE certifications within its quality and product compliance system. Specific certification documents and technical records should be confirmed according to the selected model and project requirements.
Frequently Asked Questions About Braking Choppers
1. What is the primary purpose of a braking chopper?
A braking chopper controls regenerative energy returned to the VFD's DC bus during motor deceleration or overhauling operation. It switches the excess energy to a braking resistor to help prevent excessive DC bus voltage.
2. Does a braking chopper replace a braking resistor?
No. The two components perform different functions. The braking chopper controls the switching path, while the braking resistor converts regenerative electrical energy into heat. They are normally designed to operate together.
3. Can one braking chopper support a high-power braking application?
It depends on the required braking power, duty cycle, DC bus voltage, resistor configuration, and selected model. Where a single unit is insufficient, multiple compatible choppers may be connected in parallel according to the system design.
4. Which voltage systems can the Dufew CBU Series support?
The CBU Series is available for 220V, 380V, and 690V drive systems. The appropriate model and braking voltage must be selected according to the VFD's DC bus characteristics and the application.
5. What information should be provided when requesting a braking chopper?
For accurate technical selection, provide the drive model, system voltage, motor power, load type, deceleration time, braking frequency, required braking power, braking resistor specifications, duty cycle, ambient conditions, and installation requirements whenever available.
Conclusion
A properly selected Braking Chopper can play an important role in controlling regenerative energy and maintaining stable DC bus voltage in demanding VFD applications. From elevators and cranes to centrifuges, conveyors, textile equipment, and machine tools, the right combination of chopper, braking resistor, cooling system, and protection functions can improve dynamic braking reliability. If you are evaluating a braking chopper for a new drive system or need help matching voltage, braking power, resistor specifications, and duty cycle, contact us to discuss your application requirements with Dufew Electric and identify a suitable configuration.
