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A braking module is used when a variable frequency drive needs additional dynamic braking capacity. It provides a controlled electrical path for regenerative energy when the DC-bus voltage rises during braking.
The CBU Series is connected between the VFD DC bus and an external braking resistor. The module monitors the DC-bus voltage and controls the IGBT switching circuit according to the configured braking threshold.
Unlike a regenerative drive system, the braking circuit does not return energy to the utility grid. Instead, the regenerative energy is transferred to the braking resistor and converted into heat.
This configuration is applicable to drive systems where the VFD's built-in braking capacity is insufficient or where an external braking circuit is required.
During normal motor operation, electrical energy is supplied from the VFD to the motor. During rapid deceleration or overhauling operation, the direction of energy flow can reverse and the motor temporarily operates as a generator.
The regenerative energy is then returned to the VFD's DC bus, causing the bus voltage to increase.
The CBU Series responds to this voltage change through the following sequence:
DC-Bus Voltage Rises → IGBT Turns On → Braking Resistor Receives Regenerative Energy → Energy Is Converted to Heat → DC-Bus Voltage Falls → IGBT Turns Off
The IGBT therefore functions as an electronically controlled switch between the DC bus and braking resistor.
The switching threshold determines when the braking circuit becomes active, while the resistor determines how much regenerative energy can be dissipated. Both the module and resistor must therefore be selected according to the drive voltage, braking power, braking frequency, and duty cycle.
The CBU Series uses an integrated board-level design. The main braking and monitoring functions are incorporated into the module rather than distributed among several separate control components.
The module incorporates:
- IGBT power switching circuit
- DC bus voltage detection
- Braking control circuit
- Temperature monitoring
- Cooling fan control
- Fault protection
- Relay fault output
- DC bus and braking resistor terminals
The structure is intended for direct integration into suitable VFD control cabinets.
The external braking resistor remains a separate component because it is responsible for converting the regenerative electrical energy into heat.
The braking circuit uses an IGBT as the main switching device. The switching state is controlled according to DC-bus voltage rather than by mechanical switching components.
The module monitors operating temperature and controls the cooling fan according to the specified temperature thresholds. The CBU Series starts the fan at approximately 45°C module temperature and provides over-temperature protection at approximately 85°C, according to the product configuration.
Multiple modules can be connected in parallel when the required braking capacity exceeds the capacity of a single unit. A synchronization interface is provided for coordinated operation.
The braking threshold can be configured for different DC-bus voltage conditions. For a 380 VAC system, the factory setting is DC690V, with other switching levels available according to the specified configuration.
The module incorporates protection functions for conditions such as overvoltage, overcurrent, short circuit, and over-temperature. A relay output is available for external fault monitoring.
The braking circuit, control electronics, temperature monitoring, and fault interface are integrated into one assembly, allowing the module to be installed within the available space of a VFD control cabinet.
| Parameter | Specification |
|---|---|
| System Voltage | 220 VAC / 380 VAC / 690 VAC |
| Braking Voltage --- 220 VAC System | DC 340 / 360 / 380 / 400 / 420 V ±10 V |
| Braking Voltage --- 380 VAC System | DC 630 / 660 / 690 / 730 / 760 V ±10 V |
| Braking Voltage --- 690 VAC System | DC 1140 V ±10 V |
| Control Mode | Automatic DC bus voltage monitoring |
| Hysteresis | ≤10 V |
| Parallel Response | ≤1 ms |
| Fan Start Temperature | 45°C module temperature |
| Overtemperature Protection | 85°C |
| Fault Output | Relay: 0.6 A / 250 VAC; 2 A / 30 VDC |
| Protection Degree | IP20 or above |
| Flame Retardant Grade | UL94V-2 |
| Standard | GB/T 12668 |
Note: Actual operating parameters depend on the selected CBU model and application. The braking resistor must be matched to the module and drive system.
A typical installation consists of:
VFD DC Bus → Braking Module → Braking Resistor
The VFD controls motor speed and torque. The switching unit controls when the resistor is connected to the DC bus, while the resistor dissipates the regenerated electrical energy as heat.
| Component | Main Function |
|---|---|
| VFD | Controls motor speed and torque |
| DC Bus | Provides the DC link through which regenerated energy returns during braking |
| Braking Module | Connects the braking circuit when the DC-bus voltage reaches the configured threshold |
| Braking Resistor | Converts regenerative electrical energy into heat |
The module and resistor should be selected as a matched braking circuit. Resistance value, power rating, braking energy, duty cycle, and DC-bus voltage should be considered together rather than specified independently.
| Application | Why Dynamic Braking May Be Required |
|---|---|
| Hoisting equipment | Lowering a suspended load can return potential energy to the DC bus |
| Elevators | Rapid deceleration and downward movement can generate regenerative energy |
| Centrifuges | High rotational inertia can produce significant energy during deceleration |
| Machine tools | Short deceleration times can cause DC bus voltage rise |
| Textile machinery | Repeated speed changes may require additional braking capacity |
| Industrial washing equipment | Rotating loads may need controlled deceleration |
| Conveying systems | Overhauling loads can regenerate energy during downward movement |
| VFD retrofit projects | Existing drives may require additional external braking capacity |
The need for a braking module should be determined from the actual regenerative energy and braking duty rather than motor power alone.
| Parameter | What to Check |
|---|---|
| Drive Voltage | 220 V, 380 V, 690 V or applicable system voltage |
| DC Bus Voltage | Normal and maximum operating voltage |
| Motor Power | Rated motor output |
| Load Type | Inertial, overhauling, lifting or other load |
| Deceleration Time | Required time for speed reduction |
| Braking Frequency | Number of braking events per operating cycle |
| Duty Cycle | Percentage of time spent braking |
| Braking Resistor | Resistance, power and thermal rating |
| Cabinet Conditions | Available space, ventilation and ambient temperature |
| Parallel Requirement | Whether additional modules are required |
For technical selection, the most useful information is:
Drive model + system voltage + motor power + load type + deceleration time + braking frequency + duty cycle + braking resistor data.
The module should be installed according to the CBU wiring diagram and the VFD manufacturer's DC bus requirements.
Key points include:
1. Confirm that the VFD DC bus voltage is compatible with the selected module.
2. Match the braking resistor resistance and power rating to the braking circuit.
3. Keep DC bus and braking connections appropriately sized and as short as practical.
4. Provide adequate ventilation around the module.
5. Keep the braking resistor away from heat-sensitive components.
6. Connect the fault relay when external fault monitoring is required.
7. Verify all electrical connections before energizing the DC bus.
Because the braking resistor can reach high temperatures during operation, its mounting location and thermal clearance require particular attention.
Dufew Electric manufactures the CBU Series as part of its power electronics product portfolio, with production and inspection procedures covering key electrical components, connections, insulation, control functions, and overall product performance.
Depending on the model and application, production and inspection may include electronic component inspection, IGBT component verification, PCB assembly inspection, terminal inspection, insulation testing, electrical function testing, protection function verification, temperature control verification, fault relay testing, and final product inspection.
Product-specific inspection records and technical documents can be provided according to the model and project requirements to support product evaluation and technical verification.
The CBU Series is manufactured according to applicable requirements of GB/T 12668.
Dufew Electric also holds ISO and CE certifications within its quality and product compliance system. Applicable certificates and technical documents should be confirmed according to the specific product configuration.
For applications requiring additional drive-system components, Dufew Electric's product range includes:
Braking Resistors · Braking Choppers · Braking Modules · Input Reactors · Output Reactors · DC Reactors · EMI Filters · dv/dt Filters · Sine Wave Filters · Harmonic Filters · Transformers · Industrial Resistors
These components cover braking, filtering, reactor and power-control requirements used in industrial drive systems.
A Braking Module controls the transfer of regenerative energy from a VFD's DC bus to an external braking resistor when the bus voltage reaches the configured braking threshold.
No. The module is the switching component, while the resistor converts regenerative electrical energy into heat. They work together as a dynamic braking circuit.
It is connected across the VFD DC bus and is normally installed close to the drive when the cabinet layout permits. The connection must follow the product wiring diagram and the drive manufacturer's specifications.
The resistance value, power rating, braking energy, braking frequency, and duty cycle should all be considered. The resistor must also be compatible with the DC bus voltage and the selected unit.
Yes. Multiple units can be connected in parallel when additional braking capacity is required. Parallel operation requires appropriate synchronization, DC-bus wiring, resistor configuration, and thermal management.
The basic braking function operates automatically according to DC-bus voltage and does not normally require software programming. Correct wiring, resistor selection, cooling, and protection connections should be checked before operation.
Yes. The board-level construction allows cabinet integration, provided that adequate electrical clearance, ventilation, heat dissipation, and installation space are available.
Useful information includes the drive voltage, motor power, load type, deceleration time, braking frequency, duty cycle, braking resistor specifications, and installation conditions. These parameters are used to determine the appropriate configuration for the application.
For CBU Series selection, Dufew Electric recommends providing the following information:
Drive model · System voltage · Motor power · Load type · Deceleration time · Braking frequency · Duty cycle · Braking resistor specification · Cabinet installation conditions
The selection should be based on the complete braking system rather than motor power alone. This approach helps determine the appropriate module rating, resistor configuration, parallel arrangement and thermal requirements.
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