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A Variable Frequency Drive Filter is installed around a variable frequency drive to control electrical interference generated during motor speed regulation.
A typical connection is:
Power Supply → Input Filtering → VFD → Output Filtering → Motor
The two sections address different parts of the drive system.
Input filtering controls conducted electromagnetic interference between the VFD and power network.
Output filtering attenuates high-frequency components produced by PWM switching before they reach the motor through the cable.
This configuration is intended for applications where both power-side EMI and motor-side high-frequency effects need to be considered.
It is different from a conventional input EMI filter, which only filters the connection between the power supply and the drive.
Switching devices inside a VFD generate high-frequency electrical components that can travel through the power supply and affect other equipment on the same distribution system. The input section uses magnetic and capacitive components for common-mode and differential-mode attenuation, which may include common-mode chokes, differential-mode inductive components, X capacitors, Y capacitors, and resistors.
The input section is intended for conducted EMI suppression and does not replace a dedicated harmonic compensation system where specific low-frequency THD requirements apply.
A VFD produces a PWM output waveform with rapid voltage transitions. With long motor cables, distributed capacitance and impedance can affect the voltage waveform at the motor terminals. The output section attenuates high-frequency components and can help reduce motor-side dv/dt, reflected-wave effects, motor winding insulation stress, and certain high-frequency motor noise.
Actual performance depends on the VFD switching characteristics, cable length and construction, motor insulation, grounding, and selected filter configuration.
Not every VFD installation requires both input and output filtering.
The required configuration depends on the problem being addressed.
| Application Condition | Typical Filtering Consideration |
|---|---|
| VFD interference entering the power network | Input-side EMI filter |
| Interference affecting nearby control equipment | Input-side EMI filter |
| Long motor cable | Output-side filtering may be required |
| High motor-side dv/dt | Output-side filtering |
| Reflected-wave voltage concern | Output-side filtering |
| Both power-side and motor-side interference | Integrated input/output filter |
This distinction is important during product selection. The filter should be specified according to the actual electrical problem rather than installed simply because a VFD is present.
Dufew Electric combines the input and output filtering circuits within one assembly.
The two sections have separate electrical paths and terminal areas for connection to the power supply, VFD, and motor.
The filtering network can incorporate:
- Common-mode magnetic components
- Differential-mode inductive components
- X capacitors
- Y capacitors
- Damping resistors
- Other components required by the selected configuration
The integrated construction reduces the need to install two separate filter housings when both input and output filtering are required.
The actual internal arrangement depends on the product rating and configuration.
| Parameter | Specification |
|---|---|
| Rated Voltage | 220VAC / 380VAC / 690VAC / 1140VAC |
| Operating Frequency | 50Hz / 60Hz / up to 500Hz |
| Rated Current | 5A--1600A |
| Dielectric Strength, Line to Line | 1500VDC / 60s |
| Dielectric Strength, Line to Ground | 2500VDC / 60s |
| Insulation Resistance | >100MΩ at 1000VDC |
| Overload Capability | 1.4 × rated current for 1 minute |
| Minimum Overload Interval | 15 minutes |
| Maximum Cable Length* | 400m shielded / 300m unshielded |
| Protection Grade | IP00 / IP20 |
| Insulation Class | T40 / F (155°C) |
| Flame Retardant Grade | UL94V-2 |
| Product Standard | GB/T 15287/8 |
* Maximum cable length is application-dependent and should be verified according to the VFD output characteristics, motor, cable type, grounding arrangement, and selected filter model.
A typical Dufew filter model is: CAF-4 3 1-0010
| Code | Description |
|---|---|
| CAF | Dufew Electric filter series |
| 4 | Voltage class; 2 = 220V, 4 = 380V, 6 = 690V |
| 3 | Phase configuration; 3 = three-phase, 1 = single-phase |
| 1 | Filter category; 1 = input filter, 2 = output filter |
| 0010 | Rated current; 0010 = 10A |
For the integrated input/output configuration, the applicable model code should be confirmed against the corresponding product drawing and specification.
| Application | Main Requirement | Filtering Function |
|---|---|---|
| Variable Frequency Drive Systems | Control EMI generated during VFD operation | Input-side conducted EMI suppression and output-side high-frequency filtering |
| Servo Drive Systems | Reduce electrical interference around servo equipment | Input-side EMI control and output-side motor-side filtering |
| Industrial Motor Control | Improve EMC performance of motor drive systems | Suppress conducted interference and high-frequency switching components |
| CNC Machines & Machine Tools | Reduce interference affecting control and drive equipment | Input EMI filtering and output-side dv/dt reduction |
| Long Motor Cable Installations | Control reflected-wave and high-frequency voltage effects | Output-side filtering between VFD and motor |
| Conveyor, Pump & Fan Systems | Reduce interference from variable-speed motor operation | Input-side EMI suppression and, where required, output filtering |
| Industrial Automation Equipment | Limit interference between drive systems and nearby electronics | Common-mode and differential-mode filtering |
| Manufacturing Equipment | Address both power-side and motor-side interference | Integrated input and output filtering |
Note: The required filter configuration depends on the VFD, motor, cable length, EMC conditions, and the specific interference problem. Not every VFD application requires both input and output filtering.
| Selection Parameter | Information Required | Purpose |
|---|---|---|
| VFD Model | Manufacturer and model number | To determine the applicable input/output configuration |
| Rated Voltage | 220VAC / 380VAC / 690VAC / 1140VAC | To match the filter voltage rating with the drive system |
| Rated Current | VFD input or output current | To determine the required filter current rating |
| Motor Power | kW or HP | To evaluate the motor-side filtering requirements |
| Motor Rated Voltage | Motor operating voltage | To verify output-side compatibility |
| Motor Cable Length | Actual cable length in meters | Important for evaluating dv/dt and reflected-wave effects |
| Cable Type | Shielded or unshielded; cable construction where available | To assess EMC and high-frequency characteristics |
| Switching Frequency | VFD carrier/switching frequency, if available | Helps evaluate high-frequency filtering requirements |
| Installation Environment | Control cabinet, machine, production line, etc. | To determine installation and EMC considerations |
| Interference Condition | EMI, motor noise, dv/dt, reflected wave, nearby equipment interference, etc. | To identify whether input filtering, output filtering, or an integrated configuration is appropriate |
| Grounding Arrangement | Grounding and cable shielding method | Important for effective high-frequency interference control |
For a preliminary evaluation, customers can provide:
VFD model + rated voltage + rated current + motor power + motor cable length + cable type + switching frequency + observed interference
This information is generally more useful for filter selection than specifying the filter only by motor power.
Correct installation is important because high-frequency interference can bypass part of the filtering circuit through unsuitable wiring.
Connect the input section between the power supply and VFD.
Connect the output section between the VFD and motor.
Input and output terminals must be connected according to the product wiring diagram and must not be interchanged.
Power-side and motor-side cables should be routed separately.
Avoid long parallel runs between filter input and output conductors, as electromagnetic coupling can reduce filtering effectiveness.
The filter should be grounded according to the applicable electrical installation requirements and VFD manufacturer's EMC instructions.
For high-frequency interference, a short, low-impedance grounding path is generally preferred.
Where shielded motor cable is used, the cable shield should be terminated according to the VFD manufacturer's EMC requirements.
Before energizing the system, verify:
- Filter voltage and current rating
- Terminal connections
- Grounding
- Input/output cable routing
- Motor connection
- Mechanical mounting
After installation, verify normal VFD and motor operation and check the original interference condition.
Dufew Electric manufactures power electronics components including resistors, braking systems, reactors, filters, transformers, and customized electrical components. Variable Frequency Drive Filters are produced according to the required electrical configuration and application.
The production process typically covers component inspection, magnetic component processing, winding and insulation, filter assembly, electrical testing, final inspection, and packaging. Depending on the product configuration, quality checks may include component specification, winding, insulation, terminals, insulation resistance, dielectric strength, electrical performance, and dimensions.
Product-specific drawings, test records, and technical documents can be provided according to project requirements.
Dufew Electric has ISO and CE certifications supporting its quality management and product compliance requirements.
The applicable certificate and technical documentation should be confirmed according to the specific product model and destination market.
Quality inspection covers relevant stages from component verification and assembly through electrical testing and final inspection.
Dufew Electric supplies filters and other power electronics components to OEMs, distributors, system integrators, and industrial users.
Packaging and delivery arrangements are selected according to product dimensions, weight, quantity, destination, and customer requirements.
Available shipping arrangements may include:
- Sea freight
- Air freight
- Express delivery
- Customer-nominated forwarder
Packaging is selected according to the product construction and transportation conditions.
An input filter is installed between the power supply and VFD to control conducted EMI. An output filter is installed between the VFD and motor to control high-frequency components, dv/dt, and reflected-wave effects.
No. The requirement depends on motor cable length, VFD output characteristics, motor insulation, EMC conditions, and application requirements.
Yes. It can be evaluated for servo drive applications where input-side EMI or motor-side high-frequency interference needs to be controlled. The electrical rating must match the drive system.
Yes. The output section is designed to attenuate high-frequency switching components and can reduce dv/dt at the motor terminals. The actual result depends on the VFD, filter configuration, cable, and motor.
Yes. Long motor cables can increase reflected-wave and high-frequency voltage effects, making output filtering more relevant. The allowable cable length must be confirmed for the specific application.
Not necessarily. This product is primarily intended for EMI and high-frequency filtering around VFD systems. If the requirement is to control specific power-system harmonic orders or THD, a dedicated harmonic mitigation solution should be evaluated.
No electronic adjustment is normally required because the filter is passive. Correct model selection, wiring, grounding, and installation are still necessary.
The VFD model, supply voltage, rated current, motor power, motor cable length, cable type, and the specific interference or motor-side issue are useful for selecting the appropriate configuration.
Dufew Electric manufactures Variable Frequency Drive Filters for VFDs, servo drives, motor control systems, and industrial automation equipment.
The integrated configuration provides input-side EMI filtering and output-side motor filtering within one assembly. Selection can be based on drive rating, motor characteristics, cable length, EMC conditions, and installation requirements.
For product evaluation, provide the VFD model, motor power, rated current, motor cable length, cable type, and supply voltage.
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