| Motor power | 5.5 kW, approximately 7.5 hp for a standard three-phase induction motor | Select a VFD whose continuous output-current rating matches or exceeds the motor nameplate current | Power rating alone is not sufficient because motor current varies by voltage, efficiency, power factor, and duty | Compare the VFD output current with the motor nameplate current, not only the stated kW size |
| Input voltage | Common international versions include 200–240 V three-phase and 380–480 V three-phase | Choose the voltage class that matches the available supply and motor connection | A 400 V motor is normally connected in star or delta according to its nameplate; a 230 V motor requires a different voltage class | Confirm rated input voltage, allowable voltage tolerance, input phase configuration, and local grid frequency |
| Output configuration | Variable-frequency three-phase AC output; typical adjustable frequency range is 0–400 Hz, depending on model | Use a three-phase output model for a three-phase motor | The motor should not be switched between the VFD and the load while the VFD is running | Check maximum output frequency, carrier-frequency range, and motor insulation requirements |
| Load duty | Normal-duty applications generally require about 110% overload for 60 seconds; heavy-duty ratings are often about 150% for 60 seconds, but values vary | Choose normal duty for fans and pumps; choose heavy duty for conveyors, mixers, crushers, hoists, and high-starting-torque loads | Heavy-duty operation may require a larger VFD frame even when the motor power is 5.5 kW | Review both continuous current and overload current in the technical datasheet |
| Control method | V/f control is common; sensorless vector control provides improved torque and speed regulation | Use V/f for simple variable-torque loads and sensorless vector control for conveyors, compressors, and constant-torque machinery | Closed-loop vector control is more suitable when precise low-speed torque or speed accuracy is required | Confirm whether autotuning supports the motor type and whether an encoder interface is needed |
| Starting torque | Fan and pump loads usually have lower starting-torque requirements; loaded conveyors and mixers may need high starting torque | Select a model with sensorless vector control, torque boost, and suitable overload capacity for demanding starts | Incorrect sizing can cause overcurrent trips during acceleration | Ask for starting-torque curves, acceleration-time limits, and overload test conditions |
| Speed regulation | Basic open-loop V/f control commonly provides adequate regulation for general-purpose speed control; exact accuracy is model-dependent | Use sensorless vector or closed-loop control where speed variation under changing load must be minimized | Printing, winding, positioning, and synchronized processes may require feedback control | Check stated speed accuracy, torque response, encoder options, and control-loop parameters |
| Braking requirement | Coasting or normal ramp-down may not need a braking resistor; rapid deceleration or high-inertia loads may | Choose a built-in braking-chopper model when dynamic braking is required, then size the resistor separately | Centrifuges, hoists, elevators, and high-inertia fans can regenerate energy during deceleration | Confirm chopper availability, minimum resistance, resistor power, duty cycle, and braking energy |
| Pump and fan functions | Variable-torque control, sleep/wake function, PID control, and water-pump protection are commonly useful | Select a model with built-in PID, dry-run protection, low-water protection, and multi-pump logic when applicable | These functions can reduce the need for an external controller in HVAC and water systems | Verify the number of PID inputs, relay outputs, sensor signal types, and pump sequencing functions |
| Enclosure protection | IP20 is common for control cabinets; higher protection such as IP54 or IP65 is used for exposed installations | Use an IP20 unit inside a clean, ventilated cabinet; choose a higher-rated enclosure for dust or moisture exposure | The enclosure rating applies to the complete installation, not necessarily the internal drive module | Confirm the certified IP or NEMA rating, cooling method, cable glands, and cabinet ventilation |
| Environmental conditions | Many drives are specified for approximately −10 °C to +40 °C without derating; higher ambient temperatures may require derating | Select a model with documented derating curves for the actual temperature, altitude, humidity, and dust conditions | Altitude above approximately 1,000 m may reduce cooling performance and require current derating, depending on the design | Request temperature, altitude, humidity, vibration, storage, and chemical-environment specifications |
| EMC and harmonics | An input EMC filter, shielded motor cable, correct grounding, and suitable cable separation may be required | Choose an integrated-filter model when installation standards or sensitive equipment require controlled emissions | Long motor cables and nearby communication equipment can increase electromagnetic interference | Check applicable EMC category, filter type, cable-length limits, leakage current, and harmonic requirements |
| Communication | RS-485 with Modbus RTU is widely used; Ethernet-based industrial protocols may require an optional communication module | Select the interface that matches the PLC, building-management system, or supervisory control network | Digital communication reduces hard-wired control signals and enables parameter monitoring | Confirm protocol, baud rates, register map, isolation, termination method, and available communication options |
| I/O capability | Typical features include digital inputs, relay or transistor outputs, analog voltage/current inputs, and an analog output | Choose the I/O quantity and signal types required by sensors, start/stop stations, interlocks, and speed references | Insufficient I/O can create additional panel hardware and wiring costs | Review terminal functions, sink/source logic, 0–10 V and 4–20 mA compatibility, and relay contact ratings |
| Safety functions | Safe Torque Off may be available on some models, but it is not universal | Use a model with certified STO when the machine risk assessment requires it | STO can remove motor torque without disconnecting the main power supply, subject to the applicable safety design | Request the safety certificate, SIL or PL data, terminal details, and wiring instructions |
| Protection functions | Common protections include overcurrent, overvoltage, undervoltage, overload, overheating, phase loss, and short circuit | Select protection functions that correspond to the motor, supply, load, and operating environment | Protection functions reduce damage risk but do not replace correct fusing, grounding, guarding, or maintenance | Check fault codes, trip thresholds, restart behavior, thermal model settings, and external protection requirements |
| Compliance and documentation | Export projects may require applicable electrical, EMC, machinery, and environmental compliance documentation | Choose a supplier that provides current test reports, declarations, manuals, wiring diagrams, and traceable serial records | Documentation supports customs clearance, system approval, commissioning, and after-sales service | Verify the exact model variant, certification scope, language of manuals, and document revision |
| Manufacturer evaluation | Technical support, sample testing, production consistency, spare parts, warranty, and delivery capability are key factors | Prioritize suppliers that can provide application sizing, parameter backup, test records, and responsive technical support | A lower purchase price may create higher commissioning, downtime, and replacement costs | Request a sample unit, load test evidence, warranty terms, lead time, spare-parts policy, and service response process |
