| Motor nameplate and load current | Motor rated voltage, phase, frequency, and full-load current; actual load type and operating conditions. | Choose a converter whose continuous output-current rating meets or exceeds the motor’s rated current for the applicable duty. Use current ratings, not motor kW alone, when comparing models. | Allow for process conditions that can increase motor current, such as higher fluid density, mechanical wear, or sustained overload. |
| Load and duty classification | Whether the load is variable torque, such as many fans and centrifugal pumps, or constant torque, such as many conveyors and positive-displacement pumps. | Confirm that the converter has the required variable-torque or constant-torque rating. A model’s published power rating may differ by duty category. | For changing or heavy loads, use the more demanding applicable duty rating and verify it against the manufacturer’s load and overload curves. |
| Overload capability | Permitted overload current, overload duration, repetition interval, and starting or acceleration requirements. | Compare the converter’s overload rating with the machine’s worst-case starting and operating demand. Overload specifications vary by product and duty; do not assume a standard value. | Repeated overloads can cause thermal trips and shorten component life. Size the converter for normal operating conditions rather than relying on short-term overload capacity. |
| Supply voltage and input conditions | Available supply voltage, number of phases, frequency, voltage variation, and prospective fault current. | Match the converter’s input rating to the site supply and verify that its short-circuit rating is suitable for the installation’s available fault current. | Check the installation manual for permitted voltage tolerance, protective-device requirements, and any restrictions on supply systems or grounding arrangements. |
| Temperature and altitude | Maximum enclosure ambient temperature, installation altitude, ventilation, and heat from nearby equipment. | Use the converter’s specified rating at the actual site conditions. Many models require output-current derating above a stated ambient temperature or altitude; limits differ by model. | Keep cooling-air paths clear and account for cabinet temperature. High temperature and poor airflow can accelerate aging of electronic and capacitor components. |
| Enclosure and installation environment | Dust, moisture, washdown, corrosive substances, vibration, and indoor or outdoor location. | Select an enclosure protection rating appropriate to the exposure. An IP rating describes protection against access, solids, and water under specified test conditions; it does not by itself guarantee corrosion resistance. | Use suitable cabinet filtration, cooling, and corrosion protection where needed. Inspect seals and filters regularly, especially in dusty or humid environments. |
| Switching frequency and motor noise | Required acoustic performance, cable length, motor insulation, and the converter’s current rating at the selected switching frequency. | Choose the lowest switching frequency that meets the application’s noise requirements unless the equipment documentation supports a higher setting. Higher switching frequency can increase converter heating and may require derating. | Review motor temperature and converter thermal load after commissioning; do not change switching frequency without checking the applicable ratings. |
| Motor cable length and insulation | Cable length, cable type, motor insulation suitability, and the converter’s permitted motor-lead length. | Follow the converter instructions for maximum cable length. Long motor cables can increase reflected-wave voltage and electrical stress; an output reactor or dV/dt filter may be required. | Use correctly rated shielded or screened cable where required, and install grounding and cable terminations according to the equipment instructions and local electrical rules. |
| Braking and deceleration | Required stopping time, load inertia, overhauling loads, and frequency of deceleration cycles. | Check whether the converter can handle regenerative energy internally or needs a braking resistor, braking unit, or regenerative solution. Verify resistor ratings and duty cycle. | Provide adequate ventilation and clearance around braking components, which can become hot. Confirm protective measures for resistor overheating. |
| Harmonics and power quality | Supply-system impedance, number of converters, sensitive equipment, and applicable site or utility requirements. | Assess harmonic impact at the point of common coupling when required. Line reactors, DC-link chokes, or harmonic filters may be appropriate depending on the installation. | Evaluate the complete electrical system rather than selecting mitigation from converter size alone; verify compliance with applicable project and utility requirements. |
| Protection and safety functions | Overcurrent, motor thermal protection, ground-fault protection, safe torque off, and required emergency-stop architecture. | Confirm that built-in functions meet the application requirements and that any safety function has the required rating and is integrated into a validated safety system. | Test protective and safety functions during commissioning and at the intervals required by the risk assessment and applicable regulations. |
| Controls and communications | Local and remote control, analog or digital I/O, network protocol, feedback devices, and integration with the automation system. | Verify the needed I/O count, signal types, communication options, and control modes, including any encoder or closed-loop requirements. | Document parameter settings and network configuration. Confirm that replacement parts or compatible communication options can be obtained for the expected service life. |
| Maintenance and service access | Cooling-fan serviceability, filter access, diagnostics, spare-parts availability, and operating environment. | Prefer an installation that permits safe inspection and replacement of service parts without disturbing adjacent equipment. | Establish a maintenance plan based on the manufacturer’s instructions and site conditions. Keep suitable spare parts and record alarms, operating hours, and parameter changes. |
