Variable frequency drives

What a variable frequency drive is

A frequency drive rectifies the mains voltage and then, with power transistors (IGBTs), forms an output voltage with the required frequency and amplitude. The speed of an induction motor is proportional to the frequency, so the drive lets you adjust the speed smoothly from zero to rated speed and above.

Unlike a direct-on-line start, a motor controlled by a drive starts without an inrush current and mechanical shocks. This extends the life of bearings, gearboxes and couplings.

Where they are used

Frequency drives are installed wherever the speed has to be changed or a motor has to start smoothly:

• pumps and water supply systems — holding the pressure instead of throttling with a valve;
• ventilation and air conditioning — adjusting fan output;
• conveyors, mixers, extruders and machine tools;
• lifting mechanisms, elevators and cranes (with a braking resistor);
• compressors and refrigeration equipment.

How to choose a drive

The main parameters to look at:

• Power and current — the rated output current of the drive must not be lower than the motor current; allow a margin for a heavy start.
• Supply voltage — single-phase 220–240 V (usually up to 2.2 kW) or three-phase 380–480 V.
• Type of load — fan/pump (variable torque) or constant torque (conveyors, hoists).
• Control method — scalar (V/f) for simple tasks, vector for accurate torque at low speed.
• Interfaces — Modbus RTU, Profibus, Profinet, EtherNet/IP for integration with a PLC.
• IP protection rating — IP20 for a cabinet, IP54–IP66 for mounting outside a cabinet.

New and used frequency drives

The ElectroEU catalog includes both new drives and used equipment. Used drives are tested before dispatch, and the condition of each item is shown on its page. Used equipment is a way to quickly replace a discontinued drive or to save money on non-critical tasks.