Frekvensdrive

Frekvensdrive, often referred to in English as a variable-frequency drive (VFD) or AC drive, is an electronic motor controller that varies the speed of an alternating-current (AC) motor by adjusting the frequency and voltage of its supply. By matching motor speed to load requirements, frekvensdrive enables energy efficiency and improved process control across many industries.

A typical frekvensdrive comprises a rectifier, a DC link, and an inverter that converts DC back to AC with a controllable frequency. Using switching devices such as IGBTs and PWM, it can produce smooth waveforms. Basic V/f control preserves torque by keeping volts-per-hertz constant; more advanced methods include vector control and direct torque control for precise torque response.

Common applications include pumps, fans, conveyors, machine tools, HVAC, and robotics. Benefits include energy savings from speed matching, soft-start to reduce mechanical stress, smoother operation, and better process control. Limitations include harmonic distortion and EMI, potential motor overheating if misapplied, inrush currents, and the need for proper sizing, cooling, and protective measures. Effective installation often requires harmonic mitigation, proper shielding, and suitable cable routing.

Standards and safety: drives must comply with electrical safety and EMC standards (for example IEC 61800 series, CE marking, and regional certifications) and require appropriate grounding and protective measures. Etymology: Frekvensdrive is the Norwegian term for a frequency drive; in English usage VFD is common. The technology has evolved from thyristor-based rectifiers to PWM-based inverters and advanced control algorithms, supporting automation and energy efficiency in a wide range of applications.