VHzkontroll

VHzkontroll is a method of controlling alternating-current motors, commonly used in variable-frequency drives. The term combines V for voltage and Hz for frequency, reflecting the central rule of the strategy: keep the supply voltage proportional to the applied frequency to maintain approximately constant motor flux.

In practice, the controller adjusts the output voltage as the frequency changes. Below a base frequency, voltage is scaled linearly with frequency to keep the V/f ratio constant. Once the base frequency is reached, voltage is kept at its rated value to avoid overflux. Some implementations apply a small voltage boost at higher speeds to sustain torque or compensate for electrical losses in cables.

VHzkontroll can be implemented in open-loop form, which does not rely on speed feedback, or in closed-loop form with speed or torque feedback. It is simple, robust, and inexpensive, but offers limited dynamic performance and torque control compared with more advanced methods such as field-oriented control (FOC) or direct torque control (DTC).

Applications include industrial drives for pumps, fans, conveyors, and other non-critical loads where smooth torque delivery and energy efficiency are desirable and cost and reliability are priorities. The approach is widely used where the primary goal is broad-speed-range operation rather than high-precision speed or torque tracking.

Related topics include variable-frequency drives, V/f control, induction motors, and broader electric motor control techniques.