Inverter TIPS: Soft-Start and V/f technique

Our RDI team continously works to improve the design and functionality of our devices, so testing processes are part of day-to-day activities. Download and read this new technical article, where we offer you tips to use and maintain 3ph DC/AC inverters and methods to control induction motors.

Inverter TIPs: Soft-Start and V/f technique

Nowadays, about 90% of industrial motor applications use three-phase induction motors as they are simple in design, easy to maintain and less expensive than other solutions. There are many induction motor control techniques in practice today, however, the most popular control technique is the generation of a variable frequency supply, which has a constant relationship between voltage and frequency. This technique is popularly known as V/F speed control technique.


The main issue when using an induction asynchronous motor is the inrush current in the start-up. This current is named by the manufacturers as locked rotor current (LRA) and can go from 5 to 12 times the nominal current of the motor for some hundreds of milliseconds, depending on the inertia of the load.