Motor soft-starter control

A method for controlling a motor soft-starter for starting an electric motor on a three-phases electric network, the soft starter comprising three arms, each arm comprising two thyristors in antiparallel configuration and each arm connecting a respective phase of the electric network to a respective winding of the electric motor, the method comprising:

• determining, during a startup phase of the motor soft-starter, an amplitude misbalance between the three phases of the electric network, wherein the amplitude misbalance occurs when the three phases of the electric network do not all have the same amplitude of voltage and/or current;
• computing a first firing angle for the thyristors of a first arm of the three arms based on the determined amplitude misbalance between the three phases;
• and
• applying, during the startup phase of the motor soft-starter, a trigger pulse on a specific thyristor of the first arm at the first computed firing angle with a capability to both increase and decrease an amplitude of voltage or current output by the first arm to a respective winding of the electric motor.