Method for controlling the direction of rotation of a fluid machine and processing unit configured to perform said method

A method for controlling the direction of rotation of a fluid machine having an oriented-blade impeller, comprising the following steps:

• starting a synchronous electric motor which operates said fluid machine until a synchronous state is reached;
• driving said synchronous electric motor at steady state by applying a first phase cutting so that, in feeding a mains current to the synchronous electric motor, a first switch-on delay is applied with respect to the change in the sign of the mains current, wherein the first switch-on delay is based on a first phase angle;
• applying a second phase cutting, so that, in feeding the mains current to the synchronous electric motor, a second switch-on delay is applied with respect to the change in the sign of the mains current, wherein said second switch-on delay is based on a second phase angle that corresponds to a reference power, wherein said reference power has a value between a value of a first power required to keep the fluid machine rotating in a right direction and a value of a second power required to keep the fluid machine rotating in a wrong direction, which is opposed to the right direction;
• wherein the step of applying said second phase cutting leads to a loss of synchronism of the electric motor when the impeller of the fluid machine rotates in the wrong direction, said method thus comprising a step of restarting the electric motor.