Turbomachine comprising an electric machine having a starter-generator function, and method for controlling the speed of such an electric machine

A turbomachine for an aircraft, comprising:

• an accessory gear box,
• a first electric machine,
• a starter-generator integrating a second electric machine configured to operate in starter mode and in a generator mode, said first electric machine and said starter-generator integrating the second electric machine being arranged to transfer electrical power from one to the other,
• control electronic means configured to control said first electric machine and the starter-generator integrating the second electric machine, by controlling the electrical power and a frequency of a current sent to said first electric machine and the starter-generator integrating the second electric machine, and
• an epicyclic reduction gear train comprising three elements, a central planetary gear, an external ring gear and a planet carrier whose planet gears mesh with said planetary gear and said external ring gear, said three elements being rotatable about an axis of the epicyclic reduction gear train, a first of said three elements being intended to be coupled to the accessory gear box, a second of said three elements being intended to be coupled to the starter-generator integrating the second electric machine, a third of said three elements being driven in rotation by said first electric machine,
• wherein said control electronic means are configured to modify a speed of rotation of the first electric machine and a speed of rotation of the starter-generator integrating the second electric machine to provide the starter-generator in the starter mode with a maximum torque, and
• wherein said control electronic means are configured to modify the speed of rotation of the first electric machine so that said starter-generator in the generator mode is driven in rotation at a constant speed.