**6. Stability in operation**

The operation of the speed multiplier is of synchronous type, with no possibility of direct control, so there is a risk of stalling one rotor relative to the other. A precise study of this phenomenon is yet to be done (because, oddly, there is nothing definite on this subject in the bibliography). It goes without saying that this issue is delicate.

In the absence of a comprehensive study, the main solution to this problem in the design of the wind system is to monitor the electrical angle, ψ, between the magnetic fields from the two rotors through position sensors placed on the two shafts, or by indirect measurement through the voltage produced by a detection coil placed at the magnetic teeth.

When ψ tends to become greater than 90°, especially during rapid changes in the mechanical power from the wind turbine due to gusts, it is possible to influence the level of electrical power delivered by the generator in order to act on the dynamics of the driven load, allow‐ ing it to follow more easily the variations in speed.

However, the system becomes more stable as the maximum torque level transmitted by the multiplier is distanced from the maximum torque absorbed by the generator. This necessari‐ ly leads to oversizing of the speed multiplier.

The consequences of a possible stall are not really problematic for the intended application, provided that there is an electrical method of slowing down the wind turbine to allow me‐ chanical braking or pitch control of the blades.

The addition of electrical conductors at the high speed rotor, intended to act as electrical shock absorbers and allowing the transmission of high asynchronous torque, makes the op‐ eration safer.
