Optimal control for a Wound Rotor Synchronous starter generator

Various types of electric machines can be considered for an application to integrated starter generator (ISG). Permanent magnet synchronous machines present interesting performances, nevertheless, it remains difficult to reach significant "constant power" zone under good conditions of efficiency and power-factor. The loss of control of electronics at high speeds may leads to high terminal voltages which can become dangerous for the whole of the vehicle. The induction machine does not present the same type of problem but is generally of a lower efficiency and its power-factor at high speed is weak what imposes an over sizing of the power electronics, in particular of the DC bus capacitors. The wound rotor machine, although understudied for ISG applications, does not present the whole of these problems and an optimal control of the injected currents can make possible to reach high power-factor and efficiency values. ISG applications impose very high constraints. So, classic control laws, based on linear models become unsuitable. This article proposes an original model of the wound rotor synchronous machine (WRSM) which makes possible to take into account the particularly significant phenomenon of cross-saturation for this type of machine. This model is then used to carry out optimal currents calculations which minimize the machine losses. The results of simulations and experimental results show that this type of machine presents a very high power-factor making it possible to avoid a over dimensioning of the power converter