The control of two-level PWM inverters has been improved these last years. Consequently, the variable speed control of medium and large power induction motor drives have better performances. Three-level inverters are recently used and allow to improve the currents in the motor and to increase the power of the drives. At first, we develop the computation methods and the limits of the main sinusoidal modulation methods. Some of them are adapted and efficient to control the asynchronous machine at low speed. We propose a systematic method to build an optimised PWM control strategy. The PWM waves are computed to minimise current harmonics and pulsating torques. The method is applied to a specific example. The control is implemented on the 80C196KC microcontroller. The simulation of the induction machine in steady state allows to study the performances of the PWM waveforms. The good agreement between theoretical and experimental results proves the preservation of the features of the optimised PWM waves by the real time generation method. The study of the association of the optimised control with a vector control law allows to prove the feasibility of such a control. It allows to project the improvement of medium and large power drives performances both in steady state and dynamic working.
