Asynchronous machines - Power supply and features

Asynchronous motors, sometimes referred to as induction motors, have been used for many years to provide speed variation not only for industrial processes, but also for transport drive trains (railways and electric vehicles) and home automation systems... For low-power applications and restricted speed ranges, speed variation can be achieved by varying the amplitude of the stator voltage using dimmers. Rotor recovery enables speed variation for high-power machines (asynchronous machines associated with wind turbines), over reduced speed ranges. At present, most variable speed drives use variable-frequency, variable-amplitude power supplies on the stator of the asynchronous machine. The speed range is much wider, and dynamic performance higher. The asynchronous machine has the advantage of being robust, simple to build and inexpensive, especially if the rotor is squirrel-cage. However, its control is more complex than that of the DC or synchronous machine. Since power is supplied by a single armature, decoupling between the two main variables of this machine, magnetic flux and electromagnetic torque, is difficult to achieve (see the following article [D 3 621] on asynchronous machine control).

After a brief presentation of asynchronous inverters with constant stator frequency (dimmer and hyposynchronous cascade), we consider the study of the static and dynamic behavior of the asynchronous machine, fed at variable frequency, according to several concerns:

• in static operation, we successively study the waveforms of electrical and mechanical signals (currents, voltages and torque) for different power supply modes, and the electromechanical characteristics in sinusoidal steady state with variable amplitude and frequency for different choices of operation and input variables;

• in the dynamic regime, we are interested in modeling around an operating point due to the non-linearity of the models. We are interested in the positioning of poles and zeros in order to define the conditions for stability and non-minimum phase response.