Abscruct -In this paper, a method for speed sensorless control of the induction machine is presented. The basic idea is to calculate the voltages induced by the main flux in the rotor field coordinates. This can be achieved by subtracting the stator voltage drops either in the stationary or in the field reference frame. The model's main drawback is the poor stability in the braking region, where a stabilization algorithm has to be performed. Also, the influence of the stator and rotor resistances evaluation error on the speed estimation is analysed. Both parameters can be adapted using the direct component of the main flux induced voltage After that, the voltage is transformed into the field coordinates: uMop L U~,~.(2)Thus we obtain the direct (3) and the quadrature (4) component ofthe induced voltage: di, 'Md = dt (3) (4) in the rotor coordinates. UMq = (1 -a)L, 0, i d . I. INTRODUCTIONIn the last decade, new approaches to the control of induction machines have been developed. A new research field that evolved rapidly, deals with the evaluation of the rotor speed without the mechanical sensor (resolver or encoder). The absence of the sensor brings several advantages in terms of cost, mechanical and electrical robustness. Mostly, these methods use the machine model in the well-known rotor or stator field reference frame [ 1, 21, but also some new methods, relying on the new powerful digital signal processors (DSP), emerged [3].The method presented in this paper uses one of the eldest approaches, that is the calculation of the rotor field and slip angular frequency (so-called "slip model") done in a new fashion. The difference between these two quantities is the rotor speed. The advantage of the proposed model is that one of the voltage components in the field reference frame can be effectively used for both the stator resistance end rotor time constant adaptation.
SENSORLESS MODELSThe first step in the presented sensorless model is the rotor flux (magnetizing current) angular frequency calculation. As can be seen in [4], this frequency is proportional to the voltage induced by the main flux (index M), which is the difference between the impressed voltage and stator windings voltage drops. This calculation can be performed either in stator or in rotor reference frame, with different performances.
A. Calculation of the Induced Voltage in Stator CoordinatesIn this approach, the first step is the main flux voltage calculation in the stator (a, 6 ) reference frame (1). 0-7803-5662-4/99/$10.00 01999 IEEE The latter is used to calculate the rotor flux frequency (*), but first the magnetizing current has to be evaluated from the current model. This part also provides a slip frequency. The complete model for sensorless speed evaluation is shown on Fig. 1.As we can see from both the equation and a figure, the direct component is not used for the frequency calculation. In fact, it is proportional to the rotor magnetizing current (flux) derivative, therefore in the constant flux region it should be equal to zero. However, a...
