I- Preliminary Issues
1) Make a constitution schematic of an AC speed variator.
2) Explain the principle of scalar control of induction machine.
II- Scientific document analysis
Let’s consider the following document excerpt (“extrait de”) from the article: “Vector Control of Permanent Magnet Synchronous Motor Based On Sinusoidal Pulse Width
Modulated Inverter with Proportional Integral Controller”, Kaushik Jash, Pradip Kumar Saha, Goutam Kumar Panda, Int. Journal of Engineering Research and Applications www.ijera.com ISSN : 2248-9622, Vol. 3, Issue 5, Sep-Oct 2013, pp.913-917
1) Synthesize the principle of machines vector control
2) Which mathematic transformations are necessary for machines vector control?
3) List the advantages and disadvantages of machines vector control
4) Knowing that for a PMSM the torque equation becomes: Te = (3/2)pØiq with p number of pole pairs, Ø flux linkage and iq Torque producing component of stator current, What is the condition to make vector control possible?
VECTOR CONTROL
«Vector control is also known as decoupling or field orientated control. Vector control decouples three phase stator current into two phase d-q axis current, one producing flux and other producing torque. This allows direct control of flux and torque. So by using vector control, the PMSM is equivalent into a separately excited dc machine. The model of PMSM is nonlinear. So by using vector control, the model of PMSM is linear.
The scheme of vector control is based on coordinate transformation and motor torque equationby means of controlling stator current to improve the performances of motor, and is widely used in the field of PMSM servo system. In the control of the three-phase PMSM system, modulated current is supplied to the A-B-C stator to built rotated magnetic field and drive the rotor .The vector control strategy is formulated inthe synchronously rotating reference fram.By Clarke-Park transformations and inverse transformations, the equivalent relations of currents are built among a,b,c stator coordinates, stationary α, β axis coordinates and rotating d, q axis coordinates. »
Figure2 shows a vector diagram of the PMSM.phase a is assumed to be the reference .The instantaneous position of the rotor (and hence rotor flux) is at θr from phase a. The application of vector control, so as to make it similar to a DC machine, demands that the quadrature axis current iq be in quadrature to the rotor flux.Consequently id has to be along the rotor flux since in the reference used id lags iq by 90° .
CORRECTION
I- Preliminary Issues
1) Make a constitution schematic of an AC speed variator.
Son principe est de maintenir V/f = constant ce qui revient à garder le flux constant .Le contrôle du couple se fait par action sur le glissement. En effet, d’après le modelé établit en régime permanent, le couple maximum s’écrit: Cmax = 3p/2Nr’(Vs/ωs)2. On constate donc que le couple est directement proportionnel au carré du rapport de la tension sur la fréquence statorique. Cette quantité est proportionnel au flux. pour s’en convaincre, il suffit de partir de la relation de Faraday pour une spire supposée sans résistance(on la trempe dans l’hélium liquide ):
En maintenant V/f =constant et en faisant varier la fréquence statorique, on déplace la courbe du couple électromagnétique (en régime quasi-statique) de la machine asynchrone comme le montre la figure 5.47 de la page 231. En fait, garder le rapport constant revient à garder le flux constant .Quand la tension atteint sa valeur maximale, on commence alors à faire décroitre ce rapport ce qui provoque une diminution du couple que peut produire la machine. On est en régime de “défluxage” . ce régime permet de dépasser la vitesse nominale de la machine, on l’appelle donc aussi régime de survitesse.
A basse vitesse, la chute de tension Ohmique ne peut pas être négligée. On compense alors en ajoutant un terme de tension V0. (Figure 6.1)
Le schéma de commande de la Figure 6.1 la manière de réguler la vitesse de la machine en reconstituant la pulsation statorique à partir de la vitesse de la pulsation rotorique. Cette dernière, qui est l’image du couple de la machine est issue du régulateur de vitesse. Si la machine est chargée, la vitesse a tendance à baisser, le régulateur va fournir plus de couple (donc plus de glissement) afin d’assurer cet équilibre. La pulsation statorique est donc modifiée pour garder cet équilibre. La tension est calculée de manière à garantir le mode de contrôle en V/f de la machine.
II- Scientific document analysis
1)Vector control is also known as decoupling or field orientated control. Vector control decouples three phase stator current into two phase d-q axis current, one producing flux and other producing torque. This allows direct control of flux and torque. So by using vector control, the PMSM is equivalent into a separately excited dc machine. The model of PMSM is nonlinear. So by using vector control, the model of PMSM is linear.
2) Clarke–Park transformations and inverse transformations
