Method and control apparatus for controlling an AC-machine

#1. Technical Field

#The invention relates to the field of drive and regulation technology.

#2. Description of the Prior Art

#FIGS. 1a and 1b illustrate a Maxwell transverse force acting on the rotor that can be generated in an induction machine by superimposing a magnetic drive field with the pole pair number p.sub.1 on a control field with the pole pair number p.sub.2 =p.sub.1 .+-.1 and that can point in any desired direction depending on the mutual position of the fields. This circumstance is illustrated here qualitatively for the case p.sub.1 =1 and p.sub.2 =2. The control field with the pole pair number 2 weakens the drive field with the pole pair number 1 in certain regions and enhances it on the other side. The Maxwell transverse force is generated by this asymmetry. It always points here in the direction of the control flux vector .PHI..sub.2 considered in the p.sub.2 plane relative to the drive flux vector .PHI..sub.1 considered in the p.sub.1 plane. At the top both the drive flux vector and also the control flux vector point geometrically and electrically into the 1-direction, whereby the Maxwell transverse force also points in the 1-direction. At the bottom the drive flux vector again points in the 1-direction. The control flux vector, however, now points geometrically 45.degree. upwardly and electrically in the 2-pole pair plane and thus in the 2-direction, whereby the Maxwell transverse force also points in the 2-direction.

#FIG. 2 illustrates for the general case p.sub.2 =p.sub.1 -1 that the transverse Maxwell force always points into the direction of the control flux vector .PHI..sub.2 considered in the p.sub.2 plane as reflected in the one axis relative to the drive flux vector .PHI..sub.1 considered in the p.sub.1 plane.

#FIG. 3 illustrates for the general case p.sub.2 =p.sub.1 +1 that the Maxwell transverse force always points in the direction of the control flux vector .PHI..sub.2 considered in the p.sub.2 plane relative to the drive flux vector .PHI..sub.1 considered in the in the p.sub.1 plane.

#It has been known for a long time (for example from H. Sequenz "The Windings of Electrical Machines" Springer Verlag Wien, 1950) that transverse forces acting on the rotor can be generated in an induction machine by two combined windings with the pole pair numbers p and p.+-.1. An AC-machine, such as an induction machine, of this kind can be illustrated by the symbol in FIG. 7. The drive winding (4) with the pole pair number p.sub.1, the control winding (5) with the pole pair number p.sub.2 =p.sub.1 .+-.1, and the rotor (6) of the induction machine (3) are symbolized by concentric circles. The signal flux plan of such an induction machine with drive and control winding is illustrated for the case of the asynchronous machine in FIG. 9 and for the case of the synchronous machine in FIG. 10. The block which is of interest here responsible for the transverse force formation is the same for both machine types.

#A control method in accordance with a first reference (Hermann) is based on a machine model which takes account only of the Maxwell forces and considers the induction machine only in steady-state operation. The drive winding is connected to a rigid three-phase current supply. For the control of the transverse force vector, the phase currents (i.sub.S2) of the control winding are derived from the drive currents (i.sub.S1) by Hermann by means of amplitude modulation. Via a phase adjustment, the phase between the drive currents and the control currents is fixedly set for a fixed working point. With this fixed working point, the contribution of the machine flux .psi..sub.1 is constant and the flux angle .gamma..sup.S(p1) rigidly associated with the phase of the drive currents. The cross coupling taken into account in FIGS. 9 and 10 between the control current components (i.sub.S2d.sup.(T,p2), i.sub.S1q.sup.(F,p1) and the transverse force components (F.sub.x, F.sub.y) which arises as a result of the Lorentz forces, is proportional to the torque-forming drive current component i.sub.S1q.sup.(F,p1) and relatively weak. For a fixed working point, the transverse force acting on the rotor is controllable in accordance with a control process as in Hermann. A control of the transverse forces is however not possible with this process with a dynamic operation of the rotary field machine (load change, change in the speed of rotation).

#The control method in accordance with the second reference (Bichsel) is based on a machine model which only takes account of the Lorentz forces. A precise control of the transverse force is not possible with this method, since in general the Maxwell transverse forces which are not taken into account are much larger than the Lorentz transverse forces.