Losses minimisation of a field-oriented controlled induction machine by flux optimisation accounting for magnetic saturation zy - zyx 3 zyxw Amjad Baba, Eduardo Mendes and Adel Razek Laboratoire de Genie Electrique de Paris, URA-CNRS 127, UniversitCs Paris VI et XI, SUPELEC, Plateau de Moulon, 91192 Gii-sur-Yvette Cedex, FRANCE. tel. : +(33) 01 69 85 16 60, fax : + (33) 01 69 41 83 18, e-mail : mendes@lgep.supelec.fr zyx exp. : -- f=3Hz - f=l OHz num . : - f=3Hz -0- f=l OHz Abstract - In this work, the minimisation of the total copper losses in an induction motor has been achieved by optimising the zyxwvutsrq flux level as a function of the motor torque. The changes in motor parameters depending on flux level are taken into account, Three losses minimisation methods are presented and compared both by simulation and experiments. Results obtained from an appropriate benchmark show that the input machine power can be decreased by 15% when using such optimisation. I. INTRODUCTION Generally, the induction machine control is done in order to obtain the best dynamic performances. This yields in a constant rated flux operation under the nominal speed. In many industrial processes a permanent high dynamic performance is not required and hence no need to maintain a rated flux level in the motor. In such case, the introduced freedom degree, i.e. the flux level, in the machine control permits the optimisation of energetic criteria (minimum losses, unity power factor...). In a recent paper [l], the authors have proposed a simple method to minimise losses in steady and transient states by optimising the flux level but neglecting magnetic saturation in the machine. In the present paper, we will minimise the induction machine copper losses accounting for magnetic non linearities. Thus, the parameters variations depending on the flux level are determined both experimentally and numerically using the finite element method for local field computation. Three methods for the determination of the optimal flux level are presented. Two of them have been implemented both in simulation and experimentally. The induction machine is controlled using the well known field- oriented control method [2]. I1 - INDUCTION MACHINE MODEL The used induction machine model is based on the T-I equivalent circuit show on figure 1. Figure 1 : T-I equivalent circuit. A. Induction machine parameters The induction machine inductances have been determined experimentally and numerically (using the finite element method for the local field computations) [3][41. Figure 2 shows the stator inductance Ls as a function of the magnetising p.u. current (the base value is the rated rms magnetising current equals to 1.5 A) --Ls experimental (with 5% error bars) -Ls numerical & 30,2 0,O 0,5 1,0 1,5 2,O magnetising current (P.u.) Figure 2 : Stator inductance Ls as a function of the magnetising ament. The total leakage inductance oLs is shown, on figure 3, for two slip frequencies. zyxw 0,O zyxwv 0,2 0,4 0,6 0,8 1,0 1,2 magnetising current (P.u.) - 8 Figure 3 : Total leakage inductance as a function of the magnetising current. zy B. Induction machine copper losses The stator copper losses can be expressed as : Pa = Rs.lisI2 = Rs.(isdz + isq2) (1) and the rotor copper losses as : Pcr = Rr’.IirP = W.( (@m/Lm - is&? + isq2 ) (2) 0-7803~3946-0/97/S10.00 0 1997 zyxwvuts IEEE. MDI-2.1