SIMULATION OF TWO CONTINUOUS DTC SCHEMES FOR THE INDUCTION MOTOR

Transcription

1 SIMULATION OF TWO CONTINUOUS DTC SCHEMES FOR THE INDUCTION MOTOR Sergiu Ivanov Faculty of Engineering in Electromechanic, Environment and Indutrial Informatic Univerity of Craiova RO , Craiova, Romania KEYWORDS induction motor, direct torque control, continuou. ABSTRACT In the claical DTC of the induction motor, the witching period of the inverter i equal with the ampling period of the ytem. Due to thi intrinic characteritic, the real time control can be achieved only by uing high performance control ytem. Otherwie, the reult are quite unatifactory. The paper preent two continuou variant of the DTC, obtained by replacing the hyterezi controller by PI one which control the amplitude and the phae of the tator voltage. The imulation performed with different fixed tep ize (equivalent to different ampling period in the cae of real time control) how a very good behaviour which doe not depend eentially by the value of the tep. The reult are encouraging for the implementation on a uual real time control ytem. INTRODUCTION The direct torque control (DTC) of the induction motor i much lighter, a mathematical upport, than the vector control, regardle the type of field conidered for orientation. One of the main characteritic i the fact that the minimum PWM width of the inverter which upplie the motor i exactly the ampling period of the control ytem. Thi characteritic rie eriou problem for the practical implementation if moderate performance control ytem are ued. Hereby, without uing high performance command ytem, the reult can be far for the expectance. The paper deal with the imulation of uch regulation ytem and highlight the importance of the ampling period on the performance. Experimental reult obtained with a DS1102 ytem from dspace confirm the behaviour decribed by the imulation. There are propoed two implified continuou variant of DTC, where the two hyterezi controller pecific to the claical DTC plu a poible peed controller are replaced by only two or three PI one. Thu, the witching frequency of the inverter i decoupled by the ampling period of the control ytem. Conequently, the dependency of the performance by the ampling period i le tight. SIMULATION AND EXPERIMENTS ON THE CLASSICAL DTC Simulation Baically, the DTC of the induction motor control the torque by the mean of the peed of the etimated tator flux. In the ame time, the amplitude of the tator flux mut be maintained a cloe a contant. Thee two magnitude (the peed and the amplitude of the tator flux) are determined by the mean of the tator voltage applied to the motor by a voltage ource inverter. The principle and ome practical apect are well reported in more publication (Takahahi and Noguchi 1986, Va 1998, Ivanov et al 2008). The importance of the fixed tep imulation ize on the behaviour of the ytem wa reported in previou work (Ivanov 2009). Figure 1 plot only the locu of the top of the flux pace vector for two value of the fixed tep imulation ize: 100 µ and 500 µ. The two value were choen having in mind that for the real time control, the fixed tep imulation ize will be the ampling period of the control ytem, which i right the minimum value of every pule width of the voltage upplied to the motor. For 100 µ fixed tep ize one can oberve the ucceive commutation which lead to dicrete diplacement of the top of the tator flux pace vector, following one of the ix ditinct direction of the tator voltage pace vector, determined by the different topologie (tate of the witche). However, thi tep i too mall for the poibilitie of the control board DS1102 that will be ued to experimentally tet the control. Thi why, the imulation tep ize wa increaed to 500 µ, a ha been etimated that could be a feaible value for the real time control. It could be eaily noticed the quite diturbed hape of the locu, due to the reduction to about 2 khz of the witching frequency of the inverter. Conequently, high diturbed current and torque ripple are expected. Experiment The teting rig i centred on a DSP baed control all-inone board from dspace GmbH, DS1102. The main hardware facilitie of thi board are quite enough for the development of a imple teting tand. Proceeding 25th European Conference on Modelling and Simulation ECMS Tadeuz Burczynki, Joanna Kolodziej Alekander Byrki, Marco Carvalho (Editor) ISBN: / ISBN: (CD)

2 The experimental reult obtained with the control board DS1102 (Ivanov 2009), confirmed the behaviour anticipated by the imulation. Figure 1: The Locu of the Top of the Flux Space Vector for Fixed Step Simulation Size: 100 µ (a) and 500 µ (b) Additionally, thank to the advantage of the friendly interface between the DS1102 DSP board and the Matlab-Simulink environment, it i poible the quick implementation of the control algorithm and the interfacing of the enor. Uing thi friendly interface upplied by dspace, making only light change in the imulation diagram, the experimentation of different control cheme require le effort than any other experimentation platform (Ivanov and Sente 2003). Baically, the tructure of the Simulink control diagram ret a in imulation, only the block pecific to the interfacing with the power ytem mut be added. Thee block ubtitute the model of the inverter and of the motor, a can be een in Figure Contant2 R_f CdaA Mu 0 Tabel comutatii Ref_m PI_e Rate Limiter R_me Memory CdaB A Tabel comutati PI_at_err d/dt Incr CdaC dicret Mux Rotor Poition Incr dp_dt Buffer Mean 0.5 MLI_Ilim 30/pi Poz f lux Comenzi Vvit[min-1] 0 Me Ud MLI_Rec 1 Fi Curenti 1 C_GamI Mux BIT OUT Modelul fluxului DS1102PWM C_UI 1 DS1102OUT1 ADC #1 C_Mode Scal Mu ADC #2 in ADC #3 445 A_in ADC #4 G_Vdc DS1102ADC Figure 2: The Simulink Diagram for Real Time Control a) b) CONTINUOUS DTC In accordance with the principle of the claical DTC, the witching frequency of the inverter device i given by the ampling frequency of the whole control ytem. The minimum pule width i exactly the ampling period. Thi why, when large ampling period are ued, due to the limitation of the real time control ytem, the reult are not atifactory. The continuou DTC that we propoe break the dependency between the ampling period of the control ytem and the minimum pule width of the inverter. For achieving thi, the dicrete controller pecific to the claical DTC (bi-poitional for flux and threepoitional for torque), will be replaced with continuou one of PI type. A the amplitude of the flux i determined eentially by the voltage amplitude, one PI controller will compare the reference value of the tator flux amplitude with the actual one, obtained, a in the claical control, from the flux model. The output of thi controller will have the ignificance of voltage amplitude U. A econd PI controller will compare the preet value of the torque with the actual one. A in the claical DTC, the torque i controlled by the way of the peed of the tator flux which at it turn i controlled by the tator voltage, the output of thi controller will have the ignificance of the lip between the tator flux and the rotor. The output of thi controller will be added to the actual mechanical peed of the rotor (multiplied by the number of pair of pole of the motor). The reult will be the neceary tator flux peed. Thi peed will be integrated in order to obtain the poition of the anticipated tator voltage. Following, thi poition will be ued, together with the output of the firt PI controller to obtain the component of the neceary tator voltage. u u = U co, = U in. (1) It i true, the way how the further poition of the tator voltage i obtained, need the meaurement of the actual mechanical peed which i one of the drawback avoided by the claical DTC. But, if i conidered a peed loop, the meaured rotor peed i ued alo a reaction for the peed controller. Thi i the cae we have conidered and the complete Simulink model of the ytem i depicted in Figure 3. Alternately, the reference value of the torque could be directly applied a reference value to the torque controller. Thi i the cae of the ytem ued in the electric traction application.

3 Figure 3: Simulink Model of the Continuou DTC. A can be een, the reference value of the torque i the reult of the PI peed controller which i compared with the actual value given by the flux model. In the imulation diagram from Figure 3 it i not conidered any model for the inverter. Thi i becaue the reference voltage upplied by the -abc tranformation block (T2_3) will be applied to the inverter whoe witching frequency i totally independent by the ampling period of the control ytem. Otherwie, the inverter i conidered a an ideal amplifier, independent by the control ytem. The imulation of the ytem wa performed by uing a 500 µ fixed tep. The main reult are plotted in Figure 4. In Figure 4.a are plotted the phae current. A the inverter i conidered a ideal amplifier, the phae current are quai inuoidal. Conequently, the electromagnetic torque ha no ripple (Figure 4.b). The dynamic repone of the ytem i quite atifactory, the reference peed of 70 rad/ being achieved in about 0.55 after the tep application (Figure 4.c). The good behaviour of the control ytem i confirmed alo by the plot of the locu of the top of the tator flux pace vector, Figure 5. Thi one i almot a perfect circle and it mut be compared with the ditorted hape depicted in Figure 1.b, being obtained with the ame 500 µ fixed imulation tep. Figure 5: The Locu of the Top of the Stator Flux Space Vector for Continuou DTC. time [] Figure 4: Reult of the Simulation of the Complete Continuou DTC with 500 µ Fixed Simulation Step. The control diagram can be implified, by avoiding one PI controller, the torque one repectively. Indeed, by a proper tuning of the peed controller, it output can have now not the ignificance of reference torque, but directly of lip.

4 In thi cae, the reulted control diagram will have only two continuou controller of PI type, one for the voltage amplitude and the other for the peed and conequently lip, a can be een in Figure 6. Figure 6: Simulink Model of the Simplified Continuou DTC Elimination of the torque controller make unneceary the torque reaction computed by the flux model. Thi lead to an additional implification and reduction of the calculu effort of the real time control ytem. The reult of the imulation are plotted in Figure 7. A wa expected, the hape continue to be an almot perfect circle which give the guarantee that the torque ripple will be negligible. Figure 8: The Locu of the Top of the Stator Flux Space Vector for Simplified Continuou DTC time [] Figure 7: Reult of the Simulation of the Simplified Continuou DTC with 500 µ Fixed Simulation Step. The reult mut be compared with the one obtained with the complete implified DTC (Figure 4). It i to notice the high imilarity between the two et of waveform. Thi confirm the good behaviour of the implified control ytem. Thi control will be ued to be implemented on the teting rig. For completing the comparion with the complete DTC, Figure 8 plot the locu, during the whole dynamic regime, of the tator flux pace vector top. CONCLUSIONS The paper preented two variant of the continuou direct torque control (DTC) technique for the induction motor. The claical DTC ha great advantage, but alo one diadvantage: it lie the witching frequency of the inverter by the ampling period of the control ytem. Thi implie the neceity of a high quality real time control ytem. Otherwie, the reult are quite unatifactory. The propoed trategie break the link between the witching frequency of the inverter and the ampling period of the control ytem, being able to obtain good reult, even with large ampling period.

5 REFERENCES Caadei, D.; Profumo, F.; Serra, G.; Tani, A FOC and DTC: Two Viable Scheme for Induction Motor Torque Control. IEEE Tran. Power Electronic, Vol. 17, nr.5. Ehani, M. et al Propulion ytem deign of electric and hybrid vehicle. IEEE Tran. Indutrial Electronic, vol. 45, nr.1, pp Faiz, J. et al Direct torque control of induction motor for electric propulion ytem. International Journal on Power Sytem, vol. 51, pp Haddoun, A. ; Benbouzid, M.; Dialo, D.; Abdeemed, R.; Ghouili, J.; Srairi, K A lo-minimization DTC Scheme for EV Induction Motor. IEEE Tranaction on vehicle technology, vol.56, nr.1, pp Ivanov, S.; Câmpeanu, A.; Bitoleanu, A MATLAB- SIMULINK Library for AC Drive Simulation. In Proceeding of the IEE Conference on Simulation, Univerity of York, UK, Ivanov, S.; Sente, P Library for AC Drive Simulation and Real Time Control. In Proceeding of the 7 th World Multiconference on Sytemic, Cybernetic and Informatic (SCI 2003) (Orlando, FL, July 27-30). Ivanov, S.; Grenier, D.; Labrique, F.; Reende, M.J.; Robyn, B Online Interactive Leon on the Principle of the Direct Torque Control of the Induction Machine. WSEAS Tranaction on Advance in Engineering Education, ISSN , Iue 4, Vol. 5, Ivanov, S The influence of the ampling period on the performance of the regulation by DTC of the induction motor. In Proceeding of the 23 rd European Conference on Modelling and Simulation, Madrid, Spain, Takahahi, I.; Noguchi, T A new quick-repone and high efficiency control trategy of an induction motor. IEEE Tranaction on Indutrial Application. vol. IA- 22, no.5, Va, P Senorle Vector and Direct Torque Control, Clarendon Pre, Oxford. SERGIU IVANOV wa born in Hunedoara, Romania. He wa graduated in 1986 at the Univerity of Craiova, where he tudied electrical engineering. He wa with the Intitute for Reearch in Motor, Tranformer and Electrical Equipment Craiova till 1991, when he moved to the Univerity of Craiova. He obtained hi PhD in 1998 with a topic in the field of the control of the electric drive ytem. He i involved in modelling of the electromechanical ytem.