SUMMARY OF PHD THESIS

Transcription

1 Investeşte în oameni! FONDUL SOCIAL EUROPEAN Programul Operaţional Sectorial Dezvoltarea Resurselor Umane Axa prioritară: Educaţia şi formarea profesională în sprijinul creşterii economice şi dezvoltării societăţii bazate pe cunoaştere Domeniul major de intervenţie:.5 Programe doctorale si postdoctorale în sprijinul cercetării Titlul proiectului: Proiect de dezvoltare a studiilor de doctorat în tehnologii avansate- PRODOC Cod Contract: POSDRU 6/.5/S/5 Beneficiar: Universitatea Tehnică din Cluj-Napoca Eng. Arthur-Richard MÁTYÁS SUMMARY OF PHD THESIS STUDY OF THE SIX-PHASE PERMANENT MAGNET SYNCHRONOUS MACHINES USED IN ASSISTED STEERING SYSTEMS PhD Advisor, Prof. dr. ing. Károly Ágoston BIRÓ Evaluation commision of Phd thesis: PRESIDENT: MEMBERS: -Prof.dr.ing. Radu CIUPA - Dean, Faculty of Electrical Engineering, Thechnical University of Cluj-Napoca; -Prof.dr.ing. Károly Ágoston BIRÓ - PhD Advisor, Faculty of Electrical Engineering, Thechnical University of Cluj-Napoca; -Prof.dr.ing. Nicolae MUNTEAN - Scientific reviewer, Technical University of Timișoara; -Prof.dr.ing. Marius BIRIESCU - Scientific reviewer, Technical University of Timișoara; -Prof.dr.ing. Ioan-Adrian VIOREL - Scientific reviewer, Faculty of Electrical Engineering, Thechnical University of Cluj-Napoca.

2 The general trend in the automotive industry is the introduction of electric actuators in different operation systems on the car, thus increasing comfort and safety, helping to improve performance, reduce fuel consumption and emissions[n]. Average number of existing electric motors in a car is somewhere in the figure 3 and will grow in the future to [K]. The evolution of automotive steering systems closely followed the development of operating systems (hydraulic, electro-hydraulic and electric). If the first generation of cars were equipped with a mechanical steering system, in the 5s they started to use a hydraulic steering system, it has the advantage of reducing wear of mechanical parts, namely greater maneuverability. Hydraulic systems allowed easy handling at low speed of heavy vehicles, but these systems had a number of disadvantages such as high cost and high mass and greater fuel consumption. It proved to be very effective for low speeds, but also had a high risk to high speeds of the car, because "excessive support". The hydraulic function works only as long as the internal combustion engine is working, such assistance is stopped when the engine is stopped. The first electrically assisted steering systems (electrical power-assisted steering "EPAS"), appeared in the late '8s, by which an electric motor was used to produce torque assistance, thus replacing the hydraulic system. EPAS is consuming power only when needed, thus realizing the reduction of fuel consumption. The first electric motors used in power steering systems were brush DC machines and with permanent magnet excitation. The accessible controllability and the use of permanent magnets with superior features allowed the development of compact, small size, high performance electrical motors. The presence of the collector-brush system which limits the speed of work and maintenance activities required are two of the main disadvantages of this type of motors. Development of materials for permanent magnets, their production on a larger scale and the progressive reduction of the purchase price have facilitated the expansion of permanent magnet synchronous machine (DC and AC Brushless Synchronous Machines - BLDC and BLAC). Key parameters in choosing electric motors for power steering systems are high torque density, low torque ripples, low noise and energy efficiency. It is proposed to use a synchronous machine in the EPAS concept by introducing a major constraint: the reliability. An AC motor, synchronous or induction is powered by the car battery through a DC- AC converter, it is not desirable that the function provided by the electric motor function disappear in case of loss of a phase or malfunction of the inverter power switches. The main goal is to maintain assisted steering in case of a defect, so for this a six-phase permanent magnet synchronous machine (PMSM6) was built, which must be simple in terms of construction and reliable. In case of one or more stator phases loss the motor works but producing less torque. Chapter I presents the overall concept of steering. The first part of the chapter introduces the steering systems and their role in motor vehicles. After this the evolution in time of the steering system is presented, with different types of existing assisted steering systems. This part of the chapter is completed by a current state of electric steering systems used in small car class. After establishing the criteria for selection and presentation of the steering actuators used, in the second part of chapter I a more detailed description of the chosen motor for this type systems is given. The motor type and the characteristics of the permanent magnets are detailed. Last part of the chapter presents the need for fault-tolerant system design, the emphasis is on using a motor with a multiphase winding, the stator phase number is higher 2

3 than three. A brief overview of the various types of multiphase existing machines is presented, and a synchronous machine with six-phase winding is chosen. Fig. Assistance torque/speed characteristics After studying the various systems: the torque and steering wheel speed was determined, thereby results a maximum torque of 5 Nm at a speed of 2rpm. The chapter is completed by presenting the main parameters for the six-phase permanent magnet synchronous motor. Tab. Electrical machine specification DC bus voltage U bat 42V c.c. Frequency f 5Hz Nominal power P u 9W Pole pair number p Rated speed n N 3rpm Rated torque T n.3nm Rated power factor cosφ.83 Efficiency η.73 Chapter II details the design of the motor; the design follows the requirements specified in chapter I. A six-phase synchronous machine will be designed: 3rpm, with an output of 9W and 2 poles. The PMSM6 winding is performed in such way that the motor functions with 6 phases supplied with a voltage adapted from the 42 V c.c. bus of the vehicle. In the first part the design of the machine geometry is presented, following a study based on equivalent magnetic circuit and the losses in the machine. In the second part the motor characteristics are calculated according to the phase diagram and internal angle. The chapter is completed by thermal calculation to determine the impact of heat on the permanent magnets. 3

4 Fig. 2 The PMSM6 stator winding Fig. 3 Main stator dimensions Chapter III aims to identify the values of induction, torque an induced phase voltage with the help of the finite element software, JMAG-Studio. Two different rotor structures were studied: the one resulted from calculations in chapter II with rectangular magnets and the ideal rotor structure with circular magnet rotor surface. The chapter is completed with a study of PMSM6 operating under fault with non-powered stator phases. Tensiune [V] Amplitudine [V] Fig. 4 Induced phase voltage for no load Ordinul Armonicii Fig. 5 Harmonic content of the induced voltage 4

5 Cuplu [Nm] Fig. 6 Cogging torque of the PMSM6 Inductie [T] Pozitia rotor [ ] Fig. 7 Airgap flux density distribution Tab. 2 The electromagnetic torque of PMSM6 Electromagnetic torque [m.u.] Maximum value [m.u.] Minimum value [m.u.] Pulsation amplitude.34 Nm.495 Nm.7 Nm 45.4 % Chapter IV is divided into three main parts: the first part the voltage equations of PMSM6 are set in the natural system (A, B, C, D, E, F), and the model systems (α, β, z-z2- z3-z4) and (DQ). The second part presents the vector control principle (mathematical model and the model built in Maltab / Simulink) and the third part presents the results of simulations. Fig. 8 Vector control of PMSM6 Simulations were conducted with the PMSM6 powered with a balanced six-phase voltage system. The voltages have an actual value of 4 V and 5 Hz power frequency. Voltages are out of phase by 6 between them to form a balanced system of six voltages. Simulation duration is.8 seconds; simulation time is divided into two parts: in the first.5 seconds of simulation the starting and operating of the machine is presented with no load, and between.5-.8 sec load operation is presented. After.5 seconds a rated load of.3 Nm is connected. 5

6 Cuplu referinta Curent [A] Fig. 9 The stator currents Cuplu [Nm] Fig. The electromagnetic torque Mean torque is.3 Nm at load operation and rotor speed is 3 rpm. This allows the PMSM6 to develop an output power of 97.7 W. This power value is corresponding to the specifications set in the first chapter (9 W) Viteza referinta 35 Viteza [rot/min] Fig. The speed of the PMSM6 In the first part of chapter V the constructive elements of the prototype are presented. The second part presents a detailed test bench of the PMSM6, used to determine the main characteristics: leakage inductance determination and determination of reactance. The last part presents experimental results obtained for no-load, load test operation and with phase fault operation. Data from experimental measurements were compared with those resulting from calculations in chapter II. Fig. 2 Test bench Fig. 3 Block diagram of the test bench The test bench consists of: PMSM6, Two three phase converters SEMITeach (Semikron), Six phase current measurement transducers box, Incremental encoder for measuring the rotor position, PC with Matlab/Simulink and dspace ControlDesk softwares installed, 6

7 dspace d4 development board. Curent [A] Amplitudine [A] Fig. 4 The stator currents Ordinul Armonicii Fig. 5 The harmonic content of the stator currents.2 Factor de putere(exp) Factor de putere(calc) Curent(exp) Curent(calc).8.4 Factor de putere.6.4 Curent [A] Putere utila [W] Fig. 6 Comparasion between measured and calculated power factor Putere utila [W] Fig. 7 Comparasion between measured and calculated stator current Randament(exp) Randament(calc).4.35 Cuplu(exp) Cuplu(calc).3 Randemant [%] Cuplu [Nm] Putere utila [W] Fig. 8 Comparasion between measured and calculated efficiency Putere utila [W] Fig. 9 Comparasion between measured and calculated electromagnetic torque The final part of the thesis is represented by the Final Conclusions, since each chapter ends with conclusions, the final part of the thesis outlines the main contributions of this work: - Study in the first chapter for permanent magnet synchronous machine, proposing concrete solutions for its use in steering systems. 7

8 - Develop a design algorithm for six-phase permanent magnet synchronous machines. - Verification of the algorithm by calculating magnetic equivalent magnetic circuit. - Study of PMSM6 through numerical modeling in JMAG-Studio program and compare the results obtained in chapter II. - Study the influence of the shape of the magnets on the electromagnetic torque. - Vector control model built in Matlab / Simulink. - Realization of the PMSM6 stator and rotor. - Building a test bench, experimental measurements and validation of results obtained in previous stages. - Study of the motor operation in case of failure. REFERENCES [B2] C. Bălă Mașini electrice Teorie și încercări, Ed. a doua, Editura Didactică și Pedagogică, București, 982. [B4] M. Biriescu Maşini electrice rotative, Editura de Vest, Timişoara, 997, ISBN X. [B6] I. Boldea Parametrii maşinilor electrice; identificare, estimare şi validare, Editura Academiei Române, Bucureşti, 99. [B8] K.A. Biro, I.A. Viorel, L. Szabo, G. Henneberger Mașini electrice speciale, Editura Mediamira, Cluj-Napoca, 25, ISBN: [C2] I. Cioc, N. Bichir, N. Cristea, Maşini electrice. Îndrumar de proiectare. Vol. II, Ed. Scrisul Românesc Craiova, 985. [D2] T. Dordea Proiectarea şi construcţia maşinilor electrice, Litografia U., P., Timişoara, 98. [K] D. Iles-Klumpner Automotive Permanent Magnet Brushless Actuation Technologies, Teză de doctorat Universitate Politehnică Timișoara, 25. [M2] R. Măgureanu, N. Vasile Motoare sincrone cu magneți permanenți și reluctanță variabilă, Ed. Tehnică, București. [M4] A. Matyas, C. Martis, G. Aroquiadassou, A. Mpanda & K.A. Biro Design of sixphase synchronous and induction machines for EPS", ICEM 2 Roma, ISBN: [N] P.R. Nicastri, H. Huang Jump starting 42V PowerNet vehicles, IEEE Aerospace and Electronic Systems Magazine, Vol. 5, Issue 8, Aug. 2, pp [S4] L. Szabo Medii de programare uzuale în ingineria electrică - MATLAB, Editura Mediamira, Cluj-Napoca, 23. [V3] I.A. Viorel, K.A. Biro Permanent-magnet synchronous motor simplified field - circuit model, Proc. of Electromotion Int. Symp., Cluj, România, 995, pp [V4] P. Vas Sensorless Vector and Direct Torque Control, Oxford University Press, New York, 998, ISBN