PARAMETRIC ANALYSIS OF THE PM MOTOR FOR HYBRID ELECTRIC VEHICLES

Transcription

1 11 th National Congress on Theoretical and Applied Mechanics, -5 Sept. 009, Borovets, Bulgaria PARAMETRIC ANALYSIS OF THE PM MOTOR FOR HYBRID ELECTRIC VEHICLES G. VELEV Institute of mechanics,bulgarian Academy of Sciences, Acad. G. Bonchev str.q lok Sofia, Bulgaria ABSTRACT. I considered modern electric motors with permanent magnet (PM motors) to power hyrid (HEV) vehicles. It is an analysis of technical, operational and economic characteristics of various systems for electrical drives HEV vehicles and the electric motors availale on the world market. On the asis of the analysis selected the appropriate type of electrical motor vehicle HEV. It is an analysis of the parameters of power, management and implementation of the PM motor in order to develop original Bulgarian mechatronic system for HEV propulsion of vehicles in uran environments. KEY WORDS: EV - Electric Vehicle; HEV - hyrid electric vehicle; AC motors - Asynchronous electric motor; PM motors - electric motor with permanent magnets; RMDC - the direct electric motor with permanent magnets;bdcms - Brushless PM motor; PMSM - synchronous electric motor with permanent magnets; IPM - electric motor with interior permanent magnets CPSR - Constant power speed ratio; PWM - Pulse width modulation; DTC - Direct torque control. 1. Introduction. Overview of the technology of electric motors. In this study presented several configurations of electric motors, each of which has specific positive and negative sides. Certain configurations are not for the automoile industry ecause of their inaility to meet specific requirements, such as certain power at peak load, constant power, the volume density of kilowatts of power, efficiency, minimum weight and duraility. Marketing of a model is also difficult undertaking, hiding many risks [1].. Purpose of work To analyze the current electric motors to power EV / HEV vehicles. On the asis of the analysis to choose the most appropriate for the purposes of the study type electric motor for HEV. To analyze the parameters of power, management and

2 G. Velev administration of electric motor in order to develop original Bulgarian mechatronic system to power HEV vehicles. 3. Types of electric motors Electric motor power HEV cars are the main species. Each has advantages and disadvantages, as shown elow Asynchronous (induction) motors Asynchronous electric motors has a long history of successful applications in industry and is very durale and reliale. Manufacturers of induction electric motors have much knowledge and experience in the design and manufacture of asynchronous motors, which can e easily used for planning a drive motor for a hyrid car. The project FREEDOMCAR [], asynchronous motor is presented as less effective and less powerful engines than RM. Although some manufacturers promise low udget concepts, it seems there will e a shortage of new ideas for making significant improvements to enhance their performance. Expect only small improvements in the characteristics (performance, power) in the near future. Therefore, low cost, high reliaility and low technological risk will likely remain a primary advantage of this technology for the future. 3. Brushless PM motors Brushless PM motors are designed so that, in the stator induce electrical magnetic field acting on the permanent magnets in the rotor [1]. There are several configurations of the conventional motors. In recent years, there were more new concepts to improve the PM machines. PM motor configuration and connection of a rotor with stator determine the form of a rotating magnetic field. The shape of the magnetic field is the main feature. Engines, in which direction the field is radial, are classified as machinery radial action. They have a cylindrical form, rotor is usually located in stator, ut can also e placed efore stator. PM engines in which direction the field is axis are classified as motorcycles with axes action. They may have forms of rotor disc and stator. Stator-rotor-stator configuration is typical. The shape of the magnetic field of PM coincides with the engines of passing power and can e trapezoidal or sinusoidal. Although oth types are rushless and synchronous, RM engines with trapezoidal magnetic field are often called rushless DC motors (BDCMs), while motorcycles PM y sinusoidal magnetic field is called synchronous motors (PMSM). PM engines generally have higher efficiency as a result of passive emotion-ased permanent magnet field. PM engines are more powerful per unit weight than other types of electric motors, as are light and occupy less space. The price of the material for the magnets, which are necessary to achieve a power is the main consideration in the choice of technology. The cost of the material of the magnet is higher than the cost of other materials which are used for electric motor. The stators of PM motors are usually produced in the same way as stators of induction motors IPM motors

3 Parametric Analysis of the PM Motor for Hyrid Electric Vehicles Unlike surface-mounted magnets of PM engines, internally mounted magnets in IPM motor offers certain advantages - such as higher speed of rotation, which is the most ovious advantage. The main difference e, that the placements on the surface of the rotor magnet, the flow can not e touching the magnets connected in order to rotor - stator phase advance, while if it is emedded magnet rotor over which flow may e connected tangents stator - rotor phase is done in advance. When the permanent magnet (PM) are mounted on the rotor surface, increasing surface induction. Represents the saturation magnetic field, which is not used effectively in creating an effective torque. All forms of weakening of the field, regardless of the type of ike, are loss of motor efficiency. IPM engines facilitate the use of quality produced rectangular or other convenient forms of permanent magnets. Another advantage is that IPM engines with high energy magnets can provide rapid acceleration due to their high proportion "torsion/inertia, so compact versions (IPMs) are usually used in systems servomehanizmi [1]. 4. Analysis of technical parameters of the variale field in PMSM motors with surface mounted permanent magnets An important sign of traction motors is that they provide a wide CPSR (constant-power speed ratio). In this study CPSR is defined as the ratio of the highest possile speed at which the specific power can e developed to the lowest possile speed at which the specific power can e developed while working within the nominal power of the engine. The asic speed N is defined as the lowest revolutions per minute of the rotor in which a power can e achieved. Relative to the rotor speed n, is the ratio of turnovers per minute of rotor N, to asic speed. PM engines need special magnetic flow. Through control of the inverters, which provides protective magnetic flow level is reached aove the ase rate under the constant power. Control is not implemented "variale ox" on the merits, ut the effect is similar to the reduction of current flow in the field of classic ikes with dual power, such as the rotor of the synchronous motors. RM of winding engines with permanent magnets mounted on the surface may e divided so as to make the achievement of sinusoidal or trapezoidal voltage induction induction voltage. Engines with sinusoidal induction voltage is usually called PMSM (synchronous motors with permanent magnets), while those with trapezoidal induction voltage are called BDCM (rushless DC motors). In this study analyzed only variale field PMSM engines, which are most suitale for hyrid vehicles (HEV). Primary factor characterizing the aility of the motor to work with a wide CPSR (constant-power speed ratio) is the inductance of the windings. There are specific formulas in order to estalish a limit, which puts inductance of CPSR. Analysis misses the secondary effect of induction and the specific loss of speed, which include loss of friction, windage, hysteresis, turulent currents and the effect of the electrical resistance of the windings. These losses will limit the speed in practice CPSR any electric motor to a limited value. Sinusoidal induction voltage is considered y the impact of inductance on the CPSR of PMSM. Direct torque control (DTC) can e realized in a current power of the synchronous motor of inverters. Such systems have advantages row - reached staility in terms of

4 G. Velev differences in parameters simplify key management for the account of the asence of a current loop regulation, provide a high expedition system. Of course, this method has serious shortcomings - in the case of small angles arise pulsation of the load torque and speed fluctuations in the rotor [3, 4, 5]. The figure also defines the various parameters. The air-gap flux is estalished y the PM field, and there is no field winding. Thus this machine is singly fed. The line-to-neutral ack-emf of the PMSM is sinusoidal, and the motor runs on sinusoidal phase currents. The magnitude of the emf is linear in motor speed; and the voltage constant, v K, with units of rms volts per electrical radian per second, is fixed. Thus the rms value of the ack-emf at any speed is given y Ω (1) Е = КvΩ = KvΩ = ne, Ω Where E is the rms magnitude of the line-to-neutral ack-emf at ase speed and n is relative speed. Similarly, the motor reactance can e expressed as Ω () X = ΩL = ΩL = nx Ω where X is the reactance at ase speed. Fig. 1. Scheme of inverters for variale speed up to the PMSM motors p = numer of poles N = actual rotor speed in rpm N = ase speed in rpm n = relative speed = N/N; p mv Ω = ase speed in electrical radians/sec = 60 Ω = actual rotor speed in electrical radians/sec = nω = rms magnitude of the phase-to-neutral emf at ase speed

5 Parametric Analysis of the PM Motor for Hyrid Electric Vehicles Ir = rated rms motor current Pr = rated output power = 3EIr Ls = self inductance per phase Lo = leakage inductance per phase M = mutual inductance L = equivalent inductance per phase = Lo + Ls + M R = winding resistance per phase van = applied phase A to neutral voltage ean = phase A to neutral ack-emf ea = phase A to phase B ack-emf Diagram of motor and inverters is shown in Figure: Fig.. Scheme of AC cycle in PMSM motor In the figure, V is the line-to-neutral fundamental frequency voltage phasor applied y the inverter to the motor. The angle of the applied voltage phasor, δ, is called the inverter lead angle. E is the ack-emf voltage phasor, line-to-neutral, and I is the motor current phar. Up to ase speed, the magnitude of the applied voltage, V, and the lead angle, δ, can e adjusted, allowing the motor current phasor to e put in phase with the ack-emf. This maximizes the torque produced per ampere. Voltage magnitude V and lead angle δ, required to support any relative speed elow ase speed, n 1, and rms current, I, are found from _ (3) V = ne + I( R + jnx ) = ( ne + IR) + ( nix ) Neglecting the winding resistance, Eq. (3) ecomes _ (4) V ne + jnix = ( ne ) + ( nix ) 1 nix j tan ne = e e 1 nix j tan ne + IR

6 G. Velev The rms magnitude of V increases with speed and is limited y the availale dc supply voltage and the type of modulation used to control the inverter switches. The maximum magnitude is otained at ase speed where n = 1 and at rated rms motor current for which I = Ir, then (5) ( ) ( ) ( ) Vmax = E ) + ( Ir X = E + Ir ΩL Similarly, the lead angle δ at ase speed and rated current is given y: 1 I r X (6) δ = tan E The power developed at ase speed and rated current is the rated power of the motor, and since the current is in phase with the ack-emf, we have: (7) Pr = 3EIr The dc supply voltage necessary to support operation at ase speed and rated current depends on the modulation level allowed in the inverter. If the inverter control scheme is sinusoidal PWM without linear modulation, then the required dc supply voltage is: V dc = V (8) max However, if over-modulation is allowed, a smaller dc supply voltage can e used to otain the same fundamental frequency voltage, πv max (9) V dc = Let us restrict our attention to operation aove ase speed such that n >1and max V V =. Neglecting the armature resistance, the phasor current of the motor is V max E Vmax (10) I = sinδ + j cosδ, nx X nx which has rms magnitude Vmax n V cosδ + n E (11) I =. nx The total power injected into the motor y the inverter is: 3V maxe (1) P = 3Re( VI ) = sinδ, X,while the total power converted y the motor is: 3V maxe (13) Pm = 3Re( EI ) = sin δ X Since we have neglected the winding resistance, in P equals m P and the common value is:

7 Parametric Analysis of the PM Motor for Hyrid Electric Vehicles 3 max V E (14) P = Pm = sinδ.. X This expression shows that it is easy to control the motor to deliver rated power aove ase speed. All that is necessary is that the inverter lead angle, δ, e held fixed at that value that causes m P in Eq. (14) to e equal to the rated value r P given in Eq. (7), that is: 1 X Pr 1 E (15) δ = sin = cos 3V maxe Vmax While constant lead angle control allows the PMSM to operate at constant power aove ase speed, it is not a certainty that doing so results in operating within the rated current. The critical factor is the motor inductance, as shown elow. Equation (E.11) gives the rms motor current, I, when operating at any speed aove ase speed. Using lead angle δ from Eq. (E.15) so that rated power is produced, we require that the rms current in Eq. (E.11) e no greater than the rated value r I, that is: Vmax nv maxe cosδ + n ( n ) E Vmax n( n ) E (16) I = = Ir nx nωl Evaluating the inequality in Eq. (E.16) at relative speed n equal to the CPSR yields a minimum requirement on the motor inductance, (17) L min = V max + CPSR( CPSR ) E CPSRΩ I Since max V as given y Eq. (5) depends on L, Eq. (17) has to e applied iteratively to get an exact inductance oundary for fixed values of,,, and r CPSR E I Ω. For example eginning with max V E =, Eq. (17) is processed to get a value of L. That value of L is used in Eq. (5) to get a corresponding value of max V, and the process is then repeated. Typically, the value of L converges within a few iterations. Note that Eq(17) implies that an infinite CPSR can e achieved provided the motor inductance is greater than. E (18) L = Ω I. r While Eqs. (17) and (18) place lower ounds on the motor inductance to achieve either a finite or an infinite CPSR, there is also an upper ound that can e found y recognizing in Eq. (14) that the lead angle cannot exceed 90. This results in a maximum inductance. 3V maxe Vmax (19) Lmax = =. Pr Ω ΩIr 4. Conclusions r

8 G. Velev Presented for the aove parametric approach for the management of PMSM motors can make the following conclusions: 1. The proposed algorithm offers greater accuracy of the programming task (speed or position of the rotor). In PMSM engines this is very important to eliminate possile viration of the rotor. Determining the limits of the dynamic mode motor has significant scope for development of methods of management.. Expands the scope of regulation in the field of small speeds. The prolem is related to the impact of torque pulsation in the field of small speeds. Large speed pulsation torque does not have a significant impact, they polish the expense of inertia of the rotor [34]. 3. Simplicity of the key management. Notwithstanding the constant increase in the power of processors, simplified algorithms provide less time for the estimate, which means reducing the phase delay control. This allows to use less expensive microprocessors management. PMSM popularity of motorcycles is growing steadily, it is necessary the development of algorithms for management related to the direct control of torque, inductance, voltage and current of the motor to ensure optimization of the power used and quality indicators. This parametric study is one step towards achieving high performance configuration for PMSM motor drive system of EV / HEV vehicles. R E F E R E N C E S [1] R. STAUNTON, S. NELSON AND ETC.., PM Motor Parametric Design Analyses for a Hyrid Electric Vehicle Traction Drive Application, Department of Energy, Washihgton, URNL/TM-004/17. [] D. SPERLING, Transitioning from PNGV to FreedomCAR. Institute of Transportation Studies, University of California, Davis, Research Report UCD,00-ITS-RP [3] L. ZHONG, M. RAHMAN, W. HU, K. LIM, A Direct Torque Controller for Permanent Magnet Synchronous Motor Drives. // IEEE Trans. on Energy Conversion Vol. 14, 3.- P [4] M. RAHMAN, L. ZHONG, Voltage Switching Tales for DTC Controlled Interior Permanent Magnet Motor.//IECON-99.-PE-0. [5] M. RAHMAN, L. ZHONG, Comparison of Torque Responses of the Interior Permanent Magnet Motor under PWM Current and Direct Torque Controls. //IECON-99.-PE-0. [6] B. LAM, S. PANDA, J.-X. XU, K.W. LIM, Torque Ripple Minimization in PM Synchronous Motor Using Iterative Learning Control. // IECON PE-0. [7] R. MONAJEMY, R. KRISHNAN, Control and Dynamics of Constant Power Loss Based Operation of Permanent Magnet Synchronous Motor Drive System. // IECON PE-0