Design and Optimization of mild hybrid BLDC based starter generator for two wheeler

Transcription

1 Design and Optimization of mild hybrid BLDC based starter generator for two wheeler Venkateshwaran B 1, Pushparajesh V 2, Kamalakannan D 3 1 Dept of EEE, Power Electronics and Drives, Kongu Engineering College, Perundurai 2 Assistant Professor (Sr Gr), Dept of EEE, Kongu Engineering College, Perundurai 3 Assistant Manager, Advanced Engineering, Lucas TVS, Padi. 1 venkateshbav@gmail.com, 2 rajesh@kongu.ac.in, 3 kamalakannan.engg@lucastvs.co.in Abstract-This project on the design ofintegrated Starter Generator (ISG) for two wheeler, aims at developing an ISG design that meets the requirements of both the existing starter motor and magneto in the two wheeler. The ISG to be developed was proposed to be a Brushless DC (BLDC) machine similar in shape to that of the magneto with outer rotor configuration but differing in a few dimensions, occupying the place of the magneto in the vehicle. In the existing magneto, the main loads are the head lamps and the battery charging unit. The ISG would initially help to crank the engine while starting and would serve as a generator while running. Hence only one machine would be needed in the place of two. Promising designs were simulated using MAGNET (a Finite element electromagnetic analysis tool) to verify the performance. While simulating in Magnet, static 2D simulations were performed initially and later, to get finer results, transient simulations were performed as transient simulations are time consuming compared to static 2D simulations. Keywords 2 Dimensional (2D);Brushless DC Machine (BLDC);Interpolar gap(ipg); Integrated Starter Generator (ISG); Permanent Magnet Synchronous Motor (PMSM); I. INTRODUCTION A. Objective Designing a BLDC motor that fulfills the requirements of both starter and magneto in two wheeler. B. Introduction The Brushless DC (BLDC) motor is the ideal choicefor applications that require high reliability, high efficiency, and high power-to-volume ratio [1]. Generally speaking, a BLDC motor is considered to be a high performance motor that is capable of providing large amounts of torque over a vast speed range. In conventional starter motors, gear noise is very prominent. As the ISG would occupy the place of the magneto, it would be directly coupled with the engine crank shaft without any gear. Hence in an ISG, gear noise would be eliminated with quick and smooth start, facilitating implementation of Start Stop System (i.e. automatic shutdown of engine when it idles beyond a pre-defined time at traffic junctions and quick engine start when signal is ready by throttle actuation with necessary safety features). With this feature fuel consumption is reduced, thereby improving overall vehicle efficiency and also reducing the emissions. In this paper, the design parameters, analysis of a machine in transient, flux weakening operation is discussed for two configurations ( air and steel) and the corresponding graphs are plotted. II. REQUIREMENTS OF INTEGRATED STARTER GENERATOR 1. The existing starter motor (DC motor) had cranked the engine with sufficient torque in coupling the starter motor pinion with engine crank shaft via geararrangements. 2. The ISG is different from the existing starter motor. As the ISG would directly couple to the engine crank shaft, it need to produce more torque than starter motor to crank theengine. 3. Thus the new design had to produce a maximum torque which is sufficient to crank the engine with relevant speed without any demagnetizationoccursin themagnets. 4. The existing magneto supplied a lamp load of 50W and a battery charge load of 30W.A design had to be fixed such that it met the requirements of both motoring and generating mode. The performance parameters of both the starter motor and magneto were benchmarked to arrive at the design ofisg. 5

2 III. SIMULATION OF ISG FOR MOTORING MODE OPERATION A 16 pole 18 slots BLDC motor with inter polar gap (IPG) with air (see Fig 1b) and steel (see Fig 1c) in yoke has been selected to achieve the requirements of an ISG (Integrated Starter Generator). The purpose of introducing an steel in yoke is to achieve a high speed during fieldweakening. The model implementation was designed using the MAGNET (Infolytica corporation) software[2]. The first stepof the design process is to draw the motor dimensions withspecified diameter using AUTOCAD or MAGNET itself. If the 2D model is drawn by AUTOCAD, the dxf file format is imported into the magnet. After that material related to particular parameter is assigned. Here for stator core and yoke, silicon steel (M36 26Ga) and (M33035A) respectively are used and NdFeB magnet is used. Concentric winding is employed for themotor[4]. A. Staticanalysis: Fig 2 Finite Element Mesh The static model for BLDC was designed to check the current flow and flux in the different coils by varying the position of rotor. By the prediction of no load analysis the line voltages and phase voltage are derived. B. No loadanalysis: For no load analysis, the rotor is rotated about 45 deg mechanical angle i.e it corresponds to one full electrical cycle and this model consists of moving parts Yoke, Rotor airgap and the magnets. Flux linkage with the conduction of 120 deg is shown in fig 3 and the flux lines counter plot is shown in fig 4. Fig 1(a) Solid model of BLDC motor Fig 3 No load Flux linkage plot air Fig 1(b) Inter Polar Gap with Air steel Fig 1(c)Inter Polar Gap with Steel In the finite element method of analysis, the model is divided into a mesh ofelements. 6 Fig 4 No Load Flux Lines of BLDC motor

3 C. Loadanalysis: This analysis is mainly verified for the motor to check the desired torque characteristics. From the line voltage in no load analysis, any two phases are excited and the torque Vs current characteristics are obtained. Here the Y and B phases gets excited with positive and negative current respectively to certain angle and R phase with zero current. The flux density plot of stator and rotor when passing operating current is shown in figure 5 and 6(a,b) respectively. Fig 6(b) Flux Density Plot of Rotor with IPG-Steel D. Demagnetization: When machines are subjected to external magnetic fields and/or temperature changes, the magnetic properties of permanent magnets may change, leading to demagnetization, which may affect the performance of such machines[2]. It is therefore very important to take this phenomenon into account when designing suchmachines. Fig 5 Flux Density Plot of stator Demagnetization of an ISG starts at 140 o C since thehc (coercivity) value of the magnet exceeds the ihc value. Magnet get Demagnetized Fig 6(a) Flux Density Plot of Rotor with IPG-Air E. Transientanalysis: Fig 7 Demagnetization Effect Transient analysis is also carried out for two designs in the BLDC motoring mode to exactly predict the performance of the motor by applying necessary velocity to the machine. It is usually carried out to predict the results of current for various speeds and to identify the losses associated with the machine. The results of transient analysis are shown in Table 1 and DC and RMS currents for is shown in Fig9. 7

4 IV. SIMULATION OF ISG FOR GENERATING MODEOPERATION Once the engine is cranked by an ISG, the same machine can acts as a generator to produce a required amount of power for auxiliary requirements. This is achieved by implementing a diode bridge rectifier setup and voltage regulator for batterycharging. Fig 8 Simulation Circuit Diagram for motoring mode Fig 10 Simulation Circuit Diagram for generating mode Table 2 Transient Analysis Results for Generator Mode Fig 9 DC Current and RMS Current plot Table 1 Transient Analysis Results for motoringmode IPG WITH AIR IPG WITH STEEL Input power (W) Copper Output Speed Loss Power (RPM) (W) (W) Efficiency (%) The circuit diagram (Fig 8) shown above is used to carry out the transient analysis. In the circuit, the DC voltage source is connected to the inverter circuit for the trapezoidal commutation of 120degswitching. The result obtained in transient analysis clearly shows that the promised design meets the requirements of existing starter of the two wheeler. IPG WITH STEEL IPG WITH AIR The circuit diagram in Fig 10 showedthe transient analysis of an ISG in generating mode of operation where the stator coils get connected to the uncontrolled full bridge diode rectifier whose output is connected to the battery via voltagesource. Power(W) SPEED (RPM) OUTPUT POWER (W) SPEED Vs OUTPUT POWER Speed (RPM) Fig 11 Generation mode performance curve steel air 8

5 The result shown above in Fig 11 clarifies the generator performance that meets the requirements of charging the battery and powering the auxiliary equipment s as same as existing magneto. V. FIELD ORIENTED CONTROL OF AN ISG During field weakening mode, the machine operates as a (Permanent Magnet Synchronous Motor)PMSM and delivering a high speed for different current angle. In the field weakening range, some of the stator current, and in some cases, finally all the stator current is consumed in reducing the stator flux linkage. Consequently, more stator current is required in the field weakening range than for the corresponding torque in the constant flux range [3]. Fig 8 shows the Vectordiagram [5] for the speed above the rated value. VI. RESULTS ANDCONCLUSION In this paper, the design methodology of Integrated Starter Generator using BLDC/PMSM motor which meets the requirements of both motoring and generating mode is designed and the analysis of dynamic response is evaluated with MAGNET (Infolytica Corporation) software and MATHCAD (Lucas-TVS). VII. ACKNOWLEDGEMENT I,Venkateshwaran B hereby thank Lucas TVS Ltd., Chennai & their dynamic engineers for their constant support and proper guidance to the successful completion of the project. VIII.REFERENCE [1] R. Hendershot, Jr. president, Design of Brushless Permanent- Magnet Motors James Magna Physics Corporation. [2] Electromagnetic Field SimulationSoftware. [3] JuhaPyrhönen Electrical Drives, LUT, Department of ElectricalEngineering pp [4] Juhapyrhonen, TapaniJokinen, Valeria Hrabovcova, "Design of rotating electrical machines", John Wiley & sons,ltd [5] Shivarajappa, J.Sassikumar, Dr.P. Meena, "Performance Analysis of Surface Permanent Magnet Synchronous Motor", IICPE 2014, 6th IEEE India International Coferenceon Power Electronics, 8-10Dec, NIT KuruKshera,India. [6] Jung-Moo Seo, Jung-Hwan Kim, Se-Hyun Rhyu, Jun-Hyuk Choi, and In-Soung Jung, Senior Member, IEEE, A Study on Brushless DC Motor for High Torque Density, International Journal of Mechanical, Aerospace, Industrial, Mechatronic and Manufacturing Engineering Vol:5, No:10,2011. [7] Stefan Sjokvist Demagnetization Studies on Permanent Magnets UppsalaUniversitet. Fig 12 Vector Diagram of Flux weakening-above the base speed The field weakening of an ISG is simulated with MATHCAD (Internally designed software by Lucas-TVS) and the performance of Speed Torque characteristics are obtained for constant torque and constant power region. It is benchmarked that the design of machine with IPG-Steel is giving better performance of speed above RPM compared to the machine with IPG-Air. So the machine with IPG-Steel is taken to next proceedinglevel. 9