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Institutionen för systemteknik Department of Electrical Engineering Examensarbete Modeling and Control of Electromechanical Actuators for Heavy Vehicle Applications Examensarbete utfört i Fordonssystem

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Institutionen för systemteknik Department of Electrical Engineering Examensarbete Modeling and Control of Electromechanical Actuators for Heavy Vehicle Applications Examensarbete utfört i Fordonssystem vid Tekniska högskolan vid Linköpings universitet av Alexander Pettersson och Patrik Storm LiTH-ISY-EX--12/4556--SE Linköping 2012 Department of Electrical Engineering Linköpings universitet SE Linköping, Sweden Linköpings tekniska högskola Linköpings universitet Linköping Modeling and Control of Electromechanical Actuators for Heavy Vehicle Applications Examensarbete utfört i Fordonssystem vid Tekniska högskolan i Linköping av Alexander Pettersson och Patrik Storm LiTH-ISY-EX--12/4556--SE Handledare: Examinator: Andreas Thomasson isy, Linköpings universitet Anders Larsson Scania CV AB, Södertälje Lars Eriksson isy, Linköpings universitet Linköping, 5 June, 2012 Avdelning, Institution Division, Department Division of Vehicular Systems Department of Electrical Engineering Linköpings universitet SE Linköping, Sweden Datum Date Språk Language Svenska/Swedish Engelska/English Rapporttyp Report category Licentiatavhandling Examensarbete C-uppsats D-uppsats Övrig rapport ISBN ISRN LiTH-ISY-EX--12/4556--SE Serietitel och serienummer Title of series, numbering ISSN URL för elektronisk version Titel Title Modellering och reglering av elektromekaniska aktuatorer för tunga fordonstillämpningar Modeling and Control of Electromechanical Actuators for Heavy Vehicle Applications Författare Author Alexander Pettersson och Patrik Storm Sammanfattning Abstract The possibility to develop control systems for electromechanical actuators at Scania is studied, in particular the focus is on how to exchange the intelligent actuators used today with dumb ones. An intelligent actuator contains its own control electronics and computational power, bought as a unit from suppliers by Scania and controlled via the CAN bus. A dumb actuator contains no means of controlling itself and its I/O is the motor s power pins. Intelligent actuators tend to have limited control performance, time delays and poor diagnose systems, along with durability issues. A dumb actuator could have the benefit of avoiding these disadvantages if the system is designed within the company. A literature study concerning the different types of electrical motors available and their control methods is performed, the most suitable for use in a heavy vehicle is deemed the brushless DC motor, BLDC. An intelligent throttle is chosen for a case study and has its control electronics stripped and replaced with new sensor- and control cards. The case study is used to investigate the possibilities and difficulties of this design process. A simulation model is developed for the electronics, motor and the attached mechanical system. With the aid of this model a controller architecture is designed, consisting of PI controllers with feed-forward and torque compensation for non-linearities. The developed controller architecture is tested and in theory it can compete with the intelligent throttle s performance. The model is also adapted to allow for code generation. The simulation model is used to study some common electrical faults that can effect the system and the possibilities for diagnosis and fault-remedial actions. The hardware prototype system shows that a current controller is necessary in the control architecture to achieve decent performance and the prototype is developed in such a way as to make future studies possible. The conclusion of the thesis is that Scania would be able to design control systems for dumb actuators, at least from a technical perspective. However more studies, from an economical point of view, will be necessary. Nyckelord Keywords BLDC, modeling, control, electrical actuator, throttle, TPU, Simulink Abstract The possibility to develop control systems for electromechanical actuators at Scania is studied, in particular the focus is on how to exchange the intelligent actuators used today with dumb ones. An intelligent actuator contains its own control electronics and computational power, bought as a unit from suppliers by Scania and controlled via the CAN bus. A dumb actuator contains no means of controlling itself and its I/O is the motor s power pins. Intelligent actuators tend to have limited control performance, time delays and poor diagnose systems, along with durability issues. A dumb actuator could have the benefit of avoiding these disadvantages if the system is designed within the company. A literature study concerning the different types of electrical motors available and their control methods is performed, the most suitable for use in a heavy vehicle is deemed the brushless DC motor, BLDC. An intelligent throttle is chosen for a case study and has its control electronics stripped and replaced with new sensor- and control cards. The case study is used to investigate the possibilities and difficulties of this design process. A simulation model is developed for the electronics, motor and the attached mechanical system. With the aid of this model a controller architecture is designed, consisting of PI controllers with feed-forward and torque compensation for nonlinearities. The developed controller architecture is tested and in theory it can compete with the intelligent throttle s performance. The model is also adapted to allow for code generation. The simulation model is used to study some common electrical faults that can effect the system and the possibilities for diagnosis and fault-remedial actions. The hardware prototype system shows that a current controller is necessary in the control architecture to achieve decent performance and the prototype is developed in such a way as to make future studies possible. The conclusion of the thesis is that Scania would be able to design control systems for dumb actuators, at least from a technical perspective. However more studies, from an economical point of view, will be necessary. v Sammanfattning Möjligheterna att flytta styrsystemsutvecklingen för elektromekaniska ställdon till Scania undersöks, särskilt fokus ligger på hur intelligenta aktuatorer som används idag kan bytas mot dumma. En intelligent aktuator innehåller sin egen styrelektronik och beräkningsenhet och köps in som en färdig enhet från en underleverantör och styrs via CAN-bussen. En dum aktuator innehåller ingen egen styrelektronik och dess I/O är endast motorns faslindningar. Intelligenta aktuatorer har begränsad reglerprestanda, tidsfördröjningar och bristfälliga diagnossystem, tillsammans med problem med robustheten. En dum aktuator skulle kunna undvika dessa nackdelar om designen gjordes inom företaget. En litteraturstudie om olika typer av elektriska motorer och deras styrmetoder genomförs, och den mest lämpade för aktuering av ett motormonterat ställdon bedöms vara en borstlös likströmsmotor, BLDC. En intelligent inloppstrottel väljs för en fallstudie, där den befintliga elektroniken tas bort och ersätts av nya drivsteg- och sensorkort. Hårdvaran används för att undersöka möjligheterna och svårigheterna med att göra aktuatorstyrningen inom företaget. En simuleringsmodell för elektronik, elmotor och mekanik utvecklas. Med hjälp av simuleringsmodellen kan en regulatorstruktur tas fram, vilken består av PIregulatorer med framkoppling samt kompensering för olinjäriteter hos trotteln. Den föreslagna regulatorstrukturen visar att den önskade reglerprestandan kan uppnås. Modellen anpassas också så att den kan kodgenereras för användning i riktig hårdvara. Simuleringsmodellen används också för att undersöka några vanliga elektriska fel som kan uppkomma i ett BLDC-system. Prototypstyrsystemet påvisar att avsaknad av strömregulator gör systemet svårstyrt ur reglersynpunkt men designades för att vidare studier skulle vara möjliga. Slutsatsen av arbetet är att Scania klarar av att göra dumma aktuatorer ur ett tekniskt perspektiv, men vidare studier rörande de ekonomiska effekterna måste göras. vi Acknowledgments This thesis work has truly been an interesting journey, where we got the opportunity to get an insight into the company and to learn a lot of new things. Many thanks to our supervisor Anders Larsson, for his help and support and the interesting discussions we have had. Also thanks to our boss, Henrik Flemmer, for giving us this opportunity and always keeping our spirits up. We would also like to thank our examiner at Linköping University, Lars Eriksson, and our supervisor, Andreas Thomasson, for answering our many questions. Special thanks goes to Rasmus Backman at Scania, for his help with the hardware. The group NEPS should also be mentioned, for their help with different software issues. We also thank our office neighbor, Carin Carlsson, for her patience with our silly pranks. Last, but not least, thanks to our colleagues at the group NEPP, as well as all other Scania employees that we have gotten the pleasure of meeting and working with. Alexander Pettersson Södertälje, May 2012 Patrik Storm Södertälje, May 2012 vii Contents 1 Introduction Background Purpose and goals Problem formulation Expected results Related research Modeling Control Electrical actuators Principles and definitions Electrical motor definitions Electromechanical conversion principles Pulse Width Modulation Commutator DC motors Definition DC motor control Applications Stepper motors Permanent magnet stepper motors Variable reluctance stepper motors Applications Brushless motors BLDC motors BLAC motors Position sensors Current control Applications Synchronous motors Control Applications Asynchronous motors ix x Contents Control Applications Modeling BLDC motor Power electronics Throttle model Gears Throttle Parameter estimation BLDC motor Throttle Hardware setup Actuator Processor Hall decoder General Purpose Input Output Speed Controller PWM master for DC motors PWM full and PWM commutated Power stage Current measurement DRV Sensor card Austrian Microsystems 5040 Rotary Encoder PCB: One card solution using DRV PCB: Two card solution PCB: Sensor card Cable usage Control system Overview Simulation model Hall decoder and PWM generator Current controller Speed and position control Hardware Hall decoder Speed control Throttle position control Fault detection and diagnosis Open circuit winding Hall sensor faults Open transistor fault Shorted transistor fault Contents xi 7 Results Simulations Motor with no load Motor with throttle, using pole-placement Motor with throttle, using hand-tuned parameters Case study Hardware etpu systems structure overview Conclusions and future work Conclusions Future work Bibliography 125 A Abbreviations 129 Chapter 1 Introduction In this chapter, an introduction to the thesis work is given, which includes background, purpose and goals, problem formulation and expected results. 1.1 Background In many vehicle applications, electrical DC motors have been used for actuation for a long time, for example to control the intake throttle. The simple design and the possibility to obtain good control performance has made it a solid choice amongst vehicle producers [1]. In the heavy-duty vehicle industry, the use of electrical motors is newer and pneumatic actuators have previously been the more common type, since compressed air is already available in the vehicle. However, pneumatic actuators tend to have unwanted properties such as hysteresis and dead-time when the cylinder has to build up pressure for actuation, along with poor efficiency [2]. Because of tougher legislation demands on emissions, better control over the actuators in the vehicle is needed and the pneumatic actuators are being exchanged for electric ones. Today most electromechanical actuators in heavy-duty vehicles are of intelligent type, which means that it is purchased from a supplier as a unit, complete with sensors, control electronics and processor. The actuator is then controlled via the CAN bus [3], and is provided reference values for the desired speed, position etc. The self-contained control unit then handles the actuation of the electric motor, see [4] and [5] for examples of commercial solutions. If these intelligent actuators were flawless in execution, this would make control of the actuators easy and without problems. Unfortunately, the supplied actuators are often prone to having undesirable control properties, such as large overshoots, and are sensitive to vibrations which causes them to be a source of faults in the engine. The CAN bus also has limited band-width which leads to time delays and limits the control performance [6]. Alternatives to the intelligent actuators are interesting to study because of these drawbacks. 1 2 Introduction 1.2 Purpose and goals The purpose of this thesis is primarily to bring knowledge on electrical actuators to the pre-development branches of Scania s research and development on power trains, establishing a foundation for further research within the company. Because of this increased emphasis on education the initial, theoretical, chapters of this thesis will be extended to cover multiple subjects. This thesis consists of a theoretical study on electrical motors, their respective properties and control methods, along with a practical case study to verify some of the theoretical claims. The case study aims to bring practical knowledge concerning BLDC motor amplifier construction and sensor usage along with the confidence to dare expand on that knowledge to the research and development part of Scania. The main goal is to investigate if Scania should develop their electrical actuators themselves instead of using complete solutions from suppliers. 1.3 Problem formulation With the disadvantages that come with intelligent actuators, the question arises if Scania instead should use dumb actuators. A dumb actuator could be controlled either via an existing processing unit or by adding a new one that could potentially control several actuators, placed apart from the actuators. This would have numerous benefits such as increased understanding of the control of the motor type and the possibility to move the control electronics to a less harmful environment. It is then possible to include the control algorithms for the actuators within other processing units in the vehicle (thus saving money and space), and get a smaller cost for developing the control chip within the company instead of buying it from the manufacturers of the actuator. For all of this to be possible, the knowledge of modeling and control of electrical actuators must exist within the company. Durability, fault detection and fault identification is another challenge that must be considered. The scope of this thesis will include recommended electric motor type, economic aspects, the ability to diagnose the system as well as recommended strategy for handling intelligent or dumb actuators. 1.4 Expected results The expected results from this thesis work is presented in the list below. Increase the knowledge base within Scania concerning electric actuators. Literature study of different types of electric actuators, from technical and economical perspectives. Design and implementation of a dumb actuator for an intake throttle, developed from an earlier intelligent one. This includes design of a drive stage 1.4 Expected results 3 for the motor along with implementation of a control application in the processing unit. This is considered as a case study of what can be achieved in-house. A study on the robustness and possibilities of making diagnoses of faults for the actuator. To start the construction of a prototype platform where Scania can try out control strategies on a BLDC actuated throttle. Development of a simulation model of the dumb actuator so that a controller can be designed. This model includes a mechanical model of the throttle, a model of the motor and a model of the drive electronics. Parametrization of the simulation model. Give insight to whether Scania should use dumb or intelligent actuators, based on the literature study and experiments. The results from this thesis work will mainly be data plots of various types, along with a discussion concerning the outcome of the case study. Chapter 2 Related research In this chapter, related research concerning modeling and control of electrical actuators is presented. Furthermore, earlier work within these research fields are set in relation to this thesis work. 2.1 Modeling The construction and control of electric motors is a subject that is widely researched. Several books have been written on the subject, see e.g. [7], [8], [9] and [10]. Theory for different types of electric machines is presented in [7], with exception for BLDC motors, which are described better in [8]. In [9], the electric motors are treated a little less theoretical, with several examples of applications. An engineering approach to electric motors is presented in [10]. The model of the BLDC motor in this thesis work is inspired by [11], which is a paper about BLDC motor modeling for vehicle applications. The equations in [11] are used to model the BLDC motor dynamics in this report. The speed of the motor is controlled by a variable voltage source modeled in the Matlab toolbox SimPowerSystems in [11]. A variable voltage source is a simplification of the reality, since the voltage source in the vehicle, i.e. the battery, has constant voltage. The goal with the modeling in this thesis is to make the models as close to the hardware implementation in the case study as possible, to obtain better understanding for the whole process. Several Master s theses have treated the subject of modeling and control of BLDC powered actuators. Modeling of BLDC motors and the effect of cable length on disturbances carried through to the sensors is studied in [12]. In [13], the advantages of using an electric actuator instead of a pneumatic one is studied, by tests on an exhaust brake throttle. A very thorough Master s thesis on modeling and control of BLDC motors is [14]. The work is very theoretical and includes a good study on how different control methods and amplifier modifications affect torque ripple. This will prove a good foundation on how to model the electric motor 5 6 Related research along with hints regarding the design of the amplifier. In [15], the focus is on the hardware to control a BLDC motor, like how to generate a PWM signal, to determine the rotor position and the drive electronics, as well as differences between BLDC and BLAC motors. That report serves as an input on the hardware part of this thesis work. A quite theoretical study is found in [16], which is useful for this thesis work. DC and AC motors and different strategies to control them are discussed. Furthermore, a study on how to determine different parameters in electric motors, such as motor constants, winding losses and electrical component values is included. In [2], the actuation of a butterfly valve with a BLDC motor is studied. These Master s theses focus either on BLDC motors in theory, or actuation with BLDC motors on a higher level of abstraction, meanwhile this thesis work aim to focus on the hardware at a lower level. The mechanical model of the throttle is based on the model equations in [17]. Some changes are made to fit this thesis work, e.g. by modeling a backlash in the throttle that is not modeled in [17]. The decomposition of the motor, throttle and gearbox into subsystems is inspired by the driveline model in [18]. The friction model in [17] is used in this thesis work, but is modified to be more computationally feasible. A presentation of some different friction models and compensation of friction effects in control of machines can be found in [19]. In [20], several different friction models that can be used are described. A modified static friction model like in [17] was ho
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