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Simulation Instruments to Study Power Electronics of Motor Drives Zoja Raud, Valery Vodovozov, Tanel Jalakas and Juhan Laugis Tallinn University of Technology (Tallinn, Estonia)
[email protected] Abstract - Different simulation instruments to study power electronics of motor drive are described. For each educational level, the specific approach and soft tool is proposed. The simulation instruments have been examined and compared in learning environment of Tallinn Technical University.
I.
INTRODUCTION
Power electronics is a wide-ranging field of rapid growth and expansion knowledge area. The life cycle of electronic devices involves four stages: design process, manufacturer and user training, manufacturing, and maintenance. In these stages, the models help to study the combined performance of the system, the new engineering solutions may be found as well as authors’ proposed ideas may be tried [1]. An effective library of models should be eminently suitable to improve design, educational and training processes. The models help to examine and to predict various situations occurring in an engineering system. Further, the models may be useful to plan the processes and to carry out different performance testing steps in the laboratory and workshop. Safety specialists and managers may obtain better answers their questions, using computer models [2]. Engineering facilities are under continuous development, and many models tend to become outdated. The use of outdated models leads to errors, delays and loss of information. This imposes requirements for reusability of the source code for component and system models. Correspondingly, a new notion in computer simulation is elaborated. This so-called "reusability" refers to the compatibility of computer models to keep pace with the development of the real engineering object in time. Experience shows that the more an object is changed, the more likely is to rebuild its model. This increases the costs of the maintenance, educational and training technologies. An electric motor drive is a very popular power electronics consumer. It represents an inhomogeneous, nonlinear, and nonstationary class of systems. Object heterogeneity reflects in various natures of structural components and assemble of informational and energetic processes. Heterogeneity deals with the discrete nature of inputs and variables. Power pulse conversion with continuous electromechanical transformation and continuous-discrete informational conversion is referred to the same processes as well. Non-linearity is produced by the limited controller and sensor code lengths and by technical and program non-linear chains and blocks. They course amplitude modularity of digit-to-analog conversion, unstable signal levels, and semi-controllability of power converters, saturation
in magnetic chains of electric machines, plugs, gaps, backslashes, Coulomb and fluid friction of mechanical gears and actuators. A non-stationary property of motor drive results in changing of the system parameters and varying load torques and moments of inertia of mechanical transmissions. Therefore, the simulation of motor drive with electronic converters involves a number of complex problems. The goal of this work is to describe a new paradigm developed by the authors. It envelops three constraints in the building of a reusable soft tool [3]. First, the developed models must contain certain resources, such as structural and information redundancy. Second, their redundancy and application must be suitably documented by clear explanation of the functions and methods of use. Third, the tool must be convenient for future development. In that case, the usefulness of the models will not deteriorate with the introduction of new engineering techniques or materials. II. SIMULATION STAGES FOR BEGINNERS The simulation stage for beginners has some particular qualities [4]. It concerns the first steps of inexperienced users in computer science therefore the simplest software instruments are introduced here [5]. Particularly, MathCAD of MathSoft and Microsoft Excel are the most popular products for beginners. Another peculiarity deals with the restricted knowledge level of students proceeded to the electronics study. Thus, the main emphasis is placed here on the basics of electrical engineering, such as the Ohm’s and Kirghoff’s Laws application in passive circuits constructed on resistors, capacitors, and inductors. Next feature belongs to the calculations accompanied the simulation processes. All calculations on this stage use the simple mathematical apparatus, such as arithmetic, linear algebra, geometry, and ordinary differential equations using the ordinary and software calculators. TABLE I SOFT TOOLS TO STUDY ELECTRONICS BY BEGINNERS Problem R circuit supplied by dc power source RL circuit supplied by ac power source RC circuit supplied by ac power source
978-1-4244-2856-4/09/$25.00 ©2009 IEEE
Report contents Virtual measurements, input and output timing diagrams
Calculation Voltages and currents of elements, amplitudes, and phase shift
ELECTRO-MECHANICAL ENERGY CONVERSION Problem RC circuit supplied by ac power source Series RLC resonant circuit Parallel RLC resonant circuit
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307 Calculation
Table I above gives the list of the developed simulation models and the problems solved during the simulation. III. SOFT TOOLS FOR BACHELORS’ TRAINING Bachelor study is the main educational stage to understand the principles of electronic components operation and to teach the low-power electronic circuits that control different kinds of electrical motors. Here, the most popular toolboxes are introduced into the learning process [6]. The first of them is the educational network Multisim of Electronics Workbench. Other concerns the LabVIEW of National Instruments. Both products are mainly intended for teaching purposes. The bachelor curriculum makes provision for the circuit design, which contain ac and dc power sources, active and passive electronic components, measuring equipment, as well as arrangement of the correct circuit loading. In addition to the measurements, characteristics and other diagrams are normally examined on the studies, such as the step and frequency responses, the vector diagrams, and multiple parameter dependencies. Most experiments are provided by the supply and load analysis influencing the electronic system operation. Table II gives the list of the simulation models developed in accordance with the given specifics as well as the problems being solved during the model use in the learning process. TABLE II SOFT TOOLS TO STUDY ELECTRONICS BY BACHELOR STUDENTS Problem Passive RC and LC low-pass, high-pass, band-pass, and bandstop filters Diode volt-ampere curves and circuits like series and parallel clippers, limiters, and Zener circuits Transistor amplifiers and characteristics of CE, CC, and CB circuits Op amps use for inverting and noninverting amplifiers; null-point, positive and negative detectors on comparators, and Schmitt trigger
Report contents Virtual measurements, input and output timing diagrams and frequency responses Virtual measurements, volt-ampere curves, and timing diagrams Virtual measurements, input and output characteristics Virtual measurements, timing diagrams, and input/output characteristics
Calculation Voltages and currents of elements, amplitudes, phase shift, and cutoff frequencies Knee voltage, signal clipping levels, supply voltages and currents Cutoff voltage, saturation current, load line, Q point, alpha and beta gains Input and feedback resistors, voltage amplification, and hysteresis
Problem Math converters: summer, subtracter, integrator, differentiator, and PID controller Oscillators: astable multivibrators and Wien bridge oscillators with unipolar and balanced supply
Report contents Virtual measurements, timing diagrams, and frequency responses Virtual measurements and timing diagrams,
Calculation Supply and output signals, input and feedback resistors and capacitors Supply and output signals, input and feedback resistors and capacitors
IV. MASTER STAGE IN LEARNING POWER ELECTRONICS In distinct from bachelors, master students have enough knowledge in the basics of electronics and motor drives. Power electronics raises the educational level in the field of converters and supplies, which action strongly depends on the load [7], [8]. The power circuits with gating arrangement require more accurate simulation instruments. The toolboxes PSCAD and PSPice are the best suited for the proper simulation of complex electronic circuits and their components used in the motor drive. They contain the reach libraries of semiconductor components and additional tools to derive the systems of linear and non-linear differential equations [9], [10]. Table III gives the list of the simulation models developed by authors and the problems solved during the simulation. TABLE III SOFT TOOLS TO STUDY ELECTRONICS BY MASTER STUDENTS Problem Single-phase half-wave rectifiers: diode and thyristor units with resistive and inductive loads and LC filters Single-phase diode and thyristor full-wave rectifiers with resistive and inductive loads and LC filters of midpoint and bridge topologies Three-phase diode and thyristor rectifiers of midpoint and bridge topologies AC converters, such as single-phase voltage regulators, bridge inverters, voltage source and current source inverters, and frequency converters DC-DC converters: stepdown, closed-loop buck choppers, step-up and closed-loop boost choppers, step-down/step-up choppers, closed-loop buck/boost choppers, and Cuk converters
Report contents
Calculation
Virtual measurements and timing diagrams of the load voltage and current waveforms
Source voltages and converter parameters
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V. SIMULATION INSTRUMENTS FOR ADVANCED USERS The goal of further training and the skill-level raising is to develop the design methods and complex calculations of the mixed electromechanical applications [11]. For this purpose, Matlab is the well-known application soft tool, where different libraries for the broad problem spectrum solution may be used. Along with it, Simulink helps to describe the searched system by different kinds of transfer functions and feedbacks thus giving the possibility to use the preliminary built models and functions. Matlab/Simulink united by the PowerLib libraries are enough suitable for the electromechanical and electronic devices, schematics, and circuits development [12]. Nevertheless, they involve such drawbacks as the significant computer simulation time and often losing the steps during the solving of the non-linear differential equation systems. The toolbox eDrive developed by authors serves correctly and effectively on this stage [13]. Table IV gives the list of the developed simulation models and the problems solved during the simulation TABLE IV SOFT TOOLS TO STUDY ELECTRONICS BY ADVANCED USERS Problem DC motor drive design including selection of gearbox, motor, and power converter, their open-loop research and closed-loop tuning and optimization. Asynchronous motor drive design including selection of gearbox, motor, and power converter, their open-loop research and closed-loop tuning and optimization. Synchronous motor drive design including selection of gearbox, motor, and power converter, their open-loop research and closed-loop tuning and optimization.
Report contents
Calculation
Virtual measurements and timing diagrams of the load voltage and current waveforms
Gear box, motor, converter, and controller parameters
VI. EDRIVE TOOLBOX The eDrive package is an integrated toolbox containing the instruments to develop and investigate electric drives with power electronic converters. Thanks to the strong orientation on the driving applications, this software takes some advantages for power users and students as compared to other programs. To compute equipment, the leading companies have developed their specific technologies. Examples are the guides and software of Siemens, Omron, Sew Eurodrive, Maxon Motors, Mitsubishi, etc. In these packages, the search of decision is accomplished by automatic checking of the preliminary worked-out databases. With the help of the corporative databases, the certain combinations of parameters are selected. A scope of allowable environment condition is
displayed to a certain data area. The system tuning is executed in accordance with corporative methodic also. Such approach is conventional for the majority of firms that carry out project designs and have rich experience in acceptance of the decisions on the basis of extensive computer databases, coming up to numerous catalogue archives and "absorbing" their contents and structures. The main its drawback is the technological restriction and data limiting that deprive a designer of optimum way in the project. It is of particular importance in the first design stage, when critical decisions are taken. In distinct from the companies, which promote and propagate their products, the eDrive approach is addressed to the overall equipment selection, tuning, and optimization independently on the firm interests. The eDrive program is available for: • simulation of systems and components of three-phase induction drives, synchronous servo drives, and dc drives with shunt-wound excitation; • selection of power converters along with motors and gears in the process of system design; • analyze of steady-state and transient modes of drives with open-ended and closed-loop control systems supplied from the mains and power converters; • research of options, disturbances, and input signals action on the drive performance; • tuning the drive systems; • building the reports about the drive arrangement and operation. The eDrive software is the real example of the implementation of an object-oriented technology [13]. It supports the uniform and versatile approach to the objects of different nature: mechanical, electrical, and informational, undoubtedly required by an electric drive. Its generalized object description gives an effective tool to design the model base classes, which applies an inheritance of the new modules without deconstruction of the main model structure. The developed class library comes up to ANSI standards and contains the components, fully described in the scientific and educational literature as well as in the toolbox documentation. The software demonstrates the clear and user-friendly performance for those who decided to learn about electric drive with electronic converters, get an experience in the project development in a cost and time effective manner. The package includes numerous simulation tools: • a set of adjustable controller schemes; • models of power converters along with motors, gears, and regulators; • equipment databases of the world leading companies; • the graphic package for representation of steady-state and dynamic simulated processes with automatic and manual scaling, system analyzer, and preview means; • the signal generator to supply the test reference and loading signals as well as non-linear curves, noses, and filters imitation;
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•
Fig. 1. Database pane
Fig. 2. Model window
the report generator with powerful graphic multi-format support. The generalized discrete converter description is proposed as the base of power converter model of different types. Transistor and thyristor converters of different nature are considered as the particular cases and the inheritors of the selected model. Such approach helps to develop the system in accordance with the technique renovations. Besides the data sheets, a user may work with queries written in the standard SQL language, which serves as another source of the model information. In the design process, a learner generates numerous test signals that are required: • to enter the necessary speed and path; • to generate various references and disturbances to the simulated electric drives; • to examine the influence of distortions and disturbances upon the behavior of drive components; • to select filters and correcting circuits for designed systems, which improve their performance. To satisfy the last purpose eDrive includes: • the group Signal that represents the numerous sources of references and disturbances; • the group Distorsion that brings distortions of any kind to the transmission path of a signal selected in previous group; • the group Filter/corrector that simulates a digital conversion of a signal selected in a previous group in accordance with the proposed transfer function; • the chart of output signals of all mentioned groups. Moreover, a designer may utilize the simulation result as a new signal. The program receives speed or current (torque) trace for its further processing and analyzing. All these units are available as variants of a common transfer function, which simulates the same amplifiers, filters, and circuits that was studied earlier with Multisim. Such interconnection of the toolboxes is a significant advantage of the described approach. Another benefit presents the most complete and comprehensive drive educational range of topics as compared with earlier published results, particularly [11][12]. VII. APPLICATION EXAMPLES
Fig. 3. Simulation result window
Fig. 4. Signal generator window
The described toolbox has been used to study a number of drive systems having the power converters that supply motor with a gear and controller for industrial, domestic, and medicine applications. Figure 1 shows the first database window before the selection of motors, gears, and converters that match the requirements of the desired system. Sorting may be executed on any column. A short description of the selected equipment is presented in the separated area of the screen. The status bar keeps information about the number of equipment sets and the current group number. The Open button represents the selected equipment database where the particular machines, gears, or converters search is processed. The overall database size is as
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much as some thousands records with a dozen of text, numbers, and graphics data fields. One of the model window pages is shown in Fig. 2. The full information concerning the selected motor, load, source, and controller is presented here. A student may try different variants of parameters, speeds, loads, and controller tunings on these pages. He can save each result as a model file and open any previously saved file to continue the design process. The help system includes the detailed information about each mastering step. Simulation accompanies the drive designing stages. The simulation results are placed in the three panes of the special window shown in Fig. 3. One can evaluate a step response, static, and analytical figures, compare different variants, and select the best one. The necessary input signals, nonlinear inputs, and load disturbances are arranged by mean of the signal generator that forms a dozen of signal shapes and distortions of various values and frequencies (Fig. 4). VIII.
CONCLUSIONS
The simulation instruments to study the drive power electronics have been examined and compared in educational environment of Tallinn Technical University. The practice showed their effectiveness and suitability. Some novel textbooks and manuals support the described approach [14], [15]. ACKNOWLEDGMENT This paper was supported by Estonian Science Foundation Grants ETF7572 “High Power DC Voltage Converters with High Frequency Transformer Link” and ETF8020 “Research of
Advanced Control and Diagnostics Systems for the HighPower IGBT Converters”. REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]
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[13] [14] [15]
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