基于MATLABSimulink的异步电机仿真.doc

Induction Motor Tests Using MATLAB/Simulink and Their Integration Into Undergraduate Electric Machinery CoursesAbstractThis paper describes MATLAB/Simulink implementation of three induction motor tests, namely dc, no-load,nd blocked-rotor tests performed to identify equivalent circuitparameters. These simulation models are developed to supportnd enhance electric machinery education at the undergraduate evel. The proposed tests have been successfully integrated intolectric machinery courses at Drexel University, Philadelphia, PA,and Nigde University, Nigde. Turkey.Index TermsEducation, induction motors, MATLAB/Simulink, software laboratory.I. INTRODUCTIONWITH THE advent of low-cost personal computers and various easily accessible software packages, computer-aided teaching tools have become an essential part of both classroom lectures and laboratory experiments in electrical machinery education 16. The computer models and simulations of induction motors, as teaching tools, support the classroom teaching by enabling the instructor, through the computer-generated graphics, to illustrate easily steady-state operation of themotor under various loading conditions . The computational tools as a part of laboratory experimentsenhance laboratory experience by providing students with the opportunity to verify the results of laboratory experiments and compare them with those obtained by computer simulations.Such a comparison opportunity helps students realize the limitations of hardware experiments and, as a counterpoint, appreciate that computer models cannot substitute for actual hardware experiments that might not exactly represent the operation of induction motors because of some modeling assumptions.Moreover, an undergraduate electric machinery course that integrates up-to-date computer hardware and software tools in both lecture and laboratory sections also meets the expectationsof todays students who want to use computers and simulation tools in every aspects of a course, and thus, possibly attracts more students. Electrical machinery courses at the undergraduate level typically consist of classroom and laboratory sections. The classroom section covers the steady-state operation of the induction motor in which the per-phase equivalent circuit is used to compute various motor quantities, such as input current and power, power factor, developed torque, and efflciency. The computations associated with the steady-state operation require the knowledge of equivalent circuit parameters. These parameters are obtained by performing three tests, namely dc, no-load, andblocked-rotor tests on the motor in a typical laboratory experiment. The laboratory section includes these tests and a load experment that allows students to become familiar with the inducion motor operation and to gain invaluable hardware and measurement experiences. The authors experience while teaching nduction motors at Drexel University, Philadelphia, PA, indicates that students generally have difflculty when they come to he laboratory to carry out these experiments even though the corresponding theory is extensively covered in the classroomsection with a detailed hand-out describing laboratory facilitiesand the procedure of the experiments, given to them at least a week before the laboratory. Students are not familiar with a laboratory environment that contains large machines and relatively complex measurement methods and devices as compared with other laboratories they have been to before. The time constraints during the laboratory exercise are also a difflcult adjustment. In a usual two-hour laboratory section, students are required to set up and perform four induction motor experiments, to take the necessary measurements, and to investigate steady-state performance of the motor under various loading conditions. Because of the time limitations, students often rush through the experiments in order to flnish them on time, which unfortunately prevents them from getting a true feeling of motor operation and rom appreciating what has been accomplished during the laboratory practice.Therefore, simulation tools must be developed for induction motor experiments to serve as useful preparatory exercises before students come to the laboratory. The objective of this paper is to present simulation models of these induction motor experiments in an effort to design a computational laboratory.The dc, no-load, and blocked-rotor simulation models are developed as stand-alone applications using MATLAB/Simulink and Power System Blockset (PSB) . For the load experiment, students are required to write a computer program using MATLABs M-flle programming for the per-phase equivalent circuit of the induction motor to compute operating quantities.Such an assignment improves students programming skills that would be helpful in other classes as well. The remainder of the paper is organized as follows. Section II describes the dc, no-load, and blocked-rotor tests. For the sake of completeness, first the experimental setup for each test is provided with a brief explanation of how these tests are conducted and how the corresponding measurements are used to compute the equivalent circuit parameters. Then, for each test, the corresponding Simulink/PSB model is presented and compared with the actual experimental setup emphasizing the similarities and discrepancies. Section III compares the equivalent circuit parameters determined using simulation data and data obtained from experiments. Section IV explains how to integrate these simulation models into undergraduate electric machine courses at two different universities, while the last section concludes the paper. II. INDUCTION MOTOR TESTS:EXPERIMENTAL SETUPS AND SIMULINK/PSB MODELSThe steady-state operating characteristics of a three-phase induction motor are often investigated using a perphase equivalent circuit as shown in Flg. In this circuit,R1 and X1 represent stator resistance and leakage reactance, respectively;R2 and X2 denote the rotor resistance and leakage reactance referred to the stator, respectively;RC resistance stands for core losses;XM represents magnetizing reactance; and S denotes the slip. The equivalent circuit is used to facilitate the computation of various operating quantities, such as stator current, input power, losses, induced torque, and efciency. When power as pects of the operation need to be emphasized, the shunt resistance(Rc)is usually neglected; the core losses can be included in efflciency calculations along with the friction, windage, and stray losses. The parameters of the equivalent circuit can be obtained from the dc, no-load, and blocked-rotor tests .In the following, both experimental setup and Simulink/PSB models of each test are described The PSB is a useful software package to develop simulation models for power system applications in the MATLAB/Simulink environment. With its graphical user interface and extensive library, it provides power engineers and researchers with a modern and interactive design tool tobuild simulation models rapidly and easily. MATLAB and Simulink/PSB have been widely used by educators to enhance teaching of transient and steady-state characteristics of induction machines. Of course, other commercial software packages, such asMaple andMathCad, are commonly used in electrical engineering education with their advantages and disadvantages 12. The reason that MATLAB with its toolboxes was selected is that it is the main software package used in almost all undergraduate courses in the authors institutions as a computation tool to reinforce electrical engineering education. Therefore, students can easily access to MATLAB,and they already have the basic programming skills to use the given Simulink models and to write computer programs when required before coming to the machinery class.The dc test is performed to compute the stator winding resisance . A dc voltage is applied to the stator windings of an induction motor. The resulting current flowing through the stator windings is a dc current; thus, no voltage is induced in the rotor circuit, and the motor reactance is zero. The stator resistance is he only circuit parameter limiting current flow. Fig. 2 showsthe experimental setup of the dc test conducted at the Interconnected Power Systems Laboratory (IPSL) 13 of Drexel University. A 120-V dc power source is applied to the two phasesof a Y-connected induction motor. A group of light bulbs are nstalled in the circuit as a resistive load in order to adjust dc current to the rated value. The current in the stator windings Idl and voltage across the two phases of the motor Vdc are measured. Depicts the Simulink/PSB implementation of the dc test. From the PSB machine library, an induction motor block is used whose electrical parameters (such as nominal voltage and equivalent circuit parameters) and mechanical parameters (such as inertia and number of poles) can be specifled in either International System of Units (S.I.) or in per unit. Similar to the experimental setup, a 120-V dc source is applied to the two phases (phases A and B) of the induction motor through a series resistance, while the phase C is grounded through a resistance branch in order to have a complete electrical connection. The purpose of the series resistance between the dc source and the induction motor is to limit the current flowing through the two windings of the motor to its rated value, which is sim ilar to the lighting bulbs used in the hardware setup of Fig. 2 Voltage and current measurement blocks measure the instanta neous voltage across two phases and the current flowing through the windings, respectively. Two scopes display the waveform of the voltage and current, while two display boxes are used to obtain the steady-state values of the dc voltage,Vdc and current Idc.With these two measurements, the stator resistance can easily be computed asIII. COMPARISON OF EQUIVALENT CIRCUIT PARAMETERS To illustrate the effectiveness of the proposed simulaon models, one compares the equivalent circuit parameters etermined by simulations with those obtained from hardware experiments. The motors used for this purpose are the hree-phase 60-Hz Y-connected, and the 5-Horse Power (HP)nduction motors of 200-V rating 1735 r/min located at Drexel Universitys IPSL. A set of hardware experiments are rsterformed (i.e., dc, no-load, and blocked-rotor tests) on four nduction motors to obtain appropriate equivalent circuit paameters for software simulations. The resulting parameters are resented in Table I. For each induction motor tested the Simulink/PSB models of the dc, no-load, and blocked-rotor testswere run. The simulation data of no-load and blocked-rotor tests for motor 1 is shown inTable II, where various quantities, such as voltage, current, and power required to compute equivalent circuit parameters, are presented. The dc test simulation data for motor 1 is as follows:Vdc=12.66V and Idl=15.74A The simulation data for the other three motors is similar to that of Motor 1 and, thus, is not given here Table III gives the equivalent circuit parameters computed,using the simulation data and the corresponding errors relative o those obtained experimentally. The error computations asume that equivalent circuit parameters determined experimenally are accurate. The results indicate that relative errors are negligible, and the proposed simulation models accurately predict equivalent circuit parameters. The largest error occurs in he stator and rotor leakage reactances, since one assumes that wo reactances have equal contributions to the blocked-rotor re-actance, which might not be the real case.IV. INTEGRATION OF SIMULATION MODELS INTO ELECTRIC MACHINERY COURSES In this section, the authors describe the integration of these simulation models into electric machinery courses at two different universities, Drexel University and Nigde University,Nigde, Turkey. The Electrical and Computer Engineering (ECE) Department of Drexel University offers a pre-junior-level machine course (ECE-P 352 Electric Motor Control Principles) that concentrates on the fundamentals of electromechanical energy conversion and related control theory. This flve-hour course required for those who are in the power and control track has both lecture and laboratory sections that must be taken in the same quarter. The lecture section (three hours a week) introduces students to operation principles of transformers, induction motors, dc motors, and various motor control techniques, including the power-electronics-based ones. In the laboratory section (two hours a week), students are required to perform various experiments for which the necessary theoretical background is developed in the lecturesection. The experiments conducted during the term at the IPSL of Drexel University include open-circuit, short-circuit, and load tests for transformers, speed control experiments for dcmotors, and induction motor tests. The IPSL is a computerized,small-scale, energy management system that was designed toprovide students with a hands-on learning experience about theattributes and implications involved in the management and control of a small electric power system. With its customized graphic-intensive environment, it provides a set of experiments on the interaction of various system components in a real-life power system operating environment . In order to incorporate simulation models of induction motor tests into the course, the laboratory section is divided into two main components, each of which is a two-hour section: software laboratory and hardware laboratory. After being introduced to the theory and operating characteristics of the induction motors, including per-phase equivalent circuit and torquespeed curve and speed control methods, students simulate three induction motor tests presented in the previous section and record the data required to compute per-phase equivalent circuit parameters. A week before the software laboratory, the Simulink/PSB models of the tests and a detailed hand-out describing how each model is to be simulated are made available to students. An example of the procedure showing the steps involved in simulating a no-load condition is given in the Appendix. An essential part of the software laboratory is an assignment given to students to develop a computer model for the per-phase quivalent circuit of the induction motor using the MATLAB programming language. Using the computer program, students nvestigatemotor characteristics under varying conditions. Exmples of simulations obtained by students computer programs or the motor 1 are presented in Figs. 810. Fig. 8 shows motor quantities, such as input current and power, power factor, developed torque and power, and efficiency as a function of rotorpeed, and how these quantities are affected by a 20% drop n the supply voltage when the frequency is kept constant at he nominal value. Fig. 9 illustrates the same quantities when he frequency is reduced by 25% while the supply voltage is kept unchanged. Fig. 10 shows the torque-speed characteristic of themotor for different values of rotor resistance. Such studiesV. CONCLUSION AND FUTURE WORKIn this paper, the authors presented simulation models of induction motor tests performed to obtain parameters of the per-phase equivalent circuit of three-phase induction motors.Each Simulink/PSB model is explained in detail and compared with the corresponding experimental setup. Circuit parameters obtained from simulation results are compared with those obtained from hardware experiments. The error studies show that MATLAB paired with Simulink/PSB is a good simulation tool tomodel inductionmotor tests and to evaluate steady-state characteristics of the induction motor. Furthermore, a successful integration of simulation models is described in a software laboratory in an electric machines course, which complements classroom lecture and laboratory practice. A logical extension to the software laboratory would be to include Simulink/PSB models of experiments of transformers, dc machines, and synchronous machines so that a complete computational laboratory is available to support electric machinery education.基于MATLAB/Simulink的异步电机仿真摘要本文介绍MATLAB / Simulink的实施三个异步电动机试验，即直流，空载，和封锁转子测试，以确定等效电路。这些仿真模型，以支持和加强电子机械在本科的教育水平。在Drexel大学，费城，宾夕法尼亚大学和尼代，尼代，土耳其的电气机械课程。拟议的试验已经成功地融入电机课程。关键词：教育 异步电动机，MATLAB / Simulink，电机1.引言随着低成本的个人电脑和各种方便软件包的兴起，电脑辅助教学工具已经成为电动机械教育的一个重要组成部分的课堂讲座和实验室实验。计算机模型和模拟的异步电动机，作为教学工具，支持课堂教学，使教师通过计算机，以容易说明稳态运行异步电机在各种负载条件下生成的图形。计算工具的一部分，加强实验室的实验经验，提供学生有机会来验证实验结果，比较他们获得的计算机模拟图形。 这种比较的机会帮助学生认识的局限性，硬件实验，而且作为一个计算机模型不能代替实际的硬件实验，因为一些模型假设可能并不完全代表了操作的异步电动机。电动机械课程，本科课程一般包括教室和实验室课节。课堂节涵盖的稳态运行的异步电动机，其中每相的等效电路是用于计算各种汽车的数量，如输入电流和功率，功率因数，发达国家扭矩和效率。相关的计算与稳态运行需要的知识，等效电路参数。这些参数都得到了履行三项测试，即直流，无负载，并阻止转子试验电机在一个典型的实验。该实验室的部分包括这些测试和负载实验，让学生熟悉异步电动机运行、硬件和测量并获得了宝贵的经验。作者的经验表明，在教学上卓克索大学，宾州费城，当他们来到实验室进行这些实验，即使相应的理论，广泛覆盖在课堂上，给它们至少一节课详细描述出实验室设施和程序的实验，学生普遍有困难。与他们之前的其他实验室相比，学生不熟悉实验室环境，其中包含大量的机器和相对复杂的测量方法和设备。时间限制在实验室工作，也是一个艰难的调整。在通常的两小时的实验课，学生必须建立和执行四个感应电机的实验中，采取必要的测量，并调查稳态性能的电动机在各种工况.由于时间的限制，学生往往急于通过实验，以完成他们的时候，不幸的是使他们获得真正的感觉电机运行和升值所取得的成就在实验室实践。因此，在学生来实验室，仿真工具必须制定异步电动机试验充当有益的筹备工作。本文的目的是以设计一个计算实验室，介绍这些仿真模型的异步电机实验。直流，无负载，并阻止转子模拟模型的开发作为单独的应用程序中使用MATLAB / Simulink的和电气系统模块（PSB）。在负载实验中，学生必须写一个计算机程序利用MATLAB的M -文件编程的每相的等