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Magnetic Levitation Systems Using Analog and Digital Phase-Lead Controllers

Abstract

This paper addresses real-time magnetic levitation control with analog and digital controllers. The objective is to keep a ferromagnetic object suspended, without contact, beneath an electromagnet. The electromagnetic force must be adjusted to counteract the weight of the object and account for disturbances. This is accomplished by measuring the location of the object using a non-contact sensor, and adjusting the current in the electromagnet based on this measurement in order to maintain the object at a predetermined location. The system is both inherently nonlinear and open-loop unstable. Negative feedback and phase-lead controllers are designed to stabilize this magnetic levitation system. The controllers are designed using MATLAB. Analog controllers are implemented using resistors, capacitors, and operational amplifiers. Digital controllers are implemented using the TMS320C6711 DSK. In the case of digital controllers, controller coefficients are included in a C language program that implements the phase- lead controller. The Code Composer Studio that came with the TMS320C6711 DSK is then used to compile the C program and load it to the C6711 DSK. Both one-dimensional and two-dimensional systems are built and successfully tested. Theses maglev control systems (non-linear, open-loop unstable) are good examples to complement the DC motor control system (linear, open-loop stable) currently taught in many control systems courses in electrical and mechanical engineering majors. Combined with the new DSP technologies, this will make the control systems courses more exciting. On the other hand, adding another application in control to the DSP (or signals and systems) courses will make theses seemingly theoretical courses more interesting. With a good understanding of the C6711 DSK, Students can then use the newest DSP technologies to explore other applications.

1. Introduction

Control theory is one of the major areas in electrical engineering. This author has been teaching control systems courses for the past 18 years and has seen most control systems text books using the classical DC motor control as primary examples and laboratory projects. On the other hand, many new and challenging control systems are emerging and one of them is the magnetic levitation (maglev) system. Maglev train systems have been built in Japan, Germany, and recently in Shanghai, China. The one in China can reach a speed of 430km/h (268mi/h) [1]. At this speed, a maglev train could match gate-to-gate air-travel time on routes of less than 1000 km. Compelling advantages of maglev train include susceptible to weather delays (than flying), quiet ride since it is a non contact system, and environmentally friendly. The Shanghai maglev line is the first of several maglev projects planned for later this decade, including those in Munich (Germany), Pittsburgh, and Baltimore-Washington, D.C. Still more maglev projects are under

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Tang, J. (2007, June), Magnetic Levitation Systems Using Analog And Digital Phase Lead Controllers Paper presented at 2007 Annual Conference & Exposition, Honolulu, Hawaii. 10.18260/1-2--1658