Design and Implementation of Controller for Electromagnetic Levitation System in Presence of Disturbances

Abstract

Electromagnetic Levitation System (EMLS) is a friction-less and contactless mechatronics tech- nology. This technology received huge applicability in most of engineering and science sectors like transportation engineering, space science, defence engineering, material science, civil en- gineering, electrical engineering, biomedical engineering...etc. However, the first patent in this area was registered around the 1930s, the EMLS technology found their research focus around the globe in the late 1960s. Because of such focus, the EMLS gained a huge number of appli- cations as MagLev trains, magnetic bearing, wind turbine, weighing machine, rocket launching station, magnetic suspension and many more. It is noticed during the literature review that the maximum utilization of this technology is being done in the area of the mass transportation sector. The passenger-carrying trains used in the mass transportation sector with the EMLS technology is termed as a Magnetically Levitated (MagLev) trains. This MagLev system is a class of the unstable, nonlinear and coupled electromechanical system by nature. Such an open- loop benchmark behaviour attracts a large number of the researcher to perform more and more research in this technology. Levitation is the most basic and common mode for the MagLev trains. It is observed from the literature that out of the three modes namely levitation, guid- ance, and propulsion, the maximum challenges have been found in the control of the levitation mode due to open- loop instability, multi-channel disturbances and nonlinearity. To handle such challenges, the most common prototype structure out of several is the steel ball levitation sys- tem. Several researchers have demonstrated that the prototype structures of the EMLS can be majorly categorized as Current Controlled EMLS (CC-EMLS), and Voltage Controlled EMLS (VC- EMLS). In this research, mathematical modelling and controller design are investigated for both types of EMLS structures. However, out of two, the VC-EMLS is more challenging, and complex yet widely applicable structure. Hence, the proposed control algorithms are experimentally validated for the VC-EMLS. In the case of the CC-EMLS (second-order nonlinear dynamics), the stabilization of the steel ball with or without the payload disturbance is investigated using the Takagi-Sugeno (T-S) fuzzy regulator design. The Negative Absolute Eigenvalue (NAE) approach has been proposed. This approach has reduced the structural complexity, and compu- tational burden observed using the traditional PDC plus LMI approach. It is noticed that one of the state variables like the vertical velocity is not measurable for the experimental hardware. Hence, nonlinear vertical velocity estimator is designed and implemented online. It is also pointed out that the parameters of the electromagnet like the coil inductance varies with respect to the steel ball position. Change in the coil inductance (L(x)) may develop the variation in the electromagnetic force of the attraction and finally may result in unwanted lumped disturbances (i.e, unmodeled dynamics, uncertainties, and many more). Another source of the disturbance in the MagLev system is the vertical payload disturbance which may be presented in the prototype structure of the steel ball levitation as a vertical up-down disturbing force. In this research, the controller structures have been proposed for the stabilizing and tracking control of the EMLS with or without payload disturbances. It is noticed during the experimentation that the stabiliz- ing controller alone may not be capable to provide the performance robustness in the presences of the lumped disturbances (e.g., payload disturbances, uncertainties, unmodeled higher order dynamics, nonlinearities). In a further stage, the Extended State Observer (ESO) schemes have been investigated to es- timate such matched as well as mismatched lumped disturbances. In the beginning, Hybrid ESO (HyESO) based linear control structure is proposed and experimentally validated to ob- serve and to minimize the matched/mismatched lumped disturbances. As an extension of the HyESO, the Cascade-HyESO based nonlinear control structure is explored and implemented in the experimental hardware. Finally, It has been observed that the HyESO enhanced linear and nonlinear controllers have shown the robust performance in stabilizing control, tracking control and lumped disturbance rejection control for the VC-EMLS.