**2.1. Magnetic bearing system composition**

A magnetic bearing system like that of Fig. 2 is composed of the object to be levitated, core, electromagnet including the coil, amplifier to operate the electromagnet, displacement measurement system to measure the distance between the levitating object and the electromagnet, control law to calculate the control signal from the feedback signal, and control system that includes the hardware to realize the control law.

Fig. 3 is the assembly of the magnetic bearing system to make. In the assembly, the levitated object will be supported by magnetic bearing at X and Y axis direction. But thrust direction has only the mechanical backup bearing. And Fig. 4 is the levitated object that is 1.4kg.

**Figure 2.** Schematic of the magnetic bearing system

194 Performance Evaluation of Bearings

attraction.

and brake loss. Magnetic levitation that uses superconducting Meissner Effect takes advantage of the repulsion with permanent magnets caused by the strong diamagnetism from the superconductor. Like that of the induction levitation, stable levitation is possible without any control. However, the operational temperature of the levitation system using superconductor is very low: 4.2K(liquid Helium), 77K(liquid Nitrogen). Generally, the magnetic levitation applied to the magnetic bearing is the method using attraction and repulsion. Magnetic bearing systems discussed here refers to a system that utilizes the

In this chapter, the method to designing a magnetic bearing system, to obtaining a mathematical model, and understanding the preparations necessary for control will be discussed. For this, the calculation of attraction using the Probable Flux Paths Method, selection of circuitry about the amplifier to operate the electromagnet, and method to

Fig. 2 shows a schematic diagram of the magnetic bearing system to be designed in this chapter. The levitated object is supported by the attraction of the electromagnet and the attraction of the electromagnet is controlled by the current in the coil. In order to design and control such a magnetic bearing system, the amplifier to operate the electromagnet that composes the magnetic bearing system and hardware to control the whole system need to be designed first. Next, the designed magnetic bearing system is modeled mathematically, then the parameter values difficult to measure through the mathematical model are determined through experimentation. Finally, an adequate controller is designed and applied to the identified magnetic bearing system. In this chapter, the detailed control laws for magnetic bearing control are excluded and the implementation of the magnetic bearing

A magnetic bearing system like that of Fig. 2 is composed of the object to be levitated, core, electromagnet including the coil, amplifier to operate the electromagnet, displacement measurement system to measure the distance between the levitating object and the electromagnet, control law to calculate the control signal from the feedback signal, and

identify the magnetic bearing system that includes a PID controller are discussed.

**Figure 1.** Levitation system according to the magnetic levitation method

system before applying various controllers is the main objective.

control system that includes the hardware to realize the control law.

**2.1. Magnetic bearing system composition** 

**2. Magnetic bearing system design** 

**Figure 3.** Assembly of the magnetic bearing system

**Figure 4.** Levitated object

Since a magnetic bearing system like Fig. 3 has a symmetric form vertically and horizontally, the levitating object can be simply assumed as a point mass in the perspective that the object is levitated. Therefore, in this section, the elements of the magnetic bearing system excluding the levitating object are designed.

Control of Magnetic Bearing System 197

d. The material of the core and levitating object, coil and number of windings, and current at normal state is adjusted until the comparison of the calculated attractive force value

e. The electromagnet's maximum attractive force and coil's maximum current according to the core and saturation flux density of the levitating object material are calculated. f. The material of the core and levitating object, coil and number of windings, and current at normal state is adjusted until the calculated maximum attractive force of the

Since the attractive force calculated through the Probable Flux Paths Method has a large error with the actual experimentation values, in order to manufacture magnetic bearings

and the mass of the levitating object gives a satisfactory attractive force.

based on this design, it is desirable to design with a safety factor of greater than 3.

electromagnet is sufficient.

**Figure 5.** Electromagnet core

**Figure 6.** Electromagnet magnetic circuit formation
