LC Tuned Magnetic Levitation System

Aims: To design a LC tuned circuit to levitate a ferromagnetic material by magnetic levitation technique.
Study Design: To eliminate the drawbacks of position sensors, self sensing system needs to be developed. AC excitation with LC tuned circuit was found as an alternative. To further strengthen the performance of the system, a Z source inverter was designed to bring back the levitated object to the desired position when it deviated from it.
Place and Duration of Study: The work was carried out in Electrical and electronics Department of SSN College of Engineering, Chennai, TN, India.
Methodology: A combination of AC excitation and series tuned circuit can be used to levitate a ferromagnetic object by magnetic levitation technique. The electromagnet forms the inductive part of a resonating circuit. The circuit is tuned at a frequency less than that of the exciting frequency. Therefore when the distance between the object and the electromagnet increases, there is fall in inductance of the lifting magnet, the circuit approaches resonance and the coil current increases. The magnetic force on the object increases and the object moves to its desired position. Though the method is simple, for slow change in coil current the levitated object may move under influence of gravitational force and come to rest position. Hence a new circuit with Z-source inverter with shoot through is designed to bring the levitated object to its desired position.
Results: The response of a simple LC tuned magnetic levitation system without any control circuitry was experimentally obtained. It indicated that the levitated object vibrated with increasing magnitude of oscillations and hence deviated from desired position. Hence a Z source inverter with LC tuned circuit as its load and PIC microcontroller to control the current were designed such that the object is brought back to its desired position.
Conclusion: Tuned inductive capacitive magnetic levitation circuit is designed and implemented. Experimental results show that the LO oscillates around its equilibrium position. The frequency of these oscillations obtained theoretically and experimentally does not show large variation. A new circuit with Z-source inverter is designed and implemented with the tuned circuit. It is observed that when the LO deviates from its equilibrium position, the circuit is no longer tuned and the voltage across the tuning capacitor varies. This voltage is used to generate shoot through condition to boost the excitation of the inverter. The resulting increase in the current produces sufficient force to pull the LO back to its desired position. Experimental results show that with this new circuit, the LO vibrates but with much reduced amplitude and hence can be said that the circuit also nearly damp out the oscillations. The main advantage of the system developed is it eliminates the sensors and its related drawbacks. Also design of complicated controllers is eliminated.