Abstract
Power amplifier is one of the important elements of any DC attraction type levitation system. Due to the advancement in power electronics and control technology, it is now possible to develop power amplifier which will have the properties of fast dynamics, large bandwidth, ability to carry large payload, energy efficient, high reliability, cost-effective, and suitable for DCALS. Both linear and switching mode power amplifiers have been used in the field of DC attraction type levitation system. In this chapter, different possible switched mode power circuits for both single as well as multi-actuator based levitation system have been discussed, and a comparative study has been made of the different topologies of power amplifiers based on their structure, working principle, simulated, and experimental results.
TopDescription Of Switched Mode Power Amplifiers Used In Dc Attraction Type Levitation Systems
The main requirement of power amplifier is to quick control of coil-current as well as attraction force developed between electromagnet and ferromagnetic object. To satisfy this objective, both current rise and fall through the magnet-coil must be fast. This current forcing in both positive and negative directions is essential to achieve the necessary bandwidths of suspension system.
Many power supplies have been reported in the literature for DC attraction type levitation systems. For different maglev systems, both linear and switched mode type solid-state power amplifiers have been proposed which have their own advantages and disadvantages. The linear power supplies produce less switching related noise and the overall electro-magnetic interference is less when compared to the one produced by switched mode power supply (SMPS) circuits. But, in a linear power supply the transistor operates in its active region, incurring a significant amount of power loss. The overall efficiencies of linear power supplies are usually in a range of 30-60% (Mohan, et. al. 1996). For high power magnets, use of linear amplifier will mean un-practically large switch ratings and heat sink ratings. A combination of switched supply and linear amplifier circuit may be thought of to further improve the efficiency of linear amplifier circuits. The switched mode DC to DC power supply is energy efficient (70-90% range). Increased switching speeds, higher voltage and current ratings and relatively lower cost of power devices are the factors that have contributed to the emergence of switching power supplies. A transistor operating in ON/OFF mode has a much larger power handling capability compared to its linear mode. Since a high frequency isolation transformer is used (as compared to a 50-Hz transformer in a linear power supply), the size and weight of switch mode power supplies can be significantly reduced.