Study on Mechanism of a Novel Autotransformer for 18-pluse Rectifier

From the aspect of the isolated transformer for 18-pulse rectifier, a new topology of the 18-pluse autotransformer-rectifier with the advantages of small equivalent capacity, low harmonics and outstanding symmetrical structure is proposed, which is superior to the existing American patents. The relationship between the input and output currents, the distortion of input current, the relationship between the voltage of each branches and the phase shift angle and the equivalent capacity of the autotransformer are derived by using the potential vector diagram and the balance principle of the magnet potential. The phase shift angle of the proposed novel 18-pulse autotransformer is 20° that is exactly the same with the isolated transformer, which verifies the potential vector of the two is coincident. The input current distortion rate of this autotransformer is 10.05%, which reduces the harmonics of the rectifier to the power grid. The equivalent capacity is only 17.76% of the output power, which greatly reduces the volume and weight of the system. Finally, a prototype is made, which validates the correctness of the theoretical deduction and simulation, and provides a theoretical guide for future design.