Design Of Multi-Pulse Rectification System

VF (Variable Frequency) is one of the best technologies of AC (Alternating Current) moter speed regulation and energy-saving. AC-DC (Direct Current)-AC as one of the VF methods is more widely used due to its advantage. As the non-linear nature of the uncontrolled diode bridge rectifier, which has been widely used in the AC-DC-AC equipments, the input current has significant harmonics and high THD (total harmonic distortion), electromagnetism compatibility is reduced which imperils other equipments. When the power of the equipments is higher, the harmonics are larger. Suppression of harmonics is significant. At the high power applications, two multi-pulse rectifiers that can meet different need have been designed to eliminate the certain harmonics and reduce the harmonics pollution.Multi-pulse rectifier based on autotransformer can reduce the equivalent capacity, but it is lack of systematic theoretical analysis because of late start, complex structure and other reasons. With the help of broad study, a kind of 24-pulse rectifier based on autotransformer is designed. This circuit is verified in rigorous theory in the aspects of autotransformer connection, input current, interphase reactors and the capacity of autotransformer. Proved in mathematics and simulation, with less equivalent capacity (only 17.3% of output power), the designed circuit can eliminate the 5^th,7^th,11^th,13^th,17^th,19^th etc harmonics, the lowest harmonic is 23^rd, which has practicability in high power field.Both of MATLAB/SIMULINK and Synopsys Saber have their respective advantages in electric force simulation, so the designed 24-pulse rectifier is simulated respectively. The simulated waveforms are given respectively and the same to theory analysis, which validates the rationality and feasibility adequately.Autotransformer can reduce its equivalent capacity, but there are disadvantages in complex design, difficult adjustion and high isolation demand. Therefore, prolonged delta connected transformer which is steady and simple in design is a better choice in the situation which has less limit of capacity. A kind of 30-pulse rectifier based on prolonged delta connected transformer is designed and simulated with MATLAB/SIMULINK in the paper. Proved in mathematics and simulation, the input current is 30-step which is more similar to sine wave, 5^th,7^th,11^th,13^th,17^th,19^th ,23^rd,25^th etc harmonics is eliminated, the lowest harmonic is 29^th, whose peak value is 3.45% of fundamental harmonic.