New Pulse-Tripling Method for the 12-Pulse Autotransformer Rectifier

To solve the problem of the limited harmonic suppression ability of the 12-pulse rectifier, a new pulse-tripling method for the 12-pulse autotransformer rectifier is proposed in this article. The new pulse-tripling method consists of an inter-phase reactor with a secondary side winding, an auxiliary single-phase transformer (AST), and two auxiliary single-phase rectifiers (ASRs). The primary side winding of the AST and the secondary side winding of the interphase reactor are connected in series; by changing the turn ratio of the AST, ASR2 can change the working timing of the auxiliary circuit, thus constituting the three working modes of the rectifier, and the output currents of two sets of three-phase diode bridge rectifiers are modulated into a three-level waveform. Based on the affiliation between the ac and dc sides of the rectifier, the pulse number of the rectifier can be tripled to achieve a new 36-pulse autotransformer rectifier with approximately sinusoidal input current (THD is as low as 2.7%). A 2.4 kW experimental prototype is built to validate the theoretical analysis.