2.2.2. 24-Pulse Rectifier

A 24-pulse rectifier uses a zig-zag-shaped phase shifting transformer to create 24-pulse waveforms per cycle. Compared with the 12-pulse rectification method described above, this rectifier can produce better DC voltage waveforms and reduce harmonics more effectively. Figure 6 shows a block diagram of the 24-pulse rectifier. The phase shift angle of the phase shifting transformer, in this case, can be expressed via Equation (2) specified below, in particular, there is a phase difference of 15◦.

$$
\Delta = \angle \varepsilon\_{ab} - \angle \varepsilon\_{AB} = 15^{\circ} \tag{2}
$$

where, Δ is the phase shift angle, ∠*eab* is the line voltage of the primary side, and ∠*eAB* is the line voltage of the secondary side.

**Figure 6.** Block diagram and Waveforms of a 24-pulse rectifier.

Considering the total harmonic distortion in the output waveforms generated by the 24-pulse rectifier, all lower-order harmonics below the 19th order are eliminated. Therefore, the 24-pulse rectifier has significantly better harmonic output characteristics than those of the 12-pulse rectifier. In addition, because the waveforms of the DC link unit include 24-pulses per cycle, this leads to a voltage waveform that is considerably similar to DC voltage.
