Frequency Tripler

The frequency tripler affords a simple example of a frequency multiplier. It uses three saturable reactors supplied from a 3-phase source as shown in Fig. 7-4. The firing angle α_f, must be adjusted so that only one reactor is saturated at a time, otherwise a line-to-line short circuit occurs. Then, according to Eq. 7-1, the firing angle must be at least α_f, = 2π/3 for a frequency tripler, since m = 3. Wave forms of currents in each phase and in the output are shown in Fig. 7-4(b). Because there is some inductance in practical devices, even when saturated, the corners in the current waves are not quite as sharp as those shown. The current in an inductive load having a Q of about 0.5 has fairly good wave form since the inductance tends to smooth out the wave.

Figure 7-4. (a) Frequency tripler circuit; (b) wave forms of line currents and output current for noninductive load