#Multisim 14.1 rotate 45 degrees free#

There are two possibilities for this independent oscillator: The advantage of this independent oscillator would be to provide an ideal (immunized and clean) sinusoid for synchronizing and timing purposes.

This oscillator would then provide the (phase) reference for the generation of firing pulses to the ring counter during the perturbation periods and would use the steady-state periods for locking in step with the system frequency. The most obvious method is to utilize an independent oscillator at 60В Hz, which can be synchronously locked to the AC commutation voltage frequency. But as converter connections to weak AC systems became required more often than not, it was necessary to devise a scheme for synchronization purposes that would be decoupled from the commutation voltage frequency for durations when there were perturbations occurring on the AC system.

#Multisim 14.1 rotate 45 degrees free#

For strong AC systems, the frequency is relatively constant and distortion free to be acceptable for most converter type applications. However, it is the frequency that is of primary concern for the synchronization of firing pulses. However, it was noted quite early on (the early 1960s) that the commutation voltage (system) frequency is not a constant, neither in frequency nor amplitude, during a perturbed state. To control the firing angle of a converter, it is necessary to synchronize the firing pulses emanating from the ring counter to the AC commutation voltage that has a frequency of 60В Hz in steady state. This is shown in fig.В 8-3d (green areas!!) The average value of v L b is zero (equal surface area criterion, see p. The exact form of i o is provided by expression (7-1). Between 180В° and П‰t 2В =В Оґ the output voltage of this circuit is negative ! At this point the magnetic energy starts to discharge and the current starts to decrease.ДЄt the instant t 2В = Оґ/П‰ the current has reached the holding value I H and the thyristor switches off. From this instant the polarity of v L b reverses. This instant corresponds to the end of the magnetic charging of the coil, in other words the current i o has reached its maximum. In addition, at every moment in time v oВ = v R bВ + v L b.ДЄt the instant that v R bВ = v o, v L b becomes zero, see fig.В 8-3d to the right. With a current i o through a coil, there is a corresponding magnetic energy L b в‹… i o 2 2 The current can only gradually increase because of the inductive nature of the load. Jean Pollefliet, in Power Electronics, 2018 2.2 Current flowДЄfter the firing angle О± the thyristor starts to conduct.