Consideration of a stage of switching of thyristors for a full-wave rectifier with centre tap and active - inductive load with infinite inductance

Figure 1.16

Let’s consider that VS1 is turned on just as a control pulse is applied and this moment should be a moment of a reference mark. VS2 is beginning to turn off.

During an interval γ i_T1 is growing up from 0 to I_d;

i_T2 is growing down from I_d to 0.

According to first Kirchhoff’s law

I_d = i_T1 + i_T2

Since L_d = ¥ a load current have only a direct component; hence, an alternating component of thyristors’ currents flows through phases of the transformer and the thyristors witch are both turned on.

We should designate it as i_C.

Then

i_T1 = i_C; i_T2 = I_d – i_C;

Inductance of a branch of the thyristor

х_а = wL_a

According to 2-nd Kirchhoff’s law

i_K = i_T1

Let's discover γ from a condition:

At u = γ i_T1 (γ) = I_d

According to the theorem of the equivalent generator during the interval γ

Figure 1.17

Let's discover an average rectified voltage

where no-load EMF is

Commutating voltage drop is

From here, we could get an equation of the external characteristic