ECE 6300 TRANSMISSION SYSTEMS CONTROL SPRING 2015
HOMEWORK #1 DUE: 02/08/2016
A dc motor with armature resistance, Ra, of 0.6 Ω and armature inductance of, La, is 4 mH is
supplied from a phase-controlled six-pulse rectifier as shown in Fig. 1. It is fed from a 3-phase
460-V, 60-Hz line. The motor rotates with such speed that the armature EMF, Ea, is 510 V. The
firing angle is  = 60o.
(a)
(i)
(ii)
Determine if the output current is continuous or discontinuous.
If you determined in (a)(i) that the output current is discontinuous, derive the
condition (an expression) for discontinuous output current.
(b)
Determine an expression for the load current i0(t).
(c)
If you determined in (a)(i) that the output current is discontinuous, determine the
following:
(i)
(ii)
the angle  when the output current drops to zero, and
the conduction angle .
(d)
(i)
(ii)
Determine the dc-output voltage, V0dc.
The value of V0dc depends on your finding to (a)(i). Comment on the value of V0dc
with respect to your finding of (a)(i).
(e)
Determine the dc-output current, I0dc.
(f)
The power line inductance seen from the input terminals of the rectifier is 1 mH/phase.
The anode voltages of thyristors T1 and T3 will be equal and both thyristors will
conductor for “a certain period which is called commutation (or overlap) angle ”.
(i)
(ii)
(iii)
(iv)
Determine an equation for the current of thyristor T1, iT1.
Determine an equation for the current of thyristor T3, iT3.
Determine an equation for .
Neglecting resistances of the supply circuit, find the overlap angle, .
T1
a
c
n
T3
La
T5
Ra
b
T4
T6
T2
Fig. 1
Ea
Lf
if
vf