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‫بسم هللا الرحمن الرحيم‬
The Islamic University of Gaza
Faculty of Engineering
Electrical Engineering Department
POWER ELECTRONICS
EELE 5450 — Summer 2012
Instructor: Eng. Jalal Al Roumy
Lecture 8
Chapter Three
Series and Parallel operation of SCRs
In high voltage and high current applications, Power diodes
have to be connected in series and parallel.
Similarly, for high voltage and high current applications, SCRs
also have to be connected in series and parallel.
Chapter Three
Series operation of SCRs
If the input voltage is higher than the voltage rating of the
available SCR, two or more SCRs must be connected in series.
Chapter Three
Series operation of SCRs
In
Due
toreverse
the
production
region
and
spread,
thethe
forward
characteristics
are
region
not
,there
At the
Under
any
steady
further
state
increase
condition
ininvoltage
,external
,Vbo2 blocking
resistor
on Scr2 would
(R)
have
be
to be
identical.
is
a different
The
inforward
theeach
voltages
Breakover
due
tovoltages
the
same
current
are
innot
these
thewill
exceeded,
connected
and
across
this
Scr
would
SCR.
break
And
here
over
the
in(VBO)
the
SCR
forward
currents
same.
two
regions.
The two
not equallywill
sharing
Es=1000v.
direction.
differs
and hence
the Scrs
new will
characteristics
appears.
Chapter Three
Series operation of SCRs
R=(2Emax-Es)/∆Ib
For
more
than
two
Scrsleakage
we
assumeis
that
thetheother
The
transient
sharing
of will
voltages
accomplished
The
(∆
Ib=
forward
Ibmax
and
– Ibmin)
reverse
current
through
SCR by
Ibmaxis
isthe
only
available
in thespread.
datasheet
, so
current
are
equally,
so.
connecting
capacitor
across
each
varies
Emax
due
tomaximum
the
production
voltage
acrossSCR.
Scr1
The have
worst
case
is Ibmin=0.
Ibmin
We
andI1>I2
Ibmax
is worst case (∆ Ib= Ibmax – Ibmin)
Es=Emax+(ns-1)*R*I2
R<=(2Emax-Es)/Ibmax
for sharing
voltages
Emax=
I1R RT in series(Rwith
I2=I1-∆Ib
The
resistor
the capacitor
is on
to SCR)
prevent
(R must
be largecurrent
to decrease
power
large
discharge
through
Scrlosses
during turn on.
R=(2Emax-Es)/Ibmax
Chapter Three
Parallel operation of SCRs
When
theload
current
through
Scr1 increase
over
Scr2, an
When the
current
requirements
are high
thanthat
a single
opposing
voltage the
is induced
proportional
to the
difference in
SCR can handle,
devices must
be connected
in parallel.
current through Scr1. then boosting voltage is induced in series
with scr2 increasing the current flow through the device.
Chapter Three
SCR di/dt Calculation
di/dt depends on V&L
the type
so we
of component
increase L being used and it
appears in datasheets.
Chapter Three
Snubber circuit in dv/dt
The circuit used to limit the dv/dt (specified in datasheet)
across SCR is called snubber circuit.
Chapter Three
dv/dt calculation method1
Chapter Three
dv/dt calculation method2
End of Lecture