AN-3008 RC Snubber Networks for Thyristor Power Control and ...

APPLICATION NOTE
AN-3008
1.8
I ER
ξ = ------ – ---------- L
C S L
⎛dV
------ ⎞ = initial instantaneous dV ------ at t = 0, ignoring any instantaneous voltage step at
⎝ dt ⎠0
dt
t = 0 because of I RRM
1.9
⎛dV
------ ⎞
⎝ dt ⎠0
=
R T
V OL ------ + ξ. For All Damping Conditions
L
2.0
When I = 0,
⎛ dV ------ ⎞ =
⎝ dt ⎠0
ER
---------- S
L
⎛dV
------ ⎞ =
⎝ dt ⎠max
t max =
Maximum Instantaneous dV ------
dt
Time of maximum instantaneous dV ------
dt
t peak = Time of maximum instantaneous peak voltage across thyristor
Average dV ------ = V
dt PK ⁄ t PK = Slope of the secant line from t = 0 through V PK
V PK
=
Maximum instantaneous voltage across the thyristor.
Constants (depending on the damping factor):
2.1
No Damping ( ρ = 0 )
ω = ω 0
R T = α = ρ = 0
2.2
Underdamped ( 0 < ρ < 1)
ω = ω0 2 – α 2 = ω0 1–
ρ 2
2.3
Critial Damped ( ρ = 1)
α
ω0, ω 0R , 2 L C --- , C 2
= = = = ----------
αR T
2.4
Overdamped ( ρ > 1)
ω = α 2 – ω0 2 = ω0 ρ 2 – 1
Laplace transforms for the current and voltage in Figure 42 are:
3.0
E⁄
L+
SI E
SV OL
– ξ
i ( S)
= -------------------------------------
S 2 S R ; e = -- – -------------------------------------
T 1 S
+ ------ + ------- S 2 R T 1
+ ------S + -------
L LC
L LC
R L
L
+
–
t = 0
I
C S
R S
e
INITIAL CONDITIONS
I = I RRM
VC S = 0
Figure 42. Equivalent Circuit for Load and Snubber
REV. 4.01 6/24/02 21