Page 391 - Renewable Energy Devices and System with Simulations in MATLAB and ANSYS

378 Renewable Energy Devices and Systems with Simulations in MATLAB and ANSYS ®
®

+ L s
DC bus
R s L C capacitor
0 s DC

R s – L s C DC
DC/DC or DC/AC
module
DC bus of
super UPS

(d)

FIGURE 14.22 (Continued) Types of short-circuit fault: (d) Type IV, short-circuit fault of both positive and
negative bus to neutral bus.

i(t) L s

R s +
C DC
u(t)
C
L s DC
–
FIGURE 14.23 Type I failure equivalent model.

 di t ()
⋅
u t
 2L s + 2Ri t () = ()
s
 dt
 du t () (14.17)
 . + it () = 0

 05C DC dt
The initial state is given in Equation 14.18. U(0) is the initial value of the DC bus voltage, and
I(0) is the initial value of the current:
,
I 0
U 0 () = 2 V DC () = 0 (14.18)
By solving Equation 14.17, the expression of short-circuit current i(t) can be given in the follow-
ing equation:

 − R s + R s 2 − 4 − R s − R s 2 − 4 
sDC 
sDC
U() 0 2 4  L s L s 2 LC t L s L L s 2 LC t
it () = ⋅ R s 2 −  e 2 − e 2  (14.19)
L s L s L C DC  
s
 
 
Based on Equation 14.19, take a 100 kW AC/DC converter module as an example with the speci-
fications of the system shown in Table 14.2. The calculation results are shown in Figure 14.24.