European Journal of Scientific Research - EuroJournals

897 K. G. Firouzjah, H. Eshaghtabar, A. Sheikholeslami and S. Lesan
dI F 2
V AB 2 = L2 + VC
dt
Discrete time state:
(10)
IF2( n + 1) −IF2(
n)
V AB 2( n) = L2 + VC( n)
T
where:
(11)
VC( n + 1) = VC Ref
= 1 pu . .
Also, the average voltage of VAB1, based on bipolar switching technique of full bridge power
converter (F1 to F4), is as follow:
V AB1 = (2D −1)
V Fdc
(12)
dI ′ 2
V AB1 = LT + RTI′ 2 + V ′ AB 2
dt
That RT and LT are the transformer’s impedances.
(13)
N 1 V ′ AB 2 = V AB 2
N 2
(14)
N 2 I′ 2 = I 2
N 1
In discrete form we have:
(15)
(2 D ( n) − 1) V FCdc = LT I′ 2( n + 1) −I′
2(
n)
+ RTI′ 2( n) + V ′ A B 2(
n)
T
(16)
Where, subscript (n) in (11) and (16) represents the present time values that can be easily
measured. Consequently, by having these values from (11), we will obtain IF2(n+1) that is the required
reference current of next situation. We can obtain the duty cycle of D(n) by considering IF2=I2 (Fuel cell
can supply the load merely).
N 2 N 2 T
I1( n + 1) = I2( n + 1) = ( V AB 2( n) + IF2(
n)
)
N1 N1 L2
(17)
I1( n + 1) −I1(
n)
LT + RTI1( n) + V ′ AB 2(
n) + V FCdc
D( n)
= T
2 V FCdc
(18)
If the resultant D is less than 1, fuel cell would have the capability of supplying the load by
desired duty cycle. Thus, the battery is not needed. But, if D>1, Fuel cell would have not that
capability and therefore, we should calculate the maximum power of fuel cell at the first step by
considering D=1, and in the second step, supplying the remain power by using battery with DB, which
is related with its converter.
If D=1, then we would have:
V AB1= V FCdc
(19)
dI 1
V ′ AB 2 = V FCdc −LT−RTI1 dt
That in discrete time situation:
(20)
I1( n + 1) −I1(
n)
V ′ AB 2( n) = V FCdc −LT −RTI1(
n)
T
By having the values of current state we can obtain I1(n+1) with D=1 as:
(21)
T
I 1( n + 1 ) =
LT
[ V FCdc −RTI1( n) − V ′ A B 2( n) ] + I1( n)
(22)
I1(n+1) is the maximum value of fuel cell produced current with D=1 that:
N 1
I Max _FC= I1( n + 1)
N 2
(23)