PhD Thesis - Cranfield University

Chapter 5
For the battery system, the PMS policy determines a reference power trajectory as,
P
batt
where
( t + DT)
Pb 1 Load
⎧min[
Pb1
, Pb
⎪
= ⎨max[
Pb
1 , Pb
⎪
⎪Pb
6 ⎩
2
4
, P
b3
, P
]
b5
]
if
if
P
P
Load
Load
if 0 ≤ P
143
( t)
> P
( t)
< 0
Load
avg
( t)
< P
avg
(5-12)
= P ( t + DT )
( 5-13)
Pb pbatt
2 = Pbatt
( t ) + G ⋅ DT
( 5-14)
P = P max
( 5-15)
b3
batt
Pb nbatt
4 = Pbatt
( t ) + G ⋅ DT
( 5-16)
P = P min
( 5-17)
b5
batt
P
b 6
chg
= P ( t + DT ) + P ( t + DT )
( 5-18)
Load
uc
where, P avg is the power level at or below which opportunity charging of the ultracapacitor is
chg
permissible, Puc is the battery to ultracapacitor charging power and DT is defined as the
time step of the PMS epoch where DT =∆PMS.
Formulation of the PMS policy decision criteria to determine the ultracapacitor reference
power is accomplished using a similar technique. Unlike the battery systems, the
ultracapacitors can be subjected to rapid and high power demand cycles. If the ultracapacitor
system is dimensioned with the capability to meet the maximum instantaneous load power
demands, the rate at which the power can be transferred will meet the rate at which the
power is demanded. Because of this power delivery quality, a step change limiter on the
ultracapacitor reference power is not required. This is illustrated in Figure 5.9 as a constant
discharging and constant charging power limit within the PMS decision epoch.