Page 155 - Power Quality in Electrical Systems

Uninterruptible Power Supplies 137

Fuel Cell System (FCS)
- Stand alone system utilizing a PEMFC
- Proprietary technology with proven life
and reliability
- Integrated controller

Power Conditioning System (PCS)
- Converts unregulated DC power from
the fuel-cell to 48 V DC regulated
- Standard industry hardware

Energy Storage System (ESS)
- 3 banks of ultra-capacitors, which provide
a seamless power transition during fuel-cell
start-up
- Standard industry hardware

Figure 9.8 Fuel-cell UPS, 48 V DC power, 4.5 kW [9.8].
[Courtesy UTC Power]

■ Rating, 4.5 kW, (Figure 9.8) [9.8]
■ Fuel cell–powered UPS
■ Ultra capacitors for fuel cell startup
■ Output, 28 V DC

Energy storage
The requirement for stored energy in an uninterruptible (standby) power
system is predicated on at least two parameters: (1) the time duration of
power delivery (term), and (2) the power level (energy). The requirements
further defined by the time duration can be categorized as follows [9.8]:
■ Short Term: Standby systems without available transfer means to
engine-generator sets or alternate utility feeders. These stand-alone
systems range from 100 W to 1000 kW and include 5 to 30 minutes of
stored energy capability, based on estimates of utility outage time.
■ Medium Term: Standby systems with available transfer means to
engine-generator sets, alternate utility feeders, or other sources. These
systems range up to 10,000 kW and include up to 5 minutes of stored
energy capability, based on the time to start engine-generator sets and
make the transfer.
■ Long Term: Standby systems that operate as part of a utility system,
which provide, in addition to standby function, other functions such