European Journal of Scientific Research - EuroJournals

A Predictive Current Control Technique on Fuel Cell Based Distributed
Generation in a Standalone AC Power Supply 892
1. Introduction
Previous empirical research provides contradictory and inconclusive evidence on the value relevance
of comprehensive income disclosures promulgated in different countries. Thus, present study using
comprehensive income of Iranian firm's data shed more lights on the issue.
Fuel cells are devices capable of converting chemical energy into heat and dc electrical energy
by means of the oxidation of a fuel, usually hydrogen (Padulles et al, 2000). Distributed generation
(DG) technologies can provide energy solutions to some customers that are more cost-effective, more
environmentally friendly, or provide higher power quality or reliability than conventional solutions.
The voltage of fuel cell stack decreases largely as the load current increase, and the voltage increases
as the temperature increase at the same current. Thus DGS should be interfaced with Power Electronic
systems such as DC to DC or/and DC to AC power converters to obtain a sinusoidal AC output voltage
with fixed frequency from variable or high-frequency AC voltage sources or DC voltage sources
(Haiping et al, 2005). So the DC-DC converter plays a key role in making the fuel cell DC power
available for stand-alone applications.
To boost low output DC voltage of the fuel cell to high DC voltage, a forward DC to DC boost
converter, a push-pull DC to DC boost converter or an isolated full-bridge DC to DC power converter
can be selected. In addition, various topologies such as the H-bridge series resonant buck and boost
converters have been presented in (Blaabjerg et al, 2004). Anderson et al, (2002) present a current fed
push-pull converter. This topology decreases the conduction losses in the switches due to the low fuel
cell voltage. Nergaard et al, (2002) suggest an interleaved front-end boost converter. This topology
considerably reduces the current ripple flowing into the fuel cell. A dual loop control strategy (current
and voltage loop) has been used for the interleaved converter. Jung et al, (2005;2005) introduce a Zsource
converter. This is a new concept in which a shoot-through vector directly steps up the DC
source voltage without using a boost DC-DC converter. The boost voltage rate depends on the total
duration of the shoot-through zero vectors over one switching period Jung et al, (2005). Also, In
reference (Wang and Nehrir, 2006) a non-isolated boost converter with a conventional PI controller has
been used for the converter control. Akkinapragada (2007) had been employed a non-isolated buckboost
DC-DC converter with a closed loop PWM (pulse width modulation) control strategy as
described in Reference (Mohan et al, ). The reference (Duran-Gomez et al, 2006) had been presented
an approach to convert the generated dc output voltage of a PV cell array into a higher regulated dc
voltage. The approach employs a series-combined connected boost and buck boost dc-dc converter for
power conditioning of the dc voltage provided by a photo-voltaic array. Chandrasekaran and Gokdere
(2004) introduce a novel composite integrated magnetic (IM) core structure, which minimizes inductor
current ripple. Their subject is a compact, IM core structure for a three-phase interleaved, DC-DC
boost converter that feeds off the fuel cell output and can provide a programmable, regulated, high
voltage DC bus for the distributed power system.
In recent years, the higher efficiency and the more advanced power conversion, energy
utilization equipment, a variety of circuit topologies of the soft-switching DC-DC power converter are
urgently required. The reference (Ogura et al, 2003) has introduced a boost type ZVS-PWM chopperfed
DC-DC power converter with a single active auxiliary resonant snubber in the load side for the
power interface of solar photovoltaic and fuel cell power conditioners. The character of this boost type
ZVS-PWM chopper-fed DC-DC power converter is feasible. Also, a unidirectional isolated full-bridge
DC to DC power converter can be used to boost low fuel cell voltage (Bendre et al, 2003; Aydemir,
2002; Kim et al, 1997; Jain et al, 2002; Brunoro and Vieira, 1999; Jeon and Cho, 2001). In addition, a
bidirectional full-bridge DC to DC power converter can be used for stepping up low battery voltage or
stepping down high-voltage-side DC link according to battery discharge or recharge mode (Peng et al,
2004; Jiang and Dougal, 2003). Among the presented power converters, two phase-shifted full-bridge
DC to DC converters, which are one of the most attractive topologies for high power generation are
adopted as described in (Jung, 2005; Keyhani and Jung, 2004) with a unidirectional full-bridge DC to
DC boost converter for the fuel cell and a bidirectional full-bridge DC to DC boost/buck converter for