European Journal of Scientific Research - EuroJournals

A Predictive Current Control Technique on Fuel Cell Based Distributed
Generation in a Standalone AC Power Supply 894
Figure 1: Unidirectional/bidirectional DC to DC power converters (Jung, 2005).
Fig. 2 shows power flows of DC to DC power converters for battery discharge and battery
recharge. As shown in Fig. 2, the unidirectional full-bridge DC to DC boost converter permits only one
directional power flow from the fuel cell to the load because a reverse current can damage the fuel cell.
In addition, response speed of the power converter should be slow enough to meet slow dynamic
response of the fuel cell. On the other hand, the bidirectional full-bridge DC to DC power converter
allows both directional power flows for battery discharge and recharge, and its response also should be
fast to compensate for the slow dynamics of fuel cell during start-up or sudden load changes. For
battery discharge mode illustrated in Fig. 2 (a), which occurs when a startup or a sudden load increase,
the fuel cell starts delivering electric power to the load and the battery instantly provides power until
the fuel cell reaches a full operation state. After transient operation, only the fuel cell feeds electric
power to the load. For battery recharge mode shown in Fig. 2 (b), the battery absorbs the energy
overflowed from the fuel cell to prevent DC-link voltage VDC from being overcharged during a sudden
load decrease, and then the battery is recharged by the fuel cell in a steady-state until it reaches a
nominal voltage (Jung, 2005). The adopted model of the load (RL) is a three-phase DC to AC inverter
with PWM bipolar switching strategy that is shown in Fig. 3.
Figure 2: Power flows of DC to DC power converters (Jung, 2005)
(a): Battery discharge (b): Battery recharge