Civil Engineering Reference
In-Depth Information
FIGURE 12-13
Mode controller deadbands eliminates the system chatter.
on-line, manually or automatically after going through the preplanned strat-
egy algorithm. Even with automatic transfer switches, the diesel generator
takes a long time to come on-line. Typically, this delay time is approximately
20 seconds.
The mode controller is designed and programmed with deadbands to
avoid change over of the sources for correcting small variation on the bus
voltage and frequency. The deadbands avoid chatters in the system.
Figure 12-13
is an example of 120 volts hybrid system voltage-control
regions. The deadbands are along the horizontal segments of the control line.
As a part of the overall system controller, the mode controller may incor-
porate the maximum power extraction algorithm. The dynamic behaviors
of the closed-loop system, following common disturbances such as insolation
changes due to cloud, wind fluctuation, sudden load changes and short
circuit faults, are taken into account in a comprehensive design.
6
12.4.4
Load Sharing
Since the wind, pv, battery, and diesel (or fuel cell) in various combinations,
operate in parallel, the load sharing between them is one of the key design
aspects of the hybrid system. For example, in the wind/diesel hybrid system
(
Figure 12-14
)
, the electrical properties of the two systems must match so
that they share load in proportion to their rated capacities.
For determining the load sharing, the two systems are first reduced to their
respective Thevenin equivalent circuit model, in which each system is rep-
resented by its internal voltage and the series impedance. This is shown in
Figure 12-14
.
The terminal characteristics of the two generators are then
given by the following:
EE IZ
=−⋅
1
01
1
1
(12-1)
EE I
=−⋅
⋅
Z
2
02
2
2
where subscripts 1 and 2 represent system 1 and 2 respectively, and
