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Marine and Hydrokinetic Power Generation and Power Plants 279

Individual
MHKGs
Collector
system

Submarine Cables

Substation
transformer
Point of
interconnection (POI)
Transmission
line

Grid

FIGURE 11.13 Layout of a typical MHK power plant. (Courtesy of NREL, Denver, CO.)

accomplished by supervisory control, in which the signals monitored at the POI are used to control
the entire power plant.
During a grid disturbance, the real power is often used to support the grid by providing ancillary
services to the grid. This kind of operation is usually controlled by the supervisory control to provide
a collective response at the POI. One example is called “frequency response.” Common practice in
real power control is to provide inertial response, as is found in a conventional synchronous genera-
tors. Another common practice is to control the real power with the droop control as a function of
the operating frequency.
11.3.5.2 Plant-Level Compensation
Another type of plant-level control can be accomplished by adding plant-level compensation. For
example, centralized reactive power compensation can be installed at the POI. The plant-level reac-
tive power compensation or energy storage is usually much larger in size than that of an indi-
vidual turbine. Many older wind power plants that have Type 1 WTGs (induction generators) are
enhanced by the installation of plant-level reactive compensation (e.g., DSTATCOM, DVAR, SVC,
STATCOM). For MHK generation, this type of plant-level compensation is placed at the POI at the
substation transformer onshore. This type of compensation is very significant, especially if the grid
at the POI is very weak (e.g., short-circuit ratio <3).