Page 291 - Renewable Energy Devices and System with Simulations in MATLAB and ANSYS

278 Renewable Energy Devices and Systems with Simulations in MATLAB and ANSYS ®
®

Maximize Grid
energy
capture interface Power quality
voltage control
X real and reactive
P(X,X΄) power control
X΄ P ref
Power converter

X
F(X,X΄) Limits
X΄ F ref

Load control and X,
stress reduction X΄ LSRM PTO

FIGURE 11.12 Control block diagram of a typical MHK power plant. (Courtesy of NREL, Denver, CO.)

induced signals (e.g., electromagnetic compatibility or radio frequency interferences during short
circuits or lightning strikes).
Figure 11.12 shows a typical control block diagram of a WEC with linear switched-reluctance
machines interfaced to the grid by the full-power conversion (Type 4 MHK generator). It also shows
an additional control block that can be added to control and reduce the mechanical stresses and loads
by controlling the electrical response to the mechanical excitations.

11.3.5 MHK Power Plant

As the MHK technology becomes more mature, future MHK generation can be predicted to follow
the trend of wind generation, in which an MHK power plant may consist of hundreds of MHK gen-
erators. Similarly, in the future, large-scale MHK generation will become common practice, because
the LCOE favors large-scale power generation.
It is easy to imagine that a future wave power plant or tidal power plant will consist of hundreds
of generators connected to the point of interconnection (POI) to transmit the total output of the plant
to the power system network. Similarly, the requirements for grid interconnection will adopt similar
rules and grid codes for MHK generation as those used for wind power generation. As shown in
Figure 11.13, a typical MHK power plant consists of many MHK generators interconnected in a
daisy-chain fashion and eventually connected to the substation transformer.
Although at present the level of generation is very small, eventually, when it reaches a high level,
MHK power plants will impact power system operations. System impact studies are commonly
performed in the planning stage far before the actual implementation takes place [37].

11.3.5.1 Plant-Level Control
MHK generators within a power plant can also be controlled at the plant level via supervisory
control. In an MHK power plant, the POI is the point to which all the generators are connected.
To a power system network, the response of an individual turbine is less important than the effec-
tive response at the POI—or, in other words, the collective behavior of the generators in the power
plant is more important than the behavior of an individual generator—thus, the plant controller is
implemented to shape the characteristic of the entire power plant. Plant-level control is usually