Control and Design of Microgrid Components - Power Systems ...

Prime Mover
DC Storage
Voltage Sourced Inverter
AC Interface
Generator
V
X
E
P,Q
I
DC Source
Voltage Sourced Inverter
AC Interface
+
V
X
E
P,Q
I
Figure 4.4 Replacement of Prime Mover + DC Storage with DC Source.
With storage, the value of the voltage at the DC bus is quite stiff because it is regulated by the
prime mover. Since there is a need for some sort of available storage, then it is possible to
eliminate the prime mover altogether from the model, without loss of generality. Figure 4.4
shows how the prime mover + DC storage blocks can be replaced by a DC voltage source. This
simplification is legal because the two parts in the dark dashed ovals behave essentially the same.
This simplification allows to obtain conclusions on the behavior of inverter based sources,
without having the need to use an actual prime mover. The hardware tests that will be described
in the following chapters adopt a microsource that takes advantage of this simplification.
4.3 Sizing the Coupling Inductor, Inverter Voltage and Power Angle
Microsources need a power electronics block to perform the DC/AC conversion to interface with
the local grid where they are installed. The inverter terminals are ultimately connected to the AC
system by means of an inductance. Figure 4.5 shows the details of the interface with the grid.
Measurements are taken from both sides of the inductance and a controller generates desired
values for V and δ v to track the externally commanded values for active power injection P, and
voltage magnitude E at the point of connection with the grid.
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