Environmental Engineering Reference
In-Depth Information
18
Synchronverters: Grid-friendly
Inverters that Mimic
Synchronous Generators
As discussed in Chapters 3 and 15-17, the current paradigm in the control of inverters
associated with renewable energy sources is to extract the maximum power from the power
source and inject it all into the power grid using current-controlled inverters; see for example
(Busquets-Monge
et al
. 2008b; Carrasco
et al
. 2006b; Ekanayake
et al
. 2003). This is a
good policy as long as such power sources constitute a negligible part of the grid power
capacity. Indeed, any random power fluctuations of the renewable power generators in this
case can be compensated for by the controllers associated with large conventional generators
because some of these generators are dedicated to take care of the overall power balance,
system stability and fault ride-through. When the penetration of renewable power generators
reaches a certain level, such “irresponsible” behaviour will become untenable. In responding
to the daily increasing share of electricity generated from distributed generation and renewable
energy sources, it is important for these sources to feed power to the grid in the form of voltage
sources instead of current sources, in a way similar to the conventional power generators
(Brabandere
et al
. 2007; Loix
et al
. 2007; Piagi and Lasseter 2006; Sao and Lehn 2005). This
is particularly true when the grid is weak or when an inverter or a microgrid works in the
stand-alone mode.
In this chapter, the idea of operating an inverter to mimic a synchronous generator is
developed after establishing a model for synchronous generators to cover all dynamics without
any assumptions on the signals. This means that the well-established theory/algorithms used to
control synchronous generators can still be used in power systems when a significant proportion
of the generating capacity is inverter-based. Such inverters are called synchronverters (Zhong
and Weiss 2011). The implementation and operation of synchronverters are described in
detail. The real and reactive power delivered by synchronverters connected in parallel can
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