A second order LC filter is assumed at the output of the inverter.
Similar to the control structure commonly employed in
three-phase grid connected inverters and active rectifiers [29,30], a
synchronous reference frame controller is employed here for both
the outer output capacitor voltage and inner inductor current control
loops. A similar approach has been used in [11] where the outer
voltage loop is transformed into the synchronous frame, before being
returned into the stationary frame for the current control loop.
This current loop is a proportional loop with a feed-forward term,
which reduces the need for a large gain to reduce the steady-state
error. Similar control strategies are proposed in [31–33], where the
systems described are either already in three-phase or use delays
to create the orthogonal component.