This paper proposes appropriate analytical expressions
for a deadbeat control system to be implemented in the
output inductor–capacitor–inductor (LCL) filter of a gridconnected
inverter. Unlike in a conventional analysis, the proposed
control algorithm with a settling time of three sampling periods
is derived from the system transfer function in the discretized
time domain instead of the Laplace s-domain. Furthermore, when
introducing the deadbeat control, the independent control of the
integrated active power and that of the reactive power are also
made possible. The experimental results of the proposed deadbeat
control system indicate that the feedbacks from both grid and
inverter currents have similarly high capabilities in attenuating
switching frequency components and damping resonance. Such
proficiency is brought about because the remaining two undetected
control variables of the LCL filter are taken as estimates in
the DSP when introduced to the state observer. However, feedback
from the grid currents can be seen to significantly reduce the total
harmonic distortion of the actual grid currents themselves.