Abstract—A higher order passive power filter (LLCL-filter) for
the grid-tied inverter is becoming attractive for industrial
applications due to the possibility to reduce the cost of the copper
and the magnetic material. However, similar to the conventional
LCL-filter, the grid-tied inverter is facing control challenges. An
active or a passive damping measure can be adopted to suppress
the possible resonances between the grid and the inverter. For an
application with a stiff grid, a passive damping method is often
preferred for its simpleness and low cost. This paper introduces a
new passive damping scheme with low power loss for the
LLCL-filter. Also a simple engineering design criterion is
proposed to find the optimized damping resistor value, which is
both effective for the LCL-filter and the LLCL-filter. The control
analysis and the power loss comparison for different filter cases
are given. All these are verified through the experiments on a 2
kW single–phase grid-tied inverter prototype using proportional
resonant controllers. It is concluded that compared with the
LCL-filter, the proposed passive damped LLCL-filter can not
only save the total filter inductance and reduce the volume of filter,
but also reduce the damping power losses for a stiff grid
application.