A modified division-summation digital control for grid-connected inverter with wide inductance variation of LCL filter

The natural swinging filter inductance due to core's magnetic permeability can affect control stability. Conventional control methods generally adopt larger cores to avoid this issue. Division-Summation (D-Σ) digital control, on the other hand deals with the problem by including this filter inductance variation in the control law. It allows the use of much smaller core than conventional control methods for the same power rating. Non-linear model of filter inductor is used to estimate the inductance in each switching cycle. This estimate is used to achieve optimal control and no further proportionality constant parameter tuning is required. However, wide variation in both inverter-side and grid-side inductance needs to be considered with LCL filters. A modified D-Σ digital control method is presented in this paper to address this issue. The compensation term for active damping of resonance is also logically derived. Experimental results measured from a 5 kW single-phase grid-connected inverter have verified the feasibility of the proposed method.