Modeling and control for new LLCL filter based grid-tied PV inverters with active power decoupling and active resonance damping capabilities

LLCL filters utilization decreases single-phase transformerless inverters' AC-Side volume significantly. Conversely, the inherent 2nd order power harmonic ripples burden inverters' DC-Side. In fact, the passive solution to buffer these ripples imposes a threat to inverter's reliability and power density. Hence, varieties of active power decoupling methods were introduced in the literature to improve inverter's DC-Side volume and system's reliability. Yet, most existing techniques require auxiliary power electronics and energy storage elements. This contradicts the goal of optimizing system's overall power density. Therefore, a novel LLCL filter for grid-connected applications is introduced that merges AC-Side and DC-Side volume minimization methods without additional power electronics devices. Precisely, the common-mode (CM) operation is harnessed for active power decoupling and the differential-mode (DM) is utilized for active power injection. Besides, the stability analysis of the proposed system revealed that the CM and DM are resonating. Thus, an active resonance damping control scheme based on decoupled CM and DM capacitor currents feedbacks was developed. With the proposed topology, the DC-link capacitor was reduced 40 times compared to the passive solution. The robustness of the proposed solution to the grid-side inductance variation was also verified and validated on 750 W prototype system.