Optimized Dual Loop Control Strategy for Grid-Connected Interleaved Inverters

Abstract

The topology of interleaved inverters is preferred over conventional two-level inverters because of reduced current harmonics due to its ripple cancellation effect and high power rating through paralleling of low power devices with improved availability. This topology also reduces the filter components’ size compared to conventional 2-level inverters, resulting in increased bandwidth and high harmonic impedance to the utility distortion. However, interleaved topology requires a more complex control strategy to maintain the current regulation and system stability. When an LCL filter is used, the control strategy becomes even more complex because of its resonance phenomena. This paper presents a two-loop analysis for grid-connected interleaved inverters with LCL filters. The outer loop regulates the current and ensures reference tracking, while the inner loop improves the stability and dampens the resonance. Stability analysis and the effect of harmonic impedance offered to the grid voltage by inner feedback variables are discussed in detail. Using a dual-loop control strategy, both controller and LCL filters are optimized with the help of a genetic algorithm. The filter is minimized such that the THD of the output current is below the limit set by IEEE 1547 Std. Moreover, the controller is optimally tuned to offer maximum attenuation to the current harmonics. The system that includes an interleaved inverter along with the proposed control scheme and optimized filter has been implemented in MATLAB Simulink. Simulation results presented show the effectiveness of the proposed strategy.