Autotuning of Digital Deadbeat Current Controllers for Grid-Tie Inverters Using Wide Bandwidth Impedance Identification

By injecting a wide-bandwidth small-amplitude test sequence into the inverter's pulsewidth-modulated control signal and by utilizing digital network analyzer techniques, an accurate estimation of the inverter's output inductance can be obtained without external equipment and under realistic operating conditions, which is important given the nonlinear characteristics of commonly used powdered iron cores. This knowledge can be then leveraged to tune the inverter's digital deadbeat controller for optimal performance, i.e., reaching the desired reference in n switching cycles, where n is the order of the system. A pseudorandom-binary-sequence-based injection sequence is chosen for its wideband spectral content. Experimental results demonstrate the improvement in the output-current total harmonic distortion obtainable with the proposed approach.