Low-cost digital implementation of proportional-resonant current controllers for PV inverter applications using delta operator

The performances of the P+Resonant controller in case of current control for a single phase grid connected inverter have been proved to be superior to the PI controller, since it is able to remove the phase error of the control at the fundamental frequency of the grid. It offers also the possibility of selective harmonic compensation. However, in case of digital implementation on a low-cost fixed-point DSP, the limited computational power and the limited numerical representation precision can restrict the utilization of it. The present paper proposes a different way of digital implementation of the P+Resonant controller with selective harmonic compensation on a low-cost fixed-point DSP. The resonant part of the P+R has been implemented as a second order filter based on delta operator. The current controller, together with harmonic compensation for the 3^rd, 5^th, and 7^th harmonics has been successfully tested in practice with a 1.5 KW PV inverter, achieving a 1.2% total harmonic distortion (THD) of the grid current.