Optimised PI-4VPI current controller for threephase grid-integrated photovoltaic inverter under grid voltage distortions

Abstract

This study aims to propose optimised and robust current controller for the transformerless grid-integrated photovoltaic inverter. Challenge of ensuring improved power quality while minimising the DC-component under non-ideal grid condition is at the forefront in the photovoltaic system. In this context, an advanced current controller is designed and developed in the stationary reference frame with proportional-integral (PI) plus four-vector PI (4VPI) controllers. The PI-controller modulates the shape of fundamental current to follow its reference induced from outer DC-link loop. Meanwhile, 4VPI controllers are tuned at the multiple of grid frequencies including third-(3ω0), fifth-(5ω0), seventh-(7ω0), and ninth-(9ω0) to introduce infinite gain and thereby alleviating stationary errors in the current loop of the photovoltaic inverter. The most distinguishing feature of the proposed controller is its inherent control robustness, and therefore, it operates satisfactorily against control delay time and frequency excursion. Traditionally, cumbersome trial-and-error techniques have been largely employed to adjust the PI-VPI controller gains. Nonetheless, tuning of these parameters has made many practitioners switch-off from employing the proposed controller. Given this, the particle swarm optimisation algorithm is proposed. Finally, the practicality of the proposed controller is verified through comprehensive set of simulation and experimental tests conducted on a laboratory-developed prototype using dSPACE-1104.