Dynamic Performance Improvement of a Grid-Tied PV System Using a Feed-Forward Control Loop Acting on the NPC Inverter Currents

This paper presents a three-phase grid-connected photovoltaic (PV) system, which is implemented using the neutral-point-clamped (NPC) inverter. A current feed-forward control loop (FFCL) is proposed to improve the PV system dynamic behavior, due to the PV array being constantly subjected to sudden solar irradiance change, which causes voltage oscillations in the dc bus and, hence, interferes in proper PV system operation. As the current FFCL acts to speed up the calculation of the inverter current references, the dynamic response of the currents injected into the grid is improved. As a consequence, the dynamic behavior of the dc-bus voltage is also enhanced, reducing both settling time and overshoot. Besides the injection of active power into the grid, the PV system is also controlled to perform active power-line conditioning, so that load harmonic currents are suppressed, as well as load reactive power is compensated. However, the NPC inverter must be properly designed to guarantee that its power rating will not be exceeded, since both fundamental and nonfundamental current components flow through the grid-tied inverter. Extensive experimental results based on a digital signal processor are presented in order to evaluate the effectiveness, as well as the static and dynamic performance of the PV system.