Three-phase grid-connected PV system operating with feed-forward control loop and active power-line conditioning using NPC inverter

Abstract

This paper presents a single-stage three-phase grid-connected photovoltaic (PV) system, which is implemented using the three-level neutral-point-clamped inverter. The PV system operates with an additional feed-forward control loop (FFCL), in order to improve the dynamic behavior of both dc-bus voltage and inverter currents, when the PV array is subjected to abrupt insolation changes. In other words, sudden solar radiation changes can cause large voltage oscillations on the inverter dc-bus, interfering in an adequate PV system operation, due to the generation of the inverter current references are computed taking into account the dc-bus voltage control loop. Thus, the use of the FFCL reduces the settling time and overshoot/undershoot of the dc-bus voltage. Moreover, the dynamic response of the currents injected into the grid are also improved. Simultaneously, the PV system is able to perform the active power-line conditioning by suppressing load harmonic currents and performing reactive power compensation. Although the FFCL can be used in conjunction with any maximum power point tracking technique, perturb and observe technique is adopted to generate the dc-bus voltage reference. Simulation results are presented in order the evaluate the performance, as well the effectiveness of the PV system operating with the proposed FFCL.