The main objective of this research is to propose an active and reactive power injection control in order to mitigate voltage sags. The proposed control strategy works in conjunction with a modified version of an automatic voltage regulator (AVR), where it will act on the active and reactive powers injected by the inverter to reduce the effects of voltage sags. In this way, the control will avoid possible shutdowns and damage to the equipment connected to the grid. The voltage improvement can be perceived for consumers connected to the power system. Modifications in AVR model and parameters are performed to speed up its performance, thus identifying the short-duration voltage variations (SDVV) and, consequently, the control acts to alter the powers, decreasing the active power injection and increasing the reactive power based on inverter capacity during the momentary voltage dip (MVD). Finally, when the fault is cleared, all values return to the pre-fault condition, so that the inverter only operates with active power. A 75 kW three-phase grid-connected photovoltaic system (GCPVS) equipped with the proposed control was inserted in a distribution grid of the city of Palmas, state of Tocantins, Brazil, and all of the computer simulations were performed on the Matlab/Simulink^®.

This work aims to present a control proposal for dual-stage photovoltaic inverters to supply reactive power aiming at voltage stability in steady state and during short-term momentary sags. For this, a study was carried out on the control and modeling techniques of the DC/DC and DC/AC converters of the photovoltaic generating unit, in addition, a modified MPPT algorithm was implemented that, together with an AVR system, will manage the power in transient regime, decreasing the active power and increasing the reactive power in order to restore the voltage level in the grid. In addition, the dynamic saturation of the current in the switches and the power of the inverter was carried out so that they operate within their nominal limits. The entire system was executed in a computational environment on the Matlab/Simulink platform. Satisfactory results were obtained regarding the supply of reactive power and assistance in voltage restoration carried out by distributed generation during momentary sag.

This paper aims to present a preliminary study of the behavior of a distribution network with the penetration of grid-connected photovoltaic (PV) system. The work used measurements and data from an area of Palmas, the capital of Tocantins state, Brazil, which is attended by the power utility CELTINS. Three cases were analyzed here: (1) at a given daytime with the original distribution system, (2) at the same time with part of the distribution grid supplied by grid-connected PV systems, and (3) at a given nighttime. All the simulations were performed with PSAT software.

With a great potential yet to be explored in Brazil, the grid-connected photovoltaic system, besides supplying the active power, can also contribute to improve the voltage level grid providing reactive power. Therefore, this work proposes to use a Grid-Connected Photovoltaic System (GCPVS) equipped with a control that uses the automatic voltage regulator (AVR) to balance the injection of the active and reactive powers, thus softening the short-duration voltage variation, more specifically the momentary voltage dip. For this purpose, the GCPVS was connected in part of a real distribution grid that attend the block 1106 South of Palmas city, state of Tocantins, northern region of Brazil. It is shown that the active and reactive power delivered to the grid can be controlled to help the power quality of the main grid during a disturbance. During a short-circuit situation, the active power is reduced, freeing up space from the inverter capacity for maximum supply of reactive power, in this way, helping the main grid to return to an adequate voltage level. The simulation results show that such voltage profile improvement is possible. Therefore, they confirm that photovoltaic systems, even though considered small, can also provide ancillary services to the low voltage distribution grid during abnormal conditions, adding to the actions normally performed by conventional power plants