Voltage sags can be symmetrical or unsymmetrical depending on the causes of the sag. At the present time, one of the most common procedures for mitigating voltage sags is by the use of dynamic voltage restorers (DVRs). By definition, a DVR is a controlled voltage source inserted between the network and a sensitive load through a booster transformer injecting voltage into the network in order to correct any disturbance affecting a sensitive load voltage. In this paper, modelling of DVR for voltage correction using MatLab software is presented. The performance of the device under different voltage sag types is described, where the voltage sag types are introduced using the different types of short-circuit faults included in the environment of the MatLab/Simulink package. The robustness of the proposed device is evaluated using the common voltage sag indices, while taking into account voltage and current unbalance percentages, where maintaining the total harmonic distortion percentage of the load voltage within a specified range is desired. Finally, several simulation results are shown in order to highlight that the DVR is capable of effective correction of the voltage sag while minimizing the grid voltage unbalance and distortion, regardless of the fault type.

In this paper, the hosting (or maximum allowable) capacity of a photovoltaic (PV)-based distributed generation (DG) unit for a typical two bus distorted distribution system, is analyzed. The harmonic constraints, total and individual harmonic distortion limits stated in IEEE Standard 519, and the conventional hosting capacity constraints, bus rms voltage limit and the current carrying capability limit of the supply cables are taken into account. In the analysis, various simulations are carried out to show the effect of the nonlinearity degrees of the loads on the system's hosting capacity. It is clearly seen from the analysis results that the harmonic distortion limits significantly constrain the PV-based DG unit hosting capacity for the higher nonlinearity levels of the consumer. Accordingly, a C-type filter is designed to maximize the hosting capability of the studied system while providing desired power factor and satisfying the harmonic and conventional hosting capacity constraints. Besides, the numerical results are given to point out that a higher allowable hosting capacity is obtained with the proposed filter design approach compared to two traditional filter design approaches, which aims to attain minimization of voltage total harmonic distortion and minimization of current total demand distortion by considering the same constraints of the proposed approach. It is found that passive filters, already planned in the original system, helps in improving the PV-based DG hosting capacity of distribution feeder.