Medium power distributed energy resources (DERs) are commonly connected to medium voltage distribution systems via voltage source converters (VSCs). Several guidelines and standards have been developed to establish the needed criteria and requirements for DERs interconnections. In this respect, it is preferred to reinforce the VSC fault ride through (FRT) capability, which considerably minimizes the DG outage period and reconnection time and results in a resilient system against short circuits. Considering the significant number of asymmetrical faults in distribution systems, the VSC response in such conditions must be investigated, and consequently, its FRT capability must be reinforced. In this paper firstly a comprehensive review on existing FRT methods has been presented and discussed. Accordingly, an adaptive virtual impedance-based voltage reference generation method is proposed, which enhances the VSC behavior under short circuits and increases the VSC FRT capability. Also, a fast sinusoidal current reference limiter is proposed to improve the performance. To evaluate the performance of the proposed scheme, state space analysis is presented, and a complete set of simulations is performed in PSCAD/EMTDC environment. Also, a comparison with the conventional method is presented.

This paper proposes a new control scheme to eliminate the $3^{\text{rd}}$ harmonic in the output currents of grid-following inverters under unbalanced grid conditions. Unbalanced grids adversely affect the performance of grid-following inverters due to the oscillations appearing on the DC-link voltage with a frequency twice the line frequency. The paper is based on instantaneous active reactive control (IARC) technique due to its advantages over other existing methods. However, the presence of severe asymmetrical $3^{\text{rd}}$ harmonic distortions in the inverter output currents is the main challenge with IARC method, which impairs the power quality requirements. This paper enhances the IARC scheme by proposing a $3^{\text{rd}}$ harmonic elimination approach by adopting a current reference generation method using the symmetric sequence components concept. Furthermore, the proposed scheme complies with the grid code requirements by injecting the requested reactive current. Finally, the proposed approach is evaluated by theoretical and simulation analysis and validated experimentally using a hardware setup.

Partially shaded (PS) photovoltaic (PV) arrays have multiple peaks at their P-V characteristic. Although conventional maximum power point tracking (MPPT) algorithms are successful when PV arrays are under uniform irradiance conditions (UICs), their tracking speeds are low and may fail to track global maximum power point (GMPP) for PS arrays. Several MPPT algorithms have been proposed for PS arrays. Most of them require numerous samplings which decreases MPPT speed and increases energy loss. The proposed method in this paper gets the GMPP deterministically and very fast. It intelligently takes some samples from the array's P-V curve and divides the search voltage range into small subregions. Then, it approximates the I-V curve of each subregion with a simple curve, and accordingly estimates an upper limit for the array power in that subregion. Next, by comparing the measured real power values with the estimated upper limits, the search region of GMPP is limited, and based on some defined criteria, the vicinity of GMPP is determined. Simulation and experimental results and comparisons are presented to highlight the performance and superiority of the proposed approach.

In this paper, a two stages maximum power point tracking algorithm is presented to track the global maximum power point of photovoltaic systems in partially shaded conditions. The proposed tracker uses an intelligent sampling procedure based on fractional open circuit voltage method and takes initial samples from the power-voltage characteristic of photovoltaic array. Then, it determines the marginal array power around each sample. Using these marginal powers, the samples that definitely are not in the vicinity of global maximum power point are eliminated, and neighborhood of these samples are not searched in global search stage. As a result, the search area gets smaller and global maximum power point is found accurately and rapidly. Furthermore, an algorithm is suggested to estimate module voltage at its maximum power point, which is used in the proposed maximum power point tracker. Eventually, several simulations are carried out through MATLAB/Simulink in order to evaluate the performance of the new tracking method and compare it with recently presented methods. Experimental results are also presented to verify the validity of the developed tracker.