With the increasing penetration of converter-based power sources into the power system, the performance of the converter has become a key factor for enhancing grid reliability, especially during asymmetrical faults. To meet the low voltage ride-through requirements, the converter should feed the reactive power to the grid for voltage support while ensuring the maximum current limitation for the converter’s safety. For such injections, the grid codes are defined. This paper presents a novel and simplified reference current generation scheme to fulfill the requirement of recent grid codes, ensure the current limit of the converter and confirm better utilization of the converter’s current capacity during asymmetrical faults. Moreover, it also discusses the new sequence extraction scheme based on the delay sample method in the stationary reference frame and the control modifications for the negative sequence current injection. The proposed scheme was tested for different priority injection schemes. Its performance was also compared with other control schemes. Detailed simulation studies, in MATLAB/Simulink, were presented to confirm the performance of the proposed scheme under different faulty conditions. The results confirmed the supremacy of the proposed scheme over the available schemes for better utilization of the converter’s current capacity during asymmetrical faults. It also ensured the peak current limitation of the converter while fulfilling the recent grid code requirements. Moreover, the results showed that the new scheme has 10% more current capacity compared to the other schemes due to better incorporation of the angle between the positive and negative phase sequences of the voltage.

The share of renewable energy is increasing day by day. The European Union set its target to double the share of solar and wind power by 2025 and to triple it by 2030. The renewable energy sources are mostly connected to the grid with converters. Due to the large penetration of the converters, the grid operators demand a specific negative sequence current injection from the converters for the safe and reliable operation. The grid codes define the response of the grid connected converters in case of a fault. The conventional control scheme of the converter is unable to operate properly in unbalanced situations. This paper presents a new control scheme for generating the reference converter’s current consisting of positive and negative sequences while ensuring the safety of the converter. It is capable of injecting the negative sequence current to fulfil the recent grid codes, in addition, it complies with the converter’s current limitation. The conventional and proposed methods are compared for different types of unbalanced faults. The results demonstrate the capability of the proposed scheme to fulfil the recent grid code requirements while ensuring the safe operation of the converter.

Due to high penetration of renewable energy in grid, the latest grid codes require that Wind Turbines (WT) stay connected to the grid and provide reactive power support for grid voltage recovery. This paper proposes a technique to improve Fault Ride Through (FRT) capability of a Doubly Fed Induction Generator (DFIG) bases WT system. The proposed technique is implemented through a resistive type Superconducting Fault Current Limiter (SFCL). The SFCL is introduced in two locations in DFIG circuit; firstly in Rotor Side Converter (RSC) and secondly in Grid Side Converter (GSC) to decrease rotor and stator currents respectively. The scheme is tested on a 1.5 MW DFIG based grid-connected Wind Turbine system. Simulation results show that the SFCL at proposed locations limits rotor and stator currents, electromagnetic torque oscillations, DC link over voltage and also help in grid voltage recovery. The scheme efficiently improves the FRT capability of the WT system and fulfills the grid code requirements.

This paper focuses on the enhancement of rotor angle stability (RAS), of IEEE 9-bus system, with the help of Resistive type Superconducting Fault Current Limiter (RSFCL). Different types of faults are applied, and RAS is investigated for different sizes of damper winding and R-SFCL. The damper winding is used to damp out the electromechanical oscillations in rotor angle whereas the R-SFCL is used to reduce the short circuit current. With the combination of damper winding and R-SFCL, the critical clearing time (CCT) can be enhanced. Mathematical model is developed to observe RAS. Through this model, an effective size of R-SFCL is calculated for the generators having different size of damper windings, to enhance RAS in various faulty situations. The results show the effectiveness of the developed model for improving the RAS.

This research paper is focused at the study and implementation of various protection relays and schemes in LabVIEW software for a small power system. The test power system is indigenously developed in the Lab. Hardware implementation is performed by using common modules available in laboratory, whereas interfacing is done by using LabVIEW. Various types of prototype relays are designed and tested for different faults. Performance of hardware relays and LabVIEW designed relays have been investigated. Individual LabVIEW designed relays are tested for real faults through Hardware in the Loop (HIL) simulation. A complete protection scheme of relays is designed for a simple 4-bus parallel-line meshed network. Real-time results for various faults at different buses show that the proposed scheme is accurate and fast.

The increasing share of converter-based renewable energy sources in the power system has forced the system operators to demand voltage support from the converters in case of faults. In the case of symmetric faults, all the phases have equal voltage support, but in the case of asymmetric faults, selective voltage support is required. The grid codes define the voltage support required in the case of symmetric/asymmetric faults, which is the reactive current injection in the respective sequence proportional to its voltage dip, but studies confirm that it does not result in a minimum unbalance factor in the case of asymmetric faults. The unbalance factor is an indication of the level of imbalance voltage among the phases. Moreover, it also results in fluctuated active power injection in the case of asymmetric faults, which causes dc link voltage fluctuations, and the power reversal may also occur due to such fluctuations, which leads to higher protection costs for the dc link. In order to (1) enhance the uniformity of voltage among different phases in the case of asymmetric faults and (2) minimize the real power fluctuations in such conditions, a novel control scheme is presented in this paper. It optimally distributes the negative sequence current phasor into its active and reactive components to achieve the minimum voltage unbalance factor. It also confirms the minimum real power fluctuations by adjusting the positive and negative sequence current phasors. The proposed scheme also ensures the current limit of the converter. The proposed scheme is developed in Matlab/Simulink and tested under different faulty conditions. The results confirm the better performance of the proposed scheme against the grid code recommendation under different faulty conditions.