Full-scale converter-interfaced renewable energy sources (CIRESs) can cause misoperation of distance relays installed in their vicinity. Such failure stems from the different fault behavior of CIRESs and synchronous generators (SGs), based on which available relays have been developed. Several measures have been devised to secure the performance of distance protection by modifying existing relays. This paper proposes a new approach to address misoperation of distance relays during asymmetrical faults by regulating the fault currents of CIRESs such that available distance relays function properly without requiring modification. The prime objective of this method is to mimic certain features of the symmetrical components of SGs' fault currents that affect distance relays. In the meantime, the proposed method satisfies the constraints of a converter, such as its limited phase current magnitude. As a result, correct operation of the distance relays close to CIRESs is ensured regardless of the fault conditions, including its type, resistance, and location. Some salient features of the proposed method are its simplicity, compatibility with off-the-shelf relays, and independence from the voltage and power rating of the CIRES. Moreover, the proposed method uses only local measurements, and so is cost-effective. PSCAD/EMTDC simulation studies verify the performance of this new method.

Directional, phase-selection, and distance elements of a relay are prone to misoperation in the presence of inverter-based resources (IBRs). To address these problems, modifications of relay elements as well as new control schemes for IBRs have been proposed in the literature. These methods focus mainly on addressing the misoperation of only one of the above relay elements. The available solutions that are based on a new control system focus only on the negative-sequence current loop. Thus, they work only for unbalanced faults. This paper proposes a comprehensive dual current control scheme for IBRs during all types of faults such that all of these relay elements operate correctly. The proposed method controls the IBR to operate as a voltage source behind a virtual impedance in the positive-sequence circuit, and a single impedance in the negative-sequence circuit, thereby emulating the phase angles of a synchronous generator's (SG's) fault current. The proposed method also maximizes the active, and reactive current generation of the IBR during faults, and emulates the incremental sequence current magnitudes of an SG. The proposed method does not require altering the relay elements. Moreover, correct operation of the relay elements is achieved regardless of the fault type, resistance, and location. The effectiveness of the proposed method is verified through not only simulation studies, but also hardware-in-the-loop testing of commercial relays.

This paper presents a planning model that utilizes mobile energy storage systems (MESSs) for increasing the connectivity of renewable energy sources (RESs) and fast charging stations (FCSs) in distribution systems (DSs). The proposed planning model aims at enabling high penetration levels of green technologies while minimizing the total DS cost that includes investment, operating, and emission costs. The proposed model determines the optimal MESS sizes and transportation schedules as well as the optimal sizes and locations of wind-based distributed generators (DGs), photovoltaic (PV) DGs, and FCSs. The model takes into account techno-economic and environmental factors in addition to the power variations of RESs, FCSs, and load demands. The proposed planning model is applied on two benchmark test systems (i.e., 33-bus and 69-bus DSs). To evaluate the efficacy of the proposed model, the results obtained from the model are compared to those obtained from a traditional planning technique. The comparison of the results demonstrates that the proposed model with MESSs successfully achieves a significant cost saving and increases the penetration levels of RESs and FCSs.

Inverter-interfaced distributed generators (IIDGs) are characterized by their low fault current contributions that im-pose a major challenge for microgrid protection. This paper pro-poses a new overcurrent protection strategy that utilizes a third harmonic voltage generated by the IIDG controller during short-circuit faults. By generating harmonic voltages, a new current flow layer in the harmonic domain is created during faults and is inde-pendent of the fundamental fault current, which is limited by IIDGs. A harmonic time-current-voltage directional relay is devel-oped based on the measured harmonic currents and voltages at the relay location to ensure optimal protection coordination (OPC) for isolated microgrids. The OPC with the proposed relay character-istics is formulated as a nonlinear program and equipped with a harmonic short-circuit current calculation method to determine the optimal relay settings. The 9-bus Canadian test system and the IEEE 33-bus system are adopted to validate the operation of the proposed OPC. Simulation results demonstrate that the proposed harmonic time-current-voltage directional relay is capable of de-tecting the direction of the fault current and maintaining precise protection coordination without the need for communication.

The significant differences between the fault current signatures of inverter-interfaced distributed generators (IIDGs) and conventional synchronous generator (SG)-based sources can lead to misoperation of the existing phase selection methods that operate based on the angles of sequence currents. Consequently, a selective phase reclosing/tripping scheme cannot be applied by the protection system of a microgrid, resulting in reduced resilience during asymmetrical faults. This paper develops a dual control scheme that regulates the sequence components of an IIDG current during short-circuits such that the existing phase selection methods accurately select the faulty phase(s). The proposed scheme adds a controllable voltage source and a virtual impedance to the negative-sequence circuit of an IIDG model. These newly added components are tuned to make the sequence current angles of an IIDG during asymmetrical faults similar to those of an SG while thermal limits of inverter switches are satisfied. As a result, the protection system can trip only the faulty phase(s) and the microgrid resilience during unbalanced short-circuits is substantially improved. A comprehensive performance evaluation confirms the effectiveness of the proposed control scheme under different fault conditions.

The unique fault current signatures of inverterinterfaced renewable energy sources (IIRES) hinders the correct operation of the existing phase selection methods that operate based on the sequence currents. As a result, the system resilience during unbalanced faults is imperiled. In this paper, a new dual current controller is developed to regulate the relative angles of the IIRES sequence currents during unbalanced faults to enable accurate identification of the fault type by the existing phase selection methods (PSMs). The proposed method consists of three design stages. In Stage I, the IIRES control system identifies the fault type using the sequence voltages at its terminal. Stage II aims at generating the appropriate reference angle for the IIRES negative-sequence current. In Stage III, the IIRES sequence currents are controlled in the double synchronous reference frame to track the reference angle. The proposed controller makes the existing PSMs immune against fault conditions and reactive current generation requirements imposed by grid codes. Consequently, the protection system can select and trip only the faulted phase(s), and thus, the system reliability is considerably enhanced. Time-domain simulations are used to confirm the successful operation of the proposed controller under different fault conditions and grid codes.