Power converters in the system-level real-time simulation are usually emulated by L/C-based associated discrete circuit (L/C-ADC). However, the L/C-ADC approaches may suffer from two issues: how to mitigate the unacceptable virtual power loss especially in high-frequency applications, and how to tune LC parameters setting which is affected by the external circuit. This paper proposes a novel generalized associated discrete circuit (G-ADC) model with parameterized history current sources. By utilizing the stability region of the feasible parameter space, the optimized G-ADC models with the best damping characteristic are developed for both two-level and three-level converters. The analytical results also guarantee that the parameters of the optimized G-ADC model are independent of the external circuit for most power grid applications. Furthermore, an FPGA-based real-time simulation platform is built to verify the feasibility of the proposed scheme. Extensive simulation and hardware-in-loop (HIL) experiment results demonstrate the effectiveness and superiority of best-damped models as well as the modeling flexibility corresponding to insensitivity to operating conditions and external system parameters.

Wind power is the fastest growing and environmentally sustainable source of energy among all available renewable energy resources. The primary objective of this paper is to analyze the wind characteristics and power potential at Hyderabad, Southeastern province in Pakistan. Two years of wind speed data measured at 10 m above ground level (AGL) have been considered in this study. The annually, monthly, and seasonal variations in wind speed were analyzed, and minimum, maximum, and average values of recorded wind speeds are presented in this paper. Weibull and Rayleigh distribution functions have been applied to analyze the wind characteristics and evaluate the wind power potential of the proposed site. The Weibull shape k and scale c parameters have been estimated using the Weibull function. The higher values of k showed that the wind speed is steady at the site. The average wind speed was found above 6 m/s throughout the year. The most probable wind speed (V_mp) and maximum carrying energy (V_maxE) wind speed were also calculated using Weibull parameters. Root mean square error (RMSE), the coefficient of determination (R²), and mean bias error (MBE) were computed to ensure the good fit of Weibull distribution function. The annual average wind power and energy densities were estimated at more than 255 W/m² and 2245 kWh/m², respectively. The power density calculated by Weibull and Rayleigh functions was compared with that calculated by using measured wind data. The energy output and capacity factor of different commercially available wind turbines (WTs), i.e., power ratings from 0.33 to 2.75 MW, have been calculated. The cost of energy was estimated and ranged from $19.27 to $32.80 per MWh. Wind power potential and economic analysis of the collected data reveals that the site is suitable for developing wind power generation projects to power the local communities.

The power fluctuations and utilization of renewable energy sources (RESs) in green seaports call for more flexible facilities to reduce their overall operation costs and carbon emissions. This paper proposes a robustly coordinated operation strategy for the multiple types of energy storage systems in the green-seaport energy-logistics integrated system to minimize the daily operation cost and carbon emission under the carbon trading policy, considering the uncertain power of local loads (LLs), photovoltaics (PVs), as well as wind turbines (WTs). At the day-ahead decision stage, the power of all energy storages, electro-thermal conversion (ETC) unit, reefer containers, quay cranes (QCs), yard cranes (YCs) are optimized under the worst case. At the intra-day decision stage, the power of tie line (TL), PVs, and WTs are determined sequentially according to short-leading-time predictions of uncertain values. The day-ahead optimization is formulated as a robust optimization problem solved by column-and-constraint generation (C&CG) algorithm, whereas the intra-day optimization is solved as a deterministic optimization problem. Numerical simulations are carried out to verify the effectiveness of the proposed strategy. Simulating results show that the proposed strategy can achieve the lowest cost and guarantee the feasibility of the operation scheme under different scenarios.

When single-phase-to-ground (SPG) or phase-to-phase (PP) faults occur on collection lines of an offshore wind farm with modular multilevel converter-based high voltage direct current (MMC-HVDC) transmission, the fault current level may be low or even approach zero due to the controlled current at both ends of the collection line. As a result, the traditional current differential protection may malfunction. To address this issue, a method is proposed that utilizes open circuit characteristics of the negative-sequence network to indirectly calculate the fault point negative-sequence voltage by the negative-sequence voltage at the protection installation location. The fault distance can then be determined. The introduction of a twiddle factor eliminates the influence of fault resistance, improving the accuracy of fault distance calculation. Based on this calculated fault distance, a high-sensitivity differential protection scheme is proposed. This proposed protection can maintain sufficient sensitivity and trip correctly during collection line SPG and PP faults. It solves the issue of traditional current differential protection malfunctioning in low-fault current scenarios of transmission lines with inverter-based resources (IBRs) on both ends. In addition, it can adapt to different reactive power support strategies and operation modes of offshore wind farms. Test results indicate the effectiveness of the proposed protection.

With the rapid development of renewable energy, multi-terminal flexible DC grids composed of modular multilevel converters have been widely used in power systems. To ensure the safe and stable operation of a DC grid, this paper proposes a DC line protection scheme for MMC-based DC grids using AC/DC transient information. In the proposed scheme, the difference between the transient voltage root mean square ratios (DTVR) on both sides of the current-limiting inductor of DC lines is used to identify the DC line fault, and the instantaneous zero sequence voltage (IZSV) of the AC side of the converter station is used to discriminate the faulted poles. According to the theoretical analysis result, a fault criterion setting method suitable for faulted pole discrimination is proposed. The proposed scheme is based on local information and tested in a PSCAD/EMTDC model of a four-terminal MMC-based DC grid. The simulation results show that the scheme can fast and accurately identify faults.

The increasing penetration of renewable energy sources (RESs) in modern green seaports calls for more flexible management approaches that can minimize the daily seaport operation costs and RES curtailments. This paper establishes an optimal strategy in two-time intervals for flexible operations of energy storage systems and combined electric-thermal power demands of reefer containers in the coordinated green-seaport energy-logistics systems (ELS). For the day-ahead operation, a multi-stage stochastic optimization model is established to minimize the expected ELS operation cost according to the 24-hour-ahead forecasts. Uncertainties of RES power outputs, load demands, electricity prices, and ambient temperatures are considered in the optimization of day-ahead operation. For the intra-day operation, hydrogen, battery, and thermal storage systems as well as reefer containers operations are optimized based on the short-lead-time forecasts. Numerical simulations are carried out based on the Jurong seaport operation in Singapore to verify the effectiveness of the proposed optimal operation strategy for the coordinated green-seaport ELS. Simulation results reveal that the proposed strategy can achieve the lowest operation cost and the lowest RES curtailment in a green-seaport.