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Developing pole-to-ground (PG) fault models for Modular Multilevel Converters (MMC) is not straightforward due to the fault asymmetry and converter switching concerning blocking characteristics. Various studies have been carried out regarding transient simulation of PG faults. However, there is a lack of analytical models for the first stage of the fault. Therefore, this work proposes an approximated analytical model for PG faults in half-bridge MMCs. Closed-form expressions for the MMC contribution to the fault and the fault current are derived. We show that separating the solutions in different resonant frequencies represents the system dynamics and facilitates the interpretation of the phenomena. When compared to system calculated by Ordinary Differential Equations (ODEs), the proposed model provided a good approximation for a wide range of parameters. When compared to the full PSCAD solution, the analytical model was able to precisely calculate the peak fault current value, which confirmed its validity.

With the large integration of converter-interfaced generation (CIG) and widespread of power electronic interfaced technologies, power system dynamic behaviour is becoming progressively faster. As a consequence, is often unclear when to use EMT or Phasor models in grid integration studies. Therefore, this paper presents useful simulation guidelines of Voltage-Source Converters (VSCs) used in AC grid integration studies. It also presents several EMT and Phasor models suited to simulate converter-interfaced generation (CIG) and renewable energy resources connected to power systems. Several modelling approaches and suitability analyses were provided based on a comprehensive comparative study among the models. Various studies were performed in a small system, composed of two generators, and a CIGRE benchmark system, both modelled in Simulink. We address a gap related to the suitability of CIGs phasor models in studies where the boundary between electromagnetic and electromechanical transients overlap. An insightful analysis of the adequate simulation time step for each model and study is also provided.

This article describes a hybrid topology of high-voltage direct current (HVDC) for offshore wind farms using a series connection of a voltage source converter (VSC) and six-pulse diode rectifier (6P-DR). In this topology, the offshore side VSC (OF-VSC) acts as a grid-forming converter to maintain the PCC (point of common coupling) voltage of offshore wind farms (WF) and frequency. In addition, the OF-VSC functions as an active power filter to suppress the 5th, 7th, 11th, and 13th order harmonic current components produced by the 6P-DR, making it almost sinusoidal. Due to the 6P-DR being used in the hybrid converter, this new configuration reduces the total cost of the converters and losses, while preserving the power flow to the onshore gird. Compared to the fully-rated converter and hybrid converter based on a 12-pulse diode rectifier, the power loss and cost are reduced, and in addition, the proposed hybrid converter does not require a phase shift transformer nor a high number of diodes. A 200 MW in an HVDC transmission system using the hybrid configuration was simulated in PSCAD. The results show that the system operated correctly and the harmonic components were filtered.

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increasing the integration of Renewable Energy Sources (RES), such as wind, solar, geothermal, hydro, ocean and biomass. In the same direction, the European Union has set targets for specific levels of RES integration in the future European energy mix, with progressive participation of 20% in 2020, [28] 32% in 2030 and two-thirds in 2050. [24,25,27] These goals are to be achieved considering the participation of all Member States, which are defining their own policies and goals to match the general targets. For instance, Spain has established a target of 42% of RES share on energy end-use by 2030. [74] Germany and France defined a target of 65% and 40% of RES in the final electricity consumption, respectively. [26] In order to achieve the aforementioned targets, realistic power systems models are required, considering a variety of technologies, system topologies, and elements such as high-voltage direct current (HVDC), [78] microgrids, [34] virtual power plants, and dynamic virtual power plants. [53] Various future scenarios are being analyzed for each system and region to ensure that the future energy systems, composed mostly of RES, can remain stable, reliable, match the demand during the seasonal variations across the year, and are economically feasible. These studies are regional by nature as they consider local weather and the availability of resources. Some examples were conducted for provinces or regions, such as Ontario, [55] British Columbia, [63] the New York State, [51] among others. [7,13,31,46] Similar studies have also been performed using data from countries, such as Australia, [15] Bangladesh, [33] Brazil, [72,14] Chile, [54] France, [47] Germany, [66] India, [4] Italy, Pakistan, [71] Portugal, [65,30] United Arab Emirates, [3] and the United States. [52] Other studies have also analyzed systems with an ambitious goal of 100% of RES. [36,50,58,62,81] Moreover, as the number of studies has largely increased, several tools have been proposed to assist the generation expansion planning and RES design, such as EnergyPLAN, [22] EnergyScopeTD, [49] HOMER, [37] LEAP, [75] SILVER, [55] TIMES, [39] among others. [11] However, most of these studies focus on renewable resources while keeping the electrical grid out of their analysis. The contrary is also true for the grids, as several power system benchmarks have been proposed without a clear rationale for the resource type and location in the grid. A few examples are the IEEE and the CIGRE benchmarks. [64] As the power systems are adapting to support a massive integration of RES, both the resources and the Recent environmental policies have led academic, industrial, and governmental stakeholders to plan scenarios with a high share of renewable energy sources (RES), to ensure that future energy systems, composed mostly of RES, can remain stable, match the demand during seasonal variations and are economically feasible. This article considers different energy scenarios to obtain various options in terms of size, generation technologies, and grid configuratio...

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The sharp rise in short-circuit currents of voltage-source converters is still a challenge for DC grid reliability, which imposes stringent requirements on DC breakers. Therefore, fault current limiters are used for slowing down the rise in short-circuit currents. This paper proposes a control-based fault current limiter (CbFCL) for modular multilevel converters (MMCs). The proposed method reduces the fault current purely by control action, thus not incurring costs and not leading to reduced stability, energy storage, conduction losses or the need for maintenance as impedancebased fault current limiters do. The CbFCL does not affect the system in normal operation, acting only in the presence of a fault. The CbFCL performance was evaluated performing simulations of a four terminal DC grid. The results confirmed that the CbFCL was able to limit the fault current of the MMC while keeping the AC currents within their nominal limits, and thus producing a minor impact on the grid operation.