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This paper presents an alternative control scheme for offshore wind turbines (WTs) connected to the mainland grid through high voltage dc (HVDC) links based on voltage source converters (VSCs). The proposed WT controller inherently provides rapid droop-type frequency response, without the need to implement an additional WT frequency controller. A coordinated control approach is proposed between the WT and HVDC controllers in order to achieve fault ride-through (FRT) and frequency response capabilities, relying solely on offshore frequency modulation. To demonstrate the FRT capability of the VSC-HVDC link, a detailed EMT-type model is first developed in Matlab/Simulink, where onshore grid faults are tested. Then, the offshore wind farm is connected to a study case system in order to assess the contribution of the VSC-HVDC link to frequency regulation, by exploiting the proposed WT controller along with the communication capability between the two HVDC VSCs. [ABSTRACT FROM PUBLISHER]

Increasing penetration of Renewable Energy Sources (RES) to the power systems leads to the continuous evolution of grid interconnection requirements, which now include Low Voltage Ride Through (LVRT) practically for all types of generating units connected to the MV or HV networks, including photovoltaics (PV). It is essential that the Distributed Generation (DG) models used in power system studies properly represent the enhanced response characteristics of the stations. In this paper, a model is presented for a PV system with grid-code compatibility, which is suitable for power system dynamic and transient analysis studies. For this purpose, an overall control strategy is introduced to achieve LVRT capability, while elements essential for the correct representation of the dynamic performance of the system, such as the Phase Locked Loop (PLL) and the output LCL filters, are properly accounted for. Time domain simulations are provided for balanced and unbalanced voltage dips, in order to demonstrate the performance of the PV system and evaluate the accuracy of the proposed simplified model. The response of the detailed switching model is also included in the simulation results. [ABSTRACT FROM AUTHOR]

Photovoltaic (PV) system performance is influenced by several factors, including irradiance, temperature, shading, degradation, mismatch losses, soiling, etc. Shading of a PV array, in particular, either complete or partial, can have a significant impact on its power output and energy yield, depending on array configuration, shading pattern, and the bypass diodes incorporated in the PV modules. In this paper, the effect of partial shading on multicrystalline silicon (mc-Si) PV modules is investigated. A PV module simulation model implemented in P-Spice is first employed to quantify the effect of partial shading on the I–V curve and the maximum power point (MPP) voltage and power. Then, generalized formulae are derived, which permit accurate enough evaluation of MPP voltage and power of mc-Si PV modules, without the need to resort to detailed modeling and simulation. The equations derived are validated via experimental results. [ABSTRACT FROM PUBLISHER]

Autonomous power systems, such as those existing in small and medium-size islands, typically consist of medium voltage networks fed by conventional power stations and present characteristics not typical for large interconnected grids. In this paper, results are presented and analyzed from a power-quality measurement campaign, conducted in a diesel-powered island system with significant wind penetration. Emphasis is placed on the voltage flicker, which was found quite increased under all operating conditions. It is shown that the diesel engines of the conventional power station are the main source of flicker in the system, due to the pulsed variation of their torque. The operation of the wind farms, on the other hand, does not result in any notable deterioration of the voltage quality level in the system. [ABSTRACT FROM AUTHOR]

In this paper, new expressions are introduced for the determination of the maximum power point (MPP) of photovoltaic (PV) systems as explicit functions of the five parameters of the single-diode model employing the Lambert W function. These equations provide the voltage and current at MPP in a direct and straightforward manner, thus dispensing with any need for iterative solution. They are initially derived for a PV system operating under uniform conditions, and subsequently extended for mismatched conditions at the PV string level. The novelty of these formulae lies in their solid theoretical foundation, which supports their validity in the general case and offers a well-founded symbolic formulation for the MPP evaluation problem. Extended simulations and experimental validation are performed to verify the accuracy and computational efficiency of the proposed equations compared with other methods available in the literature. [ABSTRACT FROM AUTHOR]