Abstract
The power quality analysis is an essential issue in the integration of distributed energy resources to the grid. Recent standards regulate the harmonics disturbances due to the increasing penetration of intermittent energy sources interconnected with the grid employing power converters. This paper aims to analyze the power quality of an interconnected wind turbine system based on a Squirrel Cage Induction Generator (SCIG) driven by an Electromagnetic Frequency Regulator (EFR). The steady state of the EFR harmonic model is developed in the stationary frame based on the conventional induction generator modeling, which allows the study of the harmonic disturbances in the electrical and mechanical variables due to the PWM inverter of the EFR’s armature voltage. There is no electrical connection between the EFR and SCIG, and the results show that the inherent system inertia contributes to the mitigation of the harmonic content at the grid side generated by the switching. In addition to the steady-state results, the Total Rated Distortion (TRD), which considers the harmonics and interharmonics components, was computed and presented a good performance compared to the IEEE 1547 standard and real data extracted of a single Doubly Fed Induction Generator (DFIG). Finally, the harmonic performance of the proposed system was evaluated considering the impact of the equivalent Thevenin impedance of the grid at the Point of Common Coupling (PCC).
Highlights
The paper’s key contributions are (1) a generic model of the Electromagnetic Frequency Regulator (EFR) suitable for harmonic, interharmonic, and mechanical disturbances analysis under different operation conditions and (2) analysis of harmonic mitigation of the proposed system based on the limits imposed by the IEEE 1547-2018 standard
Despite the harmonics and inter-harmonics components, it has been shown that the high-frequency components due to the Pulse Width Modulation (PWM) switching are naturally attenuated by the inherent inertia of the mechanical system
By analyzing the grid-side current and detecting harmonic frequency with the maximum current in different working conditions, it is found that the interharmonics of EFR-based systems have typical peaks, smoothly reducing with the increase of the active output power
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. In [18], a mathematical model of DFIG is proposed in the fundamental positive stationary reference frame, dq+ , for the fifth- and seventh-order components of grid voltage harmonics, added to experimental results of distortions in stator and rotor currents and the oscillations in the active, reactive powers, as well as the electromagnetic torque in the stator. The use of a real case of collected data of a DFIG harmonic distortion in PCC is used as an element of comparison with the SCIG driven by the EFR, as both are VSWT and based on the conventional induction generator.
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