Modeling and mitigation of harmonic resonance between wind turbines and the grid

Abstract

Harmonic resonance can happen in traditional power systems between power factor correction (PFC) capacitors and transformer leakage inductance. In a distribution network with high penetration of renewable generation sources, inverter PWM harmonic currents can be a source of harmonic excitation for system resonance. This paper discusses harmonic resonance problems caused by impedance interactions between the wind inverter and the grid. An impedance-based analysis approach is used to characterize such resonance. Modeling of inverter output impedance directly in the phase domain to enable such analysis is presented. Possible mitigation methods by active damping and grid synchronization design are presented, and their effectiveness demonstrated by simulations and experiments.

Analysis of phase-locked loop influence on the stability of single-phase grid-connected inverter

“…PLL and current control, and grid impedance [2]. A well-established technique to analyze such interconnected systems is the impedance-based stability analysis with Nyquist stability criterion [6], [10], which predicts the system stability based on the ratio between the grid impedance and inverter output admittance.…”

Modeling and Analysis of Resonance in LCL-Type Grid-Connected Inverters under Different Control Schemes

“…If we assume that the inverter is stable when connected to a grid with zero impedance, and the grid is stable when an ideal current source with infinite impedance is connected to it, then the interconnected system is stable only if the impedance ratios Zg/Z0 conform with the Nyquist stability criterion. Considering a three-phase system, both the positive-and negative-sequence impedance should conform with this criterion, but the positive-sequence impedance turns out to be more critical in terms of stability [21]. Therefore the following analysis mainly aims at comparing the impedance ratio Zg/Z0p.…”

Small-signal stability analysis of offshore wind farms with LCC HVDC

“…The basis of the analysis is the impedance-based system stability criterion developed in [7] for grid-connected converters that are controlled as current sources. This method has been proven effective in predicting harmonic resonances involving single-phase [8] as well as three-phase inverters [9] connected to weak ac grids. The offshore ac bus is an ultimate weak grid as there is no rotating machine behind it.…”