Abstract
There are significant concerns regarding the stability of increased wind power generation in weak power grids. This paper investigates and improves the stability of Wind Turbine Squirrel Cage Induction Generators (WT-SCIGs) with series compensation and weak interconnections to the power grid. Detailed time-domain and state-space modeling have revealed new bifurcations and oscillatory modes for a WT-SCIG connected radially to a weak grid through a series compensated line. The stability domain analyses are carried out by computing bifurcations in the system by analyzing eigenvalues of the linearized system. The analyses demonstrate for the first time how the degree of compensation at which the Hopf bifurcation occurs depends on the X/R ratio of the line, operating slip of the induction generator, and voltage regulator parameters as well as the time delays in measurements. A new damping controller is proposed, which greatly improves the dynamic stability of the WT-SCIG and eliminates destructive Hopf bifurcations in weak grids for a wide range of series compensation. This allows for a much larger percentage of series compensation than what is usually possible, while avoiding instabilities, thereby maximizing the power transfer capability.
Highlights
The critical bifurcations encountered in this study are the Hopf bifurcation and the saddle-focus [15] bifurcation, which result in a change in the stability of the equilibrium point
There is a possibility of nonoscillatory instability for small values of percentage series compensation at higher wind speeds due to the presence of a saddle-focus equilibrium point, resulting in an unstable node
In addition to a Hopf bifurcation, a node-focus bifurcation is introduced into the system, which may not affect the stability of the system
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Utilizing series capacitors in power systems is one of the most economical ways to improve the power flow through existing transmission lines [1]. The level of series compensation is often limited in many systems by the existence of Hopf bifurcations giving rise to subsynchronous resonance (SSR), which has been known to cause severe instabilities in transmission systems [2,3,4]
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