Nonlinear Controllers Based on Exact Feedback Linearization for Series-Compensated DFIG-Based Wind Parks to Mitigate Sub-Synchronous Control Interaction

Penghan Li,Jie Wang,Linyun Xiong,Fei Wu

doi:10.3390/en10081182

Abstract

The increasing penetration of wind power in the grid has driven the integration of wind farms with power systems that are series-compensated to enhance power transfer capability and dynamic stability. This may lead to sub-synchronous control interaction (SSCI) problems in series-compensated doubly-fed induction generator (DFIG)-based wind farms. To mitigate SSCI, nonlinear controllers based on exact feedback linearization (EFL) are proposed in this paper. Before deriving the control laws, the exact feedback linearizability of the studied system is scrutinized. Frequency scanning analysis is employed to test the designed EFL controllers. Moreover, the performance of the EFL controllers is compared to that of classical proportional-integral (PI) controllers. A series-compensated 100 MW DFIG-based wind park is utilized to assess the performance of the designed controllers through the alleviation of sub-synchronous resonance. Analyses of the studied system reveal that the resistance is negative under sub-synchronous frequency conditions, whereas the reactance becomes negative at approximately 44 Hz. The designed EFL controllers effectively alleviate SSCI and result in positive reactance and resistance values within the whole sub-synchronous frequency range. The results from the frequency scanning method are also validated through the time domain simulation and the eigenvalue analysis.

Highlights

In recent years, wind energy has been the fastest-developing type of renewable resource compared to other green resources
When doubly-fed induction generator (DFIG)-based wind parks are connected to the grid through capacitive series compensation, there can be a risk of sub-synchronous resonance (SSR), even though the compensation level is not too high
Wind parks, this paper proposes nonlinear controllers based on an exact feedback linearization (EFL)

Summary

Introduction

Wind energy has been the fastest-developing type of renewable resource compared to other green resources. Variable speed generator wind turbines are predominating in China, North. Over the last few decades, the doubly-fed induction generator, an important type of variable speed generator wind turbines, has drawn much attention owing to its independent power control and low converter rating [2,3]. The integration of huge-scale DFIG-based wind parks requires the considerable upgrading of distribution and transmission infrastructures. Capacitive series compensation, a classical type of such upgradation, is an economical method for increasing dynamic stability and power transfer capability in transmission lines [4,5]. When DFIG-based wind parks are connected to the grid through capacitive series compensation, there can be a risk of sub-synchronous resonance (SSR), even though the compensation level is not too high. SSR is a condition in which the wind park exchanges energy with the electric network at one or more natural frequencies of the mechanical or electrical part of the system [6]

Methods

Results

Conclusion