The effect of wind turbines on subsynchronous resonance

Abstract

With the rapid growth of the penetration of wind power into the power system, fixed series compensation is considered as an economic solution to increase power transfer capability. This will render the power system vulnerable to Sub-Synchronous Resonance (SSR). This thesis conducts research on the effect of wind turbines represented by Fixed Speed Induction Generator-Based Wind Turbines (FSIG-WTs) and Fully Rated Converter-Based Wind Turbines (FRC-WTs) on damping SSR. Firstly, SSR is investigated through mathematically modelling IEEE First Benchmark Model (FBM) using MATLAB package. Modal analysis is used to study SSR over a wide range of series compensation percentages. Secondly, the effect of incorporating FSIG-WTs into FBM on SSR is studied over a wide range of series compensation percentage and different power size of FSIG-WTs. Furthermore, the ability of the grid-side converters of the FRC-WTs connected with the FBM to damp SSR occurrence in the steam turbine shafts is evaluated using two different types of control. An optimal controller based on a Linear Quadratic regulator (LQR) has been designed as an auxiliary controller of the grid-side converter of FRC-WTs. A full-order observer was designed to estimate the unmeasured state variables to enable a vii full-state feedback. Finally, eigenvalue sensitivity was studied to choose the most suitable feedback signal for an SSR damping controller. Lead/Lag compensation controller based on the residue method is designed as an auxiliary controller within the grid-side converters of FRC-WTs. Eigenvalue analysis and time domain simulations over widely varying levels of series compensation have been carried out. The simulation studies were carried out in MATLAB and PSCAD. Connecting FSIG-WTs to the FBM increases the range of series compensation level at which SSR can occur. Therefore, it was shown that FSIG-WTs have an adverse effect on the SSR occurring at the multi-mass synchronous generator. If the system is visible, LQR as an auxiliary damping controller within the grid-side converters of FRC-WTs is an effective controller to damp SSR over a wide range of series compensation percentages. Based on eigenvalue sensitivity technique, synchronous generator speed deviation is the most suitable feedback signal for damping SSR occurrence in the steam turbine shafts