Stability Analysis of Large Wind Farms Connected to Weak AC Networks Incorporating PLL Dynamics

Abstract

Voltage source converter interfaced wind turbines connected to weak grids can induce system instability. A state space model is used in this paper to study the stability of large wind farms. Dynamics of the phase locked loop is integrated to the state space model. The advantage of this model is that it allows study the stability of systems with parallel wind turbines. Studies on the dynamic responses of the system show the importance of including phase locked loop as its existence can induce system instability especially under weak network conditions. This model can be used to study the stability of converter interfaced wind farms and helps to design the converter controller to ensure wind farm system stability when connected to weak grids.

Machine learning based impedance estimation in power system

“…As the DC link decouples the dynamics of the distributed energy source side's dynamics from the grid side converter [3], the grid side converter of the distributed energy source is only presented. Furthermore, for simplicity, it is assumed that the rated values of the converter terminal voltage and grid at the PCC are similar.…”

“…The increasing penetration of power electronic converter interfaced distributed energy sources into the power grid, introduced new challenges to the monitoring, protection and control of the system [1]. The high amount of converter interfaced sources impacts the stability of the system, especially in a weak grid with high inductive impedance [2][3][4][5][6]. The knowledge of the grid impedance at the connection point of the converter to the grid (PCC) is essential for improving the control strategy and overall grid stability by either changing the control action or re-tuning the controller [7].…”

Current Error Based Compensations for VSC Current Control in Weak Grids for Wind Farm Applications

“…For convention current loop setting with PI regulator in Fig. 2 (a), the proportional and integral gains can be conventionally set at Kp = 141πL1 and Ki = 10000π 2 L1 respectively, which corresponds to a 50 Hz bandwidth current loop with damping coefficients of 0.707 connection with 2.5 kHz switching frequency [28]. The sampling process of current and voltage is typically considered as twice of the switching frequency since the modulation input of a practical SVPWM module used (for the prevalent digital signal processor of TMS320F28XX series produced by Texas Instrument) can be effectively updated twice per switching cycle [34].…”

“…A sub-model based on state space model is established for the impedances of VSC output and the main grid as [28]. To validate the frequency domain model, a comparison of step response test is performed in Fig.…”

An Alternative Current-Error Based Control for VSC Integration to Weak Grid

“…The main circuit of a converter is considered to be connecting to the grid, which can be modelled as a state-space model [16] as…”