Dynamic analysis and oscillation elimination of brushless doubly fed wind power generation system during symmetrical voltage dips

Abstract

In the dynamics of grid‐connected operation of brushless doubly‐fed generators, grid voltage dips can cause the extreme imbalance between the voltage and the back electromotive forces in power winding. When these imbalances are combined with the influence of the inertia link composed of converter and generator, a serious over‐current and current oscillation forms in power winding and control winding. This paper gives a process analysis and proposes an improved control to the system during the low voltage ride through event. According to the mathematical model of the generators, the correlation between the power winding and control winding currents is established and then a fully equivalent simplified model is obtained accordingly. When the voltage suddenly drops to zero, the analytic expressions of power winding and control winding are calculated in the complex frequency domain and the influence factors of overshoot and oscillations are analyzed. The conventional control method relies on limited PI regulation that cannot eliminate the oscillations completely. It is found that after adjusting a proportional coefficient and eliminating the integral link of the control winding current controller, the order of the control system reduces. Therefore, the generation system can quickly recover to a steady state without oscillations. Finally, the analysis and improvement are verified by the simulation model and experimental results.

Recent Advances of Control Technologies for Brushless Doubly-Fed Generators

“…As can be seen from these experimental results, the LVRT performance got by the hardware-based methods in [65] and [66] is a bit worse that that obtained by the software-based method in [60]. In [67], in order to achieve LVRT under symmetrical grid voltage dips, the integral part of the CW current PI controller is removed and the proportional gain is optimized in the LVRT mode, so that the order of the control system can be reduced and the d-and q-axis currents of CW and PW can quickly converge. Consequently, the overcurrent and oscillation of the CW and PW currents can be avoided during symmetrical grid voltage dips.…”

“…The LVRT capability indicates that grid-connected wind turbines must remain connected and supply reactive current to the grid during grid voltage dips. The LVRT is the most important indicator in many national grid codes [60]- [67].…”

“…the crowbarless LVRT control methods, can be implemented in the rotating frame and the static frame. To date, the crowbarless LVRT control schemes for BDFIGs developed in [63]- [67] are all essentially implemented in the rotating reference frame. LVRT The control strategies proposed in [63] and [64] can compensate for the couplings between the two axes of the CW current, with different compensation terms.…”

Extensive model validation for generic IEC 61400-27-1 wind turbine models

“…In line with the above, the main objective of the present paper is to help the user of these models to understand their capabilities and limitations based on a broad and comprehensive comparison with measurements, as well as demonstrate their practical applicability and accuracy. Thus, the paper focuses on the assessment of the responses of the generic Type 3 and Type 4 WT models under one of the most critical situations faced by WTs, i.e., voltage dips [5,6].…”