Effect of transient flux compensation control on fault ride through of doubly fed induction generator wind turbine

Abstract

Abstract. The fault ride through (FRT) of doubly fed induction generator (DFIG) is studied in this paper. Two different FRT strategies are compared. First strategy uses only active crowbar to protect the turbine and the second strategy uses transient flux compensation in addition to the crowbar. Simulations are carried out using Matlab/Simulink. The aim of the study is to reveal how the transient flux compensation improves the operation of DFIG during a fault. If the transient flux is removed the DFIG is controllable during a fault and the reactive power injection to the grid can be maximized. This is an important aspect since the latest grid codes insist that wind turbines should be able to inject reactive power during a fault in order to support the depressed grid voltage. Thus, this paper proposes that after a fault it is reasonable to use the current capacity of rotor side converter to remove the transient flux. This leads to better performance of wind turbine, improved power quality and maximized voltage support.

Sizing of the series dynamic breaking resistor in a doubly fed induction generator wind turbine

“…In order to avoid rotor over voltage, and RSC saturation, it is important to cancel the transient flux, this can be done through generating a rotor current from RSC, which opposes DC and negative sequence components of the stator flux linkage during a fault [8]. If the RSC saturation can be avoided the currents in the rotor circuit can be controlled and limited during the fault which stands for successful FRT without using any external devices, such as a crowbar.…”

Influence of DFIG reactive current injection during a voltage dip on the operation of wind turbine circuit breaker

“…In addition, the grid side converter feeds reactive current to the network during the whole fault period. [8] [9] The aim of the study is not to investigate the effectiveness of the used FRT strategies but to show the existence of interactions between the reactive current injection and the operation of the circuit breaker. It is found in this study that the reactive current injection and proper crowbar resistance selection enhances the operation of wind turbine protection since the zero crossings of the circuit breaker currents are reached earlier.…”

“…These oscillations may activate repititive crowbar activation when reactive current is attempted to maximize. [9] However, the transient flux decays quite rapidly and when the calculated i rtf is smaller than the current capacity of the RSC the rest of the capacity is utilized for reactive current injection to the grid. In other words, the x-component of the rotor current is maximized while the y-component is set to zero in Fig.…”

“…This is because the transient flux has not disappeared and due to the flux the current oscillates around its reference. [9] Repetitive crowbar activation could be avoided for example by increasing the crowbar connection time.…”

“…[9][12] The DSOGI-FLL is used to calculate the positive sequence component from the stator flux. The transient flux linkage tf is the difference between the total stator flux linkage s and the positive sequence component of the flux linkage s+ .…”