Co‐ordinated voltage control of DFIG wind turbines in uninterrupted operation during grid faults

Abstract

Emphasis in this article is on the design of a co‐ordinated voltage control strategy for doubly fed induction generator (DFIG) wind turbines that enhances their capability to provide grid support during grid faults. In contrast to its very good performance in normal operation, the DFIG wind turbine concept is quite sensitive to grid faults and requires special power converter protection. The fault ride‐through and grid support capabilities of the DFIG address therefore primarily the design of DFIG wind turbine control with special focus on power converter protection and voltage control issues. A voltage control strategy is designed and implemented in this article, based on the idea that both converters of the DFIG (i.e. rotor‐side converter and grid‐side converter) participate in the grid voltage control in a co‐ordinated manner. By default the grid voltage is controlled by the rotor‐side converter as long as it is not blocked by the protection system, otherwise the grid‐side converter takes over the voltage control. Moreover, the article presents a DFIG wind farm model equipped with a grid fault protection system and the described co‐ordinated voltage control. The whole DFIG wind farm model is implemented in the power system simulation toolbox PowerFactory DIgSILENT. The DFIG wind farm ride‐through capability and contribution to voltage control in the power system are assessed and discussed by means of simulations with the use of a transmission power system generic model developed and delivered by the Danish Transmission System Operator Energinet.dk. The simulation results show how a DFIG wind farm equipped with voltage control can help a nearby active stall wind farm to ride through a grid fault, without implementation of any additional ride‐through control strategy in the active stall wind farm. Copyright © 2006 John Wiley &Sons, Ltd.

Control of Grid Voltage and Power of Doubly Fed Induction Generator wind turbines during grid faults

“…This raises problems in terms of generator/converter protection and control. In the case of grid faults, the controllability of the DFIG variable speed wind turbine embraces both the wind turbine control for preventing over speeding of the wind turbine and the control and protection of the power converter during and after grid faults [6]. Figure 1 shows the main components of the DFIG wind turbine system configuration [6], [7]:…”

“…The pitch angle control, in Figure 1, is realized by a PI controller with anti wind up, using a servomechanism model with limitation of both the pitch angle and its rate-of-change [6]. In the present work, the pitch angle control is implemented in such a way that the pitch angle controls the generator speed, i.e.…”

Grid voltage control by using DFIG during grid faults

“…This raises problems in terms of generator/converter protection and control. In the case of grid faults, the controllability of the DFIG variable speed wind turbine embraces both the wind turbine control for preventing over-speeding of the wind turbine and the control and protection of the power converter during and after grid faults [6]. Figure 1 sketches the main components of the DFIG wind turbine system configuration [6], [7]: • Wind turbine -drive train, aerodynamics and pitch angle control system • DFIG system -control and protection …”

“…This simplified aerodynamic model is typically based on a two dimensional aerodynamic torque coefficient table [3], provided by a standard aerodynamic program. The pitch angle control, in Figure 1, is realised by a PI controller with antiwind-up, using a servomechanism model with limitation of both the pitch angle and its rate-of-change [6]. In the present work, the pitch angle control is implemented in such a way that the pitch angle controls the generator speed, i.e.…”

Dynamic security issues in autonomous power systems with increasing wind power penetration

“…The grid-side converter is not blocked at a grid fault and continues its operation as a STATCOM. The controllability is thus improved providing the DFIG with grid voltage support in uninterrupted operation during the transient instant, [17]. The voltage control is also activated in the rotor side converter control system, thus the wind farm manages to provide with additional reactive power supporting the grid voltage.…”