Control Strategy of a DVR to Improve Stability in Wind Farms Using Squirrel-Cage Induction Generators

Abstract

This work presents a control strategy of a dynamic voltage restorer (DVR) to improve the stability in wind farms based on squirrel-cage induction generators. The DVR controller is tailored to work under unbalanced conditions, which allows overcoming most faults in the power grid. The proposed strategy is capable of balancing voltages at wind farm terminals obtaining several advantages. Firstly, negative-sequence currents are eliminated; thus, overheating, loss of performance, and decreasing of generator useful life are avoided. Secondly, by nullifying negativesequence voltages, 2 pulsation in the mechanical torque is prevented, reducing high stress in the turbine mechanical system, especially in the gearbox. The proposed control strategy for the DVR is compatible with farms which already have installed a static VAR compensator. Several scenarios and disturbances, carefully chosen to provide a realistic assessment, have been tested showing the adequacy of the proposed arrangement and controllers.Index Terms-Dynamic voltage restorer (DVR), fault ride-through capability, grid codes, squirrel-cage induction generators (SCIG), unbalanced conditions, wind energy conversion system (WECS).

Controlling SCIG-based Wind Turbine to Satisfy the Power System Operator’s Requirement

“…Many publications, [7][8][9][10][11][12][13][14][15][16][17], pointed out methods that help wind farms to reach to these requirements. Authors in [7][8][9] recommended that reactive power compensation equipments such as STATCOM, SVC and so on should be installed at SCIG-based wind farms to improve their FRT ability.…”

“…Authors in [7][8][9] recommended that reactive power compensation equipments such as STATCOM, SVC and so on should be installed at SCIG-based wind farms to improve their FRT ability. Moreover, a battery system was also offered as an effective method for wind farms so that their power output becomes smoother or constant [10][11][12][13][14][15].…”

Coordinated Control of a DFIG-Based Wind-Power Generation System with SGSC under Distorted Grid Voltage Conditions

“…For the severe grid short-circuit fault and unbalanced grid voltage conditions, some improved excitation control strategies or an additional series voltage compensation method using a dynamic voltage restorer (DVR) have been proposed to effectively enhance the low voltage ride through (LVRT) capability of the DFIG system [1,2,[15][16][17][18][19]. Besides, the overall operation performance of the whole DFIG system can be improved by coordinately controlling the rotor-side converter (RSC) and parallel grid-side converter (PGSC) during a network unbalance, and some enhanced operation functionalities such as eliminating the oscillations in the active or reactive power from the whole system, or suppressing the negative-sequence currents injected to the grid have been achieved [6,11].…”

“…However, the operation and control of such a DFIG system under grid voltage harmonic distortion have not been discussed in detail. Unlike other series voltage compensation methods using a DVR mentioned in [15][16][17][18][19], the DFIG system with SGSC can also cope with the case of steady-state grid voltage harmonic distortions as the SGSC is directly connected with the PGSC and RSC through the dc-link.…”

Robust nonlinear control strategy to maximize energy capture in a variable speed wind turbine with an internal induction generator

“…Iyasere et al [10] proposed a robust control strategy to control the blade pitch angle and rotor speed in a variable speed variable pitch wind turbine in order to maximize the energy capture, without the knowledge of the optimal tip-speed ratio and in the presence of model structural uncertainties. An area of particular importance is the control of the internal generators used in wind turbines [15]. The most commonly used generator is the induction generator, of which the types include cage, wound rotor and doubly fed induction generator (DFIG).…”