Enhanced control of a DFIG-based system by sliding-mode control method during network disturbances

Abstract

This paper presents a new method for control of the grid-side converter (GSC) of a doubly fed induction generator (DFIG) system under unbalanced and harmonic grid voltage conditions. The proposed controller is designed based on the sliding-mode control (SMC) method, and operates better than the current ones as the power quality of the DFIG is improved. The fluctuations in electromagnetic torque and stator reactive power are removed by control of the rotor-side converter (RSC). In addition, the GSC keeps the DC-link voltage at a reference value and mitigates not only fluctuations but also oscillations in steady injected active power to the network. Therefore, the output power of the system is free from any fluctuation and distortion. The control algorithm is implemented in the stationary reference frame and it is not necessary to extract voltage or current sequences in either of the converters. The proposed control algorithms are also robust against parameter variations and the resulting dynamic response is fast. The simulation results confirm the validity of the mentioned advantages and the effectiveness of the proposed method.

Sliding-Mode Control for a DFIG-Based Wind-Power Generation System with Series Grid-Side Converter under Unbalanced Grid Voltage Conditions

“…This, in turn, improves the operation of the DFIG system and the output power quality. The operation of RSC represented in [26] is similar to [32]. This implies that SMC of the RSC for both methods are the same.…”

“…Also, after the second 5.5, the load is changed. Considering Figure 6 (b), (c) and (d), despite unbalanced voltage, the RSC (with the help of GSC) can control the electromagnetic torque, the reactive and the active powers of the stator as investigated in [26] and [32]. But the oscillations with the frequency of 100 Hz exist still.…”

“…In addition, the fluctuations of the injected power to the network is increased which decreases the quality of the output power of the system. Therefore, in this paper to solve these problems, the DC-link is controlled by the sliding-mode control method of [32], but with the difference that 2 dc V is controlled (instead of dc V 1 ) which has a more simple control algorithm. Figure 4 shows the structure of the GSC.…”

“…Under unbalanced grid voltage, the grid voltage with respect to the stationary reference frame can be expressed as [32]:…”

“…Details of the simulated 2MW DFIG system with parameters were adapted from [32] are given in Appendix A and D and practical parameters of 5kW DFIG system with experimental parameters were adapted from [26], [30] are given in Appendix B and C. In accordance with [26], the set point of the stator active power is calculated from the rotor speed-optimal power curve and the set point of the stator reactive power is achieved with respect to the required 0.95 leading power factor. The simulation results are divided into four parts in which the corresponding results are compared to [26] and [32] to assess the proposed controller and evaluate its effectiveness. Sections 7.1, 7.2 shows the desirable performance of the DFIG system accompanied by SGSC under unbalanced grid voltage conditions and section 7.3discuss the robustness of the proposed control strategy.…”