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This paper proposes a sliding-mode direct power control (SMDPC) strategy for doubly fed induction generator (DFIG) under both balanced and unbalanced grid conditions using extended active power. When the traditional power theory is used under unbalanced grid condition, the control strategies usually need to be modified and become more complicated. Therefore, an extended active power is proposed in this paper, which is effective under both balanced and unbalanced grid conditions with a simple control strategy. Based on the extended active power, elaborated analysis of the mathematical model of DFIG is obtained. Furthermore, an SMDPC strategy using the extended active power is proposed, which can obtain sinusoidal stator currents and restrain electromagnetic torque ripples under unbalanced grid condition without the need of decomposition process and phase-locked loop (PLL). Comparative experimental studies of the SMDPC using the extended and traditional active powers for DFIG are conducted to validate the effectiveness of the proposed strategy under both balanced and unbalanced grid conditions. In addition, the dynamic performance and robustness of the proposed SMDPC are also proved to be satisfying by the experimental results. [ABSTRACT FROM AUTHOR]

This paper proposes a resonant-based backstepping direct power control (BS-DPC) strategy for doubly-fed induction generator (DFIG) under both balanced and unbalanced grid conditions. Proper formulae for the BS-DPC strategy are obtained based on the elaborated analysis of the mathematical model of DFIG. The influence of the unbalanced grid voltage on the normal BS-DPC is analyzed. Furthermore, a resonant-based improved strategy is proposed to achieve different control targets under unbalanced grid condition without the need of decomposition of positive- and negative-sequence components. Comparative experimental studies of the resonant-based BS-DPC and the normal BS-DPC for DFIG are conducted to validate the effectiveness of the proposed strategy under both balanced and unbalanced grid conditions. In addition, the experimental results also prove that the proposed resonant-based BS-DPC can achieve a satisfying transient performance. [ABSTRACT FROM AUTHOR]

This paper proposes a three-vector-based low-complexity model predictive direct power control (LC-MPDPC) strategy for doubly fed induction generators (DFIGs) in wind energy applications. Previous studies have applied one- and two-vector-based LC-MPDPC strategies for ac/dc converters with a satisfactory control performance. In this paper, an elaborated analysis of the DFIG mathematical model is made and then the feasibility of one- and two-vector-based LC-MPDPC strategies for DFIG are analyzed. However, using these approaches, the steady-state errors cannot be eliminated completely. Thus, a three-vector-based LC-MPDPC is further proposed to eliminate the power error. Both simulation and experimental results indicate that the proposed three-vector-based LC-MPDPC can significantly improve the steady-state performance and achieve an error-free control. In addition, its dynamic performance remains satisfactory compared with one- and two-vector-based LC-MPDPC. [ABSTRACT FROM AUTHOR]

This paper proposes a low-complexity model predictive direct power control (LC-MPDPC) strategy for doubly fed induction generator (DFIG) under both balanced and unbalanced grid conditions. Based on the elaborated analysis of the mathematical model of DFIG, proper formulas for the LC-MPDPC strategy are obtained. A unified power compensation strategy is proposed to achieve various control targets flexibly during unbalanced grid condition. Comparative experimental studies of lookup table-based direct power control and LC-MPDPC for DFIG are conducted to validate the superior steady-state and dynamic performance of the LC-MPDPC under balanced grid condition. Furthermore, the experimental results also prove that the proposed LC-MPDPC with power compensation can satisfy different operation requirements of the DFIG system under unbalanced grid condition, and the dynamic response is satisfactory when the control target changes. [ABSTRACT FROM PUBLISHER]

Virtual synchronous generator control is considered as an effective solution to optimize the frequency response characteristics of doubly fed induction generator. However, due to the insufficient control bandwidth of the original virtual synchronous generator, it has little control effect over the oscillating components of the power caused by the unbalanced grid voltage. Therefore, long-term unbalanced voltage will cause a series of problems, such as distortion of stator and rotor currents, as well as oscillations of power and electromagnetic torque, which seriously affect the power quality and the operating performance of the doubly fed induction generator. To solve these problems, the concept of extended power is introduced, and the second-order generalized integrator-based resonant controller is used to control the extended power and traditional power. Control targets of the extended power method are discussed and extended, so that the doubly fed induction generator system using extended power resonant control-based virtual synchronous generator control can realize three different control targets under the unbalanced grid condition. The three control targets are: balanced and sinusoidal stator current, sinusoidal stator current and constant active power, and sinusoidal stator current and constant reactive power and electromagnetic torque. The three control targets can also be flexibly switched according to the real-time requirements of the grid with unbalanced voltage. The simulation results verify the effectiveness of the control method. [ABSTRACT FROM AUTHOR]