Abstract
In a wind turbine system, a doubly-fed induction generator (DFIG), with nonlinear and high-dimensional dynamics, is generally subjected to unbalanced grid voltage and unknown uncertainty. This paper proposes a novel adaptive-gain second-order sliding mode direct power control (AGSOSM-DPC) strategy for a wind-turbine-driven DFIG, valid for both balanced and unbalanced grid voltage. The AGSOSM-DPC control scheme is presented in detail to restrain rotor voltage chattering and deal with the scenario of unknown uncertainty upper bound. Stator current harmonics and electromagnetic torque ripples can be simultaneously restrained without phase-locked loop (PLL) and phase sequence decomposition using new active power expression. Adaptive control gains are deduced based on the Lyapunov stability method. Comparative simulations under three DPC schemes are executed on a 2-MW DFIG under both balanced and unbalanced grid voltage. The proposed strategy achieved active and reactive power regulation under a two-phase stationary reference frame for both balanced and unbalanced grid voltage. An uncertainty upper bound is not needed in advance, and the sliding mode control chattering is greatly restrained. The simulation results verify the effectiveness, robustness, and superiority of the AGSOSM-DPC strategy.
Highlights
Over the past decade, renewable energy generation has continued to grow rapidly due to widely known problems such as environmental pollution and resource shortage [1]
The main contributions of the paper include the following: (1) Under a two-phase stationary reference frame, a novel AGSOSM-direct power control (DPC) strategy for doubly-fed induction generator (DFIG) is proposed that can solve the abovementioned key issues simultaneously; (2) using adaptive control gain, the upper bound of uncertainty is not necessarily known in advance; and (3) rotor voltage control chattering is highly suppressed via a super-twisting algorithm
The reference values of power, stator voltage, stator flux linkage, and stator current are applied as inputs of the AGSOSM direct power controller
Summary
Renewable energy generation has continued to grow rapidly due to widely known problems such as environmental pollution and resource shortage [1]. Good results were achieved, some drawbacks still exist, and positive and negative sequence decomposition is needed [23]; all these studies focused on the conventional first-order sliding mode (FOSM), with unsatisfactory control switching and variable switching frequency These intrinsic drawbacks caused by the FOSM may produce torque ripple, harmonic current, overheating of the windings, etc. The main contributions of the paper include the following: (1) Under a two-phase stationary reference frame, a novel AGSOSM-DPC strategy for DFIG is proposed that can solve the abovementioned key issues simultaneously; (2) using adaptive control gain, the upper bound of uncertainty is not necessarily known in advance; and (3) rotor voltage control chattering is highly suppressed via a super-twisting algorithm.
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