Second‐order sliding mode control of wind turbines to enhance the fault‐ride through capability under unbalanced grid faults

Abstract

The integration of wind generation to the grid is growing rapidly across the world. As a result, grid operators have introduced the so-called grid codes (GC), which nowadays include a range of technical conditions and requirements, which wind generators must fulfill. Among these, the low voltage ride through (LVRT) is a requirement for wind turbines to stay connected to the grid and continue to operate during the disturbance. In this study, a control structure, combining inertial kinetic energy storage with a crowbar circuit, is proposed to enhance the ride-through capability of a wind turbine generator (WTG) based on a wound-field synchronous generator (WFSG) under unsymmetrical voltage dips. For the grid-side converter (GSC), a decoupled double synchronous reference frame (DDSRF) d-q current controller is used. Furthermore, a Second-Order Sliding Mode Controller (SOSMC) with Super-twisting (ST) algorithm is proposed for the GSC and the machine-side converter (MSC) to improve the response speed and achieve an accurate regulation of the dq-axis current components simultaneously. The main objectives of the GSC are to achieve a balanced, sinusoidal current and smooth the real and reactive powers to reduce the influence of the negative sequence voltage. A series of simulations are presented to demonstrate the effectiveness of the proposed control scheme in improving the LVRT capability of the WFSG-driven wind turbine and the power quality of the system under unbalanced grid voltage conditions.

A state‐of‐the‐art comprehensive review of modern control techniques for grid‐connected wind turbines and photovoltaic arrays distributed generation systems

“…The DPC configuration [77], which is similar to the DTC configuration, is preferred over VOC [68,75,76] because it does not need the CC and has an improved dynamic performance compared to the VOC. Also, the DPC employs a hysteresis comparator and switching table and instantaneously controls the active/reactive powers.…”

“…However, the proposed SMC [75] causes a more overshoot value of 0.16% than that obtained with the conventional PI control‐based GSC CB, that is, 0.13% [68]. In [76], the SOSMC with the super‐twisting algorithm is proposed to reduce the influence of the negative‐sequence voltage by obtaining smoothness ( P g , Q g ) with a balanced and sinusoidal grid‐side current. Moreover, under grid faults, the proposed GSC CB offers an enhanced LVRT capability and transient stability of the WT DGS.…”

“…Moreover, under grid faults, the proposed GSC CB offers an enhanced LVRT capability and transient stability of the WT DGS. Under both the normal and LVRT operations of the WT DGS, the proposed GSC CB in [76] achieves lower SSEs of 1.8% than that obtained with the traditional PI control (i.e. 2.95%) [68].…”

“…The GSC CB independently controls the active power (P g ) and reactive power (Q g ) flowing from the DGS to the utility grid and guarantees the grid code requirements under normal operation and during grid faults [30,61]. To achieve this, two types of control configurations are employed: voltage-oriented control (VOC) [68,75,76] and DPC [77]. The generalized control configuration using VOC with dual control loops is displayed in Figure 10 [ 75,76].…”

“…The important control techniques used to implement VC/QC are PI control [68], dual dq theory‐based control [69], quasi‐centralized direct‐MPC (QC‐DMPC) [70], fractional‐order PI (FOPI) control [71], symbiotic organisms search‐based PI (SOS‐PI) control [72] and steady‐state active power reference generation (APRG) control [73]. Finally, the endorsed modern CCs of the GSC CB for the grid‐side current control are made up of repetitive control [74], SMC [75], second‐order SMC (SOSMC) [76], direct power control (DPC) [77] and MPC [78, 79].…”