Control Design of a Dynamic Voltage Restorer for Wind-Driven Induction Generators during a Low Voltage Fault at Grid Bus

Abstract

To reduce the parallel transient and resume the power balance immediately after fault clearing, many countries have included the low voltage ride through (LVRT) requirements in the grid codes for grid-connected wind turbines (WTs). Although the removal of the WT from the power grid in the conventional approach is beneficial to alleviate severe mechanical stress incurred by the low voltage fault, remaining the WT to be connected to the grid during the low voltage fault becomes obligate to reduce the risk of voltage collapse for the power system associated with the ever-increasing WT installation. This article presents a control strategy to which the LVRT capability enhancement of a wind-driven squirrel cage induction generator (IG) by the use of a dynamic voltage restorer (DVR). The DVR, with the flexibility of changing output voltage polarity in series with the power source, can sustain the excitation of IG subjected to the low voltage fault and the random change in load and wind speed. A DC voltage regulator is employed to support the DC-link voltage of the DVR for generating appropriate AC voltage level required for the IG. The AC output voltage of the DVR is controlled by an AC voltage regulator according to the IG terminal voltage deviation from the desired value. To achieve voltage and current decoupling control between distinct coordinate axes in the stationary reference frame, a proportional-resonant (PR) controller is adopted. The DVR output voltage can be instantaneously tracked by the PR controller according to the sinusoidal command comes from the DC and AC regulators. To fully utilize the compensation capacity for the DVR, the dynamic estimation of grid voltage lower limit for recasting the AC voltage command (ACC) of the DVR in response to the low voltage fault is proposed to prevent DVR from malfunction due to controller saturation. The experimental results confirm the effectiveness of the proposed strategy.

Keywords:

• low voltage ride through (LVRT)
• dynamic voltage restorer (DVR)
• induction generator (IG)

Additional information

Funding

This work was supported in part by the Ministry of Science and Technology under Contracts MOST 103-3113-E-002-008, NSC 102-2221-E-182 -030, and NSC 101-2632-E-182-001-MY3 and in part by Green Technology Research Center of Chang Gung University.

Notes on contributors

Woei-Luen Chen

Woei-Luen Chen received the M.S. and Ph.D. degrees from National Taiwan University in 1997 and 2006, respectively. Since 2006, he has been with the Electrical Engineering Department at Chang Gung University, Taiwan, where he is currently an Associate Professor. His present research interests include power electronic applications, reactive power compensation systems and wind energy conversion systems.

Meng-Jie Wang

Meng-Jie Wang received the B.S. degrees from Chung Yuan Christian University, Taiwan. He is currently working toward the Master degree at Chang Gung University, Tao-Yuan, Taiwan. His areas of research include power electronic applications and renewable energy conversion systems.