Voltage regulation and reactive power compensation to improve low voltage ride-through capability for doubly fed induction generator-based wind turbine

Abstract

Of all the renewable energies, wind power is proliferating and it now plays a significant part in the power supply. The system known as Doubly Fed Induction Generator (DFIG) is the most popular wind turbine, because it plays a very significant role in enhancing low voltage ride through (LVRT) capability. Ancillary services such as voltage control and reactive power capability are the main concerns in wind power control systems and need to be managed in detail and with great care. The lack of reactive power during a fault period can result in instability in generators and/or disconnection of a wind turbine from the power system. The main aim of this study is to explain and describe the most effective and efficient approaches for improving the stability and reliability of wind power plants. This theme is closely associated with LVRT capability enhancement. Wind farms are regarded as large-scale power plants with interconnected systems, where all systems interact with each other to improve the efficiency of the plant and thus the quality of the output power. However, the conventional centralized controller is inappropriate for such plants. Also, not many studies have paid attention to this fact due to strong nonlinear behavior of such plants. Accordingly, a new control strategy is presented in Chapter 3 based on employing MPC and incorporating the voltage and current constraints. LVRT capability is extended by adding a series of dynamic breaking resistors to deal with severe faults and to short circuit the RSC. In Chapter 4, an asymptotic model of a wind farm equipped with DFIG is given with a description of the outcomes of interconnections. The LVRT capability is improved by introducing a class of plant-wise controller for a decentralized system. This is done by taking care of voltage at an individual point of common coupling (PCC) and controlling the DFIG active and reactive power, separately. Further, a new reactive power control strategy for voltage stability and improvement of LVRT capability is presented in Chapter 5. Both RSC and GSC are taken into account for the purpose of voltage stability and improvement of systems robustness. In the algorithm developed, the required reactive power is optimally managed at an individual point of common coupling (PCC) by using linear matrix inequality (LMI) technique. JR has also been employed to have better accuracy and realize the required bound of injected reactive power. To minimize the systems conservative nature, dynamic couplings of the system are considered, unlike the existing methods. This research aims to address these shortcomings using novel methodologies. By identifying the drawbacks of existing LVRT solutions, the study specifically focuses on addressing three problems to regulate the voltage at individual points of common coupling. The objective is to maximize the DFIG output reactive power concerning the stability of the entire large- scale wind power plant by designing multiple local controllers. To sum up, the key contribution of the study is to design a control strategy that gives DFIG the ability to full the two main grid code requirements in one inclusive approach, while other existing proposals treat each requirement as a separated issue. To demonstrate the effectiveness of all approaches presented in this the- sis, MATLAB software is used for simulation. After all, the results have been demonstrated the flexibility of model predictive control technology and motivated numerous novel works and researches to address practical problems in the field of the wind power industry.

Date of Award	2019
Original language	English