Modelling and Control of Nine-Switch Converter-Based DFIG Wind Power System
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ORIGINAL ARTICLE
Modelling and Control of Nine‑Switch Converter‑Based DFIG Wind Power System DongLiang Liu1 · Xu Zhang1 · Lei Pan2 · Aqiang Li1 Received: 25 December 2019 / Revised: 4 May 2020 / Accepted: 3 August 2020 © The Korean Institute of Electrical Engineers 2020
Abstract In this paper, nine-switch converter (NSC) is used to replace the Back-to-Back converter of DFIG wind power system. In order to simplify the control process and improve the performance, the switching function model of nine-switch converter under ABC coordinate system is established, and the mapping relationship between the parameters of NSC’s loads and those of DFIG wind energy conversion system is given. Meanwhile, a Resonant-proportional-integral (Resonant-PI) control strategy for NSC-based DFIG wind energy conversion system is proposed, and the PI controller is used for static control under steady state and the resonant controller for suppressing harmonic content in this method. The proposed method performs better than PI control in harmonic content and dynamic response. The simulations and experimental results verify the validity and reliability of the proposed mathematical model and control algorithm. Keywords Nine-switch converter (NSC) · Resonant-proportional-integral (resonant-PI) control · Doubly-fed induction generator (DFIG) · Switching function model
1 Introduction Doubly-Fed Induction Generators (DFIGs) are widely used in the wind energy conversion systems because of its small capacity, low price and low harmonics of excitation converter [1–4]. As shown in Fig. 1, DFIGs’ stator port is connected to the grid directly, while the rotor port is connected to the grid through the Back-to-Back (BtB) converter [5–10]. In the BtB converter, the crowbar or the active circuit for inrush energy absorbing was used to protect the converter and also achieve Low Voltage Ride Through (LVRT) successfully [11–15], but they increase the cost, size, and complication of the system. Recently, NSC using nine switches is developed and has been tentatively used to replace BtB converters in the DFIG wind energy conversion system [16–18]. As shown in Fig. 2, the number of switches, as well as the associated gating drivers, heat-sinks, protection circuits, and snubbers * Xu Zhang [email protected] 1
College of Automation, Hangzhou Dianzi University, Hangzhou, China
School of Control and Mechanical Engineering, Tianjin Chengjian University, Tianjin, China
2
can be reduced from 12 to 9, and thus, the structure of the system can be simplified. Generally, in the NSC-based DFIG wind energy conversion system, one case is the mathematical model of the system is established by combining the output phase voltage of the NSC, the voltages and currents of the filter link and the grid-side voltage; according to the characteristics of the mathematical model, the appropriate control strategy is selected to realize the global control of the system [19, 20]. The other case is that in the NSC-based DFIG wind energy conversion system, the NSC is equivalent to th
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