Voltage Coordinated Control Strategy for Modular Multi-Phase PMSG-Based Series-Parallel DC Connected Offshore Wind Farm
Cui Hesong1, Li Xueping1, Huang Sheng1, Huang Lingxiang2, Shen Feifan1, Huang Shoudao1, Luo Derong1, Wu Gongping3
1. College of Electrical and Information Engineering Hunan University Changsha 410082 China; 2. Harbin Electric Corporation Wind Power Co. Ltd Xiangtan 411101 China; 3. School of Electrical & Information Engineering Changsha University of Science & Technology Changsha 410114 China
Abstract：With the fast development of offshore wind farms (WFs), the cost-effective collection and transmission of large-scale offshore wind power has been extensively studied. Compared to the existing AC collection system with a VSC-HVDC system, a full DC WF has a number of advantages, e.g., they potentially eliminate the large AC transformers, increase efficiency and power density, and reduce the size and weight of the cable. The multi-winding PMSG has strong fault tolerance and small stator current, which can be directly connected to the grid through the multi module converter, therefore, it has been widely used in the high power wind energy conversion system in recent years. In this paper, a novel series-parallel DC connection topology for multi-phase permanent magnet synchronous generator (PMSG)-based offshore wind farm (WF) was proposed to meet the high voltage、high power and high reliability requirements of wind farm DC transmission system power transmission. Considering the stochastic and intermittent nature of wind energy and wake effects, the available wind power of the WTs might be different, which may result in the differences of the DC terminal voltages of the WTs. The WTs with the high wind speed condition have a risk of being tripped because their terminal voltages may exceed their threshold. Therefore, a voltage coordinated control strategy for modular multi-phase PMSG-based series-parallel DC connected offshore wind farm should be developed. Several overvoltage elimination control strategies have been proposed for the series-parallel DC connected WF. However, these control methods do not consider the network loss and voltage drop on the transmission cable. In this paper, a new overvoltage elimination control strategy considering the network loss and voltage drop on the transmission cable is developed, which can enhance the safe operation of WF and improve the overvoltage elimination capability of WTs. The mathematical model of DC wind turbine (WT) system with the modular multi-phase PMSG was established. Based on the mathematical model, the modular multi-phase permanent magnet wind turbine deadbeat power prediction controller was designed to improve the dq axis current tracking accuracy and dynamic response speed, and compensate the one beat delay. Moreover, according to the characteristics of the modular multi-phase PMSG-based series-parallel topology, a power and voltage coordinated control strategy considering power flow of the WF DC collection system was developed to suppress the overvoltage of the WT terminal to ensure safe operation of the WF by adjusting the reference value of the active power of the wind turbine in real time. A WF model with three clusters in parallel and each cluster consisting of 6×5 MW modular multi-winding PMSG in series is used to validate the proposed deadbeat power predictive control strategy and power and voltage coordinated control. Simulation results show that, the proposed predictive power control strategy can achieve excellent tracking performance and compensate the control delay. The overvoltage problem of the WT terminal caused by the DC series connected topology can be effectively solved by the proposed coordinated control strategy for the multi-winding PMSG-based WF. Furthermore, the network loss and voltage drop on the transmission cable has been taken into consideration to improve the overvoltage elimination performance of WTs and guarantee the safe operation of the WF.
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2023, Vol. 38 
