The Low Voltage Ride Through (LVRT) technology with low-speed direct-drive Permanent Magnet Synchronous Generator (PMSG) is studied in this paper. Based on the system structure and its controller options, a class of LVRT control strategies are proposed in terms of energy flow, which can make sufficient use of power characteristics of wind turbine and the large moment inertia of the system to achieve LVRT and are suitable for various running conditions. Simulation results verify that the proposed control strategy meet the LVRT requirements thoroughly and demonstrate superior dynamic performance.
Hybrid Active Power Filter (HAPF), which consists of Passive Power Filter (PPF) and Active Power Filter (APF) in series, is suitable for large capacity and high voltage application.Conventional controllers e.g. PI and proportional resonant ones etc., have their disadvantages diversely to control the output voltage of the APF part as a controlled harmonic voltage source as desired, which is crucial to the whole HAPF. In this paper, a high-performance control strategy based on PI-inner and repetitive-control-external loop is firstly adopted into the HAPF. Compared to mere PI controller, it has wider bandwidth and smaller phase lag. As a result, it can tremendously improve the harmonic compensation precision. Configuration, modeling and parameters optimization are analyzed. Design method of the proposed double-loop controller is also given in details. Simulation results show that it can not only effectively improve the accuracy of steady-state compensation, but also guarantee good dynamic performance.
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