Research On Control Technologies Of Low Voltage Ride Through For Direct-drive Permanent Magnet Wind Power System

With the continuous development of the wind power industry, the lack of low voltage ride through capability of wind turbine has become the key factor that has an impact on its connected grid operation. This paper focuses on the low voltage ride through technology of the permanent magnet direct-drive wind turbine with the main work done and results achieved shown as follows:(1) The working principle and operational characteristics of the permanent magnet direct-drive wind turbine are studied in-depth and the corresponding mathematical model is established. Furthermore, the low voltage operational characteristic of the wind turbine is investigated so as to demonstrate that the critical issue of achieving low voltage ride through is to inhibit DC voltage fluctuations of the converter.(2) The control strategy of achieving low voltage ride through of the permanent magnet direct-drive wind turbine based on the paralleled Crowbar protection circuit on the DC side of the converter is designed. This strategy can inhibit the DC voltage fluctuations of the converter through the shunt resistor on the DC side which consume a portion of the power that charge the DC capacitor of the converter.(3) A low voltage ride through control method of the permanent magnet direct-drive wind turbine based on power tracking optimization is proposed. This method can regulate the output power of the wind turbine and eliminate the power imbalance on both sides of the converter to stabilize the DC voltage through the switching of the maximum power tracking curve.(4) A control method that achieving the low voltage ride through of the permanent magnet direct-drive wind turbine based on coordinated control of the active and reactive power is proposed. This method adopts the generator-side converter to control the stability of DC-link voltage while utilizes the grid-side converter to control the maximum power point tracking as well as coordinates the active and reactive power. Using the grid voltage to regulate the reactive power improves the low voltage ride through capability of the wind turbine as well as achieving the control of its high voltage ride through low voltage ride through.(5) A complete simulation model of the permanent magnet direct-drive wind power system is built. Then a dynamic simulation that involves the above control strategy which aims to improve the low voltage ride through capability is conducted. The experimental results verify the effectiveness and superiority of the proposed control strategy.