Research On Low Voltage Ride Through Of Permanent Magnet Direct-Drive Wind Power System

With the continuous application of megawatt permanent magnet direct drive wind turbines, electric power system stroke capacity proportion is more and more big, when the power system fault voltage drop, wind farm will seriously affect the stability of the system operation, which requires the wind turbines have low voltage across ability, assurance system failure after wind turbines uninterrupted parallel operation. This paper puts forward the optimization control strategy with the super capacitor energy storage system, can effectively stabilize the dc voltage, and meet to the grid power grid failure wind power system to provide reactive power support, come true the low voltage ride through the wind power system.In this paper, under grid symmetrical fault conditions, the motor-side converter and grid-side converter DC link voltage power imbalance increased the problem of super capacitor capacity to the best goal of economic analysis and calculation, made with super machine side converter and grid-side converter capacitor energy storage system of coordinated control strategy. Simulation results show that: limited, by the side of the machine converter generator output power, the use of super capacitor energy storage system for the remaining DC link power absorption, as well as network-side converter reactive power compensation, can effectively inhibit the DC link voltage increased to improve grid fault when the capacity of reactive power compensation of wind power systems, and ensures the stable operation of the security system, and verify the reasonable super capacity calculation methods.For the wind power system in a two-phase power asymmetry fault, the grid-side converter generates an asymmetric current and power doubler fluctuations, this article will be broken down into two asymmetrical current component symmetrical components constructed two-coordinate system dq control system, depending on the power of three different sub-control operation, and according to the operating characteristics of three kinds of situations, are designed grid-side converter output power limit, effectively suppress negative sequence current and power doubler fluctuations. The simulation results showed that: asymmetry fault, the grid-side converter double coordinates dq control strategy to ensure reliable operation of the wind power system to meet the needs of low voltage ride through.