Research On Voltage Fault Ride-through Technology For High-speed Permanent Magnet Wind Power System

There are abundant wind energy resources of China.Therefore,the development of wind power will strongly support economic and social development,ensure energy security and promote the achievement of the "dual carbon" goals.Nevertheless,since the operation ability of wind turbines during grid-connected point voltage faults is directly related to the stability of the power system,it is necessary to improve the voltage ride-through capability of wind turbines.At present,permanent magnet synchronous(PMSG)wind turbines have gradually become the mainstream of wind turbines due to technological advances.Based on permanent magnet synchronous wind turbines,this thesis studies the voltage ride-through technology of high-speed permanent magnet(H-PMSG)wind power system under different voltage faults.The following work is done:1.Aiming at the fault ride-through problem of H-PMSG wind power system during symmetrical voltage dips at the grid-connected point,a symmetrical low voltage ride-through technology scheme combining auxiliary hardware circuit and improved control strategy of grid-side converter is proposed:(1)A DC-Crowbar circuit based on double unloading resistors is designed,and the unbalanced power between the generator side and the grid side is consumed by putting different unloading resistors with different resistance values at different voltage dip depths;(2)The control strategy of the grid-side converter during the symmetrical low voltage ride-through is improved,the grid-side power factor is adjusted by adjusting the given active current and reactive current,so that the system can issue a certain reactive power during the fault ride-through period responding to the voltage dip depth,which realizes the support of the grid-connected point voltage.The simulation results show that the proposed symmetrical LVRT scheme effectively improves the symmetrical low voltage ride-through capability of the H-PMSG wind power system when the grid-connected point voltage dips symmetrically.2.Aiming at the fault ride-through problem of H-PMSG wind power system when symmetrical high voltage and continuous faults occur at the grid-connected point,a symmetrical high voltage ride-through and continuous ride-through scheme for H-PMSG wind power system is proposed:(1)During symmetrical high voltage faults,by improving the grid-side control strategy,the grid-side converter is controlled to absorb reactive power from the grid according to the degree of voltage surge to promote the recovery of the grid-connected point voltage,and the DC-Crowbar circuit is also used to achieve symmetrical high voltage ride-through;(2)During low-high voltage continuous faults,the control mode of the grid-side converter is switched according to the voltage of the grid-connected point at different fault stages,and the reactive power exchange between the system and the grid is adjusted in different fault stages to realize symmetrical low-high voltage continuous ride-through.The simulation results show that the proposed symmetrical high voltage ride-through and continuous ride-through schemes effectively improve the symmetrical high voltage ride-through and low-high voltage continuous ride-through capabilities of the H-PMSG wind power system when symmetrical high voltage faults and low-high voltage continuous faults occur at the grid-connected point.3.Aiming at the fault ride-through problem of H-PMSG wind power system during asymmetric voltage dips at the grid-connected point,based on the control objective of eliminating the double frequency fluctuation of active power,an improved control strategy of grid-side converter during asymmetric low voltage ride-through is proposed: The active and reactive current commands of the positive sequence control loop are given according to the symmetrical low voltage ride-through method,while the active and reactive current commands of the negative sequence control loop are given according to the relationship between the positive and negative sequence voltage and current,which simplifies the control of the grid side converter.The simulation results show that the proposed asymmetric LVRT scheme effectively improves the asymmetric low voltage ride-through capability of the H-PMSG wind power system when the grid-connected point voltage dips asymmetrically.