Research on Low-voltage Ride-through Technology of grid-connected Doubly - Fed Wind Power Generation System

摘要

According to the demand of the regulations of the gird, within a certain period of time after power failure, the wind power systems should be able to maintain uninterrupted power supply to the grid, which called for low voltage ride through capability (LVRT) of the wind power systems. To achieve the LVRT ability, a relatively common practice is to install the rotor side crowbar protection circuit. When the grid voltage dips happen, Crowbar protection circuit will be activated in order to protect the converter. But in this way, DFIG will degenerate into a wire-wound induction motor with a variable resistor connected to the rotor side. At this time the motor needs to absorb reactive power from the already vulnerable power grid in order to establish the motor's magnetic field. This will undoubtedly result in a negative impact to the rapid recovery of the grid voltage. On the bases of the research of the transient characteristics of DFIG in the case of the grid voltage dips, this paper introduced the concept of LVRT and its relevant standards in our country, and analyzed the various kinds of schemes which has already been proposed to achieve the LVRT ability. With the most common practice which installs the rotor side crowbar protection circuit, a proved protection and control strategy to enhance the LVRT capability of a wind turbine driven by DFIG was proposed. In this strategy, we will add a RPC circuit in the stator side to compensate the reactive power demand of the DFIG during the LVRT period with the expectation of reducing the reactive power load of the already blooey power grid as much as possible. The simulation resualts reviewed that the proposed strategy could help the power grid survive during the shot period of voltage dip and the grid could eventlly return to the stable operation conditions.