Research On Subsynchronous Oscillation Damping Control In The Power System Connected With Wind Farm

Although there are many differences in the types of wind turbine generators and the transmission systems of wind power,large-scale wind farms face the threat of sub-synchronous oscillation or even super-synchronous oscillation.If the subsynchronous(supersynchronous)oscillation of wind farm is not handled in time,it will lead to more serious safety accidents.It may cause a large number of wind turbine generators to be disconnected,and excite the torsional vibration of the turbine shafting.In this paper,wind farms with different types of wind turbine generators and different transmission systems are studied.The mechanism of subsynchronous(supersynchronous)oscillation in wind farms is explored.And damping control schemes are proposed to suppress subsynchronous(supersynchronous)oscillation in wind farms.The main works are presented as follow.(1)Previous studies only considered the phenomenon of subsynchronous oscillation in DFIG-based wind farms and its suppression measures.But the possibility of supersynchronous oscillation in DFIG-based wind farms were ingnored.The mechanism of subsynchronous/supersynchronous mixed oscillation in DFIG-based wind farm connected to a power grid via series compensated capacitor lines is explained in the 3rd chapter of this paper.Then a wind-farm-level damping control scheme which can simultaneously suppress subsynchronous oscillation and supersynchronous oscillation in DFIG-based wind farms is proposed.(2)There may be multiple subsynchronous(supersynchronous)oscillation modes in wind farms.To solve this problem,in the 4th chapter of this paper,multiple subsynchronous(supersynchronous)oscillation modes in the PMSG-based wind farm connected to the power grid are classified into two categories.One is called inside-wind-farm oscillation,and the other is called wind-farm-grid oscillation.The mechanism of inside-wind-farm oscillation and wind-farm-grid oscillation in PMSG-based wind farm connected to the power grid is explained.A double-level damping control scheme for PMSG-based wind farm is proposed,which can simultaneously suppress inside-wind-farm oscillation and wind-farm-grid oscillation.(3)Subsynchronous oscillation may occur and the design process of subsynchronous damping controllers is very complicated when there are a large number of PMSGs in the wind farm.In order to simplify the design process,the reduced-order model of PMSG-based wind farm connected to the power grid is obtained by transforming and reducing the order of the linearization model of PMSG-based wind farm connected to the power grid.The mechanism of subsynchronous oscillation in PMSG-based wind farm is explained based on reduced-order model of PMSG-based wind farm.And the effects of operation parameters,control parameters and the number of wind turbine generators in PMSG-based wind farm on subsynchronous oscillation are analyzed.Afterwards,a reduced-order design method of subsynchronous damping control for PMSG-based wind farm is proposed to suppress the subsynchronous oscillation in the PMSG-based wind farm.(4)The subsynchronous(supersynchronous)oscillation will occur due to the increase of the number of PMSGs in the wind farm connected to power system via VSC-HVDC.At the same time,the subsynchronous(supersynchronous)oscillationwill also occur in VSC-HVDC system under the influence of PMSG-based wind farm.Based on the reduced-order model of the wind farm connected to power system via VSC-HVDC,the mechanism of subsynchronous(supersynchronous)oscillation in the system is explained in the 6th chapter of this paper.A joint damping control scheme of PMSG-based wind farm and VSC-HVDC system is proposed to enhance the damping of subsynchronous(supersynchronous)oscillation mode in the system.