Analysis Of Subsynchronous Oscillations Characteristics And Suppression Strategies Of Doubly-fed Wind Power System With SVG

With the promulgation of the "14th Five-Year Plan",the state has put forward higher requirements in terms of green and energy saving.As the main renewable energy,wind power is developing rapidly,and the installed capacity is increasing year by year,and it is widely distributed,mainly in the northwestern region of China,the Inner Mongolia region and the eastern coastal region.In 2017,the doubly-fed wind farm in the south area of Jingxia experienced multiple Sub-synchronous oscillations.According to on-site analysis,there are a large number of reactive power compensation equipment around it.There is a risk of Sub-synchronous oscillations in the interaction between the equipment and the wind power system.Therefore,in order to ensure the safe and stable operation of the power system,it is of great significance to model the Sub-synchronous oscillation problem of the doubly-fed wind power grid-connected system with Static Var Generator(SVG),analyze the characteristics and propose corresponding suppression measures,This paper has carried out the following researches on the abovementioned related issues.(1)The small signal model of the doubly-fed wind power grid-connected system including SVG is established.Mainly include doubly-fed induction generator,Roter Side Converter(RSC)and its control system,Grid Side Converter(GSC)and its control system,back-to-back DC converter,the 36-order small signal mathematical model of the electrical part of SVG,the control system and the grid-connected external transmission line.(2)The eigenvalues and participation factors are analyzed for the established small-signal model,and the oscillation mode produced by the interaction between the SVG control system and the doubly-fed wind turbine rotor converter control system is determined to be the dominant oscillation mode of the system.From the perspective of system operating parameters and system control parameters,the characteristics of this Sub-synchronous oscillation mode are analyzed and time-domain simulation verification is performed in PSCAD/EMTDC.The research results show that when the reactive power of SVG is insufficient or excessive,the damping of the oscillation mode will be weakened;When the phase-locked loop control parameters in SVG and the reactive power outer loop control parameters of the doubly-fed wind turbine rotor converter change,they will have different effects on the damping and frequency of the oscillation mode.(3)Based on the subsynchronous oscillation caused by the interaction between SVG control system and rotor side converter control system of doubly-fed wind turbine,two suppression measures are proposed.Suppression strategy 1: To add a supplementary sub-synchronous damping controller with the rotor current as the input signal to the rotor voltage at the current inner loop in the rotor converter control system of the doubly-fed wind power grid-connected system.Suppression strategy 2: A parameter optimization method for sub-synchronous oscillations in the system is proposed,and a set of reasonable control parameters for suppressing the oscillation mode are obtained by using this optimization strategy.The results of time domain simulation on PSCAD/EMTDC show that the two suppression measures are effective.