Research On Power Loss Optimization And Dynamic Power Flow Of Wind Power System With DFIGs

Large-scale wind power penetration affects the economy and security of the power system.In order to improve the economic of wind power system,it is necessary to research on the impact of wind power integration on power loss.Considering the internal loss of doubly-fed induction generator(DFIG),under the maximum power point tracking(MPPT)strategy,the active output of DFIG is unknown before power flow calculation.However,the existing sensitivity index of power loss cannot reflect the influence of wind speed fluctuation;therefore,it can not be used in the wind power system with DFIGs directly.With the increased capacity of wind power integration,wind turbines replace synchronous generators(SGs)partially and participate in frequency regulation.The dynamic power flow distributes the unbalanced power to generators,and can quantify the change of system frequency.The existing dynamic power flow literatures focus on the SG,and do not consider the primary frequency regulation capability of wind turbine generators.In order to solve above problems,the detailed power flow model of DFIG is introduced to quantify its internal loss.Based on this,the power loss optimization and dynamic power flow of wind power system with DFIGs are investigated.The main contents are as follows:(1)Based on the MPPT strategy,the conventional power loss sensitivity model is extended to establish relationship between the active power loss of the system and wind speed,and a new active power loss sensitivity model is proposed to reflect the influence of wind speed on power loss.The numerical results validate the feasibility and accuracy of the proposed sensitivity model.And the proposed sensitivity index can be regarded as an auxiliary criterion to choose the var control modes for DFIGs and the location of wind farm.(2)Based on overspeed and pitch angle control and droop control,the dynamic power flow model considering DFIGs participating in primary frequency regulation is proposed.In this model,the captured power,rotate speed,and slip of the DFIG are decided by frequency change.And the inertia of the DFIG is quantified.The constraints of the DFIG and the power system are solved together to quantify the output power.The numerical results show that inertia of the DFIG is decided by the wind speed and the deloading level.With the deloading level fixed,the higher wind speed yields the more effective frequency support ability of DFIGs.(3)Although the existing economic dispatch literatures consider the system frequency and the frequency regulation capability of the SG,but ignore the wind power or use the simplified model of wind turbine.In order to take DFIG's primary frequency regulation capability into consideration in economic dispatch,a probabilistic optimal power flow(OPF)model with the DFIGs participating in the primary frequency regulation is newly proposed.The dynamic power flow model considering DFIGs participating in primary frequency regulation is introduced to the OPF to quantify the deviation of system frequency.The frequency is introduced in the optimization object and security constraints.And the wind forecast error is sampled to implement the probabilistic OPF model.The proposed model is validated to be effective through calculation and analysis.With the suitable weighting coefficients of the object function,the generation cost and the frequency deviation may be coordinated.