| Power factor is an important technical index of power system,which can reflect the line loss and measure the efficiency of electrical equipment,and is the standard to measure the reward and punishment of reactive power to power users.With the renewable new energy and large-scale power electronic equipment getting accessible,the power quality problems such as harmonic and negative sequence become increasingly prominent,and the energy flow in the system becomes more complex and changeable,and the current power factor calculation method is controversial.The rationality and accuracy of power factor depend on the correct definition of power.How to determine the power definition suitable for nonlinear unbalanced system by taking negative sequence,harmonics and other power quality interference factors into account has been concerned by researchers at home and abroad.Firstly,the characteristics of nonlinear and asymmetric loads in power system are analyzed and summarized,and the types of nonlinear load and asymmetric load and the resulting power quality problems are introduced.Taking harmonic generated by nonlinear load and negative sequence generated by asymmetric load as the research objects,the power direction of negative-sequence and harmonic is analyzed,and the influence of harmonic and negative sequence on power grid and electric energy metering is analyzed.Secondly,the current power factor in China and the equivalent power factor based on the IEEE Std.1459-2010 standard are studied,and based on the characteristic that the power loss and the square of the apparent power in the power system approximately satisfy a linear relationship,the system power loss models under linear symmetric load,asymmetric load and nonlinear load are established respectively in the three-phase system,and the rationality of traditional power theory and equivalent power theory under different power quality influences are compared and analyzed,which is also verified by the MATLAB simulation model and measured data of traction substation.The results show that the equivalent power factor calculation method can accurately measure the power factor of the system under situations with negative-sequence and harmonic.Finally,based on the current power factor assessment standard in China,the power factor assessment mechanism under situations with negative-sequence and harmonic is studied.Taking the analysis of filtering cost,the analysis of negative-sequence compensation cost and the analysis of reactive power compensation cost for electric energy users as foundation,construct the model of power factor incentive mechanism and the model of power factor constraint mechanism under situations with negative-sequence and harmonic,and the feasibility of the models are verified by examples. |
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