Electric Energy Metering Method Of Unbalanced Power Supply System And Its Application In Electrified Railway

With the rapid development of modern industry and power market,more and more non-linear and asymmetric loads are connected to the power grid,such as electric locomotive,electric arc furnace and welding machine,which makes the problem of negative-sequence pollution of public power grid increasingly serious.As a result,there are many shortcomings in the existing active energy metering methods and power factor adjustment schemes under the balance condition,and there are unreasonable charges.Therefore,it is urgent to study the reasonable methods of unbalanced responsibility division and the electric energy metering,to clarify the responsibility of each responsible party,reasonably meter electric energy and charge the electric charges,and then force all responsible parties to take corresponding measures to control the electric energy pollution through economic means,to create a good electricity environment.Firstly,the traditional unbalanced pollution evaluation indexes are summarized and analyzed in this thesis.Aiming at the shortcomings of traditional evaluation indexes and methods,based on the power theory of the IEEE Std 1459-2010,a new set of the unbalance pollution evaluation index is proposed from the perspective of apparent power by decomposing the equivalent apparent power under unbalanced conditions.For three-phase power systems with different wiring forms,the corresponding simulation models are built in Matlab/Simulink software to verify the effectiveness and practicability of the proposed new evaluation indexes.The simulation results show that,compared with the traditional evaluation indexes,the new evaluation index can comprehensively reflect the unbalance degree of the system and customers,which is more in line with the actual engineering requirements,has good application value,and effectively solves the problems existing in the traditional evaluation method.Secondly,taking the three-phase unbalanced system as the research object,the negative sequence equivalent circuit model of the unbalance system is constructed in this thesis.Through formula derivation,this thesis analyzes the essence of the traditional unbalance responsibility quantitative indexes and methods,proves that the evaluation essence of the conventional unbalanced responsibility quantitative indexes is inconsistent,and verifies the correctness of the theoretical analysis results with specific examples.Thirdly,aiming at the defects of the traditional unbalanced responsibility division methods,according to the decomposition form of equivalent apparent power,the evaluation index system of unbalanced responsibility is established,and a method of unbalanced responsibility division considering index weight under a multi-index system is proposed.The new method comprehensively considers the influence of negative-sequence voltage and current,and is more reasonable and accurate than the conventional methods of the unbalanced responsibility division.This thesis takes the typical unsymmetrical traction load as the customer object,builds the simulation model in Matlab/Simulink,and designs specific examples for different working conditions.On this basis,this thesis compares and analyzes the results of unbalanced responsibility division calculated by the new method and the traditional methods,and verifies that the new method proposed in this thesis is more accurate and reasonable.Fourthly,taking the fundamental negative-sequence energy generated by the asymmetric load in the power grid as the research object,the flow direction of negative-sequence active power in the unbalanced system is analyzed,which proves that the current total electric energy metering method is unreasonable in the power grid with serious negative-sequence pollution,and the fundamental positive-sequence active electric energy metering method also has some limitations.Aiming at the problems existing in the traditional active electric energy metering method,a new method of rewards and punishments for active electric energy metering considering unbalanced responsibility is proposed.This method not only considers the negative-sequence power flow direction,but also assesses the unbalanced responsibility of customers.It can force those customers who cause negative-sequence pollution to the power grid to take active measures to control them through economic means,to improve the power quality,and effectively maintaining the economic interests of both sides.Finally,this thesis introduces the current power factor adjustment electricity charges method in China,analyzes the rationality of power factor under different definitions under unbalanced conditions,and draws the conclusion that it is more reasonable to adopt equivalent apparent power factor under unbalanced conditions.However,aiming at the shortcomings of the current power factor adjustment electricity charges method in China,in order to comprehensively assess the customer’s electricity behavior,this thesis discusses an adjustment scheme of rewarding and penalizing electricity charges considering unbalanced responsibility.The new scheme not only assesses the influence of fundamental active power consumed by customers,but also comprehensively assesses the impact of negative-sequence unbalanced apparent power generated by both sides of power supply and customer on the system.Compared with the current scheme,the new scheme is more reasonable and feasible,which is helpful for the power supply department to control power quality pollution.Finally,the feasibility and accuracy of the proposed method are verified by a specific example.