Research On Electric Energy Metering Method Under Non-sinusoidal And Unbalanced Conditions

Electric energy metering is a basic work related to whether China can smoothly implement energy policy and electric power system reform and whether the national economy can develop rapidly.Traditional electric energy metering method was proposed in the period when the power system is approximately under perfectly sinusoidal and balanced status.However,harmonic and three-phase unbalance pollution caused by the large-scale application of nonlinear asymmetric loads such as electric arc furnace,spot welder and electric locomotive make traditional electric energy metering method far from satisfactory.Therefore,it is valuable for both economical development and technological development to explore an electric energy metering method that charges more fairly and reasonably and can encourage customers to actively adopt effective solutions to control harmonic and unbalance.Firstly,aiming at the problem that existing harmonic voltage or current distortion rate and the three-phase fundamental voltage or current unbalance factor are not comprehensive,can only assess the unbalance in the fundamental component and easily lead to contradictory evaluation results,a set of new evaluation indexes of harmonic and unbalance pollution level are obtained according to the IEEE Std.1459-2010 power theory and its decomposition method for apparent power.A single-phase system and a three-phase system simulation model are set up and every existing and newly proposed evaluation indexes are calculated and compared.The results show that all new indexes combine voltage and current from the perspective of apparent power and take into account the unbalance in harmonic components,so they can more accurately,comprehensively and effectively assess harmonic and three-phase unbalance interference factors.Then,through the formula derivation,the detailed analysis of the active power metering ways under the three conditions is carried out,and it can be known that the full active power metering way is no longer applicable under any conditions.Therefore,under the most general non-sinusoidal and unbalanced condition,this dissertation points out that the fundamental positive-sequence active power metering way is more reasonable.According to the fundamental positive-sequence power factor,effective power factor defined by IEEE Std.1459-2010 power theory and new harmonic and unbalanced pollution comprehensive evaluation index,the theoretical calculation formula of the metering error between the full active power metering way and the fundamental positive-sequence active power metering way is derived.The analysis results of the example verify the rationality of the fundamental positive-sequence active power metering way and the correctness of the metering error formula.In the practical issues,it is usually necessary to consider the background harmonic and background unbalance of the power grid.However,the power quality responsibilities of the utility side and the customer side cannot be apportioned according to the evaluation indexes of the power system harmonic and unbalance pollution level.Based on this,two new metering indicators—the billing fundamental active power and the billing fundamental power factor are defined by introducing harmonic responsibility analysis model based on the reference impedance method.Thus a new electric energy metering method which considers harmonic responsibility and is suitable for single-phase non-sinusoidal condition is proposed.The simulation analysis is carried out on three different examples,and the various metering indicators required for the existing and new electric energy metering method in each example are calculated.The calculation results show that the new electric energy metering method not only improves the existing electric energy metering method which can not compensate and punish the users according to the harmonic responsibility of the utility side and the customer side,but also has good practical value.Finally,analogous to the single-phase system electric energy metering method considering harmonic responsibility,combining with the unbalance responsibility analysis model,a new electric energy metering method which comprehensively takes into account harmonic and unbalance responsibility and is suitable under non-sinusoidal and unbalanced condition is proposed.The new method can compensate and punish the three-phase users for being forced to absorb the harmonic and unbalance and generating harmonic and unbalance respectively by examining the billing fundamental positive-sequence active power and the billing fundamental positive-sequence power factor which are two newly defined metering indicators.Therefore,it can effectively promote the power supply system and the users to take certain measures consciously for dealing with the harmonic and three-phase unbalance pollution problems caused by themself.