Research On Power Factor Calculation Method Under Non-sinusoidal Unbalanced System

Power factor is an important parameter that reflects line power loss and equipment utilization.China's current power factor index is proposed under the single-phase sinusoidal system.However,with the wide application of power electronic devices,voltage and current distortion and imbalance are becoming more and more serious.China's current power factor assessment indicators cannot accurately reflect system power loss.Therefore,it is imperative to redefine the power factor calculation method in the three-phase non-sinusoidal unbalanced system.In view of the controversy and uncertainty of apparent power calculation in three-phase non-sinusoidal unbalanced systems.The meaning and the scope of application of vector apparent power,arithmetic apparent power and equivalent apparent power based on the criterion that "the apparent power square should be linear with power loss"are deeply analyzes,the difference between the power factor,the power loss,the reactive power compensation effect and the applicability based on the three apparent powers is explored in this paper.On this basis,the equivalent apparent power is chosen as the benchmark for the new power factor calculation.In view of the existing power factor calculation method can not consider the power loss caused by harmonics and imbalance,the paper starts from the essential physical meaning of power loss metric,based on the nature of power factor,defines the power that causes power loss in harmonic and unbalanced environments.The flow and power components are studied to analyze the physical properties of"useful" current and"ideal"load in three-phase systems,and a new power factor calculation method for non-sinusoidal unbalanced systems is proposed.The new calculation method highlights the fundamental positive-sequence active power.The power factor method of the three-phase three-wire system and the three-phase four-wire system is unified on the basis of the loss caused by the neutral line and the phase-to-phase flow power.The power loss caused by fundamental reactive power,harmonics and imbalance is measured accurately.And the new calculation has the characteristics of compatibility,clear physical meaning and wide application range.In view of the fact that the existing power factor does not link the power quality problem and the power loss organically,the apparent power is decomposed into"useful"power and non-"useful" power that consists of fundamental positive-sequence reactive power,unbalanced power,and non-fundamental equivalent apparent power.Based on this,a power factor system including sequence power factor,unbalanced power factor,and harmonic power factor is established.The system measures the power loss and the ratio of equipment capacity caused by the fundamental phase shift,distortion and imbalance respectively.In the calculation of unbalanced power factor,the integrated imbalance is introduced to characterize the overall imbalance of voltage and current.When calculating the harmonic power factor,the harmonic pollution degree is introduced to reflect the overall nonlinearity of voltage and current.The views that the fundamental positive-sequence active power is the only useful power of the three-phase AC system and the three-phase system power loss is regarded as the sum of the power loss of the three single-phase systems is not in line with reality is considered in this paper.The new definition provides a clearer and more scientific basis for improving reactive power compensation,loss reduction and assessing user power efficiency.It has strong guiding significance in guiding users'electricity tariff calculation and pricing the electricity market.