Harmonic impedance assessment using prevailing phasors

Abstract

In accordance with the IEC 61000-3-6, the evaluation of the harmonic emissions requires an accurate harmonic impedance representation of the system. However, the assessment of a harmonic impedance is understood to be a very complex problem and that the available methods are not entirely satisfactory. Yet, utilities and other network users are expected to prove compliance to apportioned emission limits. To enable the online assessment of harmonic emissions, this paper proposes the use of prevailing phasors to enable the monitoring of the network's harmonic impedance. The proposed method has been validated using network simulations and practical measurements at a windfarm were used for offline assessments.

Study on the Estimation of Utility Harmonic Impedance Based on Minimum Norm of Impedance Difference

“…The existing noninvasive methods include: the fluctuation methods [15]- [17], the regression methods [18]- [22], the method based on covariance characteristic of random vectors [23], ICA methods [11], [24], [25], and other methods [26]- [30]. The fluctuation methods and regression methods can get accurate results with the preconditions, that is background harmonic is stable and customer harmonic impedance is much larger than that of the utility side.…”

“…In addition, the aforementioned methods [15]- [30] are all based on this assumption that the harmonic impedance of utility side is invariable in a measurement period. However, in practice, the harmonic impedance of utility side is timevarying provided the loads of the grid change continuously, but the variation of the impedance is very small at adjacent sampling time.…”