Relative Stability Assessment for Wideband Harmonic Resonances in Distributed Generation Power Plants

For assessing the influence of feeder's distributed parameter on the grid-connected current which is emitted by distributed generation power plants (DGPP), hyperbolic function should be introduced in the process of feeder modeling. However, the Taylor approximation of the hyperbolic function makes the Norton equivalent of the DGPP possess a certain number of poles in the right-half s plane. This pole configuration violates the impedance-based stability criterion to be applied. To this end, we proposed equivalently transforming the hyperbolic function via Euler's formula. The advantage of this transformation includes the following two aspects: 1) it could establish the direct correlation between time-domain eigenvalues and system frequencies; 2) it enables us to assess the relative stability of systems in terms of pole-zero method. By using the proposed Eu-ler's formula-based stability-analysis approach, we found that: 1) the underlying causes of the wideband harmonic resonances correlated with the motion patterns of the eigenvalues on the s plane; 2) with the system frequencies increasing, the frequencies of the arc resonance peaks exactly corresponded to the frequencies which made the dominant pole traverse the negative real axis in the s plane from top to bottom.