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Almost all existing relevant literatures are focused on the multi-inverter system that only contains one type of inverter. Till now, the interactions in multi-inverter system consisting of polytype inverters have been not investigated systematically. To fill this gap, the paper is aimed at the stability study of the generic system containing multiple types of inverters. The mathematic model of interactions...
Instabilities due to mutual interactions among inverters in a grid system are sometimes observed. This paper proposes a stabilization method which adds feed-forward (FF) loop characteristics to improve output frequency impedance characteristics which satisfy the Nyquist stability criterion. The principle is that the output impedance is compulsively made passive with the FF loop characteristics and...
The asymmetric inverter controller structure or parameters result in frequency coupling in phase domain for the three-phase grid-connected inverter system. And it is difficult to measure the inverter admittance matrix in engineering practice due to the coupling term. What's more, applying the coupled admittance matrix to analyze the system stability, the generalized Nyquist criterion (GNC) has to...
Phase locked loop (PLL) and Park transformation largely affects the stability of a grid-inverter system. Impedance-based approach is employed to analyze the effect of PLL to stability in this paper. Self-admittance and accompanying admittances are set up to represent the inverter including the PLL effect, and Nyquist criterion is employed to analyze the system stability. An asymmetric current control...
To address the instability issue in renewable systems of a radial-line structure with multiple current-controlled interface inverters, this paper proposes a practical stability criterion to easily analyze the system stability and a controller parameter design method to guarantee stable system operation with good oscillation damping performance. The proposed impedance-based sufficient stability criterion...
The interaction between STATCOM and voltage-source inverter (VSI) may cause instability in an islanded micro-grid. Impedance models of storage battery power convert system (PCS) and cascaded multilevel static synchronous compensator (STATCOM) are established based on which the interaction mechanism between PCS and STATCOM is studied. Using Nyquist stability criterion and admittance ratio analysis,...
A controlled power inverter can cause instability at the point of common coupling (PCC) with its output filter and the grid. This paper analyzes the influence of the Phase-Locked Loop (PLL) on the output admittance of single-phase current-controlled inverters with different grid stiffness. It shows that the PLL introduces a paralleled admittance into the output admittance of the inverter, which may...
This paper investigates the dynamic interactions of current controllers for multi-paralleled, grid-connected inverters. The consequent harmonics instability phenomena, which features with oscillations above the fundamental frequency, are evaluated by the impedance-based stability criterion. The frequency range of effective impedance-based stability analysis is first identified. The effect of each...
Grid-connected inverters are known to become unstable when the grid impedance is high. Existing approaches to analyzing such instability are based on inverter control models that account for the grid impedance and the coupling with other grid-connected inverters. A new method to determine inverter-grid system stability using only the inverter output impedance and the grid impedance is developed in...
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