Stability analysis of multi-paralleled grid-connected inverters including the distribution parameter characteristics of transmission lines

Abstract

The sparse distribution characteristics of renewable energy resources can lead to there being tens of kilometers of transmission lines between a grid-connected inverter and the actual grid. Accurate analysis of the stability of such grid-connected inverter systems currently involves using a complex hyperbolic function to shaped model of the transmission line circuit. This has proved to be problematic, so, drawing upon the distribution parameter characteristics of transmission lines, this paper looks at how to use impedance-based stability criteria to assess the stability of multi-paralleled grid-connected inverters. First, the topology of multi-paralleled inverters connected to the grid via transmission lines is established, using each transmission line terminal as a grid connection point. Each grid-connected system is taken to be equivalent to a small-signal circuit model of the source-grid. Euler's formula and the Nyquist stability criterion are combined to assess the stability of the associated grid-connected current transfer functions and evaluate the stability of the grid-connected current. Finally, a simulation analysis circuit is constructed to verify whether power line intervention will cause stability problems in the grid-connected system. Overall, it is found that long-distance transmission lines are more likely to cause unstable output of the grid-connected current. It is also found that the number of grid-connected inverters, the short-circuit ratio (SCR), the distorted grid and the inverter parameters can all have a significant impact on the stability of the grid-connected current.