Resonance characteristics analysis of paralleled inverters based on Resonance Stability Margin

With increasing penetration of renewable energy sources into modern power systems, multi-parallel inverters are commonly employed in the interface to the utility grid, giving rise to potential resonance problems. Firstly, 2-parallel inverters equivalent circuit model is established based on its control. In order to decouple inverter output current, the components characteristics of inverter output are analyzed in different frequencies, and one of 2-parallel inverter output current under condition of synchronized and asynchronized carriers are worked out. An idea “Resonance Stability Margin” is raised to investigate and evaluate resonance characteristics, variables that represent the stability of the system are found in control system of single inverter, and are used to record when the system achieves the same closed-loop dominant pole position or open-loop phase margin under different conditions. Values of those variables recorded indirectly reflect the degree of resonance in the paralleled inverters system. Experimental results validate the developed resonance characteristics and the proposed resonance stability margin.