Nonlinear behaviors in parallel-connected half-bridge inverters

Based on a case study example of a voltage-mode controlled half-bridge inverter, this paper illustrates the slow-scale instability and fast-scale instability phenomena mathematically. An average model for slow-scale instability analysis and a discrete-model for fast-scale instability analysis are presented. The main results are illustrated by simulations. It is shown that the slow-scale instability happens as low frequency oscillation anywhere in a cycle, while the fast-scale instability happens as a period-doubling bifurcation in a local zone. The paper is also extended to include the parallel-connected inverters. Parallel-connected inverters have different properties for both slow-scale and fast-scale instability. Using the similar approach as that used for analyzing the single inverter, the relationships between parameters and slow-scale and fast-scale instability of the parallel-connected inverters are derive.