Study on transient characteristic analysis and stable operation region characterization of parallel heterogeneous inverter systems

New energy power stations adopt a hybrid control mode combining grid-following and grid-forming strategies, which can simultaneously achieve efficient energy capture and reliable active grid support. This is not only an important technical approach to improve the stable operation capability of new energy grid-connected systems, but also an objective requirement for promoting the construction and development of new-type power systems. In heterogeneous systems composed of multiple types of inverters, complex dynamic coupling relationships exist between grid-following inverters and grid-forming inverters. As a result, traditional stability analysis methods for single-machine grid connection are difficult to accurately reflect the overall operating characteristics of the system and have obvious limitations in application. To this end, this paper first constructs a transient mathematical model of a parallel system of heterogeneous inverters, analyzes the coupling mechanism between different types of inverters under various synchronization modes, and derives the phase correlation law when the impedance between inverters and the point of common coupling (PCC) is small. On this basis, the stable operation boundary of the parallel heterogeneous inverter system under grid fault conditions is further characterized, and the theoretical research results are effectively verified through simulation analysis.