A new hybrid virtual synchronous machine control structure combined with voltage source converters in islanded ac microgrids

The high potentiality of integrating renewable energies into a microgrid system using voltage source converters (VSCs) raises some system stability issues as a result of the absence of inertia in VSCs. The virtual synchronous machine (VSM) control concept was consequently introduced to mimic the properties of traditional synchronous machines (SMs). Several VSM controllers with different structures have been introduced in different studies. However, since all VSM swing equation-based models mimic traditional SMs, these models require the reconstruction of a converter controller with a different control structure. This paper proposes a new yet simple and straightforward way to implement a VSM control concept that offers several advantages, one of which is that the proposed hybrid virtual synchronous machine (HVSM) provides a wide stability region compared to a system based on a conventional droop controller. In fact, the proposed HVSM can be applied via modifying only the first low pass filter (LPF) in the power controller. This paper further presents a comparative comprehensive study of the proposed HVSM with the existing VSC based-droop control and VSC based-VSM control based on the islanded AC microgrid, which was introduced in previous work. The stability of the system has been evaluated on a small signal representation model while the performance of both systems has been validated and investigated in a time-domain simulation environment, namely a PSCAD/EMTDC. The results show promising and significant outcomes that will further extend the field of VSM research.