Synchronous converter and synchronous-VSC- state of art of universal control strategies for smart grid integration

As voltage source converters (VSCs) are finding expanded use, their integration into future smart grids is becoming challenging. The main problems can be categorized as poor frequency regulation because of low overall physical inertia, interactions between synchronous generators (SGs) and VSCs, and switching between grid-connected and islanded modes. To overcome these problems the concept of synchronous converters is introduced to facilitate a general framework for interfacing VSCs to smart grids with emulated inertia, generality for all operational modes, constant frequency and current and voltage regulation capacities augmented in one compact structure. The proposed controllers are also applicable to conventional SGs realizing a unified control strategy for all types of generation units. To integrate VSCs to power system with dc-link voltage regulation ability such as rectifiers, dc, and hybrid dc/ac grids concept of synchronous-VSC and hybrid dc/ac droop or equivalently dc-link vs. frequency droop is developed which provide a tool for bidirectional power flow from dc-link capacitor similar to a virtual rotor. Both simulation and experimental results are presented to validate the practicability of the controllers.