## 5 Hybrid AC/DC Microgrid Control Strategies
### Power Generation Control  
In [93], the authors achieve optimized transient performance in hybrid DC/AC microgrids by an improved virtual synchronous generator (VSG) for its high-performance control strategy. This improved control strategy is achieved by modifying a standard virtual synchronous generator. An additional controller is embedded in an improved virtual synchronous generator to use in grid-connection, which is pre-synchronized. To analyze the stability of a system, a small-signal model for an improved virtual synchronous generator is also built. The power output of the hybrid DC/AC microgrid is assisted by another controller, which is built for the energy storage system. Various transient cases of conventional virtual synchronous generator control, droop control, and the improved virtual synchronous generator were tested under all possible conditions. The pre-synchronized controller is also tested. The results of the tests show that the performance of the improved virtual synchronous generator is smoother than the conventional virtual synchronous generator. Randomness and uncertainties in distributed generations cause an effect on permeability. Due to vulnerability and uncontrollability to interference, the conventional power transformers in the architecture of smart micro are not suitable in smart buildings [94]. To segregate the obstruction to the grid and to enhance the saturation of distributed generation, hybrid microgrid architecture for a smart building is present. Thus, in a complicated and changing grid environment, the stability and the safety of a system can be ensured. This architecture got the following advantages. (1) Modular multilevel converter-based solid-state transformer (MMC-SST) is fully used for controllability. (2) The complementary space of distributed generations and the time characteristics. (3) The energy storage systems have the peak shaving capacity. The typical operating mode characteristics were analyzed, i.e., off-grid mode and grid-connected mode. The complete control strategy merging with the features of each mode is aimed. After all, the complete control strategy and the efficiency of the architecture are tested through a simulation. For the effective utilization of distributed renewable energies, a microgrid is an efficient method. Due to the high perforation of distributed renewable energies, consuming and coordinating a huge quantity of distributed generators within alone microgrid has become infeasible, which causes a continuing transformation in distribution systems [95]. The forming of a microgrid cluster by interlinking multiple microgrids is an effective way to enhance the quality of operation for the larger-scale integration of distributed generators. To form the microgrid clusters, the control coordinated operation and the flexible configuration between multiple microgrids have not been sufficiently referred to. The solution to this problem is a novel design of architecture for numerous microgrids and their coordinated control schemes. In a first step hybrid unit of common coupling is designed, which is an advanced microgrid interface and used in place of the traditional point of common coupling. The hybrid unit of common coupling utilizes a modular multilevel converter as its main module and delivers DC and AC interfaces mutually. The hybrid unit of common coupling based is developed for multiple microgrids, where these microgrids were interconnected via the DC interface and were grid-connected via the AC interface. The coordinated control schemes beneath various operation circumstances are built on the suggested architecture. The hybrid unit of common coupling-based architecture was tested in PSCAD based on the demonstration project in Guangxi, China. The results of the simulation of interconnected microgrids with a suggested architecture and control schemes show that it works efficiently and effectively under various scenarios. The suggested