Aiming at the problems in the coordination control of multi-power conversion unit and system energy management in multi-terminal flexible interconnected AC/DC power distribution systems

we propose a hierarchical control strategy based on different time scales. The first layer control is the modulation mode and basic control mode of each transform unit

ensuring that each transform unit can normally perform its function. The second layer control achieves stable operation of the system under normal and fault conditions

it divides the system into three operating intervals and five working modes according to the DC bus voltage of the system

and generates a first layer of control commands according to different working modes

which is used to switch the flexible interconnecting device and the photovoltaic power generating unit in the system. The third layer control comprehensively optimizes multiple targets such as maximizing the new energy utilization

minimizing the system loss

optimizing the state of charge of battery

and minimizing the system total electricity price

thus generates second-level scheduling instructions to achieve optimal operation under normal operating conditions of the system. Finally

the proposed control scheme is verified by system simulation. The system can be switched according to the control scheme in each working mode

and the optimal energy scheduling of the system can be realized at the same time.