Optimal Operation Strategy Combination Of Multifunctional Power Electronic Transformer

Power electronic transformer(PET)is a new type of power transformer developed with the development of power electronic devices.In addition to the voltage level conversion that can be achieved with traditional transformers,it can also realize the functions of power flow control,reactive power compensation and power quality adjustment.By using multi-port PET,distributed renewable energy can be integrated at multiple voltage levels to achieve flexible networking of system.Multi-port PET contain multiple AC and DC ports at the same time,which are strongly coupled to each other,it is very important to properly coordinate the control between each ports.Compared with the hybrid microgrid power control,in the AC/DC hybrid network composed of multiple multi-port PETs,PET ports is greatly increased,each port may operate in much complicated condition,the power control of each port getting more difficult,and the port operation mode combination is more diverse.What's more,it is necessary to take account the large amount of renewable energy access to the system when controlling the PET port.Due to the fluctuation of renewable energy,the same port of PET may need to run in different mode under different circumstances.At that time,the choice of operation mode of each port will undoubtedly be more complicated.It is urgent to reasonably select the operation control mode of each port of PET,while ensuring the safety of the system and realizing the improvement of the system economy.In the existing control methods,the DC side control methods such as master-slave control,voltage margin control,and droop control all have their own drawbacks.More importantly,the control of the AC side is mostly just equivalent to a PQ or PV node in existing literature,the AC system frequency response problem caused by the interaction between the AC system and DC system in the AC/DC hybrid system is not considered.In view of the above problems,this paper proposes a generalized AC-DC droop control method suitable for AC-DC port control of PET,in which the traditional mode switching is converted into coefficient adjustment,and the scheme reflecting multiple control modes of PET port can be obtained.In order to solve the proposed control coefficient of generalized AC-DC droop control,and obtain the optimal control strategies combination of each port of PET,this paper builds a long-term robust optimization model considering the control strategy of PET,which solving the uncertainty of renewable energy with robust optimization.Bi-level optimization method is used to transform the robust optimization model with uncertain variables into bi-level deterministic optimization model,which is solved alternately.In this paper,the AC/DC hybrid system connected by two 4-port power electronic transformers is built for simulation analysis,and the model is solved based on the ipopt toolbox in matlab.The simulation results verify the effectiveness and feasibility of the proposed control strategy.For the purpose of making the power electronic transformer operation strategy optimization method more intuitive and universal,this paper designs the power electronic transformer operation strategy optimization combination prototype software based on matlab gui function module.After the analysis of the functional requirements and the design of the interface,the corresponding operation interface of the prototype was designed.Including the prototype home interface,the prototype operation main interface and the additional interface of each sub-module of the main interface.After reasonable setting of each module of the prototype,the corresponding program is written and connected to realize the operation and analysis function of the whole prototype,and finally the system data in the third chapter is used to verify the feasibility and effectiveness of the designed power electronic transformer operation strategy prototype.