Fractional Control Of MMC Based On Ant Colony Simulated Annealing Algorithm

With the rapid development of power electronic technology,the research of multi-level converter and its related technology has gradually become a hot spot in the field of high-voltage and high-power power application..As a new type of multi-level converter topology,MMC overcomes the shortcomings of traditional multi-level converter with its unique structural advantages and is widely recognized in the field of HVDC transmission.Aiming at the limited choice of the parameters of the traditional integer order PI controller,which can lead to the poor control effect of the DC side voltage and circulation of MMC,and the problem that the traditional algorithm is easy to fall into the local optimal solution and slow convergence speed when setting the controller parameters,This paper takes MMC as the research object and proposes MMC fractional order controller design method based on ant colony simulated annealing algorithm.It mainly includes the following contents:Firstly,the research background and significance of this paper are briefly described,and the topological structure and working principle of MMC are expounded.The topological structure and the operation mechanism of sub-modules of MMC are elaborated in detail.The mathematical equivalent model of MMC is deduced,and the control mode and modulation strategy of MMC are analyzed respectively.Secondly,according to the theory of fractional-order controller,the function module of fractional-order controller is built.Aiming at the problem of fractional PI parameter setting,the advantages and disadvantages of the ant colony algorithm and the simulated annealing algorithm are analyzed in this paper.In order to overcome the disadvantages of the two algorithms,the pheromone updating rules of the traditional ant colony algorithm are improved,and the Metropolis criterion,the core of the simulated annealing algorithm,is introduced into the improved ant colony algorithm.Ant colony simulated annealing algorithm is proposed.Ant colony simulated annealing algorithm takes ITAE as objective function,and three algorithms are simulated on MMC model with constant DC voltage fractional PI controller.Simulation results show that the proposed algorithm has faster convergence speed and better searching effect for controller parameter tuning.Finally,in order to verify the superiority of fractional-order controller applied to MMC,the fractional-order controller is applied to the constant DC voltage controller and the circulation suppression controller respectively,and compared with the integer-order controller system.When applied to constant DC voltage controller,the simulation results show that the fractional order controller can make the system have better dynamic characteristics,In addition,the DC side voltage has better robustness when the AC side is disturbed by sudden rise.Simulation results show that the circulation of the bridge arm can be further suppressed by the introduction of the fractional PI controller in MMC system.