Inter-phase And Intra-phase DC Voltage Balancing Control Strategy Of Three-phase Cascaded Rectifier

As the power grid gradually develops towards intelligence,there are higher requirements for its fault isolation capability,power quality,energy management,compatibility,etc.Traditional transformer has been unable to adapt to the needs of future smart grid.Compared with traditional transformers,the power electronic transformer has a variety of topological structures,and it can use power electronic technology to achieve flexible power control control purposes.So it has great prospects in the power grid.However,unbalanced loads can cause voltage unbalancing in cascaded power electronic transformers.Aiming at the problem of DC voltage unbalancing in three-phase cascaded H-bridge power electronic transformer,this thesis completes the following work:First of all,the development of power electronic transformers is elaborated.then the typical topological structures and control methods are mentioned.On this basis,the topology of the three-phase star cascaded H-bridge rectifier studied in this paper is proposed.For the three-phase star cascaded converter,its mathematical model and active power model are established.Secondly,On the basis of the mathematical model,the thesis studies the DC voltage unbalancing of the three-phase star-cascaded H-bridge rectifier and the reason for the unbalanced DC voltage of the inter-phase and intra-phase modules is analyzed.Aiming at the problem of inter-phase DC voltage balancing,a hybrid modulation strategy that combines sinusoidal pulse width modulation technology and sequencing voltage balancing is proposed.Then aiming at the problem of intra-phase DC voltage balancing,a voltage balancing algorithm by zero-sequence compensation is proposed.Finally,combined with the three-phase DQ decoupling control,the overall voltage balancing control algorithm is proposed.。Then,the simulation model of the three-phase star cascaded H-bridge rectifier is established based on MATLAB/Simulink.Simulation experiments are carried out on the system load switching,the input process of the voltage balancing algorithm,and the dynamic and static performance.Finally,the feasibility and correctness of the voltage balancing algorithm proposed are verified.Finally,on the basis of theoretical research and simulation verification,a low-power experiment platform for three-phase star cascade rectifier is established.And the control program is designed based on FPGA controller.Finally,the experiment verifies the system’s DC voltage balancing ability and dynamic/static performance.