Research On Topology And Control Strategy Of Cophase Compensation Device Based On MMC

The power quality problems such as negative sequence, reactive power, harmonic and electrical sectioning exist in the existing traction power supply system, these problems have been solved by the co-phase power supply system. At present, the single-three phase combined co-phase power supply system can effectively reduce the capacity of the co-phase compensation device to meet the national standard of power quality, which has a good application prospect. MMC technology is applied in single-three phase combined co-phase power supply system, which has many advantages in high voltage and large capacity converter. Starting with the main circuit topology and control strategy of the co-phase compensation device, the design scheme of Single-three co-phase power supply system based on MMC is studied. The following works are completed in this paper:1.The mathematical model of single-three co-phase power supply system is established, and the principle of power quality compensation and current detection algorithm based on negative sequence are studied. The optimal compensation strategy of the Single-three combined co-phase power supply system is presented based on the limited value of the power quality standard. By the simulation of this model, the validity is verified by good performance.2. A single-three combined co-phase power supply system based on MMC is constructed, and its equivalent model and parameter setting method are given. The differences between topologies in DC side voltage, power distribution and control strategy are compared, and the main circuit topology of the co-phase compensation device based on the four bridge arm of MMC structure is determined.3.The modulation strategy and the control scheme of sub module voltage are studied, The carrier phase shift modulation strategy and the step wave modulation strategy based on sorting algorithm are combined, and an improved carrier phase shift modulation strategy is adopted. With the combination of optimal compensation strategy and improved carrier phase shift modulation, a hierarchical model of upper level converter compensation current calculation and lower level converter output control is established. The proposed model can meet the power quality compensation requirement but also can balance the bridge arm voltage, and the normal operation of MMC is ensured.4. All kinds of load conditions including traction and regeneration are simulated, based on the simulation platform of MATLAB/Simulink. The correctness of the topology and control strategy of the single-three co-phase power supply system based on MMC are proved, which provides an important basis for the design and application of the project.