Research On Three-level Three-phase Unbalance Regulator

With the rapid development of economy and the continuous improvement of industrial level,the phenomenon of power system pollution caused by the extensive application of non-linear loads is brought about at the same time.In China's urban and rural power grids,a large number of Y/yn0 transformers are used for power transmission and distribution,and three-phase four-wire system is adopted.Phase voltage 220 V or line voltage 380 V are used as common power supply.Single-phase load users generally have the characteristics of different load sizes and power consumption simultaneity,and have the problems of low power factor and high harmonic content.When the asymmetric distorted current of the user converges to the bus circuit,the macroscopic phenomenon is the voltage distortion caused by the distorted current in the network,and the increase of the midline current caused by the unbalanced three-phase current.In this paper,a three-level three-phase unbalanced regulator is designed to compensate three-phase harmonics and reactive power while adjusting three-phase unbalanced current.After choosing three-level NPC converter topology as the main circuit of the regulator,the working principle and mathematical model of the topology are analyzed,the hardware circuit and main circuit parameters are designed,and the DC side capacitance is calculated and designed from the angle of the influence of the middle line current on the DC side capacitance.Secondly,the problem of neutral point potential caused by DC component of capacitive current is clarified,and the voltage feedback is fed into the instruction current as DC component to realize the stability of neutral point potential.Subsequently,the principle of multi-harmonic detection is explained,and single-phase harmonic detection with clear physical meaning and simple use is selected as the load current processing algorithm.Finally,the modulation method and control strategy of the three-level three-phase regulator system are designed,and the system is simulated and experimented to verify the effective compensation of the three-level three-phase regulator for harmonics and three-phase unbalance,so as to achieve the goal of the project.