Research Of Three-phase Voltage-source PWM Rectifier And It’s Control Strategy Under Unbalanced Source Voltage

In recent years, the rapid development of power electronic technology makes the products of converter technology distribute in every corner of the national economic system. The voltage source rectifier in three-phase three-wire system are widely used because of a series of advantages like, high dc voltage output, two-way energy flow, no pollution, unit power factor operation and so on. As long as the industrialization process forward, human demand for electricity volume increased year by year, the development of the grid technology is not good enough to maintain the grid balance and stability all the time. First, it is because of the uncertainty of power capacity in the single-phase. Second, in some places the machine need to work with a larger single phase load. Last, the single phase load in the gird s is not at the same time in our daily life, etc. The control structure of traditional VSR does not take into account the situation of the grid voltage unbalanced, it will cause the VSR abnormal operation, power quality decline and even result in the damage to the VSR. So, the study about the performance of VSR under the condition of unbalanced power grid has become a hot issue at that [4].Usually, the input voltage can be equivalent to the three-phase symmetrical positive and negative sequence and zero sequence voltage combined when VSR under power grid voltage unbalance fault. The measurement of grid angular velocity can’t be accurate as a result of the existence of negative sequence voltage component, and leads to the unbalance of the ac current even lead to the VSR overheating or burned. In this paper, the following work has carried out:First of all, this paper introduces the traditional topology structure of VSR, and set up a mathematical model in(d, q) coordinates system, and briefly introduces the working principle of VSR.Second, compare the difference of between the trap and the time delay method that to extract the positive and negative sequence component under the condition of unbalanced power grid. According to different direction of application, make an analysis and research about the suppression of dc second harmonic and current negative sequence refer to the mathematical model of VSR. The main idea of the method is to filter or control the unnecessary negative sequence component, so as to achieve another state of "balance". In the process of actual operation, unbalanced power grid is a brief mutation process, in usual. Due to the disturbance resistance of PI controller is insufficient and the parameters setting is a trouble, introduces a novel fuzzy particle swarm optimization(F- PSO) algorithm, because the PSO algorithm are more vulnerable to of local convergence in peak search, by using the fuzzy controller to modify the parameters in real time to balance its strength in the global and local search, finally adjust the parameters of PI controller and improve the steady-state performance of the VSR.Finally, set up a model in MATLAB/Simulink and make a simulation about the system anti-interference ability of VSR and the inhibition of harmonic and negative sequence under grid voltage unbalance, in respectively. The simulation results show that the parameters of PI controller can make a real-time adjustment with F-PSO algorithm, and ensure the VSR have a stable operation.