Research Of Three-level PWM Rectifier Under Unbalanced Input Voltage Conditions

In recent years, with the development of power electrics technology, the application technology of power semiconductor devices have been greatly improved, thus contributing to the wide range of applications of power electronic converters installed in the industrial and agricultural production and civilian. A large part of the converters need rectification link to obtain the DC voltage to achieve’green’ power conversion to be one of the priorities of power electronics technology research. This paper in unbalanced three-phase grid conditions for neutral point clamped three-level PWM rectifier control strategy focus.PWM rectifier can achieve the network-side power factor adjustable, two-way flow of energy and non-grid pollution. This paper analyzes the problems of the conventional rectifier, described the basic principle of the voltage-type three-level PWM rectifier, to establish the mathematical model of the basic mathematical model in the three-phase stationary coordinate system and two-phase rotating coordinate system, the control strategy of the study provides a theoretical basic.The article through the three-phase software and phase lock loop realize the power grid voltage phase synchronous acquisition, and deep research on three level voltage source PWM rectifier voltage current double closed loop control and parameter design. On this basis, the equilibrium conditions of the grid voltage under steady state and dynamic simulation and experiment. Simulation results verify the correctness and feasibility of the design of this article provides a theoretical basis for the actual parameter circuit design.The traditional balance of rectifier control strategy, encountered the grid voltage imbalance will make the line-side current and dc output measured a large number of harmonics, the AC side voltage waveform distortion, serious and even burned the device burned the device, affecting the performance of the voltage-type three-level PWM rectifier. This article in view of the power grid unbalanced condition, Grid unbalanced conditions, the network side of the current symmetry control strategy and the elimination of the DC side of the second harmonic of the current control strategy used in the three-level PWM rectifier, were realized on the network side of the input current and output voltage of DC side the control.Based on the theory of the above, the grid voltage balanced and unbalanced control strategy based on the Matlab environment simulation. The simulation result show that inhibition of the exchange of negative sequence current component of the control strategy to improve the rectifier AC-side current waveform, so that the waveform of the basic symmetry; Adopt double current control strategy, basically eliminate the dc side of the second harmonic component. Through the simulation of unbalanced control strategy to achieve energy feedback, the system has good dynamic and static performance.