Research And Design Of The Three-level Rectifier Using Multi-closed-loop Control Strategy

In this thesis, the neutral point clamped three-level SVPWM rectifier is studied. Diode-clamped PWM rectifier topology is analyzed in detail. At the same time, the principle of rectifier is studied in depth in this article. Ultimately, mathematical model of the three-level rectifier is established in ABC stationary coordinate system and the dq synchronous rotation coordinate system. Through the transformation of three-phase AC variables to two-phase DC variables, model calculations and process analysis of the three-level rectifier are simplified. At the same time, three-phase to two-phase coordinate transformation laid the theoretical foundation for the controller design of the rectifier.The three-level PWM modulation algorithm is the core of the three-level rectifier. Through analyzing the three-level rectifier SVPWM modulation principle and combining with the idea of voltage vector decomposition g-h Coordinate, SVPWM modulation algorithms have been designed and implemented.On the basis of in-depth study, a new multi-loop control strategy of the working range of the dead zone for three-level SVPWM rectifier is proposed. The added closed-loop control of the working range of the dead zone can effectively suppress the rectifier line-side current harmonics. In this paper, voltage and current double closed loop direct current control strategy has been adopted. Decoupling control of the dq axis current is implemented.Current dynamic characteristics to be improved, because the current transient control strategy was introduced.This strategy adds the closed-loop control module of the working range of the dead zone to the original voltage and current dual-loop closed-loop control system and forms a three-loop closed-loop control system. The working range of the dead zone refers to the range which needs to add the dead zone in one cycle. Closed-loop control of the working range of the dead zone refers to the dynamic closed-loop control on the working range of the dead zone through the DC bus voltage and active power feedback according to the rectifier’s different working conditions. The main purpose of this control strategy is to control the working range of the dead zone at the rectifier’s different working states to suppress the harmonic due to the role of the dead zone.According to the above control strategy, the rectifier system simulation model is built in PLECS and MATLAB/Simulink system simulation software. Simulation results show that the added closed-loop control of the working range of the dead zone can effectively suppress the rectifier line-side current harmonics. The correctness of the algorithm is validated by the control algorithm simulation. This topic is supported by1140V/1MW pairs of three-level converter systems research projects. A TMS320F28335, DSP+CPLD control platform is built to do experiments. Through experiment, the correctness of the control strategy can be proved. Rectifier rectifier and energy feedback performance and other performance indicators also are verified.