The Control Strategies Of Three-Level Pulse Rectifier

Pulse rectifier is a kind of rectifier under the pulse-width modulation. Pulse rectifier had the advantages of low harmonic, small size, light weight and fast dynamic response compared to the conventional phased converter.Two-level pulsed rectifier is already quite mature after decades of development, but has a lot of difficult problems in the high-power applications. Such as need expensive and bulky transformers, high switching loss and the power switch is difficult to achieve the required. So three-level rectifier comes into being. For the IGBT in the three-level rectifier is double to the two-level, so voltage that each switch is exposed only half to the two-level, thus increasing the life of the power switch. After all the three-level can produce five kinds of line voltage level, Harmonic content of output voltage and current is far less than two-level rectifier under the same control. Finally, the cost of power devices is to engage with the high voltage levels increased, so the three-level is better than two-level in the high- power circuit. For these, the three-level PWM rectifier was used in the CRH2.Indirect current control and direct current control were the two major control methods for the three-level rectifier. Direct current control including hysteresis current control, transient control and predict current control. The paper analyzed the every control mode. Aiming at neutral point shift problem of three-level Neutral Point Clamping rectifier, two effective control schemes were presented. Calculations of main parameters were given in the paper. A supposes was confirmed that the LC circuit can remove through increase the support capacity in some certain circumstances. At last three simulation models are designed in Matlab/Simulink environment, carried out a systematic simulation and analyze when the loads were changed.The simulation results show that the whole system can achieve the unity power factor, the neutral point voltage control is fast and effective. The output voltage ripple is larger under the indirect current control, In contrast the other two control methods are better, output voltage drop is small and adjustment time is short when the load changed. However, the instantaneous current control and predict current control have some problems in some certain circumstances. In a word, the instantaneous current control and predict current control can meet the static and dynamic performance requirements for various conditions.