Research On The Control Strategies Of Single-phase Three-level PWM Rectifier

Relative to two-level PWM rectifier, the shut voltage of power devices of three-level rectifier is half of DC voltage. And equivalent switching frequency is higher than it of two-level rectifier. Harmonic characteristic of voltage and current on the AC side is better. So three-level rectifier is more suitable for high-power application. Single-phase three-level PWM rectifier has been applied in CRH2series EMU.Based on the single-phase three-level PWM rectifier as the research object, this thesis has analyzed its working principle, and has established unified mathematical model of it through the definition switching function. Control strategies of this type of rectifier are the focus in this thesis. Instantaneous current control and forecast current control have been further studied. SPWM modulation method and SVPWM modulation method suitable for single-phase three-level PWM rectifier have been introduced. This thesis has analyzed the cause of unbalance for neutral-point voltage, and proposed a control method based on hysteresis regulation for this problem.In the environment of Matlab/Simulink, a systematic simulation model of single-phase three-level PWM rectifier has been built. Simulation results have proved instantaneous current control and forecast current control can both achieve de voltage keeping stable, current tracking voltage closely on the net side, current harmonic content low. Through the simulation has also verified the instantaneous current control with good dynamic response performance. In addition, the validity of the neutral-point balance control introduced in this thesis has been verified by simulation.Through measurement for CRH380AL EMU, the performance in practical occasion of locomotive traction of single-phase three-level PWM rectifier has been understood. Based on the data measured, power factor and current harmonic characteristic of traction convertor have been analyzed in the condition of low speed. And the reliability of data measured has been verified by simulation.Consider the traction converter of CRH2EMU as the reference, a single-phase three-level PWM rectifier experimental rig has been built. The bases of design of parameters and selection of devices of this rig have been proposed in this thesis.