Analysis And Modulation Research On Zero Voltage Switching Three Phase PWM Rectifier

Three phase voltage source PWM Rectifier, due to its remarkable features of high input current Power Factor and low EMI emissions is widely used in middle and high power rectifier fields. However, the anti-parallel diodes of all the switches experience reverse recovery process, which will cause severe switching loss, high di/dt and EMI problems. The soft switching technology for three-phase rectifier or inverter can solve the diode reverse recovery problem.The Compound Active Clamping (CAC) ZVS three phase PWM rectifier has a simplified topology and can be controlled by SVM strategy. In order to optimize the circuit efficiency, this thesis builded up the loss model of hard switching and CAC soft switching three phase PWM rectifier and the resonant parameters of the CAC rectifier is optimized. The loss constitution in CAC soft switching and hard switching rectifier are compared. Under unbalanced grid voltage condition, the current control strategy suitable for the CAC rectifier is given and the influence of the unbalanced grid voltage on CAC soft switching rectifier is analyzed. A 40kW CAC rectifier hardware prototype has been developed to verify the theoretical analysis.The Minimum Voltage Active Clamping (MVAC) ZVS three phase PWM rectifier is analyzed, and an improved SVM strategy suitable for MVAC rectifier is proposed in this thesis. The topology only added one auxiliary resonant branch to realize ZVS operation for all switches. In addition, the reverse recovery current in anti-parallel diodes of all switches is suppressed well. And the switching voltage stress on all the power switches is clamped to the DC link voltage. The operation principle and the soft switching condition of the MVAC rectifier are analyzed. In order to optimize the circuit efficiency, the current stress variation and additional turn off loss of the main switch under three modulation strategies are compared. Based on the loss model of MVAC soft switching rectifier, the design guideline of the resonant parameters is described. The influence of the unbalanced grid voltage on MVAC soft switching realization is also analyzed. A 30kW MVAC three phase rectifier hardware prototype has been developed to verify the theory.