Research On Dynamic Performance Optimization Of VIENNA Rectifier

The increasing demand for high-power applications makes the application of three-phase PWM rectifiers more and more extensive.Among them,VIENNA rectifier,as a three-level topology,has became the hotspot due to the advantages of small switching voltage stress,high power density,high efficiency,low THD,etc.In order to improve the performance of VIENNA rectifier under unbalanced three-phase voltage input and load transient condition,this thesis analyzes the working principle and working mode of VIENNA rectifier,and establishes the state average mathematical model of abc natural coordinate system and dq rotating coordinate system.Combined with the mathematical model,the shortcomings of the traditional control strategy under the case of unbalanced three-phase voltage input and load transient change are discussed.Then a new nonlinear control strategy is proposed,namely current inner loop passive control and voltage outer loop sliding mode control.The control strategy can effectively improve the dynamic performance of the system,reduce the system time constant,reduce the DC side capacitance value requirement,and increase the system power density.In order to optimize the selection of DC-side capacitors,this thesis analyzes the low-frequency ripple of capacitor current under traditional SPWM modulation,harmonic injection SPWM modulation and equivalent SVPWM modulation.The results show that two modulation methods with zero-sequence component injection can effectively reduce the low frequency ripple of the capacitor current.The high-frequency equivalent simplification is used to analyze the capacitance current.The results show that the primary component of the high-frequency ripple current of the capacitor current is much larger than the low-frequency ripple.Based on this conclusion,the film capacitor with large rated current is selected to filter out high-frequency components.While the electrolytic capacitor with small rated current and a large capacitance is selected to filter out low frequency components and stabilizes the output voltage.In this thesis,the above control strategy and design method are simulated and verified,and a 10 kW VIENNA rectifier prototype is designed and implemented.The dynamic and static comparison experiments verify the effectiveness of the proposed control strategy and design method.