Design And Research On Control Strategy Of VIENNA Rectifier

With the development of science and the improvement of human living standard,power electronic devices have been widely used in various fields,but at the same time,the harmonics and reactive power pollution of power grids caused by nonlinear power devices have become increasingly serious.Under the trend of gradual promotion of new energy electric vehicles,the impact of car charging devices on the power grid can't be ignored,and it has received more and more attention and research.As a three-level power factor correction topology,VIENNA rectifiers have unique advantages such as small number of switching devices,simple circuit structure,and no shoot-through problem.They are applicable to the design and application of front-end PFC circuits in charging devices and have attracted the attention of many scholars.In this paper,the mechanism analysis and model construction of the current zero-crossing distortion problem of the VIENNA rectifier,the neutral-point voltage balance and oscillation suppression,and the system control problem under the unbalanced three-phase grid conditions are carried out,and corresponding control strategies are proposed,and mainly research and design from the following several aspects:Firstly,the topology and working principle of the high power factor VIENNA rectifier are introduced.Then,based on the switching function and the state-space averaging method,the mathematical model and equivalent circuit of the VIENNA rectifier are constructed.At the same time,the cause of VIENNA's neutral-point voltage imbalance is also analyzed,which provides theoretical foundation for the subsequent study of the control algorithm.Secondly,the generation mechanism of the current zero-crossing distortion of the VIENNA rectifier is analyzed.Then a novel carrier modulation method with zero-sequence injected component is proposed in combination with the neutral-point voltage balance control and oscillation suppression.At the same time,the double closed-loop control strategy of VIENNA rectifier based on current feed-forward decoupling control is used.The new modulation control strategy not only ensures neutral-point voltage balance,but also solves the current zero-crossing distortion problem.Thirdly,aiming at the unbalanced three-phase grid voltage,the mathematical model of VIENNA rectifier under this working condition is analyzed,and an improved single-synchronous coordinate system phase-locked control scheme is proposed.The improved phase-locked loop not only can quickly separate the positive and negative sequence components of the unbalanced grid voltage,but also can accurately track the phase information of the power grid.At the same time,the inner loop current loop adopts quasi PR controller,and its dynamic response can quickly follow the elimination of current reference signal error to ensure that the current harmonics in the unbalanced grid are reduced,and the system stably operates.Finally,the VIENNA rectifier experiment platform based on Texas Instruments'new dual-core DSP28377+CPLD controller is set up.The hardware and software design of the system is introduced in detail.Afterwards,the validity and correctness of the control strategy presented in this paper is verified by prototype experiments.