Modeling And Analysis Of AC-DC Converter For Energy Storage Based On Sequence Impedance

With the development and utilization of the new energy technologies, bi-directional converter, as a link between it and the grid connection, is directly related to the reliability and accuracy of the entire energy storage system. Due to the improvement of the technology and promotion in demand, the stability of distributed power system becomes more and more prominent. Thus it has important practical significance on the research of solving the stability problem about connecting bi-directional converter to the grid.This paper describes the impedance modeling method of three-phase uncontrolled rectifier and three-phase PWM Rectifier. The three-phase system is decomposed into two subsystems decoupled from each other. According to the concept of harmonic linearization, using analytical mapping function to describe the transfer of voltage and current to deduce positive-and negative-sequence impedance models of the subsystem. This paper focused on the analyses of the sequence impedance model of three-phase PWM Rectifier. Firstly, the author derives the input impedance model on AC side of rectifier and output impedance model of the grid. Then the author analysis the dynamic interaction of the three-phase systems by using Nyquist stability criterion and verifies effectiveness of mathematical model by the simulation experiments. Secondly, the author also analysis the influence of the size of DC bus capacitor on the DC bus voltage, and puts forward a method to stabilize the DC bus voltage by increasing the passive damping. Experiments show that when an RC damper access, the changes of the DC bus voltage. Finally, the influence of the PLL on stable operation of the converter is analyzed. Based on the basic SPF-PLL, the author has derived a small signal model on it and verifies the sequence impedance model under dq current control by using the main circuit parameters.