Stability Analysis Of Three-phase Grid-connected Inverter System Based On Multi-frequency Small Signal Model

With the advancement of energy transformation,the proportion of new energy power generation in total power generation is increasing,power electronic devices are widely used in various links of the power system,and the trend of power electronics dominated power system is becoming more and more obvious.The dynamic characteristics of the power system also change,and the weakening of the power grid is an issue that cannot be ignored.The grid-connected inverter is a key part of the power electronics dominated grid-connected system.It is different from traditional mechanical devices and generates a lot of harmonics during operation.At the same time,the coupling between the grid-connected inverter and the weak grid is very complex.The stability of grid-connected inverter systems has received the common attention of academia and industry.In this paper,the three-phase LCL grid-connected inverter system is taken as the research object,and several main grid-connected interface filter structures and their damping characteristics are analyzed.Aiming at the inherent resonance peak in the LCL filter,the passive damping scheme and the active damping scheme are evaluated from the aspects of performance effect and economic value,so as to provide a basis for the reasonable selection of the damping scheme.Focus on the sideband and aliasing effects of the PWM link in the grid-connected inverter system,and a multi-frequency small-signal model of the PWM link and a multi-frequency small-signal model of the three-phase grid-connected inverter system have been established.After mathematical simplification of the multi-frequency small-signal model,a PWM link gain K^*_PWM considering sideband and aliasing effects is finally obtained.In this paper,the impedance analysis method is selected as the stability analysis method,and the influence of the grid-side impedance on the stability of the three-phase grid-connected inverter system has been studied.Under the same conditions,different stability analysis results based on the traditional PWM link gain K_PWM and K^*_PWM are compared.Finally,the basic information and working situation of the hardware-in-the-loop experimental platform are introduced.The main circuit model is built in the semi-physical simulation device Typhoon 602.The digital control is performed by the DSP TMS320F28335 and FPGA XC3S400PQ208.The hardware-in-the-loop experimental platform is used to complete the load mutation dynamic experiment and impedance switching dynamic experiment of the three-phase grid-connected inverter system.The experimental results verify the correctness of the theoretical analysis based on the impedance analysis method and show the accuracy of the stability analysis based on K^*?PWM?.