In this paper, the source converter (Voltage Source Rectifier, VSR) of a cascaded system is modeled based on small signal analysis, and the closed-loop transfer functions of the converter are obtained. Then the output impedance of the source converter is calculated. The analysis of the output impedance indicates that the smaller bus capacitance is, the worse stability of the cascaded system will be, and the smaller power can be converted by the cascaded system. Three kinds of virtual impedance control methods are proposed to reduce the output impedance of the source converter, all of them improve the stability and increase the maximum power of the cascaded system. The parameters of the three kinds of methods are designed respectively and their effects are compared. Simulation and experimental results show a good agreement with the theoretical analysis, which proves the validity of the virtual impedance control methods.

As an important interface converter, the three-phase voltage-source rectifier (VSR) connects the grid to DC-input converters. The constant power load (CPL) characteristic of the converter-load often causes large-signal stability problems. In order to solve this problem, the stability boundary of the VSR with CPL is analyzed based on the mixed potential theory, and the stability condition under large-signal disturbance is obtained; thus, the jump range of the load power can be estimated. To improve the stability of the system, a voltage loop control scheme based on ADRC is proposed. A theoretical analysis based on the mixed potential theory shows the proposed scheme expands the power jump range of the VSR with CPL effectively, and improves its disturbance rejection performance. Finally, experimental results prove the effectiveness of the proposed control scheme.