A General Modeling Approach of Bidirectional Disturbance Loops Between DC-Link and Permanent Magnet Synchronous Motor Drives

Voltage oscillation is an essential concern in dc-link capacitance motor drive system, and various stability assessment and active damping control strategies have been developed using impedance network analysis. However, existing techniques primarily focus on power disturbances caused by rectification, with relatively limited discussion on disturbance loops, particularly the bidirectional disturbance transmission between the dc-link and motor stage. This article explores all disturbance loops within the cascaded system, covering the dc-link stage, the motor stage, and their bidirectional transmission. In addition, an innovative decoupling modeling method is proposed to express the bidirectional disturbance interaction, where the dynamic behavior at the motor stage is treated as an equivalent dc-link current disturbance. Furthermore, particular attention is paid to the additional dc-link voltage oscillations caused by the motor behaviors. These additional oscillations are then superimposed on the motor stage, potentially degrading the expected control performance. Taking the motor speed command disturbance as a case, the control structures and transfer functions of each disturbance loop are deduced. The strong agreement between the analytical expressions and the frequency-sweeping method in simulations confirms the accuracy of the proposed method. Furthermore, the dc-link voltage oscillation induced by motor behavior was successfully validated through experimentation. In short, a general analytical modeling process was presented, along with potential areas for improvement.