Impact of Voltage Modulation Module on Negative Input Impedance and DC-Link Stability in Permanent Magnet Synchronous Motor Drives

The stability of cascaded systems is a critical concern in dc-link voltage oscillation for VSI (Voltage Source Inverter)-driven motor drive systems. To address this issue, impedance network analysis is emerging as a promising assessment solution. Although several analytical models for input impedance have been developed, it is still quantitively unclear which one is more effective or accurate. This manuscript discusses the impact of the voltage modulation module on the input impedance. It reveals that the reference voltage of the modulation module directly determines the input impedance, and common analytical modeling methods need to carefully consider this factor. Discussion and comparison are conducted on transfer functions and stability margins. Simulation results verify the proposed viewpoints by comparing the analytical expressions with the frequency-sweeping results. In summary, this manuscript highlights the impact of modulation modules on input impedance and provides potential guidance for stability assessment and active damping control.