2. Impedance Model of Reduced DC-Link Capacitance IPMSM Drives

This chapter delves into the impedance model of PMSM drives with reduced DC-link capacitance, focusing on the stability and dynamic performance implications. The text begins by introducing the impact of small capacitance film capacitors on drive characteristics, followed by a detailed derivation of the mathematical model based on constant-power load characteristics. Frequency response analysis is employed to verify the model's accuracy, providing a theoretical foundation for subsequent stability and control optimization discussions. The chapter explores two topologies of electrolytic capacitorless drives, highlighting their differences and the role of reactors in filtering high-frequency harmonics. The state equation for the drive is derived, considering the constant power characteristics of the motor, and the equivalent model of the drive is presented. The resonance frequency and damping ratio are analyzed, with a Bode diagram illustrating the system's frequency response. The text then considers non-ideal characteristics of the motor side, incorporating sampling and update delays, and current loop bandwidth into the model. The impact of DC-link voltage sampling delay on motor admittance is examined, and the transfer function of the drive is derived. The chapter concludes with an analysis of flux-weakening control, demonstrating its influence on the motor admittance and providing a comprehensive understanding of the drive's behavior under various conditions.