Voltage Stability Analysis of Inverter-Fed Motor Multi-Machine System Employing VVVF Control

Induction motors represent the predominant dynamic loads within power systems. When operating with variable voltage and frequency control, induction motors exhibit a tendency for continuous oscillation, especially under light load or no-load conditions. This paper focuses on the cascade system comprising an inverter and induction motor. Initially, the small-signal impedance stability analysis method is introduced, which is effective in examining the impedance matching characteristics of the cascade system. Subsequently, the state-space model of the induction motor, operating under variable voltage and frequency control, and the three-phase inverter, functioning under voltage and current double closed-loop control, are derived. A 7.5 kW induction motor is chosen as the model, and the impedance stability of the cascade system is analyzed using small-signal stability analysis. This analysis identifies the frequency band where oscillations occur within the system, and the oscillatory behavior of the induction motor is simulated and validated through MATLAB/Simulink.