Impedance-Based Stability Analysis of DC Bus System for Servo Drives

Servo drive motor systems using PWM inverters has become very popular in industry due to its high controllability of torque, speed and position. Recently, the problems of EMI noise and complexity of wiring from 3-phase PWM inverter power line cables has become obvious in a factory settings. Also, utilizing the regenerative energy of the motor has become important in the industry. The DC bus system should be a good choice, however, it has a risk of system instability due to a negative impedance of the servo drives. In our previous study [1], an impedance-based stability analysis was introduced and the predicted critical point (DC bus current) of instability was confirmed by an experiment using a real motor. In this paper, a simulation model was created to see the behavior of the unstable waveform. Simulated waveforms successfully duplicated measured waveforms of the unstable oscillation behavior.