DC Bus System for Servo Drives and its Stability Analysis

A servo drive has been used widely in the industrial market. Recently, utilizing the regenerative energy of the motor has become important in the drive for energy efficiency. Also, the problems of EMI noise and complexity of wiring from a 3-phase PWM inverter became obvious in the factory application as well. A DC bus system should be a solution because it can handle a battery for the regenerative energy easily, and an integrating servo drive with motor does not diffuse noise. Further, it can save wiring dramatically. However, the system has a risk of instability between the DC bus line and the servo drives. In this paper, an impedance-based stability analysis method is introduced for the DC bus system of the servo drive. The system instability was demonstrated experimentally, and the theoretical and measured results are matching within 10% accuracy.