Tuning of phase locked loop for industrial regenerative motor-drive systems

Regenerative motor-drive systems are utilized in several industrial applications that require frequent power generation back to the grid. In these applications, the standard front-end diode bridge commonly used in non-regenerative drives is replaced by an Active Front End “AFE” power converter. The main advantages of the AFE are that it can regenerate power back to the grid, and provide unity power factor operation with a very low total harmonic distortion. The phase locked loop “PLL” is one of the most critical control subsystems in any industrial regenerative motor-drive system. It provides the control of the front-end power converter an accurate knowledge of the utility angle and frequency to ensure proper operation of the whole control algorithm. In this paper, a detailed control analysis and tuning guidelines are presented for the PLL with an adaptive filter under several practical grid steady state and transient conditions.