Modeling DC Motor Drive Systems in Power System Dynamic Studies

Direct current (dc) motor drive systems are extensively used in paper, steel, mining, material handling, and other industrial applications due to the high starting torque and easy speed control over a wide range. They could account for 10%-20% load demand in some industrial facilities and thus have significant impact on the overall system dynamics. However, an adequate dynamic model for this type of loads is not available for power system dynamic studies. In this paper, a comprehensive modeling method for dc motor drive systems is proposed considering two scenarios: 1) The drive will trip when subjected to severe voltage sags, and 2) the drive can ride through when experiencing mild voltage sags. The dc drive trip curve and a simple procedure to determine if the drive needs to be included for dynamic studies are proposed for Scenario 1. The dynamic model for dc motor drive systems, which can be readily inserted in the simulation software, is developed and verified through case studies for Scenario 2.