Steady state stability criteria of A.C. drives play a dominant role for making the drive system practically successful. Generally such analysis is done using small perturbation model. But the complexity of the mathematical formulation depends on the nature of the drive system used. This study presents a detailed analysis of steady state stability criterion based on small perturbation model of a current source inverter fed synchronous motor drive system taking d-axis and q-axis damper winding into account using generalized theory of electrical machines. The modeling also clearly shows that even at no load the system satisfies steady state stability criterion. Routh-Herwitz criterion is used to finalize the result. The methodology of the proposed research work can be stated as follows: The synchronous motor has been treated as a five coil primitive machine model using the concept of generalized theory of electrical machines. Using the concept of Parks transformation the armature current in d-q model has been represented by suitable equations as a function of armature current magnitude in phase model (IS) and the field angle (β). As the system under consideration is basically a current source inverter fed system, IS has been considered as a constant and as a consequence the field angle (β) finally appears as a control variable. Furthermore voltage balance equations of the five coils have been expressed in time domain and those equations has been transformed accordingly after applying Laplace transform technique and then small perturbation technique is applied on the transformed equations. Finally the transfer function Δβ (s)/ΔTL(s) have been formulated; where Δβ (s) and ΔTL (s) represent small change in transformed field angle and load torque, respectively. The analysis concludes that the absence of damper winding leads to instability of the machine system.
A.B. Chattopadhyay, Sunil Thomas and Ruchira Chatterjee, 2011. Analysis of Steady State Stability of a Csi Fed Synchronous Motor Drive System with Damper Windings Included. Trends in Applied Sciences Research, 6: 992-1005.