Stability Analysis and Compensator design for Cascaded Converters

Abstract

The present work deals with the modeling and the stability of the cascade converters. When a converter tightly regulates its output, it behaves as a constant power load (CPL). The problem of CPLs is that they show negative incremental resistance that causes instability in the system. Hence the CPL has been modeled and linearizaed to study its effect on the source converter. On this basis, it was found that because of the negative resistance exhibited by the CPL, the control to output transfer function possessed a RHP pole and thus makes system unstable. The effect of the introduction of small resistance in series with inductor of source converter on the stability was analyzed. Also the compensation on the basis of the passive components i.e. snubbers were designed so as to reduce the power dissipation due to the resistance. Type III compensation was designed by taking the input impedance of the load converter as the load for the source converter using K factor method. Further, based on input impedance, minor loop gain concept was used for stabilizing the system.