Stability Assessment and Simplified Control Strategy for DC Microgrids with Constant Power Load

Abstract

Dynamic performance of the DC microgrid is seri ously affected due to negative impedance characteristics of the constant power loads (CPL). It deteriorates the system damping, especially when network impedance is not negligible. In this con dition, stability margin assessment and DC-DC converter control are essential. This paper proposes a novel and straightforward virtual negative impedance-based control loop for analysing the stability and design of the controllers for DC-DC converters connected at both source and load ends to enhance the CPL stabilization. First, a simple pole-zero criterion-based strategy is used to evaluate the virtual negative resistance. Further, small signal and extended large-signal models of the bidirectional buck/boost are proposed for assessing system stability with CPL. A comparative stability analysis is conducted to illustrate the system’s resilience in the face of changes in parameter values. Also, eigenvalue analysis and real-time simulations are performed with the proposed control strategy at the load and source side converters without affecting the load side voltage profile to demonstrate its effectiveness.