Constant Power Loads: A Solution using Sliding Mode Control

Rapidly increasing penetration of renewable energy sources into conventional power distribution systems has led to the rise in power electronic converter dominated power distribution systems. However, it has been a well established that the presence of tightly regulated point-of-load (POL) converters in the power distribution system, which act as Constant Power Loads (CPLs), cause serious stability challenge in spite of ensuring stability of individual converters. In this paper, we propose a sliding-mode controller with a non-linear sliding surface to mitigate negative impedance instabilities caused by the CPLs in dc distribution systems (dc Micro-grids). The stability of proposed surface and existence of sliding modes are proved. A simplified structure of a dc micro-grid system with dc/dc boost converter and CPL is used for the implementation of the proposed controller. Proposed controller is able to mitigate negative impedance instabilities and ensures stable operation of dc micro-grid system under various disturbances. The performance of the proposed controller, under steady state, line and load variations are validated through simulations in MATLAB Simulink environment.