Control of Parallel Buckboost Converters in a Microgrid using an Extended Kalman Filter

A control scheme for a system of parallel connected buckboost converters in a microgrid is proposed in this paper. The paralleled converters supply an instantaneous constant power load (CPL). An Extended Kalman Filter (EKF) based control scheme is designed to minimize the number of state variables measured. The output voltage of the paralleled converters is the only state variable that is measured and the other state variables are estimated using EKF. The EKF based state estimates quickly converge to the actual converter state variables both in open loop and closed loop. The proposed state estimator based controller is implemented in the form of two control loops namely an inner and an outer loop. The droop based inner control loop performs current sharing and damps limit cycle oscillations due to CPL. An integral controller based outer loop is added to enable voltage regulation without affecting current sharing. Stability conditions for equilibrium point are obtained. Simulation results are presented to show the validity of the proposed control approach.