Nonlinear disturbance rejection control for a buck-boost converter with load uncertainties

For the problem of adaptiveness degradation of Buck-Boost converters in the presence of load uncertainties, a nonlinear disturbance rejection control method is proposed based on a load disturbance estimation. Firstly, a disturbance observer is constructed to estimate the disturbances caused by load uncertainties. Then, the inductance current tracking signal which ensures offset-free tracking of the output voltage is designed based on the disturbance observation value. Finally, a nonlinear disturbance rejection control approach is proposed by using the feedback linearization technique. The proposed control method can effectively address the problem of nonlinearities and non-minimum phase characteristic involved in the system when the capacitor voltage is taken as the system output. It could also overcome the undesirable influence on the output voltage caused by the uncertainty of load change. In addition, the method can effectively avoid the singularity problem led by current zero-crossing when using the duty ratio to control the output voltage directly. The simulation results show that the proposed control strategy guarantees fast output voltage regulation and offset-free tracking performance even in the presence of sudden load changes. This will eventually improve the adaptive property against load changes for the Buck-Boost converter system.