An improved LQR-based controller for switching DC-DC converters

In a previous paper, an account had been given to the various aspects for the control of PWM-type switching dc-dc converters, and an LQR-based digital combined observer controller had been proposed. This paper reports the progress on further research in this topic. It is found that the design of the state estimator (observer) according to the previous paper will lead to a steady-state error in the output voltage in comparison with the reference value and there are difficulties in designing state estimators for converters with uncertain parameters. This paper presents an improved design so that the drawbacks mentioned above can be overcome. By applying the theory of statevariable feedback, a general approach for controlling PWM-type switching dc-dc converters with or without “unstable” zeros, and capable of achieving good regulation and rejection to modest disturbances, will be presented. An application example based on a published Cuk converter will also be given.