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Abstract-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.

The control of switching dc-dc converters is reviewed. Regarding it as a general linear quadratic regulator (LQR) problem, an innovative optimal and robust digital controller is proposed. The control strategy adopted can achieve good regulation, rejection of modest disturbances, and more significantly, the ability to cater to switching converters with RHP zeroes. This controller design is a general approach that is applicable to all PWM-type dc-dc converters with their circuit topologies known or unknown. Modern CAD techniques are used to reach the final control law. Application to a published Cuk converter is illustrated as an example, and the performance evaluation is given.

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