Direct digital control of PWM converter using closed-loop identification

This paper presents a new technique of designing a direct digital controller for a single-phase pulse width modulation (PWM) converter system, based on closed-loop identification. It is difficult to analytically design a controller due to the double loop structure of the PWM converter control system. The design procedure consists of three steps. First, obtain a current controller for the inner loop system by using the error space approach, which is a powerful method for robust tracking control design. The outer loop is composed of a voltage controller, a current control loop including the current controller, a PWM converter, and a capacitor. Then, all the components, except the voltage controller, are identified by a discrete-time equivalent linear method, using the closed-loop output error (CLOE) method. Based on the equivalent model, a proper digital voltage controller is then directly designed. It is shown through PSim simulations and experimental results that the proposed method is useful for the practical design of PWM converter controllers.