Modelling and quantitative direct digital control for a DSP-based soft-switching-mode rectifier

The dynamic modelling and digital controller design for a soft-switching mode rectifier (SSMR) are presented. First, the design and implementation of an SSMR are described. This SSMR is formed from the conventional boost-type SMR by adding an auxiliary resonant branch, and zero-voltage-transition (ZVT) soft switching is achieved by applying suitably delayed pulse width modulation (PWM) signals to the main and auxiliary switches. In addition to the power circuit, sophisticated control is indispensable for the SSMR to have good sinusoidal line current tracking performance under a well-regulated DC output voltage. In dealing with the current control loop, the small-signal model is first derived using a state-space averaging method, and accordingly, the digital current-controlled PWM scheme is designed. As to the voltage control loop, its dynamic model is first estimated from measurements. Then, a quantitative design procedure is developed to find the parameters of the digital voltage controller according to the prescribed control specifications. The PWM switching scheme and the designed controllers of the SSMR are realised digitally using a DSP-based control computer. The effectiveness of the designed controllers is verified by some simulation and experimental results.