Stability Analysis of Fixed and Variable Frequency Digital Predictive Current Control Schemes

Abstract

In this paper digital predictive average, peak and valley current control schemes suitability for the fourth order boost converter is investigated. Mathematical analysis of predictive average, peak and valley current control schemes is established for fixed and variable frequency of operations. Current control laws are formulated based on the average inductor current information together with digital trailing triangle edge pulse width modulation. The analysis shows that the predictive peak current control scheme is unstable with fixed-frequency operation, while it is stable with variable frequency control. Digital predictive average and valley current control schemes are stable for all duty ratios as well as for fixed and variable frequency of operations. Converter modeling and stability evaluation is carried out using modified discrete modeling approach. Simulations results of the fourth order boost converter support the theoretical analysis. Proposed digital predictive current control schemes, with fixed as well as variable frequencies, are validated through experimental investigations. Since the control law is based on one current sample per cycle the computational burden on the processor is low.