Sampled-Data Modeling and Analysis of Closed-Loop PWM DC-DC Converters

Sampled-data analysis of converters has been a topic of investigationfor the past two decades. However, this powerful tool is not widelyused in control loop design or in closed-loop performance validation.Instead, averaged models are typically used for control loopdesign, while detailed simulations are used for validatingclosed-loop performance. This paper makes several contributions tothe sampled-data modeling and analysis of closed-loop PWM DC-DC converters,with the aim of increasing appreciation and use of the method. General models are presented in a unified and simple manner, while removingsimplifying approximations present in previous work. These models applyboth for current mode control and voltage mode control.The general models are nonlinear. They are used toobtain {it analytical} linearized models, which are in turn employedto obtain local stability results. Detailed examplesillustrate the modeling and analysis in the paper,and point to situations in which the sampled-data approachgives results superior to alternate methods.For instance, it is shownthat the sampled-data approach will reliablypredict the (local) stability of aconverter for which averaging or simulation predicts instability

Reducing Computational Time Delay in Digital Current-Mode Controllers for Dc-dc Converters

A new method to improve the performance of digital current-mode controllers used in dc-dc power conversion is introduced. The proposed scheme is based on a simple prediction method which offers more time for DSP calculations than its conventional counterparts. Therefore, there will be less DSP computational time delay, which results in faster dynamic response and more accuracy and stability in power electronic converters. Principles of operation of the proposed prediction method as well as its application to several digital control techniques are presented

Self-tuned Projected Cross Point -- An Improved Current-Mode Control Technique

Self-tuned projected cross point control for power electronic converters is introduced. Projected cross point control (PCPC) combines the advantages of both analog and digital current-mode control techniques. Despite several advantages, accuracy of the PCPC method depends on the power stage inductor value. However, ferromagnetic characteristics of the inductor core material make the inductor measurement inaccurate. Furthermore, the inductor value is subject to change due to temperature variations or other environmental effects. To overcome the dependence of the PCPC method on the inductor value, self- tuned PCPC approach is introduced in this paper. Unlike the conventional PCPC scheme, self-tuned PCPC method has excellent robustness against the variations of the inductor value. Hence, the average inductor current accurately follows its reference regardless of aging and temperature effects on the power stage inductor. Furthermore, the addition of the self-tuning mechanism does not interfere with the dynamic performance of the conventional PCPC method. Analytical analysis and simulation results show the superior accuracy and transient response of the self-tuned projected cross point control technique

Control Methods in DC-DC Power Conversion -- A Comparative Study

Several control techniques for dc-dc power conversion and regulation have been studied in this paper. Analog approaches have briefly been described since the focus is the newly developed digital techniques. Principles of operation, advantages, and disadvantages of each control method have been described. Simulation results have been used to compare the performance and accuracy of digital control techniques

Sampled-Data and Harmonic Balance Analyses of Average Current-Mode Controlled Buck Converter

Dynamics and stability of average current-mode control of buck converters are analyzed by sampled-data and harmonic balance analyses. An exact sampled-data model is derived. A new continuous-time model "lifted" from the sampled-data model is also derived, and has frequency response matched with experimental data reported previously. Orbital stability is studied and it is found unrelated to the ripple size of the current-loop compensator output. An unstable window of the current-loop compensator pole is found by simulations, and it can be accurately predicted by sampled-data and harmonic balance analyses. A new S plot accurately predicting the subharmonic oscillation is proposed. The S plot assists pole assignment and shows the required ramp slope to avoid instability.Comment: Submitted to International Journal of Circuit Theory and Applications on August 9, 2011; Manuscript ID: CTA-11-016

Advanced current-mode control techniques for DC-DC power electronic converters

There are many applications for dc-dc power electronic converters in industry. Considering the stringent regulation requirements, control of these converters is a challenging task. Several analog and digital approaches have already been reported in the literature. This work presents new control techniques to improve the dynamic performance of dc-dc converters --Abstract, page iv