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

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

Projected Cross Point -- A New Average Current-Mode Control Approach

Projected cross point, a new current-mode control technique, is introduced and analyzed in this paper. Despite having an analog nature, the proposed method combines the advantages of both analog and digital control techniques. Unlike the conventional analog control methods, it accurately controls the average value of the inductor current with no need to a current compensator or an external ramp. In addition, while resembling the deadbeat characteristics of digital controllers, projected cross point control does not suffer from computational time delay, limit cycling, and quantization and truncation errors. Dynamic performance of the proposed approach is compared with the existing control methods. Analytical analysis and simulation results show the superior accuracy and transient response of projected cross point control approach

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

Cascaded H-bridge Multilevel Inverters -- A Reexamination

Multilevel converters have gained popularity in high-power applications due to their low switch voltage stress and modularity. Cascaded H-bridge converters are a promising breed of multilevel converters which generally require several independent dc sources. Recently, existence of a redundant switching state has been utilized to replace the independent voltage sources with capacitors except for the one with the highest voltage level. Redundancy in the charge and discharge modes of the capacitors is assumed to be adequate for their voltage regulation. However, output current of the inverter as well as the time duration of the redundant switching states have been neglected. In this paper, the impacts of connected load to the cascaded H-bridge converter as well as the switching angles on the voltage regulation of the capacitors are studied. This study proves that voltage regulation is only attainable in a much limited operating conditions that it was originally reported

Numerical Simulation of the Dynamics of Water Droplet Impingement on a Wax Surface

The impact of droplets on solid surfaces is important for a wide range of engineering applications, such as ink-jet printing, spray cooling of hot surfaces, spray coating and painting, solder-drop deposition, blood spattering for criminal forensics and disease detection, etc. This paper simulated the dynamic process of a water droplet impinging onto a wax substrate in COMSOL, using the Phase Field method for tracking the free surface. The predicted spreading factor and apex height were validated against experimental results, showing good agreement during the dynamic impingement process. The effect of contact angles on the impingement process was also studied. The initial inertia driven spreading process is not affected by the contact angle, but the later spreading process and recoil process are significantly affected by the contact angle. The simulation results can provide a good understanding of the dynamic impingement process and provide insights on how surface wettability can affect the droplet spreading and rebounding process

A Nano-Cheese-Cutter to Directly Measure Interfacial Adhesion of Freestanding Nano-Fibers

A nano-cheese-cutter is fabricated to directly measure the adhesion between two freestanding nano-fibers. A single electrospun fiber is attached to the free end of an atomic force microscope cantilever, while a similar fiber is similarly prepared on a mica substrate in an orthogonal direction. External load is applied to deform the two fibers into complementary V-shapes, and the force measurement allows the elastic modulus to be determined. At a critical tensile load, “pull-off” occurs when the adhering fibers spontaneously detach from each other, yielding the interfacial adhesion energy. Loading-unloading cycles are performed to investigate repeated adhesion-detachment and surface degradation

Mechanical Property Characterization of Mouse Zona Pellucida

Previous intracytoplasmic sperm injection (ICSI) studies have indicated significant variation in ICSI success rates among different species. In mouse ICSI, the zona pellucida (ZP) undergoes a hardening process at fertilization in order to prevent subsequent sperm from penetrating. There have been few studies investigating changes in the mechanical properties of mouse ZP post fertilization. To characterize mouse ZP mechanical properties and quantitate the mechanical property differences of the ZP before and after fertilization, a microelectromechanical systems-based multiaxis cellular force sensor has been developed. A microrobotic cell manipulation system employing the multiaxis cellular force sensor is used to conduct mouse ZP force sensing, establishing a quantitative relationship between applied forces and biomembrane structural deformations on both mouse oocytes and embryos. An analytical biomembrane elastic model is constructed to describe biomembrane mechanical properties. The characterized elastic modulus of embryos is 2.3 times that of oocytes, and the measured forces for puncturing embryo ZP are 1.7 times those for oocyte ZP. The technique and model presented in this paper can be applied to investigations into the mechanical properties of other biomembranes, such as the plasma membrane of oocytes or other cell types

How to Establish Successful Cooperative Student Learning Centers for STEM Courses

Students learn more if they are actively involved in the learning process, particularly in a cooperative manner. Several UMR faculty have operated course-based learning centers (LCs) as part of the campus-wide Learning Enhancement Across Disciplines (LEAD) Program of student learning assistance and enhancement. LCs are designed to assist large numbers of students in a cost- and time-efficient manner that promotes student engagement without requiring undue amounts of faculty time. Course instructors spend time in the open learning environment of the LC, in lieu of office hours, guiding students to master course material and skills in their evolution from novice to expert techniques. The goals are to build student self-confidence through direct interaction with role models and to develop teamwork skills. LCs can be much more attractive to students than faculty office hours or traditional tutoring because they satisfy the social elements of student learning communities. However, there are a few simple practical elements instructors should orchestrate to generate high-volume LC usage. We will discuss practical issues of establishing and operating successful learning centers for STEM (science, technology, engineering, mathematics) courses