Switching frequency regulation in sliding mode control by a hysteresis band controller

© 2016 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other worksFixing the switching frequency is a key issue in sliding mode control implementations. This paper presents a hysteresis band controller capable of setting a constant value for the steady-state switching frequency of a sliding mode controller in regulation and tracking tasks. The proposed architecture relies on a piecewise linear modeling of the switching function behavior within the hysteresis band, and consists of a discrete-time integral-type controller that modifies the amplitude of the hysteresis band of the comparator in accordance with the error between the desired and the actually measured switching period. For tracking purposes, an additional feedforward action is introduced to compensate the time variation of the switching function derivatives at either sides of the switching hyperplane in the steady state. Stability proofs are provided, and a design criterion for the control parameters to guarantee closed-loop stability is subsequently derived. Numerical simulations and experimental results validate the proposal.Accepted versio

Efficiency Optimization in Burst-Mode Buck DC/DC Converters for Sensor Nodes

© 2017 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.In autonomous sensor nodes, switching dc/dc converters are usually employed to power the sensor electronics and also to maintain the operating voltage of an energy transducer around its maximum power point. In such a context, this paper optimizes the power efficiency of buck dc/dc converters when operating in burst mode, which is preferable than the conventional pulse-width modulation technique in lowpower sensor applications. The optimization is carried out by selecting an optimal inductor current to efficiently transfer the energy from the input to the output during the burst. Such optimization is applied when regulating the converter’s output voltage, which corresponds to the supply voltage of the sensor electronics, and also the input voltage, which corresponds to the operating voltage of the energy transducer that is here a photovoltaic module. The theoretical analysis and the experimental results reported herein prove the existence of such an optimal inductor current in both scenarios. Experimental tests with a commercial buck dc/dc converter (TPS62750) show that the use of this optimal inductor current provides up to 9% increase in efficiency, thus prolonging the operating lifetime of the sensor node.Peer ReviewedPostprint (published version

MODELING AND CONTROL OF DIRECT-CONVERSION HYBRID SWITCHED-CAPACITOR DC-DC CONVERTERS

Efficient power delivery is increasingly important in modern computing, communications, consumer and other electronic systems, due to the high power demand and thermal concerns accompanied by performance advancements and tight packaging. In pursuit of high efficiency, small physical volume, and flexible regulation, hybrid switched-capacitor topologies have emerged as promising candidates for such applications. By incorporating both capacitors and inductors as energy storage elements, hybrid topologies achieve high power density while still maintaining soft charging and efficient regulation characteristics. However, challenges exist in the hybrid approach. In terms of reliability, each flying capacitor should be maintained at a nominal `balanced\u27 voltage for robust operation (especially during transients and startup), complicating the control system design. In terms of implementation, switching devices in hybrid converters often need complex gate driving circuits which add cost, area, and power consumption. This dissertation explores techniques that help to mitigate the aforementioned challenges. A discrete-time state space model is derived by treating the hybrid converter as two subsystems, the switched-capacitor stage and the output filter stage. This model is then used to design an estimator that extracts all flying capacitor voltages from the measurement of a single node. The controllability and observability of the switched-capacitor stage reveal the fundamental cause of imbalance at certain conversion ratios. A new switching sequence, the modified phase-shifted pulse width modulation, is developed to enable natural balance in originally imbalanced scenarios. Based on the model, a novel control algorithm, constant switch stress control, is proposed to achieve both output voltage regulation and active balance with fast dynamics. Finally, the design technique and test result of an integrated hybrid switched-capacitor converter are reported. A proposed gate driving strategy eliminates the need for external driving supplies and reduces the bootstrap capacitor area. On-chip mixed signal control ensures fast balancing dynamics and makes hard startup tolerable. This prototype achieves 96.9\% peak efficiency at 5V:1.2V conversion and a startup time of 12$\mu s$, which is over 100 times faster than the closest prior art. With the modeling, control, and design techniques introduced in this dissertation, the application of hybrid switched-capacitor converters may be extended to scenarios that were previously challenging for them, allowing enhanced performance compared to using traditional topologies. For problems that may require future attention, this dissertation also points to possible directions for further improvements

An Overview of Fully Integrated Switching Power Converters Based on Switched-Capacitor versus Inductive Approach and Their Advanced Control Aspects

This paper reviews and discusses the state of the art of integrated switched-capacitor and integrated inductive power converters and provides a perspective on progress towards the realization of efficient and fully integrated DC–DC power conversion. A comparative assessment has been presented to review the salient features in the utilization of transistor technology between the switched-capacitor and switched inductor converter-based approaches. First, applications that drive the need for integrated switching power converters are introduced, and further implementation issues to be addressed also are discussed. Second, different control and modulation strategies applied to integrated switched-capacitor (voltage conversion ratio control, duty cycle control, switching frequency modulation, Ron modulation, and series low drop out) and inductive converters (pulse width modulation and pulse frequency modulation) are then discussed. Finally, a complete set of integrated power converters are related in terms of their conditions and operation metrics, thereby allowing a categorization to provide the suitability of converter technologies

A User Programmable Battery Charging System

Rechargeable batteries are found in almost every battery powered application. Be it portable, stationary or motive applications, these batteries go hand in hand with battery charging systems. With energy harvesting being targeted in this day and age, high energy density and longer lasting batteries with efficient charging systems are being developed by companies and original equipment manufacturers. Whatever the application may be, rechargeable batteries, which deliver power to a load or system, have to be replenished or recharged once their energy is depleted. Battery charging systems must perform this replenishment by using very fast and efficient methods to extend battery life and to increase periods between charges. In this regard, they have to be versatile, efficient and user programmable to increase their applications in numerous battery powered systems. This is to reduce the cost of using different battery chargers for different types of battery powered applications and also to provide the convenience of rare battery replacement and extend the periods between charges. This thesis proposes a user programmable charging system that can charge a Lithium ion battery from three different input sources, i.e. a wall outlet, a universal serial bus (USB) and an energy harvesting system. The proposed charging system consists of three main building blocks, i.e. a pulse charger, a step down DC to DC converter and a switching network system, to extend the number of applications it can be used for. The switching network system is to allow charging of a battery via an energy harvesting system, while the step down converter is used to provide an initial supply voltage to kick start the energy harvesting system. The pulse charger enables the battery to be charged from a wall outlet or a USB network. It can also be reconfigured to charge a Nickel Metal Hydride battery. The final design is implemented on an IBM 0.18µm process. Experimental results verify the concept of the proposed charging system. The pulse charger is able to be reconfigured as a trickle charger and a constant current charger to charge a Li-ion battery and a Nickel Metal Hydride battery, respectively. The step down converter has a maximum efficiency of 90% at an input voltage of 3V and the charging of the battery via an energy harvesting system is also verified

Design and Analysis of a Fully-Integrated Resonant Gate Driver

Several decades ago the resonant gate driving technique was proposed. Given the recent rapid growth in GaN HEMT power device applications for high-frequency power applications, research has been conducted in the power electronics field using resonant gate driving for GaN power devices. Previous research for resonant gate drivers for GaN HEMT devices mostly focused on implementing the gate driving function itself, and mostly for normally-on HEMT devices. The normally-off (enhancement mode) GaN power device was introduced to the commercial market in 2009. A new resonate gate driver is proposed in this work to implement resonant gate driving for commercial high-speed normally-off GaN power devices. The desired resonant condition is configured by different turn-on and turn-off driving pulses with specific driving time and pulse width. Using synchronous timing control within the driver integrated circuit, the power device gate voltage is securely clamped within the expected gate voltage at switching frequencies beyond 10 MHz. In this research, a customized resonant gate driver IC was designed and developed on a commercially-available silicon CMOS process. Compared with current commercial gate driver ICs, our test results demonstrate the effectiveness, advantages and limitations of the proposed gate driver IC for the enhancement-mode GaN power device using alternative resonant gate driving techniques for the first time

Design and evaluation of a very high frequency dc/dc converter

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2007.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (p. 139-143).This thesis presents a resonant boost topology suitable for very high frequency (VHF, 30-300 MHz) dc-dc power conversion. The proposed design is a fixed frequency, fixed duty ratio resonant converter featuring low device stress, high efficiency over a wide load range, and excellent transient performance. A 110 MHz, 23 W experimental converter has been built and evaluated. The input voltage range is 8-16 V (14.4 V nominal), and the selectable output voltage is between 22-34 V (33 V nominal). The converter achieves higher than 87% efficiency at nominal input and output voltages, and maintains efficiency above 80% for loads as small as 5% of full load. Furthermore, efficiency is high over the input and output voltage range. In addition, a resonant gate drive scheme suitable for VHF operation is presented, which provides rapid startup and low-loss operation. The converter regulates the output using high-bandwidth on-off hysteretic control, which enables fast transient response and efficient light load operation. The low energy storage requirements of the converter allow the use of coreless inductors, thereby eliminating magnetic core loss and introducing the possibility of integration. The target application of the converter is the automotive industry, but the design presented here can be used in a broad range of applications where size, cost, and weight are important, as well as high efficiency and fast transient response.by Robert C.N. Pilawa-Podgurski.M.Eng

Analysis And Design Optimization Of Multiphase Converter

Future microprocessors pose many challenges to the power conversion techniques. Multiphase synchronous buck converters have been widely used in high current low voltage microprocessor application. Design optimization needs to be carefully carried out with pushing the envelope specification and ever increasing concentration towards power saving features. In this work, attention has been focused on dynamic aspects of multiphase synchronous buck design. The power related issues and optimizations have been comprehensively investigated in this paper. In the first chapter, multiphase DC-DC conversion is presented with background application. Adaptive voltage positioning and various nonlinear control schemes are evaluated. Design optimization are presented to achieve best static efficiency over the entire load range. Power loss analysis from various operation modes and driver IC definition are studied thoroughly to better understand the loss terms and minimize the power loss. Load adaptive control is then proposed together with parametric optimization to achieve optimum efficiency figure. New nonlinear control schemes are proposed to improve the transient response, i.e. load engage and load release responses, of the multiphase VR in low frequency repetitive transient. Drop phase optimization and PWM transition from long tri-state phase are presented to improve the smoothness and robustness of the VR in mode transition. During high frequency repetitive transient, the control loop should be optimized and nonlinear loop should be turned off. Dynamic current sharing are thoroughly studied in chapter 4. The output impedance of the multiphase v synchronous buck are derived to assist the analysis. Beat frequency is studied and mitigated by proposing load frequency detection scheme by turning OFF the nonlinear loop and introducing current protection in the control loop. Dynamic voltage scaling (DVS) is now used in modern Multi-Core processor (MCP) and multiprocessor System-on-Chip (MPSoC) to reduce operational voltage under light load condition. With the aggressive motivation to boost dynamic power efficiency, the design specification of voltage transition (dv/dt) for the DVS is pushing the physical limitation of the multiphase converter design and the component stress as well. In this paper, the operation modes and modes transition during dynamic voltage transition are illustrated. Critical dead-times of driver IC design and system dynamics are first studied and then optimized. The excessive stress on the control MOSFET which increases the reliability concern is captured in boost mode operation. Feasible solutions are also proposed and verified by both simulation and experiment results. CdV/dt compensation for removing the AVP effect and novel nonlinear control scheme for smooth transition are proposed for dealing with fast voltage positioning. Optimum phase number control during dynamic voltage transition is also proposed and triggered by voltage identification (VID) delta to further reduce the dynamic loss. The proposed schemes are experimentally verified in a 200 W six phase synchronous buck converter. Finally, the work is concluded. The references are listed