High Speed DC-DC Converter with Self-Oscillating Control

In order to reduce the overall size of the power conversion device several advanced techniques can be applied. One of the direct ways is increasing switching frequency of DC-DC converter. This leads to decreased size of bulky energy storage components, such as inductors and capacitors. However, a rapid rise of operating frequency brings new challenges. Among those are significant switching and conduction losses, which make using conventional topologies of converters impractical. Therefore, various new topologies should be investigated. This Thesis presents design and simulations of High speed DC-DC converter with self-oscillating control. The design procedure is described in details for discrete implementation on printed-circuit board. The simulation results are analyzed and a few additional recommendations for improving efficiency and performance of circuit are given. The proposed converter consists of cascaded power stage, duty-cycle detector, pulse shaper, and transformer. The primary winding of transformer serves as a filter load coil and secondary supplies feedback signal to the gates of switching transistors by employing duty-cycle detector and pulse shaping circuit. The designed High speed DC-DC converter with self-oscillating control provides an output voltage of 2.34 V while operating at 3.4 MHz switching frequency. The reported efficiency of circuit is 70.35%. The input voltage is 4 V and duty cycle is 58%. The operation of converter is intended for variable supply voltage from 3 V to 5 V. A resonant gate driving technique with respect to the proposed DC-DC converter is also presented in that work. The converter provides 2.30 V of output voltage and efficiency of 72.4%. The operation frequency is 3.35 MHz

Dual active bridge converters in solid state transformers

This dissertation presents a comprehensive study of Dual Active Bridge (DAB) converters for Solid State Transformers (SSTs). The first contribution is to propose an ac-ac DAB converter as a single stage SST. The proposed converter topology consists of two active H-bridges and one high-frequency transformer. Output voltage can be regulated when input voltage changes by phase shift modulation. Power is transferred from the leading bridge to the lagging bridge. It analyzes the steady-state operation and the range of zero-voltage switching. It develops a switch commutation scheme for the ac-ac DAB converters. Simulation and experiment results of a scaled down prototype are provided to verify the theoretical analysis. The second contribution is to develop a full-order continuous-time average model for dc-dc DAB converters. The transformer current in DAB converter is purely ac, making continuous-time modeling difficult. Instead, the proposed approach uses the dc terms and 1st order terms of transformer current and capacitor voltage as state variables. Singular perturbation analysis is performed to find the sufficient conditions to separate the dynamics of transformer current and capacitor voltage. Experimental results confirm that the proposed model predicts the small-signal frequency response more accurately. The third contribution addresses the controller design of a dc-dc DAB converter when driving a single-phase dc-ac inverter. It studies the effect of 120 Hz current generated by the single-phase inverter. The limitation of PI-controller is investigated. Two methods are proposed to reduce the voltage ripple at the output voltage of DAB converter. The first method helps the feedback loop with feedforward from inverter, while the second one adds an additional resonance controller to the feedback loop. Theoretical analysis, simulation and experiment results are provided to verify the effectiveness of the proposed methods --Abstract, page iii

Inductive Buck Converter Based on Low Voltage NanoScale CMOS

Cascode architecture is an efficient and cost effective design technique to overcome the reliability issues regarding Gate-Oxide breakdown. This method is employed for circuits such as DC-DC converters and power amplifiers operating with input supply voltage higher than transistor breakdown voltage. Design of the gate bias circuit which controls the switching operation of the power stage transistors is the main challenge in this technique, especially for the power stage with more than two stacked transistors. The bias circuit generates the required gate drive signals with proper timing to avoid the voltage stress condition. This thesis presents design and simulation results of the buck type DC-DC converter based on 45nm CMOS technology. Breakdown voltage of the transistor is 1.1V. Therefore, 6-stacked power stage configuration is proposed for a fixed input voltage of 6V by considering a maximum supply voltage of 1V for each transistor. Switching operation of the power stage is controlled by driving signals for PMOS and NMOS stacked tran-sistors. In order to generate the driver signal, three cascade stages of high speed level shifters are employed to shift up the driver signal by 5V. Switching frequency is 52MHz and open loop control scheme is considered for the buck converter. The control circuit consists of a Schmitt trigger and a Non-Overlapping switching circuit to gener-ate the driving signals with adjusted dead times. The designed buck converter provides an output voltage of 1.25V and has an efficiency of 79.2% with a fixed input power of 207mW. A second buck converter circuit is also presented that operates under variable battery voltages from 3.5V to 6V. Using the designed circuit the output voltage is 1.25V and a maximum power conversion efficiency of 81.3% is obtained for an input voltage of 3.9V. The output power is 200mW and a high power density of 195mW/mm3 is achieve

A single stage full bridge power factor corrected AC/DC converter

Conventional single phase AC/DC converters use a two stage power configuration to provide a regulated DC power supply at high input power factor. Elimination of one of these stages can reduce the cost, weight, size, complexity and increase the overall reliability of this converter. This thesis proposes a single stage power factor correction converter circuit. This proposed converter circuit uses the traditional non-power-factor corrected circuit configuration with only few additional components. These are: an additional winding on the high frequency transformer, a small high frequency inductor and three diodes. The topology allows the output voltage regulation and input current shaping with a single power processing stage and one control chip. In addition, it is shown that this converter can be designed to offer soft switching of the full bridge switches. The operating principles of the proposed converter are discussed and its performance characteristics under steady state conditions are examined. A design procedure is illustrated to select the components of the converter for a 500 W power supply operating at 50 kHz. Theoretical results are verified with simulation and experimental tests on a 500 W laboratory prototype

Advance Three Phase Power Factor Correction Schemes for Utility Interface of Power Electronic Systems

Modern power electronic systems operate with different voltage and/or frequency rating such as Adjustable speed drive, Micro Grid, Uninterruptable Power Supplies (UPS) and High Voltage DC Transmission Systems. To match power electronic systems with the mains supply, DC link converters are used. The first stage of the DC link converter is the AC/DC conversion (rectifier). The rectifier type utility interface has substantial harmonics result in poor power quality due to low power factor and high harmonic distortion. Power Factor Correction (PFC) schemes are effective methods to mitigate harmonics and address this issue. In this thesis, analyses of three approaches for high power density rectifiers are developed. In the first study, modular three phase boost rectifiers operating in DCM are coupled in order to increase the power density. Major drawback of this rectifier is the high currents ripple in both the source and the DC link sides which require large EMI filter size -could be larger than the rectifier component size- and large DC filter capacitor size. This thesis proposes coupling modular three phase boost DCM rectifiers, the currents in both source and DC link sides are interleaved and consequently the currents ripple dramatically decreased results in small component size of the EMI filter and the DC filter capacitor leading to high power density rectification. Also, optimization of the number of the rectifier modules to achieve maximum power density is presented. Moreover, the switching function of each rectifier employs harmonic injection technique to reduce the low order harmonics. And, the DC output voltage is varied with the load power such that the operation is at the boundary between CCM and DCM to achieve maximum power density tracking. In the Second study, a resonant three phase single switch PFC is presented to overcome the high 5th and 7th order current harmonics drawback in the conventional single switch three phase PFC circuits. The input current has low THD for each individual low order harmonics with high current ripple at the switching frequency. Interleaving the input current by coupling modular rectifiers is also presented to reduce the input current ripple. System equations and modes of operation is analyzed and derived to design the circuit parameters, switching frequency and duty ratio for the desired output voltage and load power. In the Third study, an advancement of existing modular T-connected single phase PFCs by means of replacing the low frequency transformer with medium frequency electronic phase shifter to reduce the size and weight of the system. The approach has higher power density compared with the Y, delta and T-connected single phase PFC modules. The study examines the 3 to 2 phase conversion, system harmonics, switching technique for the AC chopper and the power flow of the system

One-Quadrant Switched-Mode Power Converters

This article presents the main topics related to one-quadrant power converters. The basic topologies are analysed and a simple methodology to obtain the steady-state output-input voltage ratio is set out. A short discussion of different methods to control one-quadrant power converters is presented. Some of the reported derived topologies of one-quadrant power converters are also considered. Some topics related to one-quadrant power converters such as synchronous rectification, hard and soft commutation, and interleaved converters are discussed. Finally, a brief introduction to resonant converters is given.Comment: 25 pages, contribution to the 2014 CAS - CERN Accelerator School: Power Converters, Baden, Switzerland, 7-14 May 201

Morphing Switched-Capacitor Converters with Variable Conversion Ratio

High-voltage-gain and wide-input-range dc-dc converters are widely used in various electronics and industrial products such as portable devices, telecommunication, automotive, and aerospace systems. The two-stage converter is a widely adopted architecture for such applications, and it is proven to have a higher efficiency as compared with that of the single-stage converter. This paper presents a modular-cell-based morphing switched-capacitor (SC) converter for application as a front-end converter of the two-stage converter. The conversion ratio of this converter is flexible and variable and can be freely extended by increasing more SC modules. The varying conversion ratio is achieved through the morphing of the converter's structure corresponding to the amplitude of the input voltage. This converter is light and compact, and is highly efficient over a very wide range of input voltage and load conditions. Experimental work on a 25-W, 6-30-V input, 3.5-8.5-V output prototype, is performed. For a single SC module, the efficiency over the entire input voltage range is higher than 98%. Applied into the two-stage converter, the overall efficiency achievable over the entire operating range is 80% including the driver's loss

Efficient LDO-Assisted DC/DC buck converter for integrated power management system

DC-DC Switching Converters; Voltage Linear Regulators; Linear-Assisted DC-DC Voltage Regulators.Postprint (published version

Linear-assisted DC/DC converters with modified current-mode control applied to photovoltaic solar systems

This article shows the proposal of a current-mode one-cycle control for linear-assisted DC/DC converters. Linearassisted DC/DC converters are structures that allow to take advantages of the two classic alternatives in the design of power supply systems: voltage linear regulators (classic NPN topology or LDO –low dropout–) and switching DC/DC converters. The current-mode one-cycle control technique is proposed in order to obtain the duty cycle of the linear-assisted converter switch. The proposed structure can provide an output with suitable load and line regulations. Thus, the paper shows the design and simulation results of the proposed current-mode one-cycle linear-assisted converter.Postprint (published version

Capacitorless DC–DC regulator as a candidate topology for photovoltaic solar facilities

Postprint (published version