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

Low Voltage Regulator Modules and Single Stage Front-end Converters

Evolution in microprocessor technology poses new challenges for supplying power to these devices. To meet demands for faster and more efficient data processing, modem microprocessors are being designed with lower voltage implementations. More devices will be packed on a single processor chip and the processors will operate at higher frequencies, exceeding 1GHz. New high-performance microprocessors may require from 40 to 80 watts of power for the CPU alone. Load current must be supplied with up to 30A/µs slew rate while keeping the output voltage within tight regulation and response time tolerances. Therefore, special power supplies and Voltage Regulator Modules (VRMs) are needed to provide lower voltage with higher current and fast response. In the part one (chapter 2,3,4) of this dissertation, several low-voltage high-current VRM technologies are proposed for future generation microprocessors and ICs. The developed VRMs with these new technologies have advantages over conventional ones in terms of efficiency, transient response and cost. In most cases, the VRMs draw currents from DC bus for which front-end converters are used as a DC source. As the use of AC/DC frond-end converters continues to increase, more distorted mains current is drawn from the line, resulting in lower power factor and high total harmonic distortion. As a branch of active Power factor correction (PFC) techniques, the single-stage technique receives particular attention because of its low cost implementation. Moreover, with continuously demands for even higher power density, switching mode power supply operating at high-frequency is required because at high switching frequency, the size and weight of circuit components can be remarkably reduced. To boost the switching frequency, the soft-switching technique was introduced to alleviate the switching losses. The part two (chapter 5,6) of the dissertation presents several topologies for this front-end application. The design considerations, simulation results and experimental verification are discussed

Stability Study and Nonlinear Analysis of DC-DC Power Converters with Constant Power Loads at the Fast Timescale

Rapidly growing distributed renewable networks make an increasing demand on various types of power converters to feed different loads. Power converters with constant power load are one typical configuration that can degrade the stability of the power conversion system due to the negative impedance characteristic. This paper presents a nonlinear analysis method using the developed complete-cycle solution matrix method by transforming the original linear time-variant system into a summation of segmented linear time-invariant systems. Thus, the stability of the nonlinear system can be studied using a series of the corresponding state transition matrix and saltation matrix. As this derived matrix contains all the comprehensive information relating to the system’s stability, the influence of the constant power load to system’s fast-timescale stability in both continuous conduction mode and the discontinuous conduction mode can be fully investigated and analyzed. The phenomena of fast-timescale instability around switching frequency for power converters with a constant power load are observed and investigated numerically. Finally, experimental results have proven the analysis and verified the effectiveness of the developed method

High Gain DC-DC and Active Power Decoupling Techniques for Photovoltaic Inverters

abstract: The dissertation encompasses the transformer-less single phase PV inverters for both the string and microinverter applications. Two of the major challenge with such inverters include the presence of high-frequency common mode leakage current and double line frequency power decoupling with reliable capacitors without compromising converter power density. Two solutions are presented in this dissertation: half-bridge voltage swing (HBVS) and dynamic dc link (DDCL) inverters both of which completely eliminates the ground current through topological improvement. In addition, through active power decoupling technique, the capacitance requirement is reduced for both, thus achieving an all film-capacitor based solution with higher reliability. Also both the approaches are capable of supporting a wide range of power factor. Moreover, wide band-gap devices (both SiC and GaN) are used for implementing their hardware prototypes. It enables the switching frequency to be high without compromising on the converter efficiency. Also it allows a reduced magnetic component size, further enabling a high power density solution, with power density far beyond the state-of-the art solutions. Additionally, for the transformer-less microinverter application, another challenge is to achieve a very high gain DC-DC stage with a simultaneous high conversion efficiency. An extended duty ratio (EDR) boost converter which is a hybrid of switched capacitors and interleaved inductor technique, has been implemented for this purpose. It offers higher converter efficiency as most of the switches encounter lower voltage stress directly impacting switching loss; the input current being shared among all the interleaved converters (inherent sharing only in a limited duty ratio), the inductor conduction loss is reduced by a factor of the number of phases. Further, the EDR boost converter has been studied for both discontinuous conduction mode (DCM) operations and operations with wide input/output voltage range in continuous conduction mode (CCM). A current sharing between its interleaved input phases is studied in detail to show that inherent sharing is possible for only in a limited duty ratio span, and modification of the duty ratio scheme is proposed to ensure equal current sharing over all the operating range for 3 phase EDR boost. All the analysis are validated with experimental results.Dissertation/ThesisDoctoral Dissertation Electrical Engineering 201

Stability analysis and control of DC-DC converters using nonlinear methodologies

PhD ThesisSwitched mode DC-DC converters exhibit a variety of complex behaviours in power electronics systems, such as sudden changes in operating region, bifurcation and chaotic operation. These unexpected random-like behaviours lead the converter to function outside of the normal periodic operation, increasing the potential to generate electromagnetic interference degrading conversion efficiency and in the worst-case scenario a loss of control leading to catastrophic failure. The rapidly growing market for switched mode power DC-DC converters demands more functionality at lower cost. In order to achieve this, DC-DC converters must operate reliably at all load conditions including boundary conditions. Over the last decade researchers have focused on these boundary conditions as well as nonlinear phenomena in power switching converters, leading to different theoretical and analytical approaches. However, the most interesting results are based on abstract mathematical forms, which cannot be directly applied to the design of practical systems for industrial applications. In this thesis, an analytic methodology for DC-DC converters is used to fully determine the inherent nonlinear dynamics. System stability can be indicated by the derived Monodromy matrix which includes comprehensive information concerning converter parameters and the control loop. This methodology can be applied in further stability analysis, such as of the influence of parasitic parameters or the effect of constant power load, and can furthermore be extended to interleaved operating converters to study the interaction effect of switching operations. From this analysis, advanced control algorithms are also developed to guarantee the satisfactory performance of the converter, avoiding nonlinear behaviours such as fast- and slowscale bifurcations. The numerical and analytical results validate the theoretical analysis, and experimental results with an interleaved boost converter verify the effectiveness of the proposed approach.Engineering and Physical Sciences Research Council (EPSRC), China Scholarship Council (CSC), and school of Electrical and Electronic Engineerin

Improved power quality buck boost converter for SMPS

In this paper, a Neural Network (NN) controlled Buck-Boost Converter (BBC) based Switched Mode Power Supply (SMPS) for a PC application is proposed. The proposed BBC is analyzed, modeled and designed for the rated load. Generally, the utilization of Multiple Output SMPS (MOSMPS) for PC application introduces Power Quality (PQ) issues in the power system network. Unlike conventional SMPS the proposed NN controlled BBC can accomplish improvement of power quality. The NN controller reduces the Total Harmonic Distortion (THD) of source current below 5%, maintains input side Power Factor (PF) to be nearly unity and improves the output voltage regulation. In the proposed system, NN controller replaces the conventional PI controller and overcomes the drawbacks of the conventional system. The proposed BBC is validated adopting MATLAB/SIMULINK software. The simulation analysis validate that the proposed NN controlled BBC performs better than conventional converter in terms of PQ indices under fluctuating conditions

A Novel Boost-Buck Converter Architecture for Improving Transient Response and Output-Voltage Ripple

Buck-boost converters are widely used in the development of DC-DC converters. Several techniques and algorithms have been introduced to improve the transient response of buck-boost converters. However, due to the opposite trends of the output current change and the output voltage change, undershoot or overshoot in the output voltage still seems to be inevitable. In order to overcome this problem, a novel boost-buck converter architecture is proposed to build a fast transient response DC-DC converter. The converter consists of a cascaded configuration of the boost and buck stages. The boost stage converts the input voltage to the shared capacitor voltage and the buck stage supplies energy to the load by converting the shared capacitor voltage to the output voltage. By harnessing the energy stored in the shared capacitor, the transient response of the boost buck converter can be improved to 2 µs in a step-up load current change of 1 A with an output-voltage ripple of 15 mV

Development of Medium Power High Efficiency Multi-Level Buck-Boost DC-DC Converter

Power DC/DC converters or regulators form the backbone of different portable electronic devices like cellular phones, laptops, portable electronic devices which are using batteries as their power supply. Portable devices usually comprise of several sub-circuits that should be supplied with different voltage levels, which are not the same as battery’s voltage level which is the main supply voltage. A new approach of buck-boost converter is presented in this paper, that automatically detects the zero-inductor current & compels the convertor to deliberately switch from Continuous Conduction Mode (CCM) to Discontinuous Conduction Mode (DCM), once the inductor current attempts towards negative values, restricting the inductor current to approach towards negative value, and thus enhancing the convertor\u27s performance and efficiency at low load conditions. The converter steps down 200 V input voltage to 187 V and steps up to 211 V simultaneously at 100 Ω load resistance using PSIM software at switching frequency of 100 KHz. The comprehensive analysis of the topology is carried out and the simulated results are compared with the earlier designs at variable loads to verify the performance of the converter

Development of Medium Power High Efficiency Multi-Level Buck-Boost DC-DC Converter

Power DC/DC converters or regulators form the backbone of different portable electronic devices like cellular phones, laptops, portable electronic devices which are using batteries as their power supply. Portable devices usually comprise of several sub-circuits that should be supplied with different voltage levels, which are not the same as battery’s voltage level which is the main supply voltage. A new approach of buck-boost converter is presented in this paper, that automatically detects the zero-inductor current & compels the convertor to deliberately switch from Continuous Conduction Mode (CCM) to Discontinuous Conduction Mode (DCM), once the inductor current attempts towards negative values, restricting the inductor current to approach towards negative value, and thus enhancing the convertor\u27s performance and efficiency at low load conditions. The converter steps down 200 V input voltage to 187 V and steps up to 211 V simultaneously at 100 Ω load resistance using PSIM software at switching frequency of 100 KHz. The comprehensive analysis of the topology is carried out and the simulated results are compared with the earlier designs at variable loads to verify the performance of the converter