Development of Efficient Soft Switching Synchronous Buck Converter Topologies for Low Voltage High Current Applications

Switched mode power supplies (SMPS) have emerged as the popular candidate in all the power processing applications. The demand is soaring to design high power density converters. For reducing the size, weight, it is imperative to channelize the power at high switching frequency. High switching frequency converters insist upon soft switching techniques to curtail the switching losses. Several soft switching topologies have been evolved in the recent years. Nowadays, the soft switching converters are vastly applied modules and the demand is increasing for high power density and high efficiency modules by minimizing the conduction and switching losses. These modules are generally observed in many applications such as laptops, desktop processors for the enhancement of the battery life time. Apart from these applications, solar and spacecraft applications demand is increasing progressively for stressless and more efficient modules for maximizing the storage capacity which inturn enhances the power density that improves the battery life to supply in the uneven times. Modern trends in the consumer electronic market focus increases in the demand of lower voltage supplies. Conduction losses are significantly reduced by synchronous rectifiers i.e., MOSFET’s are essentially used in many of the low voltage power supplies. Active and passive auxiliary circuits are used in tandem with synchronous rectifier to diminish the crucial loss i.e., switching loss and also it minimizes the voltage and current stresses of the semiconductor devices. The rapid progress in the technology and emerging portable applications poses serious challenges to power supply design engineers for an efficient power converter design at high power density. The primary aim is to design and develop high efficiency, high power density topologies like: buck, synchronous buck and multiphase buck converters with the integration of soft switching techniques to minimize conduction and switching losses sustaining the voltage and current stresses within the tolerable range. In this work, two ZVT-ZCT PWM synchronous buck converters are introduced, one with active auxiliary circuit and the other one with passive auxiliary circuit. The operating principle and comprehensive steady state analysis of the ZVT-ZCT PWM synchronous buck converters are presented. The converters are designed to have high efficiency and low voltage that is suitable for high power density application. The semiconductor devices used in the topologies in addition to the main switch operate with soft switching conditions. The viii Abstract topologies proposed render a large overall efficiency in contrast to the contemporary topologies. In addition the circuit’s size is less, reliable and have high performance-cost ratio. The new generation microprocessor demands the features such as low voltage, high current, high power density and high efficiency etc., in the design of power supplies. The supply voltage for the future generation microprocessors must be low, in order to decrease the power consumption. The voltage levels are dripping to a level even less than 0.7V, and the power consumption increases as there is an increase in the current requirement for the processor. In order to meet the demands of the new generation microprocessor power supply, a soft switching multiphase PWM synchronous buck converter is proposed. The losses in the proposed topology due to increasing components are pared down by the proposed soft switching technique. The proposed converters in this research work are precisely described by the mathematical modelling and their operational modes. The practicality of the proposed converters for different applications is authenticated by their simulation and experimental results

Soft-Switching Techniques of Power Conversion System in Automotive Chargers

abstract: This thesis investigates different unidirectional topologies for the on-board charger in an electric vehicle and proposes soft-switching solutions in both the AC/DC and DC/DC stage of the converter with a power rating of 3.3 kW. With an overview on different charger topologies and their applicability with respect to the target specification a soft-switching technique to reduce the switching losses of a single phase boost-type PFC is proposed. This work is followed by a modification to the popular soft-switching topology, the dual active bridge (DAB) converter for application requiring unidirectional power flow. The topology named as the semi-dual active bridge (S-DAB) is obtained by replacing the fully active (four switches) bridge on the load side of a DAB by a semi-active (two switches and two diodes) bridge. The operating principles, waveforms in different intervals and expression for power transfer, which differ significantly from the basic DAB topology, are presented in detail. The zero-voltage switching (ZVS) characteristics and requirements are analyzed in detail and compared to those of DAB. A small-signal model of the new configuration is also derived. The analysis and performance of S-DAB are validated through extensive simulation and experimental results from a hardware prototype. Secondly, a low-loss auxiliary circuit for a power factor correction (PFC) circuit to achieve zero voltage transition is also proposed to improve the efficiency and operating frequency of the converter. The high dynamic energy generated in the switching node during turn-on is diverted by providing a parallel path through an auxiliary inductor and a transistor placed across the main inductor. The paper discusses the operating principles, design, and merits of the proposed scheme with hardware validation on a 3.3 kW/ 500 kHz PFC prototype. Modifications to the proposed zero voltage transition (ZVT) circuit is also investigated by implementing two topological variations. Firstly, an integrated magnetic structure is built combining the main inductor and auxiliary inductor in a single core reducing the total footprint of the circuit board. This improvement also reduces the size of the auxiliary capacitor required in the ZVT operation. The second modification redirects the ZVT energy from the input end to the DC link through additional half-bridge circuit and inductor. The half-bridge operating at constant 50% duty cycle simulates a switching leg of the following DC/DC stage of the converter. A hardware prototype of the above-mentioned PFC and DC/DC stage was developed and the operating principles were verified using the same.Dissertation/ThesisDoctoral Dissertation Electrical Engineering 201

An Interleaved Soft Switched High Step-Up Boost Converter With High Power Density for Renewable Energy Applications

In this article, a novel soft switched interleaved boost structure with a simple auxiliary circuit is proposed which is suitable for stand-alone loads or ac grid applications. In this topology, coupled inductors and switched capacitor cells of parallel modules are merged to obtain high voltage conversion ratio. The converter also has the capability of adding extra switched capacitor cells to attain very high voltage gain. To provide soft-switching condition in the wide range of output power, a new zero-voltage transition auxiliary circuit is employed which is responsible for soft switching of both phases and benefits from low conduction losses, the minimum number of semiconductor elements, and only one auxiliary gate-driver. These merits provide very high efficiency at both full-load and light loads. More importantly, no auxiliary magnetic components are utilized by taking advantage of the leakage inductance of coupled inductors for the resonant network. All semiconductor components operate under soft switching alleviating the reverse recovery problem and switching losses. Besides, the converter benefits from common ground between input and output which simplify voltage feedback. The experimental results of the interleaved converter prototype with 400-V output voltage at 400 W and 100 kHz switching frequency are provided. The full load efficiency of 98% was achieved and the power density was observed 1.9 W/Cm3

High-Voltage-Gain DC-DC Power Electronic Converters -- New Topologies and Classification

This dissertation proposes two new high-voltage-gain dc-dc converters for integration of renewable energy sources in 380/400V dc distribution systems. The first high-voltage-gain converter is based on a modified Dickson charge pump voltage multiplier circuit. The second high-voltage-gain converter is based on a non-inverting diode-capacitor voltage multiplier cell. Both the proposed converters offer continuous input current and low voltage stress on switches which make them appealing for applications like integration of renewable energy sources. The proposed converters are capable for drawing power from a single source or two sources while having continuous input current in both cases. Theoretical analysis of the operation of the proposed converters and the component stresses are discussed with supporting simulation and hardware results. This dissertation also proposes a family of high-voltage-gain dc-dc converters that are based on a generalized structure. The two stage general structure consists of a two-phase interleaved (TPI) boost stage and a voltage multiplier (VM) stage. The TPI boost stage results in a classification of the family of converters into non-isolated and isolated converters. A few possible VM stages are discussed. The voltage gain derivations of the TPI boost stages and VM stages are presented in detail. An example converter is discussed with supporting hardware results to verify the general structure. The proposed family of converters can be powered using single source or two sources while having continuous input current in both cases. These high voltage gain dc-dc converters are modular and scalable; making them ideal for harnessing energy from various renewable sources offering power at different levels --Abstract, page iv

Two new families of high-gain DC-DC power electronic converters for DC-microgrids

Distributing the electric power in dc form is an appealing solution in many applications such as telecommunications, data centers, commercial buildings, and microgrids. A high gain dc-dc power electronic converter can be used to individually link low-voltage elements such as solar panels, fuel cells, and batteries to the dc voltage bus which is usually 400 volts. This way, it is not required to put such elements in a series string to build up their voltages. Consequently, each element can function at it optimal operating point regardless of the other elements in the system. In this dissertation, first a comparative study of dc microgrid architectures and their advantages over their ac counterparts is presented. Voltage level selection of dc distribution systems is discussed from the cost, reliability, efficiency, and safety standpoints. Next, a new family of non-isolated high-voltage-gain dc-dc power electronic converters with unidirectional power flow is introduced. This family of converters benefits from a low voltage stress across its switches. The proposed topologies are versatile as they can be utilized as single-input or double-input power converters. In either case, they draw continuous currents from their sources. Lastly, a bidirectional high-voltage-gain dc-dc power electronic converter is proposed. This converter is comprised of a bidirectional boost converter which feeds a switched-capacitor architecture. The switched-capacitor stage suggested here has several advantages over the existing approaches. For example, it benefits from a higher voltage gain while it uses less number of capacitors. The proposed converters are highly efficient and modular. The operating modes, dc voltage gain, and design procedure for each converter are discussed in details. Hardware prototypes have been developed in the lab. The results obtained from the hardware agree with those of the simulation models. --Abstract, page iv

An improved dual boost converter with zero voltage transition

This work proposes a soft switching approach for dual-boost converter using an auxiliary resonant circuit. The topology is composed of a general dual-boost converter and an auxiliary resonant circuit including one switch, inductor, capacitor and diode. The auxiliary resonant circuit helps the main switch to operate under ZVT and ZCS conditions. The auxiliary switch also operates at soft switching mode. Furthermore, the proposed circuit removes the voltage stress on the main and auxiliary switches. Under soft switching conditions the efficiency of the converter increases. The converter has various advantages compared with the conventional boost converters as higher boost rate with low duty cycle, lower voltage stress on components and higher efficiency

Analysis of a soft switched dual-boost converter

This paper proposes a soft switched dual-boost converter using an auxiliary resonant circuit. The topology is composed of a general dual-boost converter and an auxiliary resonant circuit including one switch, inductor, capacitor and two diodes. The auxiliary resonant circuit helps the main switch to operate under ZVT condition. The auxiliary switch is also operated at soft switching mode. Furthermore, the proposed circuit removes the voltage stress on the main and auxiliary switches. Under soft switching conditions the efficiency of the converter increases. The converter has various advantages compared with the conventional boost converters as higher boost rate with low duty cycle, lower voltage stress on components and higher efficiency

High efficiency and high gain non-isolated bidirectional dc-dc converter with soft switching capability

The non-isolated dc-dc power converters are considered as a unique option for flexible voltage control and adaptation in the modern energy conversion systems due to their simple and light configurations. To this date, these converters are primarily investigated to generate high efficiency and high gain with a sustained soft switching capability and a smaller footprint. On that account, this work proposes two effective solutions to address the aforementioned issues. First, a high-efficiency soft switching non-isolated bidirectional dc-dc converter with a simple configuration is proposed. The converter executes the zero voltage zero current switching (ZVZCS) over a wide operating region to ensure high efficiency. For verification, a 150 W experimental prototype is built and tested for soft switching performance by varying the input voltage, switching frequency and the loading. It is observed that the efficiency remains consistently high and has a full-load maximum of 98.2% in the boost mode and 97.5% in the buck mode. The analysis of the Electromagnetic Interference (EMI) performance of the converter also shows the improvement in the noise signature. Second, an improved high gain zero voltage switching (ZVS) nonisolated bidirectional dc-dc converter is proposed. The high gain is realized by using an intermediate energy storage cell with reduced size. Besides, the ZVS is implemented by two integrated auxiliary resonant networks. These networks ensure sustained ZVS operation over the entire duty ratio. A 200 W prototype is built to verify the concept. As a result, a full load efficiency of 97.5% (in boost mode) and 95.5% (in buck mode) is recorded at fs= 30 kHz. Also, these efficiencies are recorded as 97% (boost mode) and 94.5% (buck mode) at fs= 100 kHz. Moreover, it is observed that the efficiency (and so the soft switching) is consistent over the entire gain profile. However, there is a slight additional drop of 1.5% (boost mode) and 1% (buck mode) at extreme duty ratios. Both converters also implement soft switching for auxiliary switches and eliminate the reverse recovery loss

Design of dual-input two phase dc/dc converter with modified pulse width modulation (mpwm)

Recently, hybrid energy source/renewable energy has attracted interest as the next-generation energy system capable of solving the problems of global warming and energy exhaustion caused by increasing energy consumption. Energy sources such as wind turbines and photovoltaic (PV) systems are intermittent, unpredictable and unregulated. For such systems, the use of multiple-input converter (MIC) has the advantage of regulating and controlling multiple-input sources. With multiple Pulsating Voltage-Source Cells (PVSC) configurations, the proposed converter can deliver power to the load individually and simultaneously. Also, it has the capability of operating either in buck, boost or buck–boost mode of operation. In addition, by proposing the enhanced Modified PWM (MPWM) switching scheme, it is able to solve the issues of the overlapping unregulated input sources. Furthermore, with the proposed multiphase configuration, the input current stresses in the switching devices are reduced and it has the benefit of a reduction in conduction losses. In addition, Zero-Voltage Switching (ZVS) technique is also employed in the proposed converter to reduce the switching loss. The proposed converter circuit is simulated by using MATLAB/Simulink and PSpice software programs. The duty cycle employed to regulate output voltage is reached from Altera DE2-70 board through dSPACE DS1103 board using by Proportional-Integral (PI) controller. The dual-input converter circuit model specification with output power at 200 W, input voltages that range from 10 to 60 V, and operating with dual switching frequencies of 50 kHz and 100 kHz is simulated to validate the designed parameters. Design guidelines, simulation and experimental results are presented. The results show that the proposed two-phase DC/DC converter with ZVS technique achieves 94% efficiency for all ranges of loads compared with the multiphase hard-switching. The total power losses across the power switches are reduced by approximately 37% in the proposed converter. Thus, the proposed converter circuit model offers advantages on input current stress and switching loss reductions. The proposed circuit configuration can be used in a standalone hybrid energy system under unregulated DC input voltages. However the major disadvantages of resonant circuit are increased peak current and voltage stress and not suitable for variable frequency operation

Analysis and design of a dual series-resonant DC-DC converter

DC-DC conversion systems are vital components in DC distribution systems, renewable energy generation systems, telecommunication systems, and portable electronics devices. The extensive applications of DC-DC converter have resulted in continuous improvement in the topologies and control methods in these converters. The challenge is to build a converter that improves factors such as efficiency of conversion and power density with a simple topology, which incorporates simplified switching and control schemes and fewer numbers of active and passive components to reduce the manufacturing cost. This thesis addresses this challenge by proposing an alternative topology of a DC-DC converter based on dual series-resonant circuits. The proposed topology operates under zero voltage switching (ZVS) and zero current switching (ZCS) conditions to reduce the switching losses. It achieves two degrees of freedom (i.e., duty ratio and switching frequency) to control the output voltage of the converter, which results in both step-down and step-up voltage conversions. The number of active components is limited to two semiconductor switches and two rectifying diodes, which reduces the manufacturing cost of the converter. Detailed analytical analysis is carried out using the extended describing function methodology to characterize the steady state and small signal operation of the converter. Small-signal transfer functions are developed and used to propose a simple closed-loop control scheme to control the output voltage of the converter. An experimental 10 V, 40 W prototype of the proposed converter is built and tested to investigate its operation and confirm its features. The improvement in the efficiency of the converter and power transfer capability of the proposed dual series-resonant converter compared with the traditional single series-resonant circuit, which is used in the interleaved topologies are experimentally verified. In addition, soft switching operation of the converter is realized and a simple control scheme is developed to control the output voltage of the converter. A detailed and step-by-step design procedure is developed, which can be used to customize the design of the converter for different levels of power and voltage. It is shown that the proposed dual series-resonant DC-DC converter provides significant improvement regarding power density, efficiency of power conversion, simplicity of switching and control schemes, and reduced number of converter components resulting in a low cost and compact converter