A Novel AC-DC Interleaved ZCS-PWM Boost Converter

AC-DC converters with input power factor correction (PFC) that consist of two or more interleaved boost converter modules are popular in industry. PFC is a must in today’s AC-DC converters as their input current must meet harmonic standards set by regulatory agencies. With interleaving, the input current of each module can make to be discontinuous and the size of their input inductors since interleaving can reduce the high ripple in each module and produce a net input current with a ripple that is comparable to that achieved with a single boost converter module with a large input inductor. In high- frequency converters, so as to achieve low harmonic, fast dynamic response, low size, and high-power density the frequency should be increased. The drawback of increasing the switching frequency is increasing the switching losses. This is reason that why soft-switching methods should be used. The focus of the thesis is on zero current switching (ZCS) methods for IGBT converters. The auxiliary switch in the proposed converter is activated whenever a main converter switch is about to be turned off, gradually diverting current away from the switch so that it can turn off with ZCS and eliminate the switching losses. In addition, the auxiliary circuit is designed in a way that it can be activated only when the converter is operating with heavier loads and not used when the converter is operating with light load to maximize the overall efficiency. The operation of the novel converter will then be explained and the mathematical analysis in steady-state will be derived. Based on the results of the analysis, general design guidelines will be provided. Finally, the design procedure will be confirmed by experimental results obtained from the proof of concept prototype

Soft-Switching DC-DC Converters

Power electronics converters are implemented with switching devices that turn on and off while power is being converted from one form to another. They operate with high switching frequencies to reduce the size of the converters\u27 inductors, transformers and capacitors. Such high switching frequency operation, however, increases the amount of power that is lost due to switching losses and thus reduces power converter efficiency. Switching losses are caused by the overlap of switch voltage and switch current during a switching transition. If, however, either the voltage across or the current flowing through a switch is zero during a switching transition, then there is no overlap of switch voltage and switch current so in theory, there are no switching losses. Techniques that ensure that this happens are referred to as soft-switching techniques in the power electronics literature and there are two types: zero-voltage switching (ZVS) and zero-current switching (ZCS). For pulse-width modulated (PWM) Dc-Dc converters, both ZVS and ZCS are typically implemented with auxiliary circuits that help the main power switches operate with soft-switching. Although these auxiliary circuits do help improve the efficiency of the converters, they increase their cost. There is, therefore, motivation to try to make these auxiliary circuits as simple and as inexpensive as possible. Three new soft-switching Dc-Dc PWM converters are proposed in this thesis. For each converter, a very simple auxiliary circuit that consists of only a single active switching device and a few passive components is used to reduce the switching losses in the main power switches. The outstanding feature of each converter is the simplicity of its auxiliary circuit, which unlike most other previously proposed converters of similar type, avoids the use of multiple active auxiliary switches. In this thesis, the operation of each proposed converter is explained, analyzed, and the results of the analysis are used to develop a design procedure to select key component values. This design procedure is demonstrated with an example that was used in the implementation of an experimental prototype. The feasibility of each proposed converter is confirmed with experimental result obtained from a prototype converter

Assessment of novel power electronic converters for drives applications

Phd ThesisIn the last twenty years, industrial and academic research has produced over one hundred new converter topologies for drives applications. Regrettably, most of the published work has been directed towards a single topology, giving an overall impression of a large number of unconnected, competing techniques. To provide insight into this wide ranging subject area, an overview of converter topologies is presented. Each topology is classified according to its mode of operation and a family tree is derived encompassing all converter types. Selected converters in each class are analysed, simulated and key operational characteristics identified. Issues associated with the practical implementation of analysed topologies are discussed in detail. Of all AC-AC conversion techniques, it is concluded that softswitching converter topologies offer the most attractive alternative to the standard hard switched converter in the power range up to 100kW because of their high performance to cost ratio. Of the softswitching converters, resonant dc-link topologies are shown to produce the poorest output performance although they offer the cheapest solution. Auxiliary pole commutated inverters, on the other hand, can achieve levels of performance approaching those of the hard switched topology while retaining the benefits of softswitching. It is concluded that the auxiliary commutated resonant pole inverter (ACPI) topology offers the greatest potential for exploitation in spite of its relatively high capital cost. Experimental results are presented for a 20kW hard switched inverter and an equivalent 20kW ACPI. In each case the converter controller is implanted using a digital signal processor. For the ACPI, a new control scheme, which eliminates the need for switch current and voltage sensors, is implemented. Results show that the ACPI produces lower overall losses when compared to its hardswitching counterpart. In addition, device voltage stress, output dv/dt and levels of high frequency output harmonics are all reduced. Finally, it is concluded that modularisation of the active devices, optimisation of semiconductor design and a reduction in the number of additional sensors through the use of novel control methods, such as those presented, will all play a part in the realisation of an economically viable system.Research Committee of the University of Newcastle upon Tyn

A New ZCS-PWM Full-Bridge Boost Converter

The objective of this thesis is to propose, analyze, design, implement, and experimentally confirm the operation of a new Zero-Current-Switching PWM dc-dc full- bridge boost converter that does not have the drawbacks ofpreviously proposed circuits of the same type. In this thesis, the general operating principles of the converter are reviewed, and the converter’s operation is discussed in detail and analyzed mathematically. As a result of the mathematical analysis, key voltage and current equations that describes the operation of the auxiliary circuit and other converter devices have been derived. The steady state equations of each mode of operation are used as the basis of a MATLAB program that is used to generate steady-state characteristic curves that shows the effect that individual circuit parameters have on the operation of the auxiliary circuit and the boost converter. Observations as to their steady-state characteristics are made and the curves are used as part of a design procedure to select the components of the converter, especially those of the auxiliary circuit. An experimental full-bridge PWM dc-dc boost converter prototype is built based on the converter design and typical waveforms are presented. The efficiency of the proposed converter operating with the auxiliary circuit is compared to that of a standard PWM dc-dc full-bridge boost converter and the increased efficiency o f the proposed converter is confirme

Medical Grade High Frequncy Power Distribution Units

The focus of this thesis is to design, model, build, and test a series resonance converter that uses a high frequency isolation transformer, offering significant reduction in size and cost, for powering a Computed Tomography (CT) scanner. The design increases the power quality for the load by isolating the grid side disturbances, and providing regulated desired voltage. The proposed architecture also allows for an optimized point of integration with an UPS, a regulated DC bus to improve waveform fidelity of x-ray generator, and active monitoring and control of the power architecture. Conventional CT systems use a 60Hz transformer, which not only occupies large footprints but also uses large amounts of copper and iron with increasing cost trajectory. In comparison to the traditional Power Distribution Units (PDU), the medical grade high frequency PDU presented in this thesis provides higher power quality and performance at a lower cost. The new CT systems possess unprecedented performance capability in terms of rotational speed and x-ray voltage modulation ( Ultra-Fast kV ) fidelity. In order to achieve such capabilities, a tightly regulated high power DC bus (700VDC, 150kW) is required. The system implemented in this thesis satisfies these new requirements. Design requirements, proposed architecture and controls, modeling, implementation and test results of the proposed system, including thermal analysis and electromagnetic compatibility, are presented in details in this thesis

A New Soft-Switching Control Technique and Loss Analysis for Parallel Resonant DC-Link Inverter Connected to the Grid

This study is recommended to develop a soft-switching control software infrastructure that enables more efficient and effective use of parallel resonant DC link circuits. The fact that the control technique can be easily applied to the soft switching circuit makes it important in this field. With this proposed study, lower voltage ripple and higher efficiency are obtained. To see the results of the technique and to study its effect, a study was carried out on a grid connected inverter. When the frequency changes between 5-15 kHz and 5-10 kW power is transmitted to the grid, the soft switching effect is studied and the efficiency is increased. A software model for calculating the power losses of semiconductor switches has also been established. Using this modeling approach, the power consumption is calculated in detail and the loss analysis is performed using catalog data of semiconductor switches. The accuracy of the obtained results was compared with another simulator. While the PRDCL inverter using the new proposed switching technique transmits 10 kW of power to the grid, the efficiency increased from 97.67% to 98.61% at a switching frequency of 5 kHz, from 96.82% to 98.58% at a switching frequency of 10 kHz, and from 95.61% to 98.55% at a switching frequency of 15 kHz

A study of DC-DC converters with MCT's for arcjet power supplies

Many arcjet DC power supplies use PWM full bridge converters with large arrays of parallel FET's. This report investigates an alternative supply using a variable frequency series resonant converter with small arrays of parallel MCT's (metal oxide semiconductor controlled thyristors). The reasons for this approach are to: increase reliability by reducing the number of switching devices; and decrease the surface mounting area of the switching arrays. The variable frequency series resonant approach is used because the relatively slow switching speed of the MCT precludes the use of PWM. The 10 kW converter operated satisfactorily with an efficiency of over 91 percent. Test results indicate this efficiency could be increased further by additional optimization of the series resonant inductor

Solid-state transformers in locomotives fed through AC lines: A review and future developments

One of the most important innovation expectation in railway electrical equipment is the replacement of the on-board transformer with a high power converter. Since the transformer operates at line-frequency (i.e., 50 Hz or 16 2/3 Hz), it represents a critical component from weight point of view and, moreover, it is characterized by quite poor efficiency. High power converters for this application are characterized by a medium frequency inductive coupling and are commonly referred as Power Electronic Transformers (PET), Medium Frequency Topologies or Solid-State Transformers (SST). Many studies were carried out and various prototypes were realized until now, however, the realization of such a system has some difficulties, mainly related to the high input voltage (i.e., 25 kV for 50 Hz lines and 15 kV for 16 2/3 Hz lines) and the limited performance of available power electronic switches. The aim of this study is to present a survey on the main solutions proposed in the technical literature and, analyzing pros and cons of these studies, to introduce new possible circuit topologies for this application

Soft-switching modular multilevel converters for efficient grid integration of renewable sources

The Modular Multilevel Converter (MMC) concept is a modern energy conversion structure that stands out for a number of interesting features that opens wide application chances in Power Systems, for example for efficient grid integration of renewable sources. In these high-voltage, high-power application fields, a high efficiency is mandatory. In this regard, an interesting and promising development opportunity could be to make soft-switching the elementary converters of the submodules (cells), half H-bridges or full H-bridges, obtaining at the same time the advantage of increasing the switching frequency. The ARCP or the AQRDCL soft-switching topologies appear adequate for this purpose. This paper is dedicated to examining these development possibilities