The purpose of this thesis is to design, develop, implement and test a novel soft-switching inverter topology suitable for switched reluctance motor drives. Present research being done in the field of switched reluctance motor drive inverters, including soft-switching inverters, is discussed. The novel topology is presented and the principle of operation is described in detail. The validity of the topology is verified through simulation. The various components of the system are designed and the hardware implementation is presented. Experiments carried out to verify the operation of this inverter are explained. Results are presented and comparison is made between hard switching and soft switching inverter topologies. Conclusions are drawn regarding the effectiveness of the proposed topology. / Master of Science

The grid connected PV plants comprising of the PV cells and the power electronic inverters are a widely used technology in distributed power generation systems based on renewable energy sources. Microinverters form an extensive part of the ongoing research in this field. This thesis focuses on the inverter section of the microinverter. The cost and efficiency of the grid connected inverter is a chief contributing factor in the overall system price. The MOSFETs used in the DC/AC inverter are usually hard switched causing a lot of EMI noise and losses in the inverter. This is true for both, single and three phase inverters. A low switching frequency is desirable to increase the efficiency, which in turn imposes a large compromise in designing the output filter. In this thesis, switching losses have been minimized by incorporating zero voltage switching at switch turn on and variable dead-time control at switch turn off. The soft switching technique is based on control algorithms and involves no use of any auxiliary circuit. Also, the size of the output filter is reduced without increasing the switching frequency, by employing multiple paralleled inverters. The interleaving technique that is usually used in dc/dc converters is extended for dc/ac inverters and is well employed to maintain the quality of the current fed into the utility grid. In this way, at low switching frequency, high efficiency and reduced cost and sizes are achieved. The study is validated through simulation and lab experiments. The novel control circuit was first implemented using analog circuitry. After assessing the performance of the analog version of the proposed controller, it was then digitally implemented through the Field Programmable Gate Array (FPGA) technique. / Thesis (Master, Electrical & Computer Engineering) -- Queen's University, 2012-04-30 15:06:26.071

The power supply designers choose flyback topology due to its promising features of design simplicity, cost effectiveness and multiple outputs handling capability. The designed product based on flyback topology should be smaller in size, cost effective and energy efficient. Similarly, designers focus on reducing the circuit losses while operating at high frequencies that affect the converter efficiency and performance. Based on the above circumstances, an energy efficient open loop high frequency flyback converter is designed and operated in MHz frequency region using step down multilayer PCB planar transformer. The maximum efficiency of 84.75% is observed and maximum output power level reached is 22.8W. To overcome the switching losses, quasi-resonant soft switching technique is adopted and a high voltage CoolMOS power transistor is used.

In 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.

Conventional 'hard switching' converters suffer from significant switching loss due to the simultaneous imposition of high values of current and voltage on the devices during commutation. Resonant converters offer a solution to this problem. A review of resonant circuit topologies is presented, which includes a summary of the interference problems which may occur when using power converters in the rail traction environment. Particular attention is given to the Resonant DC Link Inverter (RDCLI) which shows a great deal of pronuse using currently available devices. The frequency domain simulation of RDCLIs is discussed as a means of rapidly evaluating circuit behaviour, especially in relation to modulation strategies. A novel modulation strategy is proposed for Resonant DC Link Inverters, based on a procedure known as Simulated Annealing which allows complex harmonic manipulations such as han-nonic minimisation, to be performed. This is despite the fact that RDCLIs are constrained to use Discrete Pulse Modulation whereby switch commutations are restricted to specific moments in time. The modulation algorithms were verified by use of a low-power test rig and the results obtained are compared against theoretical values. Details of the hardware implementation are also included. A single-phase pulse-converter input stage is described which may be incorporated into the Resonant DC Link Inverter topology. This input stage also benefits from soft-sVVItching and allows four-quadrant operation at any desired power factor. A modulation scheme based on SiMulated Annealing is proposed for the pulse-converter, to achieve hannomc control whilst also synchronising with the supply wavefon-n. Practical results are presented and compared with those obtained by simulation and calculation. Finally the design of Resonant DC Link Converters is discussed and reconunendations made for the choice of resonant components based on the minimisation of overall losses. Comparisons are made between hard-switching and soft-switching converters in terms of loss and harmonic performance, in an attempt to quantify the benefits which may be obtained by the application of soft-switching.

A new power conditioning system (PCS) for superconductive magnetic energy storage (SMES) is developed and its prototype test system is built and tested. The PCS uses IGBTs for high-speed PWM operation and has a multi-level chopper-VSC structure. The prototype test system has three-level that can handle up to 250-kVA with a 1800-V DC link, a 200-A maximum load current , and a switching frequency reaching 20-kHz with the help of zero-current-transition (ZCT) soft-switching. This PCS has a great number of advantages over conventional ones in terms of size, speed, and cost. Conventional PCSs use thyristors, due to the power capacity of the SMES system. The speed limit of the thyristor uses a six-pulse operation that generates a high harmonic. To reduce the harmonic, multiple PCSs are connected together with phase-matching transformers that need to be precise to be effective in reducing the harmonics. So, the system becomes large and expensive. In addition, the dynamic range of the PCSs are also limited by the six-pulse operation, because it limits the useful area of the PCS applications. By employing a high-speed PWM, the new PCS can reduce the harmonics without using the transformers reducing size and cost, and has wide dynamic range. However, the speed of a switching device is generally inversely proportional to its power handling capacity. Therefore, employing a multi-level structure is one method of extending the power-handling capability of the high-speed device. Switching loss is another factor that limits the speed of the switch, but it can be reduced by soft-switching techniques. The 20-kHz switching frequency can be obtained with the help of the ZCT soft-switching technique, which can reduce about 90% of switching losses from the IGBT during both turn-on and turn-off transients. There are two different topologies of the PCS; the current source converter (CSC) type and the chopper and voltage source converter (VSC) type. In terms of the SMES system efficiency, the chopper-VSC type shows a less volt-ampere requirement of the power device. Therefore, the new PCS system has a chopper-VSC structure. Since the chopper-VSC structure consists of multiple legs that can be modularized, a power electronics building block (PEBB) leg is a good choice; all of the system problems caused by the high frequency can be solved within the PEBB leg. The VSC is built with three of the PEBB legs. Three-phase AC is implemented with a three-level space vector modulation (SVM) that can reduce the number of switching and harmonic contents from the output current. A closed-loop control system is also implemented for the VSC, and shows 600-Hz control bandwidth. The multi-level structure used requires too many high-speed switches. However, not all of them are used at the same time during normal multi-level operation. A new multi-level topology is suggested that requires only two high-speed switches, regardless of the number of levels. Other switches can be replaced with slow-speed switches that can allow additional cost savings. / Ph. D.

As is the case for DC-DC converters, multi-phase converters require both high-quality power control and high power-density. Although a higher switching frequency not only improves the quality of the converter output but also decreases the size of the converter, it increases switching losses and electromagnetic interference (EMI) noise. Since the soft-switching topologies reduce the switching losses of the converter main switches, the topologies make converters partially independent from the switching frequency. However, the conventional soft-switching topologies have already proposed most of the possible ways to improve converter performance. In addition, the trends of the newly generated power devices reduce the advantages of soft-switching topologies. This critical situation surrounding soft-switching topologies gives research motivations: What features of soft-switching topologies facilitate their practical applications? Given this motivation, the dissertation discusses two aspects = simplifying auxiliary circuits and accounting for the effects of soft-switching operations on the converter control. Engineers working with medium- and high-power multi-phase converters require simplified soft-switching topologies that have the same level of performance as the conventional soft-switching topologies. This demand is the impetus behind one of the research objectives = simplifying the auxiliary circuits of Zero-Voltage-Transition (ZVT) inverters. Simplifying the auxiliary circuits results in both a smaller number of and lower cost for auxiliary components, without any negative impact on performance. This dissertation proposes two major concepts for the simplification - the Single-Switch Single-Leg (S3L) ZVT cell and the Phase-Lock (PL) concept. Throughout an effort to eliminate circulating currents of inductor-coupled (IC) ZVT converters, the S3L ZVT cell is developed. The proposed cell allows a single auxiliary switch to achieve zero-voltage conditions for both the top and bottom main switches, and it achieves the same level of performance as the conventional ZVT cell, as well. This proposal makes IC ZVT topologies more attractive to multi-phase converter applications. Because all of the top main switches generally have identical sequences for zero-voltage turn-on commutations, one auxiliary switch might handle the commutations of all of the top main switches. This possibility introduces the PL concept, which allows the two auxiliary switches to provide a zero-voltage condition for any main switch commutation. In order to compensate for restrictions of this concept, a modified space-vector modulation (SVM) scheme also is introduced. A soft-switching topology changes the duty ratios of the converter, which affects the controllability of the converter. Therefore, this dissertation selects resolution of this issue as one of the research objectives. This dissertation derives the generalized timing equations of ZVT operations, and the generalized equations formulize the effect of ZVT operation on both duty ratios and DC current. Moreover, the effect of SVM schemes is also investigated. An average model of the ZVT converter is developed using both the timing analysis and the investigation of SVM schemes, and small-signal analysis using the average model predicts the steady-state characteristics of the converter. / Ph. D.

In research environments, many soft switching inverters have been conceived, simulated, designed, implemented and proven to have advantages over hard switched inverters. To date however, no soft-switching inverters have reached commercial production for various reasons. The fixed timing coupled inductor soft-switching inverter is of interest because in simulation and previous implementation it exhibits load and source adaptability using simple RC timer circuitry and can be implemented with low cost active auxiliary devices. During the course of this implementation, it is noted that attempting to use excessively small/inexpensive active auxiliary devices has reliability ramifications related to device packaging. The issue of auxiliary active device reliability is conjectured upon by referencing available datasheet information, application specific requirements, device pulse testing and secondary research findings related to semiconductor failure characteristics. It is also noted that aspects of the simple fixed timing circuitry operation, in conjunction with coupled inductor and saturable inductor design, can lead to coupled inductor saturation if not properly addressed. Simulation is performed and validates various causes for this non-ideal behavior. / Master of Science

Recently induction cookers, which are based on induction heating principle, have become quite popular due to their advantages such as high energy efficiency, safety, cleanliness, and compact size. However, it is widely known that with current technology, induction cookers require the cookware to be made of magnetic materials such as iron and stainless steel. This is why a lot of cookware is labeled "Induction Ready" on the bottom. The limited choice of "Induction Ready" cookware causes inconvenience to customers and limits the growing popularity of the induction cooker. Therefore, a novel induction cooker, which can work for non-magnetic material cookware such as aluminum and copper, can be very competitive in the market. This thesis studies the induction cooking application; briefly introduces its fundamental principle, research background and the motivation of the development of a non-magnetic material induction cooker. Followed by the research motivation, three commonly used inverter topologies, series resonant inverter, parallel resonant inverter, and single-ended resonant inverter, are introduced. A comparative study is made among these three topologies, and the comparative study leads to a conclusion that the series resonant inverter is more suitable for non-magnetic material induction cooking application. The thesis also presents several major issues about non-magnetic material induction cooking and how to deal with these issues through induction coil design, higher operating frequency and novel control strategy. Because of non-magnetic material's low resistivity and permeability characteristics, it is difficult to be heated and to achieve soft-switching while the coupling between the induction coil and the cooking pan can be easily changed. Later in this thesis, these issues will be discussed in detail and some potential solutions to these issues such as self-sustained oscillating control, optimized induction coil design, proper selection of power semiconductor device, etc. A 1.5 kW high frequency series resonant inverter with self-sustained oscillating control is prototyped. Experimental results demonstrated successful operation of the resonant inverter under up to 1.5 kW, and the inverter's capability to maintain zero-voltage turn-on during wide operating condition is confirmed. At the end, a summary is given about the research work done in the thesis and future research work is discussed. / Master of Science

A modified space vector modulation algorithm for a zero-voltage transition three-phase voltage source inverter/boost rectifier is presented. The converter is intended for high performance medium power applications requiring bi-directional power flow. The proposed modified space vector modulation allows the main switches to be operated with constant frequency and soft switching for any phase shift between the three-phase currents and voltages. The modulation algorithm also eliminates any low frequency distortion caused by the zero-voltage transition and can be extended to other soft-switching PWM three-phase converters. Experimental verification of the proposed algorithm is also presented as well as a comparison to the hard switched PWM converter. / Master of Science