Reduced Part Count Research Articles

A Review of Some Recently Proposed Topologies for Multilevel DC–AC Conversion

Multilevel inverter (MLI) is gaining rapid popularity in high/medium power applications due to low THD and high quality output waveform. Recently, the MLI topologies with reduced part count has attracted the researchers by offering higher number of output voltage level with reduced part count as compared to classical topologies (CHB, NPC and FC). It is observed that these recently proposed topologies are aimed to increase the output level with less number of components but the discussion over their suitability for a particular application is not yet explored completely. The main purpose of this paper is to provide an instructive review and analysis of existing MLIs with reduced part count. An exhaustive comparison of MLIs are assessed based on the number of switches, standing/blocking voltage across the switches, conduction losses, switching losses and cost. With the outcome of comparison results, suitable structure of MLI can be judged with reduced number of components and losses for given applications.

Comparison of reduced part count multilevel inverters (RPC-MLIs) for integration to the grid

Multilevel inverters (MLIs) have been developed to a matured level for generating high quality output voltage, used in numerous applications. Conventional MLIs has been received more attention due to their remarkable use in medium-voltage applications. But use of high number of part counts in conventional MLIs increase the intricacy of circuitry and controlling both results in high expenses and reduced reliability. Therefore, development of newer topologies is an active attention to reduce part count compared to the conventional MLIs. This paper presents an exhaustive review of recently proposed reduced part count MLIs for grid integration application on the basis of selection of components, comparative factors and their suitability. It is aimed at presenting a state of the art on configuration, working and their features to researchers, inventors, and application engineers dealing with multilevel inverters.

Suitability of Reduced Part Count Multilevel Inverter Topologies for Grid Interfacing

Reduced part count multilevel inverters (RPC-MLIs), an emerging technology for grid interfacing applications of renewable energy sources. RPC-MLIs overcome the limitations of conventional two-level and classical multilevel inverters (NPC, FC and CHB) by the use of reduced part counts for generation of same number of levels in the output. Focus of this paper is on to present review of the RPC-MLIs for researchers and engineers and classification of all the topologies. RPC-MLIs are compared considering its circuit complexity and performance. The comparison exposes advantages and disadvantages of topologies, as well as a wide spectrum for future research. This paper also draws the most potential topology in the field of grid integrated applications. Promising topology is simulated here under the same load and input source condition using real time simulator.

Multilevel Inverter Topologies With Reduced Device Count: A Review

Multilevel inverters have created a new wave of interest in industry and research. While the classical topologies have proved to be a viable alternative in a wide range of high-power medium-voltage applications, there has been an active interest in the evolution of newer topologies. Reduction in overall part count as compared to the classical topologies has been an important objective in the recently introduced topologies. In this paper, some of the recently proposed multilevel inverter topologies with reduced power switch count are reviewed and analyzed. The paper will serve as an introduction and an update to these topologies, both in terms of the qualitative and quantitative parameters. Also, it takes into account the challenges which arise when an attempt is made to reduce the device count. Based on a detailed comparison of these topologies as presented in this paper, appropriate multilevel solution can be arrived at for a given application.

Disturbance Observer-Based Voltage Regulation of Current-Mode-Boost-Converter-Interfaced Photovoltaic Generator

In this paper, a robust control method based on a disturbance observer is proposed to regulate the terminal voltage of a photovoltaic generator, interfaced by a current mode-controlled boost dc-dc converter. The combined generator-converter-load system possesses a nonlinear behavior, highly dependent on operation point and environmental variables, thus burdening the control task. It is shown that employing a typical linear controller, designed according to a single nominal operating point, results in a closed-loop performance, varying from a highly overdamped near open-circuit condition to greatly underdamped around short-circuit conditions. On the other hand, when the proposed robust controller is utilized, the closed-loop performance remains nearly nominal throughout the whole operation range. In addition, it is shown that, by sacrificing the performance in the vicinity of the open-circuit point, it is possible to implement the controller using a single op-amp with a reduced part count. Simulation and experimental results are presented to verify the proposed method.

Ultra high voltage MOS controlled 4H-SiC power switching devices

Ultra high voltage (UHV, >15 kV) 4H-silicon carbide (SiC) power devices have the potential to significantly improve the system performance, reliability, and cost of energy conversion systems by providing reduced part count, simplified circuit topology, and reduced switching losses. In this paper, we compare the two MOS based UHV 4H-SiC power switching devices; 15 kV 4H-SiC MOSFETs and 15 kV 4H-SiC n-IGBTs. The 15 kV 4H-SiC MOSFET shows a specific on-resistance of 204 mΩ cm2 at 25 °C, which increased to 570 mΩ cm2 at 150 °C. The 15 kV 4H-SiC MOSFET provides low, temperature-independent, switching losses which makes the device more attractive for applications that require higher switching frequencies. The 15 kV 4H-SiC n-IGBT shows a significantly lower forward voltage drop (VF), along with reasonable switching performance, which make it a very attractive device for high voltage applications with lower switching frequency requirements. An electrothermal analysis showed that the 15 kV 4H-SiC n-IGBT outperforms the 15 kV 4H-SiC MOSFET for applications with switching frequencies of less than 5 kHz. It was also shown that the use of a carrier storage layer (CSL) can significantly improve the conduction performance of the 15 kV 4H-SiC n-IGBTs.

A new part consolidation method to embrace the design freedom of additive manufacturing

As additive manufacturing (AM) evolves from Rapid Prototyping (RP) to the end-of-use product manufacturing process, manufacturing constraints have been largely alleviated and design freedom for part consolidation is extremely broadened. AM enabled part consolidation method promises a more effective way to achieve part count reduction and the ease of assembly compared with traditional Design for Manufacture and Assembly (DFMA) method. However, how to achieve AM enabled part consolidation is not well developed. In this paper, a new part consolidation method comprehensively considering function integration and structure optimization is proposed. This presented method is characterized by two main modules. The first one is to achieve better functionality through surface-level function integration and sequential part-level function integration based on design specifications with an initial CAD model which is designed for conventional manufacturing process. The other module is to realize better performance through the introduction and optimization of heterogeneous lattice structures according to performance requirements. The proposed part consolidation method highlights itself from the perspective of functionality achievement and performance improvement. An example of a triple clamp is studied to verify the effectiveness of the proposed model. The optimized results show that the part count has been reduced from 19 to 7 with a less weight by 20% and demonstrates better performance.

Design considerations for HFQ®hot stamped aluminium structural panels

HFQ is a deep drawing process for alloyed aluminium sheet that can be used to produce complex-stamped forms while maintaining the high-strength of 6xxx and 7xxx alloys. By adopting a strategy to design for HFQ at the platform level, designers can reduce part count (thereby reducing cost and weight), reduce gauge (thereby reducing weight), and improve part packaging. Two simple design examples are given to assist designers in evolving traditionally formed panel designs to HFQ formed solutions. Example features are used to illustrate the effect of geometry, thickness and strength on the final structural component.

Innovative tooling concepts for cocured composite structures in aircraft applications

Cocuring process is a unique characteristic of composite materials wherein multiple parts like stringers, ribs and spars are simultaneously cured and bonded to a composite skin resulting in an integral structure. It has many benefits like reduction in part count, elimination of stress concentration due to fastener holes in the cocured regions and reduced assembly time and related costs. However, the application of cocuring has been limited on contoured components because of the complexities associated with the tooling. The basic requirements to be fulfilled are (a) consolidation of skins and stiffeners and (b) dimensional tolerance on position and thickness of stiffeners. Proper consolidation can be ensured through the faithful transfer of autoclave pressure by designing tools which are flexible so that they conform to desired shape whereas the positional tolerance can be achieved by using rigid tools. The resolution of such conflicting requirements requires a detailed study of the geometry of the part, design requirements and tolerances achievable on tools. This paper discusses design of tools for two types of cocured structures viz., open and closed cocured structures. The tooling technologies for realising above structures differ considerably. A few tooling concepts have been discussed based on the authors’ experience of developing cocured structures over the last two decades.

Comprehensive review of a recently proposed multilevel inverter

As multilevel inverters are gaining increasing importance, newer topologies are being proposed to reduce part count for large number of levels in output voltage. A simplified five-level inverter has been recently reported in the literature to reduce component count. The topology comprises of floating input DC sources connected in opposite polarities through power switches. The structure requires lesser active switches as compared with conventional cascaded H-bridge topology with much reduced switching losses. Available literature present generalisation of the topology with symmetrical sources, but no investigations are made for equal load sharing and asymmetrical configurations. This study presents a comprehensive analysis of the aforementioned topology, referred to as cross-connected sources-based multilevel inverter (CCS-MLI). The topology is analysed for both symmetric and asymmetric source configurations. Also, a new algorithm for asymmetric source configuration suitable for CCS-MLI is proposed. A control scheme is also proposed for equal load sharing in five-level topology. Investigations are made for possibility of equal load sharing in higher level structures and fundamental frequency switching of switches bearing higher voltage stresses. Various concepts are verified with simulations and experimental studies.

Free Form Fluidics

This article introduces the concept of blending fluid power with mechanical structure through addictive manufacturing. Today, fluid-powered devices are manufactured using conventional fabrication practices. The additive process enables integrated structure, actuation, fluid passages, thermal management, and control within a single fabrication process. Fluid can be routed efficiently through the structure without the need for cross-drilled holes or plugs. Fluid passages can be optimized for heat dissipation and minimized head loss. One of the primary issues regarding parts manufactured using the additive manufacturing process is their mechanical properties. Results show that components made with Ti-6-4 powders have a minimum yield stress and ultimate strength that exceeds Grade 5 specifications. The Arcan system uses a powder bed that has an elevated temperature. Therefore, the part exhibits very little residual stress during the manufacturing process. This leads to improved mechanical strength but induces challenges in powder removal. The specific advantages are reduced weight, potential for lower cost, and reduced part counts.

Modeling Contra-Rotating Turbomachinery Components for Engine Performance Simulations: The Geared Turbofan With Contra-Rotating Core Case

This paper presents a method of modeling contra-rotating turbomachinery components for engine performance simulations. The first step is to generate the performance characteristics of such components. In this study, suitably modified one-dimensional mean line codes are used. The characteristics are then converted to three-dimensional tables (maps). Compared to conventional turbomachinery component maps, the speed ratio between the two shafts is included as an additional map parameter and the torque ratio as an additional table. Dedicated component models are then developed that use these maps to simulate design and off-design operation at the component and engine levels. Using this approach, a performance model of a geared turbofan with a contra-rotating core (CRC) is created. This configuration was investigated in the context of the European program “NEW Aero-Engine Core Concepts” (NEWAC). The core consists of a seven-stage compressor and a two-stage turbine without interstage stators and with successive rotors running in the opposite direction through the introduction of a rotating outer spool. Such a configuration results in a reduced parts count, length, weight, and cost of the entire high pressure (HP) system. Additionally, the core efficiency is improved due to reduced cooling air flow requirements. The model is then coupled to an aircraft performance model and a typical mission is carried out. The results are compared against those of a similar configuration employing a conventional core and identical design point performance. For the given aircraft-mission combination and assuming a 10% engine weight saving when using the CRC arrangement over the conventional one, a total fuel burn reduction of 1.1% is predicted.

Simulation of SEPIC Converter based-drive for Unipolar Brushless DC Motor

Front-end single-ended primary inductance converter (SEPIC) and a switch in series with each phase is proposed for driving a permanent magnet brushless dc (BLDC) motor with unipolar currents. All the switches are ground-referenced, which simplifies their gate drives. The available input voltage can be boosted for better current regulation, which is an advantage for low voltage applications. The SEPIC converter is designed to operate in the discontinuous conduction mode for operation with an ac supply. In this operation mode, the line current follows the line voltage waveform to a certain extent. The reduction in low-order harmonics and improved power factor is achieved without the use of any voltage or current sensors. The simplicity and reduced parts count of the proposed topology make it an attractive low-cost choice for many variable speed drive applications. The proposed topology is simulated and verified by using MATLAB/SIMULINK. DOI: http://dx.doi.org/10.11591/ijece.v2i2.306

Characterization and Reliability of custom digital ASIC designs using a 0.8μm bulk CMOS process for high temperature applications

With today's quickly changing technology, part obsolescence often forces unanticipated and costly design changes outside the normal product life cycle. Custom ASICs can be used to fill this gap and gain other advantages such as reduced parts count, higher performance, and higher reliability. Two digital 0.8μm bulk CMOS ASICs have been successfully implemented, providing higher reliability and performance than their replacement parts at 225°C. In this paper we examine some of the design issues encountered during their implementation, including process selection, library characterization at 225°C and above, performance, testing and qualification. External analog circuitry was integrated to further reduce parts count and increase reliability. In conclusion, we have found bulk CMOS to be an acceptable process for custom ASICs in high temperature environments.

Light-activated shape memory of glassy, azobenzene liquid crystalline polymer networks

Rapidly reconfigurable, adaptive materials are essential for the realization of “smart”, highly engineered technologies sought by aerospace, medicine, and other application areas. Shape memory observed in metal alloys and polymers (SMPs) is a primary example of shape change (adaptation). To date, nearly all shape adaptations in SMPs have been thermally triggered. A desire for isothermal, remotely cued shape adaptations of SMP has motivated examinations of other stimuli, such as light. Only a few reports document so-called light-activated SMP, in both cases exploiting photoinduced adjustments to the crosslink density of a polymer matrix with UV light of 365 nm (crosslinking) and <260 nm (decrosslinking). This work presents a distinctive approach to generating light-activated SMP by employing a glassy liquid crystal polymer network (LCN) material that is capable of rapid photo-fixing with short exposures (<5 min) of eye-safe 442 nm light. Here, linearly polarized 442 nm light is used to photo-fix temporary states in both cantilever and free-standing geometries which are then thermally or optically restored to the permanent shape. The combination of thermal and photo-fixable shape memory presented here yields substantial functionality in a single adaptive material that could reduce part count in applications. As a demonstration of the opportunities afforded by this functional material, the glassy, photoresponsive LCN is thermally fixed as a catapult and subsequently used to transduce light energy into mechanical work, demonstrated here in the “photo-fueled” launching of an object at a rate of 0.3 m s−1.

Superplastic Forming – Cost Effective

When Superplastic Forming (SPF) was offered as a production process in the mid 70’s, it became the panacea of all processes for sheet metal products designed to be made from Titanium and Aluminium materials. The claims were (1) reduced part count (2) reduced assembly time (3) weight reduction (4) monolithic parts and (5) stronger structures. Following Pearson’s work in the mid 30’s with Lead-Tin and Bismuth-Tin alloys [1], showing higher than 1000% elongation without failure, the Aluminium industry developed SPF alloys and launched into numerous commercial applications. Other research facilities focused on the potential of achieving superplasticity in Titanium alloys. This was demonstrated in the late 60’s using the now well established Ti6Al4V alloy. Considerable funding was allocated, both in the USA & UK, specifically for the development of the process. The USA focused on the military programmes and the UK on the civil (Concord) and some military aircraft. Success in these programmes and the claims made, resulted with a production process. Companies invested in suitable plant and equipment, and designers grasped the process potential and applied SPF to their sheet metal designs expecting to reap the claimed benefits. The claims are valid if applied to correctly chosen components. All too often, the SPF manufacturing choice did not deliver its claims. In many cases cost of material, need to chemical mill and higher energy costs, were either not envisaged or taken into account. Today all processes, material cost and alternative material types have to be assessed before the manufacturing method is chosen. The aerospace industry is attacking the Buy-Fly ratio. Energy and labour cost are at a premium and these have caused the SPF and Hot Forming community to examine ways of producing products (a) from less material (b) by Hot Forming (eliminating the need to apply chemical milling to remove the alpha case) (c) questioning the material choice (CP instead of Ti6Al4V) and (d) by applying modern fabrication methods. The paper will illustrate this change in philosophy; shows today’s choices and demonstrate how the SPF process can be cost effective, and in fact still does have a major role to play in producing airframe and engine structures.

Superplastic Forming – Cost Effective

When Superplastic Forming (SPF) was offered as a production process in the mid 70’s, it became the panacea of all processes for sheet metal products designed to be made from Titanium and Aluminium materials. The claims were (1) reduced part count (2) reduced assembly time (3) weight reduction (4) monolithic parts and (5) stronger structures. Following Pearson’s work in the mid 30’s with Lead-Tin and Bismuth-Tin alloys [1], showing higher than 1000% elongation without failure, the Aluminium industry developed SPF alloys and launched into numerous commercial applications. Other research facilities focused on the potential of achieving superplasticity in Titanium alloys. This was demonstrated in the late 60’s using the now well established Ti6Al4V alloy. Considerable funding was allocated, both in the USA &amp; UK, specifically for the development of the process. The USA focused on the military programmes and the UK on the civil (Concord) and some military aircraft. Success in these programmes and the claims made, resulted with a production process. Companies invested in suitable plant and equipment, and designers grasped the process potential and applied SPF to their sheet metal designs expecting to reap the claimed benefits. The claims are valid if applied to correctly chosen components. All too often, the SPF manufacturing choice did not deliver its claims. In many cases cost of material, need to chemical mill and higher energy costs, were either not envisaged or taken into account. Today all processes, material cost and alternative material types have to be assessed before the manufacturing method is chosen. The aerospace industry is attacking the Buy-Fly ratio. Energy and labour cost are at a premium and these have caused the SPF and Hot Forming community to examine ways of producing products (a) from less material (b) by Hot Forming (eliminating the need to apply chemical milling to remove the alpha case) (c) questioning the material choice (CP instead of Ti6Al4V) and (d) by applying modern fabrication methods. The paper will illustrate this change in philosophy; shows today’s choices and demonstrate how the SPF process can be cost effective, and in fact still does have a major role to play in producing airframe and engine structures.

Double-Input DC–DC Power Electronic Converters for Electric-Drive Vehicles—Topology Exploration and Synthesis Using a Single-Pole Triple-Throw Switch

Hybridizing energy systems using storage devices has gained popularity in transportation and distributed electric power generation applications. Traditionally, several independent power electronic converters (PECs) were utilized in such practices. Due to their reduced part count, double-input (DI) PECs prove to be a promising choice in hybridizing energy systems. A few topologies for multi-input converters have been reported in the literature; however, there is no systematic approach to synthesize them. Furthermore, all possible topologies are not completely explored, and it is difficult to derive new converters from existing topologies. Therefore, in this paper, a systematic approach to derive DI converters by using a single-pole triple-throw switch as a building block is presented.

Nonlinear Algebraic Reduction for Snap-Fit Simulation

Snap-fits are often preferred over other traditional methods of assembly since they reduce part count, assembly/disassembly time, and manufacturing cost. A typical simulation of a snap-fit assembly entails two critical steps: contact detection and nonlinear deformation analysis, which are strongly coupled. One could rely on standard 3D contact detectors and standard 3D finite element analysis (FEA) to simulate the two steps. However, since snap-fits are slender, 3D FEA tends to be inefficient and slow. On the other hand, one could rely on an explicit 1D beam reduction for simulation. This is highly efficient for large deformation analysis, but contact detection can pose challenges. Moreover, for complex snap-fits, extracting cross-sectional properties for 1D formulation is nontrivial. We propose here a nonlinear algebraic dimensional reduction method that offers the “best of both worlds.” In the proposed method, a 3D model is used for contact detection. However, to speed-up deformation analysis, the 3D model is implicitly reduced to a 1D beam model via an algebraic process. Thus, it offers the generality of 3D simulation and the computational efficiency of 1D simulation, as confirmed by the numerical experiments and optimization studies.

High-Quality Single-Phase Power Conversion by Reconsidering the Magnetic Components in the Output Stage—Building a Better Half-Bridge

A novel half-bridge switching topology is presented which is based on using a split-wound series-connected coupled-winding inductor, interleaved switching, and zero-deadtime operation to achieve multilevel pulsewidth-modulation output with a reduced part count, reduced current ripple, and improved total harmonic distortion (THD) performance. This new topology is presented to highlight the design process for low-power high switching frequency designs requiring high performance, where circuit size and complexity are normally limiting factors. The design process demonstrated includes considering the current performance characteristics of the inverter and the design of the coupled-winding inductor. Design tradeoffs that are unique to this topology are explored that allow optimized designs for electrical performance, magnetic component size, or system losses. The benefit of the new topology is demonstrated using a case design for a class-D audio power amplifier, which shows a reduction in open-loop THD + N to as low as 0.29%.