Hybrid MMC Research Articles

A Hybrid MMC Control Strategy to Enhance the Resilience of DC Transmission System

A Hybrid MMC Control Strategy to Enhance the Resilience of DC Transmission System

AC and DC Fault Ride-Through Strategies for Hybrid MMC Based HVDC Link and Interaction With Multimachine Power System Dynamics

AC and DC Fault Ride-Through Strategies for Hybrid MMC Based HVDC Link and Interaction With Multimachine Power System Dynamics

Improved AAVM and Small-Signal Model of Hybrid MMC Considering Dynamic Differences Between Full-Bridge and Half-Bridge Submodules

Improved AAVM and Small-Signal Model of Hybrid MMC Considering Dynamic Differences Between Full-Bridge and Half-Bridge Submodules

Assessment of machinability behaviour of LM24 – nano Al2O3 – gr hybrid composites through stir casting technique

Abstract This study is focused on developing a novel combination of a hybrid MMC made of LM24 aluminium alloy, nano Al2O3 and Graphite for enhanced machinability. The study conducts a series of experimental runs and evaluates surface roughness and material removal rate. The process parameters of spindle speed, feed, and depth of cut have been varied, while different weight percentages of nano Al2O3 (1%, 3%, and 5%) were incorporated into the LM24 metal matrix alloy along with 1 wt% of Gr. Response Surface Methodology (RSM) is used to optimize the turning parameters and enhance the machining performance for better quality and productivity. The derived optimal machining parameters have been verified through confirmatory tests. An analysis of variance (ANOVA) was used to determine the individual contributions of each parameter to the machinability characteristics. Surface morphology analysis revealed the uniform distribution of nanoparticle reinforcements in the metal matrix. The surface roughness and material removal rate of the machined nanocomposites were studied. The optimized outputs are a minimum surface roughness Ra 0.522 μm and maximum material removal rate MRR 110.2 mm3s–1 The maximum hardness of the MMC composites has been 60.5 HRB.

Preparation and investigation of mechanical behavior and characterization of AA7475/ZrO2/Gr hybrid MMC

In this study, the influence of zirconium dioxide (ZrO2) and graphite (Gr) on the mechanical behavior and characterization of Hybrid metal matrix composites (HMMCs) is investigated. By using the stir casting method, the samples are prepared with aluminum alloy (AA7475) as matrix and 2, 3, and 4 weight percentages (wt%) of zirconium dioxide (ZrO2) and graphite (Gr) as reinforcements. The synthesized composites were subjected to microstructural, density, porosity, yield strength (YS), ultimate tensile strength (UTS), and hardness were examined. Microstructural characteristics were examined using scanning electron microscopy (SEM). The XRD pattern indicated the presence of the ZrO2 and Gr phases in HMM composites. By conducting a corrosion resistance test, the rate of corrosion for the HMMCs was determined. Furthermore, the Tafel plot curve was employed to probe the level of corrosion resistance. With an increase in ZrO2 the corrosion resistance increases whereas decline in ductility is noted. The HMMCs 3 sample exhibit superior physical and mechanical properties when compared to other HMMCs and base matrix. Tensile fractography was carried out to determine the various fracture mechanisms.

Fabrication and Characterization of a Stir Casting-Based Aluminium Hybrid MMC Reinforced with SiC, TiC, and MoS2

The need for strong, lightweight materials has prompted the creation of innovative metal matrix composites based on aluminum. The properties of metal matrix composites that are uniformly dispersed with nanoparticles are much superior to those of monolithic alloy and microparticle-reinforced composites. The objective of this work was to create and evaluate a metal matrix composite reinforced with MoS2, SiC, and TiC that is a hybrid aluminum alloy, Al6061. It was also investigated how the weight percentages (3, 6, 9, and 12%) of MoS2, SiC, and TiC reinforcement affected the mechanical, morphological, tribological, and physical characteristics of the metal matrix composite. The addition of SiC and MoS2 increased the density of the reinforced Al6061 composite when compared to as-cast non-reinforced Al6061. It was found that the hybrid composite Al6061/12% SiC/4% MoS2 had the maximum density. The hybrid metal matrix composite's toughness increased as the proportion of TiC weight increased. The composite made of Al6061, 12% TiC, and 4% MoS2 had the maximum hardness, measuring 114.03 HV. The composite Al6061/12% TiC/4% MoS2 has the most ultimate tensile strength. The tribology analysis revealed that when applied stress increased from 10 to 50 N, mass loss increased dramatically. Because of the solid MoS2 lubricant and the development of the TiC layer at the contact zone, Double- and triple-reinforced specimens had less wear loss than non-reinforced specimens, as shown by the wear performance of hybrid composites. The main wear mechanisms of the composites were delamination wear and wear debris.

A new hybrid multilevel thyristor-based DC-DC converter

The rapid growth in HVDC grids is becoming inevitable for long-distance power transmission. Therefore, the idea of interconnection between the point-to-point links becomes essential. However, these point-to-point connections face several challenges such as the requirement of DC fault blocking capability, interfacing of different grounding schemes, offering multi-vendor interoperability, and difficulty to achieve high DC voltage stepping. DC-DC converters are considered the optimum solution to tackle these challenges in DC grids interconnection. In this paper, a new hybrid modular DC-DC converter is proposed that achieves a low number of semiconductors, low losses, and cost in comparison to other DC-DC converters due to the utilization of thyristors. The new DC-DC converter consists of two hybrid MMC bridges connected through an isolating transformer. Each MMC bridge is comprised of half bridge submodules and bidirectional thyristors. Detailed mathematical analysis, design, and control are illustrated. A comparison is carried out between different topologies in terms of semiconductor count, power loss, and cost. Also, both simulation model and experimental test rig are built to validate the proposed hybrid modular DC-DC converter under different scenarios. Finally, another variant of the hybrid-thyristor based converter (version two) is proposed for multiport DC-Hub application to achieve DC fault blocking without turning off all connected bridges.

Investigation of machining characteristics and surface integrity for trim cut WEDM of hybrid metal matrix composite [Al 6061, SiC, and TiB2

This study is focused on fabrication of Hybrid Al6061/SiC + TiB2 MMC by stir casting process, primarily to study the effect of two different reinforcement particles on mechanical properties and microstructure. Additionally, the assessment of surface integrity has been attempted after machining the composite by trim cut WEDM process. Five samples have been fabricated with varied weight fraction of SiC and TiB2 reinforcement, keeping total weight percentage of reinforcement particles fixed to 10%. It is observed that Hybrid MMC with composition Al6061 (90%), SiC (2.5%), and TiB2 (7.5%) shows better mechanical properties which is corroborated by both the optical microscopy and SEM. A screening experiment has been designed using fold over fractional factorial technique (with resolution IV), to investigate the parametric effects on surface integrity features, i.e., surface roughness, spark gap, and recast layer for trim cut WEDM operation. Peak current (Ip) and pulse on time (Ton) have been found to be the significant parameters for spark gap as well as surface roughness. It is observed that the trim cut operation improved the surface roughness and reduced it to 2.2 µm from 3.93 µm (after rough cut). Recast layer has been reduced to a value of 4.67 µm after trim operation, from 24.6 µm for rough cut. These findings suggest that trim cut strategy is very effective in improving the surface integrity of the rough-cut machined samples. It is also observed that thickness of recast layer is directly proportional to the discharge energy during trim cutting.

Multi-Objective Optimization for the Sustainable Machining of Metal Matrix Composites Using Wire Electric Discharge Machining

Wire Electrical Discharge Machining (WEDM) is an electrothermal machining process used to produce complex profiles electrically conductive materials. In this investigation, multiobjective optimization using hybrid approach of Taguchi method (TM) and Principal Component Analysis (PCA) has been performed to find the optimal input process parameters like pulse-on time ([Formula: see text]), pulse-off time ([Formula: see text]), peak current (I), wire speed (WS) for output parameters, namely, cutting velocity (CV), power consumption (PC), and surface roughness (SR). Three different Aluminum based Metal Matrix Composites (AMMC) were fabricated using three different reinforcements i.e. 10[Formula: see text]wt.% Aluminum Oxide (Al2O3), 10[Formula: see text]wt.% Silicon Carbide (SiC), and combining 5[Formula: see text]wt.% Al2O3 with 5[Formula: see text]wt.% SiC through the stir casting process. The experiments were conducted based on the L9 orthogonal array approach of Taguchi methodology and regression equations were developed based on the experimental data for the prediction of output parameters. The results of analysis of variance (ANOVA) shows that WS and I are the two most significant factors for CV of all three developed composites whereas for SR, [Formula: see text] and I play critical role. The optimal results show that for machining of Al6061/Al2O3 and Al6061/SiC optimal input parameters are [Formula: see text][Formula: see text][Formula: see text]s, [Formula: see text][Formula: see text][Formula: see text]s, [Formula: see text][Formula: see text]A, and [Formula: see text][Formula: see text]m/s. For hybrid MMC (Al6061/Al2O3/SiC), optimized input parameters are [Formula: see text][Formula: see text][Formula: see text]s, [Formula: see text][Formula: see text][Formula: see text]s, [Formula: see text][Formula: see text]A, and [Formula: see text][Formula: see text]m/s. At optimal input parameters though the CV decreases by 1.53% the PC and SR decreases by 8.95% and 15.47%, respectively, in case of hybrid composite. The machined surface at optimal input parameters were examined by the Scanning Electron Microscope (SEM). This study will help to identify the input parameters for sustainable machining of AMMC for different reinforcements with WEDM.

A hybrid half‐bridge submodule‐based DC–DC modular multilevel converter with a single bidirectional high‐voltage valve

AbstractModular Multilevel Converters (MMCs) are promising candidates for high‐voltage high‐power applications. The main challenge of the MMCs is the zero‐frequency operation. To achieve a successful DC–DC conversion process with balanced capacitors’ voltages with limited voltage ripple, this paper suggests the employment of the conventional two‐leg half‐bridge submodule‐based MMC structure in conjunction with a single bidirectional high‐voltage (HV) valve across the low‐voltage side. In the suggested structure, the HV valve is controlled on and off to ensure energy equalization for the MMC arms. In addition, soft‐switching for the HV valve is proposed to reduce the switching losses. Detailed illustration and design of the proposed concept are presented. Simulation and experimentation results are elucidated to show the effectiveness of the proposed DC–DC hybrid MMC. The results showed efficient performance of the suggested converter.

Mechanical DC Breakers and Hybrid MMC-Based Coordinated Strategy for MMC-HVDC DC Fault Riding Through

The bipolar short circuit fault, which is the most destructive DC side fault of MMC-HVDC systems, and its riding through strategy is a current hotspot. Hybrid MMC is a promising topology for HVDC applications with the capability of DC fault isolation, however, it still suffers from the high cost. This paper proposes a mechanical DC breakers and hybrid MMC based coordinated DC fault ride-through strategy that can reduce the ratio of the full-bridge submodules (FBSMs) in the hybrid MMC and obviously cut the cost. To be specific, this strategy mainly depends on the FBSM’s negative output to suppress the fault current and eventually block it with the mechanical DC breakers. The impact on the performance of fault ride-through by the ratio of FBSMs in the hybrid MMC is analyzed, and the superiority of the strategy proposed in this paper has been proved with the analysis of conventional strategies. Finally, the effectiveness of the proposed strategy is validated with the RT-LAB experimental platform, and the optimal ratio range is obtained through the multiple groups of simulation experiments with different ratios of FBSMs in hybrid MMC base on MATLAB/Simulink.

A Hybrid Submodule Three-Phase Multiplexing Arm Modular Multilevel Converter With Wide Operation Range and DC-Fault Blocking Capability

Three-phase multiplexing arm modular multilevel converter (TPMA-MMC) possesses lower cost, smaller volume, and higher efficiency compared with MMC. However, the limited operation range limits its popularity. Hence, in this article, it redefines arm submodule (SM) configuration type, where the conventional arm is configured with full-bridge submodules (FBSMs), and the multiplexing arm is formed by half-bridge submodules (HBSMs). Meanwhile, a new energy balance principle and modulation scheme are proposed to expand TPMA-MMC’s operation range. Furthermore, the DC-fault blocking schemes could be implemented to realize DC-fault tolerance reliably without the multiplexing arm blocking. Compared with hybrid MMC(H-MMC), it could reduce by 33.33% in submodules a least, which leads lower footprint and operation loss. Due to reregulating the energy flowing path of multiplexing arm, and rearranging the chain-link voltage of multiplexing and conventional arm, it could reduce the required SM capacitance and further decrease 65% energy storage requirement, resulting in improving the power density. Finally, the topology control scheme and DC-fault blocking scheme are verified by simulation and scale-down prototype experimental results.

Microstructure Characterization, Mechanical and Wear Behavior of Silicon Carbide and Neem Leaf Powder Reinforced AL7075 Alloy hybrid MMC’s.

The demanding material quality criteria in the automotive and aerospace industries have recently had an impact on the development of lightweight aluminium alloys. The choice and application of metal-matrix composites as structural materials in this context are known to offer a variety of benefits. These benefits include the ability to combine high elastic modulus, toughness, and impact resistance; minimum sensitivity to change in temperature or thermal shock; durability of the surface is good; moisture absorption leads to the potential issue while minimum exposure which leads to environmental degradation; and improved fabricability with conventional metalworking equipment. Aluminium metal matrix composites (AMMCs) are a potential material for advanced structural, aviation, aerospace, marine, and defence applications, as well as for the automotive sector and other related fields, due to their outstanding combination of qualities. The stir casting procedure is used to create an aluminium metal matrix composite (AMMC), which is the most efficient way to do so. In this study, the aluminium alloy 7075 is strengthened using neem leaf powder and SiC. The Vickers hardness examination method is used to govern the hardness of hybrid composites. Eventually, the mechanical and tribological properties of the composites were assessed, and their relationship to the composites' matching microstructure and wear was addressed.

Reduction in Submodule Capacitance in FB- and HYB-MMCs With Variable DC Voltages

Full-bridge submodule (FBSM)-based modular multilevel converter (FB-MMC) or hybrid MMC (HYB-MMC) composed of FBSMs and half-bridge submodules are necessary in many applications. However, the arm energy fluctuation during reactive power exchange is very high, causing large sizes and high costs of submodule capacitors. Using the negative states of the FBSMs, the FB-, and HYB-MMCs can dynamically adjust the dc voltage, and this technique has been used in many commissioned projects. This study treats the dc voltage as a new dimension and proposes a new operation mode based on variable dc voltage for FB- or HYB-MMCs to reduce the arm energy fluctuations and submodule capacitance. The basic idea is to reduce the dc voltage in high reactive power and low active power conditions, thereby suppressing the arm energy fluctuations. Theoretical analysis shows that the energy fluctuation and submodule capacitance can be reduced by 30%–40%, and the valve cost can be reduced by 13%. Economic and technical comparison results show that the proposed approach can have similar reduction effects on the capacitance and valve cost, but has fewer technical limits. Simulation and experimental results verify the analysis.

Preparation and evaluation of mechanical properties of Al 7075 with B4C and coconut shell fly ash hybrid MMC by powder metallurgy

The paper describes an overview of the various aspects of the Hybrid Aluminium Metal Matrix (HAMC) and its mechanical characteristics. Due to the various advantages of Al 7075, it has been widely utilized in the aerospace industry, such as in aircraft engines and wings. However, its high hardness and wear resistance are still not enough to fully realize its full potential. To enhance its properties, Al 7075 was strengthened with coconut shell fly ash (CSFA) and boron carbide particles. Powder metallurgy was utilized to make Al 7075 composite materials. The various weight percentages of Al 7075 HAMC were then fabricated. The mechanical properties of this material are discussed. The Al 7075 composite materials exhibited a 33% increase in its hardness due to the adding of 3 wt% CSFA and 12 wt% B4C. The strength of the composites also increased by 66%. However, due to the adding of additional reinforcements, the tensile strength of the materials decreased. The reduction in the length of the composites was also caused by the addition of 3 wt% CSFA and 9 wt% B4C in the matrix. The impact energy of the materials getting increased to approximately 2.3 J. The optical micrographs of Al 7075 revealed that the distribution of the reinforcement particles was homogeneous. These particles contributed to the various mechanical properties of the Al 7075 composite materials.

Hybrid Modular Multilevel Converters for High-AC/Low-DC Medium-Voltage Applications

With ever-increasing power-density requirements, technologies such as energy storage systems and electric-vehicles can benefit greatly from interfacing medium-voltage (MV)-AC grid like 13.8kV or 30kV using high-AC/low-DC voltage converter. Using modular high-AC/low-DC voltage converter can help increase power-density and efficiency, while reducing total conversion steps and providing flexibility. Full-bridge modular multilevel converters (FB-MMC) and solid-state transformers are existing solutions for such operations, but suffer from limitations of high semiconductor requirements, large submodule capacitors and/or many high-frequency transformers. Three new hybrid-MMC (HMMC) topologies are proposed in this paper as alternative solutions for such high-AC/low-DC voltage operations. Each of the three developed HMMCs utilizes a unique combination of low-frequency high-voltage switches and fast-switching low-voltage switch based submodules to generate multilevel-AC voltage. HMMCs are compared extensively to state-of-the-art FB-MMC and are shown to have semiconductor savings of over 27%, 38% lower submodule capacitor size, and 53% lower losses for 13.8-kV-AC/6-kV-DC operation. Due to these benefits like higher efficiency, significantly smaller submodule capacitance requirements, and fewer semiconductors, HMMCs can be an excellent option for high-AC/low-DC applications. Practical considerations like snubber and DC split-capacitor requirement are also elaborated for developing and commercializing HMMCs. Comparison results are verified using a 17.5 kW three-phase MV laboratory prototype.

Research on dual-mode fault suppression strategy of AC isolation and current limiting based on hybrid MMC

Abstract The DC side fault of the high voltage DC transmission system based on modular multilevel converters high voltage DC (MMC-HVDC) is easily affected by the double influence of AC transient electrical quantity infeed and overvoltage and overcurrent, seriously threatening the safe operation of the power grid. Aiming at the problem above, a fault suppression strategy in dual mode of isolation and current limiting is proposed. Based on the half-bridge-full-bridge hybrid MMC, the fault transient mathematical model considering AC feed and sub-module switching feed is analyzed. AC isolation module with double conduction self-resistance structure and current-limiting control module is constructed, which can be adaptively adjusted to the system’s direct current parameters. The ±500 kV double-ended hybrid MMC system model is established to verify the scheme’s effectiveness. In addition, the influence of high AC modulation parameters on the suppression effect is investigated. PSCAD/EMTDC simulation results show that AC active and reactive power feed-in peaks are reduced by 388.69 MW and 119.82 Mvar, respectively, under dual-mode control. The peak value of DC overvoltage and overcurrent is reduced by 1211.53 kV and 22.5 kA, respectively, the fault self-clearing time is shortened by 43 ms, and the fault suppression effect is remarkable. In the high AC modulation ratio operating state, the modulation parameters are positively correlated with the AC power feed and negatively correlated with the overvoltage and overcurrent of the DC system. The research results provide support for the fault protection scheme of the hybrid MMC flexible and direct power grid.

Machinability Studies on Hybrid Aluminum Metal Matrix Composites

Hybrid metal matrix composites are new invention in material science and Engineering. The hybrid metal matrix composites (Hybrid MMC’s) generally consist of two or more reinforcements in it. These hybrid MMC’s have several benefits over the single reinforcement. The presence of reinforcements in it exhibits improved mechanical, tribological and machinability properties. Aluminium-based MMC’s have made attention in recent years as engineering materials. But in some Aluminium-based MMC’s the use of single reinforcement may sometimes lead to weakening in its physical properties. Conversely, to overcome the problem of single reinforced composites, the idea of the use of two different types of reinforcements is being explored in the Aluminium matrix. In the hybrid MMC’s, generally one of the reinforcements will be a hard phase and the other reinforcement being a soft lubricating phase. Hard reinforcements such as TiO2, Al2O3, SiC, etc. will improve the hardness and abrasive wear resistance of Aluminium but it has a negative effect on the machinability of Aluminium. To balance these effects, reinforcements like graphite which is a solid lubricant can be dispersed in Aluminium along with hard reinforcements. In the present study, the paper reviews on the effect of processing techniques, effect of reinforcement and effect of machining parameters on the machinability of hybrid aluminium metal matrix composites.

Evaluation of Machining Performance for Electrochemical Surface Grinding of Aluminium Based Hybrid MMC

Evaluation of Machining Performance for Electrochemical Surface Grinding of Aluminium Based Hybrid MMC

Parametric study of eco-friendly reinforcements on aluminium based hybrid MMC using Taguchi approach

ABSTRACT Aluminum metal alloys are the most commonly used for the selection of the base matrix because of their lightweight, high strength to weight ratio, anti-corrosive properties, good resistance to fatigue, and large-scale availability. The addition of reinforcements into the metallic matrix is to improve the overall physical, mechanical, chemical, and tribological properties at ambient temperature. In this context, if eco-friendly reinforcement materials are used for the fabrication of hybrid composite added more advantageous outcomes in the field of material as well as ecological sciences. Therefore, in this presented paper, an investigation on Al7075-T6/Graphite powder/Waste tire rubber powder/and S-glass fiber particles based eco-designed hybrid aluminum metal matrix composites (AMMCs) synthesized through sir casting route for lightweight and high strength applications in automotive and avionics sectors. During the morphological study, the homogenous distribution of reinforcements with fine grain boundaries over the base matrix is identified via the optical microscope technique. Furthermore, optimization of results is carried out using the Taguchi approach and analysis of variance. Results reveal that the micro-hardness and surface roughness of fabricated hybrid composite (i.e. sample no.4) is significantly increased (up to 37.93%), and slightly decreased (up to 2.86%), respectively, as compared with the unreinforced base matrix.