Abstract

A novel time–current-rate-based inverse characteristic curve for relays in a DC microgrid is proposed in this paper. Line current rise rate is used as actuating quantity, ensuring quick line fault clearing (relay operating time is in order of a few . The advantage of using line current rise rate as actuating quantity is that for a line short-circuit fault, it does not vary significantly for grid-connected and islanded modes of operation and varying network topologies of DC microgrid. Consequently, using the proposed characteristic, a single set of optimal relay settings is obtained using an optimization solver in MATLAB. The obtained settings ensure reliable and selective coordination between primary and backup relays for various pole-to-ground and pole-to-pole line faults under different operating conditions with multiple sources in two different 4-bus 400V low voltage DC microgrids. The maximum relay operating time for a high resistance fault with the proposed curve is for the first considered low voltage DC microgrid. Simulations in the Real Time Digital Simulator and comparisons with previous schemes (one comparison on the second considered DC microgrid), conventional standard inverse, and extremely inverse curves for DC microgrid protection indicate the effectiveness of the proposed scheme.

Introduction

The ease of integration of solar Photo-Voltaic (PV) and Battery Energy Storage Systems (BESSs) based renewable energy resources in a DC microgrid, compared to an AC microgrid, has led to the increased expansion and research interest of DC microgrids over AC microgrids [1], [2]. Also, DC microgrid can be a great way to power remote towns, shipboards, spaceships, and grids with sensitive loads, where the quality of power is crucial [3], [4]. However, the rate of rise of current is very high in a DC microgrid during a line fault due to the rapid discharge of the DC link capacitor and the associated low line impedance [5]. Hence, in general, the DC microgrid protection schemes follow a three-time frame based protection methodology in which the protection of the line, feeder, and the source should be done within a few milliseconds, and seconds, respectively [6]. Several DC Circuit Breakers (CBs) have been developed to support the quick isolation of lines during a fault in a DC microgrid, among which the solid-state CBs have a response time in the range of a few

Conclusion

This paper proposes a novel inverse time relay characteristic for the protection of DC microgrids against line faults using line current rise rate as an actuating quantity. It can coordinate relays in a DC microgrid with non-unit fault detection schemes or act as a backup scheme for relays with communication-based primary method. The relay coordination using the proposed characteristic is tested on a V LVDC microgrid. A single set of optimal relay settings ( and ) and a common set of values of and in (8) are obtained, considering all possible modes of operation, network configurations, and worst-case PG, PP LRFs and PG HRFs. Consequently, the proposed approach does not require an online update of and with a change in operating condition of DC microgrid. The efficacy of the proposed curve is validated with the obtained optimal unique relay settings for various PG, PP LRFs, PG HRFs for GC, islanded modes of operation, ring, radial network configurations, and intermittency of generation from renewable energy sources. Zero relay miscoordinations with a maximum primary relay operating time with the proposed curve are and for LRF and HRF faults, respectively, proving the effectiveness of the proposed technique in LVDC microgrid.

Further, the issues of using SI and EI curves to coordinate relays in a LVDC microgrid using line current and line current rise rate as actuating quantity and issues with using line current as actuating quantity in proposed scheme are discussed. It is observed that the conventional EI curve with line current rise rate may be used for relay coordination in DC microgrid. However, the high relay operating time (maximum primary relay operating time being ) may lead to prolonged line fault isolation. Additionally, the proposed scheme is fast and reliable, compared to EI curves, since the sum of primary relay operating times, considering all fault scenarios, is with the proposed curve, compared to the EI curve, which gives . The comparison with [16], [17] reveals the efficacy of the proposed scheme with the relay operating times in the proposed scheme being in the range of a few for line faults in LVDC microgrid.

Summary

Electric double-layer capacitors (EDLCs) have the potential to replace aluminum electrolytic capacitors for alternating current line-filtering, aligning with the trend of device miniaturization. However, it is challenging for EDLCs to simultaneously achieve rapid ion migration, electrical response, and high areal and volumetric capacitances. Here, we demonstrate that three-dimensional, structurally integrated multi-layer carbon tube (3D-MLCT) frameworks are used as electrodes for high-performance filtering EDLCs. By simply increasing the number of tube layers, a high specific areal capacitance of 3.08 mF cm−2 at 120 Hz is achieved with a phase angle of −80.1°, exhibiting excellent capacitance and fast frequency response. The outstanding performance of the 3D-MLCT is attributed to the high density, high orientation, and high integrality of carbon tube arrays that facilitate and accelerate ion distribution onto the electrode surface. The findings of this work provide a solution for developing next-generation miniaturized filter capacitors with high capacitance and fast frequency response.

Introduction

Converting alternating current (AC) into direct current (DC) is essential for powering electronics.1,2,3 In the process, filter capacitors play a crucial role in smoothing the ripples in the rectified DC signal.4,5,6,7 Aluminum electrolytic capacitors (AECs) dominate this field but occupy the most significant volume in circuits.8,9,10 Electric double-layer capacitors (EDLCs), storing energy physically through reversible ion adsorption at the electrode-electrolyte interface, have been anticipated for fast frequency response applications.11,12,13,14,15 EDLCs are considered promising alternative devices for AC line-filtering to meet the demands of miniaturized electronic devices owing to their several-orders-of-magnitude-higher specific capacitance than commercial AECs.16,17,18,19,20,21,22,23 However, conventional EDLCs behave more like resistors than capacitors and possess poor frequency response performance at an indicator frequency of 120 Hz because of their tortuous and complicated pore structure as well as the high resistances of the electrodes.24,25,26,27

The first filtering EDLC was reported by Miller et al.,1 with discrete vertically oriented graphene (VOG) nanosheets grown on nickel substrates as electrodes, demonstrating an outstanding AC line-filtering performance. Subsequently, various carbon-nanomaterial-based electrodes with high orientation, thin thickness, and macro-porous structures have been explored for filtering EDLCs.28,29,30,31,32,33,34,35 However, the specific areal (CA) and volumetric capacitances (CV) are still at a low level—the bottleneck of miniaturized filter devices.36,37,38,39

Results and discussion

The fabricating process of 3D-MLCT is schematically illustrated in Figure 1. A 3D-AAO template with interconnected vertical and lateral channels was synthesized by anodizing impure aluminum foil in phosphoric acid electrolyte at 0°C under a voltage of 195 V (Figure S1).40,41 The template was placed into a horizontal tube furnace and heated to 1,000°C at 10°C/min under an Ar atmosphere. The first CT layer was deposited on the pore walls of the 3D-AAO template with a flow of acetylene gas under vacuum conditions for 50 min. Subsequently, an AlOx layer was deposited via an ALD process at 250°C on the inner wall of the first CT layer using trimethyl aluminum (TMA) and ozone (O3) as the precursors.42 The second CT layer was deposited on the AlOx surface via a second-time CVD process. Similarly, repeating the ALD and subsequent CVD processes can prepare a third CT layer. Finally, the 3D-MLCT was obtained after removing the AlOx layer(s) and 3D-AAO template in hydrofluoric acid solution, and the spacing of adjacent CT layers can be precisely controlled by the thickness of the AlOx layers. Furthermore, the size of the 3D-CT films can be adjusted by varying the area of the 3D-AAO as needed, and we prepared a 3D-CT film with an area of approximately 24 cm2 (see Figure S2).

Abstract

Application of micro-grids (MGs) as a solution for future energy systems are significantly increasing in recent years. On the other hand, more stringent requirements are added to grid codes (GCs) of low-voltage distribution networks. Accordingly, this paper proposes a low-voltage ride-through (LVRT) control scheme for four-wire multi-source MGs. The novel strategy is composed of two layers for controlling each phase of the grid-connected sources independently. The primary layer contains a reverse-droop function for each phase and fractional-order sliding-mode-control (FOSMC). The secondary layer determines the total requested reactive power for each phase during symmetrical and asymmetrical voltage drops. Then, the mentioned power is shared among the phases of each inverter based on the reactive power-sharing strategy and GC requirements. Based on the proposed grid-following controller, the voltage of faulty phases is compensated by reactive power injection. In addition, power quality indexes are kept in acceptable ranges during abnormalities, and the FOSMC performs better than the conventional methods. The effectiveness of the proposed scheme is verified through offline simulations in MATLAB/Simulink as well as validation by real-time results.

Introduction

1.1. Background
The utilization of small-scale distributed energy resources (DERs) in low and medium-voltage networks is increasing, and as a result, their sudden and collective disconnection from the power system might cause voltage collapse on the grid during severe voltage perturbations. Therefore, the severe impact of the DERs cannot be ignored since their contribution to the power supply is considerable. Thus, the incremental usage of DER systems has become leverage for setting new requirements for power systems. These regulations are called grid codes (GCs), which vary from country to country and cover some grid-connected power sources such as wind turbines and photovoltaic (PV) systems [1]. The mentioned regulations force the sources to stay connected to the main grid during temporary voltage sags and support it by injecting reactive current. An essential requirement of the GC, which has gained much attraction in recent studies, is the low-voltage ride-through (LVRT) capability of the distributed generators (DGs). LVRT curves of the German and Danish GCs are highlighted in Fig. 1a [2]. Besides, in Fig. 1b amount of the reactive power injection per voltage drop is depicted for different scenarios [3]. Most studies cover symmetrical voltage disturbances that only include a minor percentage of the faults such as [4,5], etc. However, asymmetrical faults such as single-phase short-circuits are more probable with an 85 % occurrence rate [6]. In most cases, the conventional three-phase control methods for compensating voltage drops are not applicable for asymmetrical faults since they might affect the operation of safe phases by deteriorating voltage imbalance. Also, reactive power-sharing and reference power tracking in multi-source MGs are important operation factors, which has not been addressed sufficiently in previous studies.

Conclusion

MGs integration into power systems has boosted the system’s reliability and caused operational challenges for the network operators. Hence, some countries have considered a set of requirements to improve the functionality of their power systems. For this purpose, in this paper, an LVRT scheme is proposed for four-wire MGs, which can control each phase of the DGs independently through a grid-following method. The local controller of the DGs, known as the primary layer, utilizes reverse-droop control for voltage and frequency regulation and a nonlinear FOSMC. On the other hand, the secondary layer fulfills the modern GC requirements by calculating the required reactive power for the faulty phases. Next, this amount is shared between the corresponding phases of the DGs based on their free capacity. The effectiveness of the presented controller is proved by analyzing the results obtained from implementing 30 % single-phase, two-phase, and three-phase voltage sags. Accordingly, each DG phase injects reactive power during voltage sags according to the determined amount. Also, comparing the injected reactive power with the amounts of German GC demonstrates that the reactive power injection is done with acceptable accuracy. The results point out that during the external sags, the voltage of PCC, inverter terminals, and load terminals are restored to their nominal values, 30 % compensation, as if there is no perturbation. Consequently, the presented controller can realize the GC requirements and ride through during severe voltage conditions. Moreover, this control method keeps the power quality indices like THD and voltage imbalance factors in acceptable ranges during the sags. Also, the superiority of designed FOSMC over conventional current controllers such as PI and SMC are demonstrated. This outperformance is highlighted with several aspects such as MPAE index, THD values, voltage compensation, and reactive power tracking during the imposed voltage sags. It is shown that the best value for the alpha is 0.76, by which the response of the controller is fast and accurate. Finally, the simulations are validated through real-time results. Our future work is focused on the LVRT capability of the MGs including both grid-forming and grid-following inverters. In addition, the effect of grid strength and R/X ratio of the power lines can be discussed in the future investigations, which has not been addressed sufficiently in this literature.

Abstract

The research on emotional intelligence in social robots is growing. This paper provides a thematic analysis of the studies on robots and emotional intelligence, synthesising and evaluating current knowledge and research topics. In addition, based on the thematic analysis of the studies, it also provides a conceptual framework explaining the emotional intelligence of robots that includes both actors (human and robot) in a human-robot interaction setting. The findings are based on the analysis of 252 studies published until the end of 2022 and indexed in the Scopus database. The results unveiled two main themes (robot design-technical developments and characteristics and human-robot interaction), including sub-themes and topics that emerged in the literature. Finally, the themes and sub-themes were evaluated through a critical discussion to develop a conceptual framework for robots and emotional intelligence.

Introduction

1.1. Rationale
A robot is a “programmed actuated mechanism with a degree of autonomy to perform locomotion, manipulation or positioning” [1]. While robots are widely used in manufacturing [2,3] for producing goods, they find their way into agriculture [4] and the delivery of services [[5], [6], [7]] as well. Social robots help children with autism [8], assist the elderly [9], and redefine the meaning we put in sexual relationships [10].

One of the main directions of robotics research is on human-robot interaction (HRI) [11]. The topic has been researched in the context of industrial robots [12], service robots [13], and social robots [14]. A key component of HRI in the context of social robots are the emotions of humans and the emotional intelligence of both parties in the relationship [11,15] because emotions trigger specific affective, cognitive, and behavioural responses [16]. For example, when humans experience positive emotions in their interactions with robots, they are more likely to use robots and less likely to object to them [17]. Additionally, humans’ perceptions of the emotional skills of robots are positively related to the perceived appropriateness of robot use in service contexts, e.g. museums in galleries, as found by Webster and Ivanov [18].

To elicit respective emotional reactions in humans, robots need to have some degree of emotional intelligence. Emotional intelligence (EI) is defined as “the capacity to reason about emotions, and of emotions to enhance thinking. It includes the abilities to accurately perceive emotions, to access and generate emotions so as to assist thought, to understand emotions and emotional knowledge, and to reflectively regulate emotions so as to promote emotional and intellectual growth” ([19]:197). EI has four aspects measured through the Mayer–Salovey–Caruso Emotional Intelligence Test (MSCEIT) ([19]:200, [20], [21]:281–282).

Conclusion

This paper provided a thematic analysis of the studies on robots and emotional intelligence. The results uncovered two main: (i) robot design-technical developments and characteristics, and (ii) human-robot interaction. The robot design-technical developments and characteristics include sensory aspects (facial expression and voice-related), cognitive aspects and behavioural aspects, visual aspects, and other aspects. The “human-robot interaction” category comprises two main sub-themes, namely settings (health, education, and other settings) and attitudes (perceptions toward robots).

Abstract

The fast transition to the electrification of the energy system, combined with an exponential growth of the market share of electric vehicles, is leading to a tight interrelation between electric energy production and transportation, two prominent sectors in fossil fuels consumption and greenhouse gas emissions. Accelerating this process, the management of electric fluxes, aiming at optimizing production and demand coupling, plays a crucial role in reaching the net-zero emission target. The proposed software platform is designed to optimally manage the energy fluxes for a solar powered parking lot, serving a fleet of electric vehicles; the real-time knowledge of energy production and demand, in conjunction with forecasted power generation, allows the maximization of renewable energy self-consumption, thus reducing the exchange with the external grid. The software platform can work either in design mode, allowing the dimensioning of the various parking lot components, or in real-time mode managing instantaneously the energy balance. As a case study, it is tested on the 2019 parking lot mobility data of a research center, assuming a complete transformation of the then existing fleet of employees’ cars to electric vehicles. A comparison of the resulting energy flows with those projected by an established commercial tool is performed, as well as a preliminary economic evaluation. Both consistency of the simulation results and favorable economics validate the presented smart charging algorithm and Internet of Things platform for the real-time energy management of a solar parking lot.

Introduction

The steep growth of anthropogenic greenhouse gas (GHG) emissions related to the use of fossil resources requires fast and challenging solutions; transportation and electricity production sectors are responsible for around two thirds of global CO2 emissions. According to the numbers published by the U.S. Energy Information Administration (EIA) in its monthly energy review of August 2022 [1], the total consumption of primary energy in the U.S.A. in the year 2021 was 28.5 Million terawatt-hours (TWh) or 2.4546 Billion tonnes of oil equivalent (toe), 7.9 Million TWh (0.6782 Billion toe) of which are used by the transportation sector and 10.8 Million TWh (0.9267 Billion toe) by the electric power sector. 94% of the total energy used for transportation came from petroleum and natural gas and 6% from biofuels and electricity [2]. In 2021, according to EIA estimates [3], cars, light trucks, and motorcycles accounted for the largest shares of total U.S. transportation sector energy consumption, with light-duty vehicles (cars, small trucks, vans, sport utility vehicles, and motorcycles) accounting for 54.2%, commercial and freight trucks 4.5%, jets, planes, and other aircraft 8.7%, boat, ships, and other watercraft 4.6%, trains and buses 2.6%, the military sector 2.0%, pipelines 2.8%, lubricants 0.5%. Globally, carbon dioxide emissions associated with transportation accounted in 2021 for 7620 Mt; 600 Mt less than pre pandemic level by 2019 [4].

Since the onset of the industrial revolution, ever increasing amounts of GHG have been released into the atmosphere. While the energy mix and corresponding supply chains shifted from coal to oil and more recently towards natural gas, the prosperity of humankind still relies on fossil fuels and energy conversion systems based on fuels combustion. Even today, transportation and electricity production are heavily reliant on CO2 emitting technologies. But there is a silver lining, as technological improvements coupled with a strong cost reduction enabled the fast growth of the total installed energy capacity of renewable energy sources for electricity production (RES-E). Together with powerful battery energy storage systems (BESSs), they will impose drastic changes in these two historically conservative sectors. Today, the fast growth of electric vehicles (EVs) related technologies, as well as their forecasted market penetration, reaching the record of 6.6 million vehicles sold in 2021 [5], generates new scenarios impacting the electric energy production and transportation market. Based on existing climate-focused policy pledges and announcements, the International Energy Agency predicts for 2030 EVs to represent more than 30% of vehicles sold globally across all modes (excluding two- and three-wheelers) and the global electricity demand for EVs to reach 1100 TWh; then about 4% of the total final electricity demand [5].

Conclusions

This paper presented the SPEM IoT platform, capable of simulating, designing and real time managing the smart charging of EV fleets in a RES-E driven parking lot.

A deterministic rule-based algorithm was introduced for the fine-grained management of the energy fluxes between EVs and the different electric components of a solar parking lot. Since the algorithm does not utilize any assumption on the future mobility and energy demand it can handle unforeseen changes avoiding critical situations.

As it was shown, intra-day deferral serves to shift EV charging demand towards the time of maximum production, guided by MPC, constantly analyzing the momentary situation of 1) intermittent solar production, 2) stored energy and energy storage availability, 3) charging station occupancy and 4) solar production forecast.

An extensive case study was conducted, where the design mode of SPEM was applied to the historic situation of an Italian Research Center in 2019, assuming the substitution of all employee’s cars by EVs. As a benchmark for the validation of SPEM, HOMER® Grid, a commercial software for the modeling, design and simulation of electrical infrastructure, was used.

Abstract

We study a radio resource allocation problem in mobile communication systems. As the distinct characteristic of this problem, a common data transmission rate is used on all channels allocated to a user. Because the channels differ in their quality, for each user the achievable rate varies by channel. Thus allocating more channels does not necessarily increase the total rate, as the common rate is constrained to be the lowest one supported by the allocated channels. Radio resource allocation subject to the common-rate constraint is of practical relevance, though little attention has been paid to modeling and solving the problem. We take a mathematical optimization perspective with focus on modeling. We first provide a complexity analysis. Next, several integer linear programming (ILP) formulations for the problem, including compact as well as non-compact models, are derived. The bulk of our analysis consists in a rigorous comparative study of their linear programming (LP) relaxations, to reveal the relationship between the formulations in terms of bounding. Computational experiments are presented to illustrate the numerical performance in bounding and LP-assisted problem solving. Our theoretical analysis and numerical results together serve the aim of setting a ground for the next step of developing model-based and tailored optimization methods.

Introduction

Mobile communication systems have been evolving rapidly in the past decades. From an optimization standpoint, a key research topic for mobile networks is radio resource management for utilizing the radio resource efficiently, particularly because the amount of data traffic is constantly growing in the current 4th generation (4G) systems, and the trend will remain or even accelerate in the 5th generation (5G) networks. Along with this growth, 5G networks target a plethora of new services (e.g., vehicular communications), making resource management more challenging than before, as pointed out in Calabrese et al. (2018).

4G/5G networks deploy orthogonal frequency division multiple access (OFDMA). In essence, data transmission takes place in two dimensions, namely time and frequency that are divided into time slots and channels, respectively.1 Resource management for channel allocation in a time slot, as well as that across multiple time slots, is commonly called scheduling. In any time slot, a user may be scheduled to receive transmission from its base station (BS) on multiple channels, and a channel may be scheduled for at most one user of this BS. The latter is what the term “orthogonal” refers to in OFDMA. Among the BSs, the channels are reused, i.e., there is generally no dedicated (sub)set of channels for a BS. As a result, a channel is exposed to interference, if the channel is also scheduled in some nearby BSs in the same time slot. Note that even if interference is not present, the channels are still frequency-selective (Tse and Viswanath, 2005), meaning that they vary in quality and hence the achievable data rate from a user’s perspective.

Conclusions and future work

We have studied mathematical modeling of a resource optimization problem with common-rate channel allocation in mobile communication systems. We have demonstrated that the problem admits an array of integer programming formulations. The study shows that modeling does matter, analytically as well as numerically, in terms of performance in bounding and LP-based problem solving. Moreover, there is a clear correlation between the accuracy of LP and the quality of integer solution derived thereby.

As we have observed, straightforward schemes of constructing integer solutions are not practical in solution time, whereas for our resource allocation problem, the ultimate target is real-time optimization. To approach this goal with model-based optimization, we make several observations. First, to deliver a solution rapidly, the amount of computation has to be very small, and thus the LP relaxation may have to be solved approximately, followed by some primal heuristic (both admitting massive parallel computation). Second, non-compact models are also of interest, as restricting the number of columns or rows leads to approximation of the problem (and the LP relaxation). Finally, with presence of rate lower bound, obtaining solution feasibility is of clear significance, and one may need to trade solution quality against feasibility. Developing and implementing algorithmic notions along these lines form interesting topics for forthcoming research.

Abstract

Solar energy can play an important role in meeting global energy needs in a sustainable and environmentally friendly manner. However, despite solar energy’s accelerated growth in recent years, its level of diffusion is highly uneven when looked at on a global scale. The solar photovoltaic (PV) companies involved in the sales of PV systems are central to fostering diffusion. A company’s ability to devise and deliver value offerings that match customers’ needs is vital in encouraging the adoption of solar PV technology. The extent to which a company can address market needs and deliver value often depends on the business model it has adopted. The extant research has explored business models based on ownership structures, financing options, the effect of regulatory regimes and policies, industry practices, alliances, and business models for distributed generation and large-scale utility companies. However, the research to date, has mostly neglected the business models of solar companies involved in the sales and installation of solar PV. This qualitative study based on twenty semi-structured interviews contributes to the existing knowledge by exploring how sales and installation companies can enhance solar photovoltaic adoption by transforming customer interactions and engagement practices, which is a key element of a company’s business model. Companies’ ability to communicate value offerings and address consumer concerns is important in enhancing diffusion. The study highlights that transforming customer interaction and engagement practices can help companies broaden customer reach, improve the dissemination of information, reduce transaction costs and efficiently utilise market insights and trends.

Introduction

Renewable energy technologies (RETs) can play an important role in meeting global energy needs in a sustainable and environmentally friendly manner. Countries across the globe are looking to adopt measures and ways to support their development and increase their share of the energy mix [3]. Solar energy, in particular, has the potential to be used in large-scale commercial facilities, as well as serving needs at the household level [4]. Its improved efficiency, decreasing price and supportive policy regime have made solar one of the leading forms of renewable energy in the world [5], [6]. However, it is widely believed that this growth is far lower than its potential in most regions, and efforts should be made by all stakeholders to foster its development [7], [8]. The widespread adoption and use of RETs is a complex and multifarious process influenced by a number of personal, socioeconomic, technical, market-related and regulatory factors [9], [10], [11], [12]. The process is particularly challenging as the technology is disruptive in nature, and its successful diffusion requires changes in the existing structure and approaches as well as a change in mindset [13], [14].

Solar Photovoltaic (PV) companies, directly involved in interaction with consumers, dissemination and sales, become an important actor in this regard [15], [16], [17]. Companies’ ability to devise and deliver value offerings that match customer needs can play a vital role in encouraging adoption. Teece [18] suggests that the extent to which a company can address market needs and deliver value depends on the business model it has adopted. Business models direct a company’s course of action, help channel resources, address challenges and provide opportunities for growth [19], [20], [21]. RET companies often face challenges in developing market-centric business models that can enable them to thrive independently [22], [23]. A number of studies have explored business models for companies operating in the solar industry. However, an overwhelming majority of the existing research has focused on business models based on ownership structures [24], [25], [26], [27], financing options [1], [2], the effect of regulatory regimes and policies [28], [29], industry practices [30], alliances [31], business models for distributed generation [32], [33], [34] and large-scale utility companies [22]. To date, the research has overlooked customer interaction and engagement practices in the business models of conventional solar PV companies involved in the sales and installation of solar systems [35], [36], [37], [38].

Results

The result highlights that transforming customer interaction and engagement practices can help companies broaden customer reach, improve the dissemination of information, reduce transaction costs and efficiently utilise market knowledge and insights (Fig. 3).

4.1. Broadening customer reach
4.1.1. Effective means to reach customer
Companies need to adopt effective means to reach customers. Conventionally, in the early phase of market development, many companies have relied on direct approaches to reach customers through door-to-door sales, telephone marketing or similar measures. The approach worked for some but has largely been a difficult endeavour for companies seeking growth and high sales volumes due to the effort and cost involved in materialising a single sale. As one group sales manager suggested: “It was quite common for companies to directly reach out to customers. This seemed to have worked as companies were able to generate sales. … However, companies soon realised that the process is too labour-intensive and is costing too much, mainly in terms of labour hours.” On the other hand, the expense of conventional mass media marketing makes it unaffordable for companies operating in the PV sector. The manager further suggested, “…. for the vast majority of companies, the use of media such as electronic and print media has been out of reach. Companies selling solar systems are hardly of a size to afford such a thing [medium].”

Abstract

     The modern active distribution systems necessitate integrating storage systems, thereby facilitating the large-scale proliferation of photovoltaic (PV) energy resources. This further calls for the optimal planning of energy storage systems, satisfying all the operational and economic constraints. This article describes an exhaustive storage integration method, deeming the life cycle of the battery energy storage, the uncertainty of load and PV output, and the islanded mode of operation of the system. A two-stage mixed-integer linear programming problem is formulated that determines the capacity and the number of discharge cycles of the batteries in the first stage. The lifetime of the battery based on the partial depth of discharge is analyzed in the second stage. Furthermore, the uncertainty and variability of PV and demand are taken into account through probabilistic analysis and time-period clustering. The method is validated on a standard 33-bus radial distribution network for the allocation of distributed lithium-ion batteries. Also, the method’s scalability is validated on a practical Indian distribution network and a 141-bus distribution network of metropolitan area of Caracas with distributed PV installations on various nodes.

Introduction

     S MART grid is a gratuity to the consumers and the stakeholders involved in the electric grid’s generation, transmission, and distribution sections. It includes the complete modernization of the power system with smart meters, automation devices, intelligent monitoring, demand-side management, and self-healing capability schemes. Along with these activities, generation units are set up in the distribution section, i.e., nearer to the consumer premises, to reduce the transmission losses. This shift of the electric grid from a passive network to a bidirectional active network is due to the small generators being set up in the distribution grid known as distributed/decentralized generation. These distributed generators (DGs) mainly generate energy using renewable energy resources, such as photovoltaic (PV), wind, biomass, tidal, etc., as they are clean sources of energy and promote sustainable development. However, the intermittent nature and excess penetration of these resources pose problems, such as reverse power flow, voltage fluctuations, increase in losses, harmonic distortion, and instantaneous matching of demand and supply [1], [2]. Although integrating storage systems in the distribution network can help alleviate the aforementioned problems if allocated optimally. Also, India’s target of 40-GW PV rooftop installations by the year 2022 and the declining cost of batteries will provide a fillip to the installation of energy storage systems (ESSs) [3]. Therefore, an ESS can be seen as a game changer in the ever-changing power system paradigm and can serve multiple ranges of benefits. To achieve these benefits, methods for optimal sizing, allocation, and operation of ESSs are required

Conclusion

     The integration of renewable energy resources necessitates the allocation of distributed energy storage to mitigate voltage deviation and defer distribution upgrades. This article illustrated a two-stage procedure for integrating lithium-ion batteries in a PVpenetrated active distribution network. The planning methodology considered an ac-OPF model with the uncertainty of PV and demand to determine the batteries’ accurate size. Moreover, the reverse power flow due to excess PV penetration was utilized and the voltage was within limits after the integration of batteries in the system. The battery’s life cycle was examined in the second stage with the partial cycle of discharge and complete discharge cycles. For lithium-ion batteries, partial cycle discharging was fine as there was no memory effect, and the battery does not need full discharges periodically. From the results, it was illustrated that with the partial cycle of discharge, the battery will last longer. Moreover, the method used here was the mathematical programming, which provides a robust solution, but may require significant computation time for large and complex problems. Also, the maximum discharging capacity of the battery gradually declined with its cycles, which can be kept as a future research direction. Furthermore, to enhance the stability and cost-effectiveness, a smart charging and discharging operation can be added to the problem. In addition, different types of DGs, such as wind, micro-turbines, and fuel cells, can be considered an extension to the OPF formulation.

Abstract

I. Introduction

II. Three-Level Neutral Point Clamped Inverters

III. Proposed Neutral Point Clamped Inverters

IV. Operation of the Proposed Three-Level NPC Inverter

V. Comparison of the Proposed and Conventional Inverters

VI. Experimental Results

VII. Conclusion

References

Abstract

     The traditional neutral point clamped (NPC) inverter has short-circuit problem. The risk of short-circuit can be decreased by using dead-time in the switching signals. However, the dead-time decreases the achievable output voltage and causes distortion in the waveforms. To overcome the short-circuit problem, dual-buck NPC (DB-NPC) and split-inductor NPC (SI-NPC) inverters have been researched. However, the voltage stress of the two external diodes in the DB-NPC inverter is higher. On the other hand, the SI-NPC inverter has a problem of generating huge voltage spikes in the dead-time, which can destroy the semiconductor devices. In addition, the SI-NPC inverter cannot provide reactive power. This article presents a family of NPC inverters consisting of single-phase, three-phase, and cascaded inverters. The proposed inverters have no short-circuit and dead-time issues, therefore no high voltage and current spikes are caused. Also, the dead-time in the switching signals can be minimized. As a result, the magnitude of the output waveforms can be increased, and quality can be improved. Unlike the DB-NPC inverter, the voltage stress of all the semiconductor in the proposed inverter is lower, and unlike the SI-NPC inverter the proposed inverter provides reactive power. In this article, the proposed three-level NPC inverter is analyzed, designed, and tested. The voltage stress of the semiconductor devices in the proposed inverter is half of the source voltage, whereas in the conventional DB-NPC inverter the voltage stress of the two external diodes is the source voltage. In addition to the aforementioned benefits, the proposed cascaded inverter reduces the total number of inductors. To verify the analysis, detailed simulation, and experimental results of the proposed three-level inverter with input voltage 640 V, output power 1.2 kW, and output voltage 220 Vrms are provided.

Introduction

     T HE traditional H-bridge inverter is shown in Fig. 1. The voltage stress on its switches is the input voltage Vdc. Therefore, the H-bridge inverter is well suitable for low-voltage applications. In high-voltage applications [1] such as HVdc transmission [2], large motor drive [3], locomotive [4], solid-state transformers [5], and reactive power compensation [6], the multilevel inverters are preferred. Flying capacitor [7], neutral point clamped (NPC) [8], and cascaded inverters [9], [10] are the famous multilevel inverter topologies.

     The flying capacitor inverters synthesize output voltage by adding voltages of the flying and dc-link capacitors. The NPC inverters synthesize output voltage by adding voltages of the dc-link capacitors. The cascaded inverters synthesize output voltage by adding voltages of the series-connected H-bridge cells. The cascaded inverters are highly modular and can reach a higher output voltage [11]. Also, they can bypass faulty cells [12]. The multilevel inverters have the advantages of lower switch voltage stress, lower switching losses, smaller output filter, better output waveforms, and lower electromagnetic interference (EMI) noise issues.

     The multilevel inverters are also getting popular in lowvoltage and low-power applications due to the possibility of obtaining lower common-mode voltage and higher efficiency over the H-bridge inverter. In [13], multilevel inverters have been discussed for the photovoltaic (PV) systems. In [14], a half-bridge three-level NPC inverter is compared with a halfbridge two-level inverter for PV applications. It is found in [14] that a lower leakage current and higher efficiency can be realized with the NPC inverter.

Conclusion

     This article presented new types of single-phase, three-phase, and cascaded NPC inverters. The proposed inverters have no short-circuit risk. The dead-time in the switching signals can be reduced. As a result, the distortion in the output waveforms can be decreased, higher switching frequencies can be used for the passive components size reduction and maximum available output voltage gain can be reached. Unlike the conventional SI-NPC inverters, the proposed inverters do not generate high-voltage spikes in the dead-time and provide reactive power. Unlike the DB-NPC inverters, the voltage stress of all the external diodes in the proposed inverter is lower. The proposed cascaded inverter inherits all the features of the proposed three-level inverter. In addition, it reduces the number of inductors by sharing the inductors between the cascaded units.

     A 1.2-kW hardware prototype was fabricated and tested with various loads at the input voltage 640 V, output voltage 110/220 Vrms, output power 1.2 kW, line-frequency 60 Hz, and switching frequency 30 kHz. The experimental results verified that the proposed inverter could generate good output waveforms, provide reactive power, works with dead and overlap-times, and obtains higher efficiency.

Abstract

     A quad-element multiple-input-multiple-output (MIMO) antenna with fractional bandwidth (FBW) of 52.42% (3.35–5.73 GHz) is proposed for LTE, WLAN (4.9/5 GHz), and 5G (sub-6 GHz) applications. The bandwidth is improved by introducing a tapered feed line and rectangular stubs in the partial ground plane. The maximum isolation of the proposed MIMO antenna is 27 dB. The diversity performance characteristics of the proposed antenna are studied in terms of the envelope correlation coefficient (ECC), diversity gain (DG), mean effective gain (MEG), total active reflection coefficient (TARC), isolation between the ports, and channel capacity loss (CCL) and the values obtained are 0.003, 9.98 dB, ±3 dB, −4 dB, −10 dB, and 0.10 bits/s/Hz respectively. A model of the proposed antenna is fabricated on the FR-4 substrate having a dielectric constant of 4.4 and a loss tangent of 0.02 with an electrical dimension of 0.45λ0 × 0.45λ0. The measured results demonstrate a decent likeness to simulated ones in the entire operating frequency range.

Introduction

     The current scenario for mobile communication is to achieve a higher data rate, capacity, low latency, and high resolution. The fifth-generation (5G) mobile communication has been deployed around the world to fulfill the above advantage [1,2]. It has been shown [3,4] that to improve the information throughput in a multipath environment for 5G operations, the MIMO antenna system should be adopted. MIMO antenna systems should have a minimal inter-element distance, low correlation values, and better isolation between inter elements [5]. The primary advantage of adopting an MIMO network over a normal one is that it can enhance wireless connection capacity while consuming less spectrum. The system’s link dependability and data rate can be enhanced by increasing the number of antennas on the transmitter/receiver, which results in more signal routes and thus higher performance. Hence MIMO techniques become very vital for wireless communication systems which are suffering from frequency constraints [6,7].

Conclusion

     A compact quad-element MIMO antenna of 40 × 40 × 1.6 mm3 for 5G, LTE, and WLAN frequency bands is designed, fabricated, and measured. The measured results demonstrate a decent likeness to simulated ones in the whole frequency range. The proposed design’s performance was evaluated and described in terms of impedance bandwidth, surface current distribution, reflection coefficient, gain, efficiency, and radiation characteristics. The MIMO provides good diversity performance with a low envelope correlation coefficient and a better diversity gain. Furthermore, within the operating frequency band, the proposed antenna obtained a maximum channel capacity of > 20 bits/s/Hz. The antenna has a total efficiency of 85.12% and a peak gain of 2.74 dBi. As a result, it is recommended as a candidate for 5G, WLAN, and LTE applications.

Abstract

1. INTRODUCTION

2. FIVE-LEVEL SWITCHED CAPACITOR INVERTER

3. MODULATION TECHNIQUE

4. PHOTOVOLTAIC APPLICATIONS OF THE SUGGESTED INVERTER

5. SIMULATION RESULTS

6. CONCLUSION

DISCLOSURE STATEMENT

REFERENCES

Abstract

     This paper proposes a switched-capacitor based single-phase five-level inverter configuration that operates under boost operation and generates a voltage that is more than the DC source voltage. The proposed five-level inverter uses a capacitor and boots the output voltage. In this proposed inverter, capacitor gets charged in parallel while it discharges in series connections so that output voltage may attain higher magnitude than the DC source voltage. Sinusoidal Pulse Width Modulation-based techniques are considered to produce the required gate pulses for operating the switching devices of the inverter. The five-level switched-capacitor inverter is combined with the PV system via DC–DC boost converters to extract the maximum power using MPPT algorithm. To verify its capability, the PV-based system is further integrated to the utility grid. The operation and performance of the suggested switched-capacitor inverter coupled with the grid-connected PV system are also analyzed by developing its model in MATLAB/Simulink environment.

Introduction

     Power electronic converters are getting evolved due to technological advancement in the design of power electronic devices as well as increase in its demand for more applications. The growth in demand for inverters has been observed because due to its application in the renewable energy source. The lesser costs of modern power electronics components make them useful for manufacturing and helping them to compete in the market. However, multi-level inverters use more switches; it is still economical to replace two-level inverters with MLIs because of several benefits such as lesser harmonic content, switching stress, and power losses [1–3]. Many scholars have paid attention to improve inverter topologies and their control methods. The lesser number of power electronics components used in multilevel inverters can further reduce the manufacturing cost [4–6]. The Cascaded H-bridge (CHB) inverter [7] and Neutral Point Clamped (NPC) inverter [8,9] are two standard multilevel inverters and having several industrial applications such as EV/HEV, HVDC, renewable energy sources, high-power motor drives, FACTs, STATCOM [10,11]. Several three-phase and single-phase MLI topologies of high voltage and medium power have been implemented for different applications [12,13]. A five-level inverter using two diodes, six switches, and two capacitors is proposed in [14].

CONCLUSION

     The proposed five-level switched-capacitor inverter topo logy for the PV application has been investigated in this paper. The developed single-phase switched-capacitor based inverter configuration consists of eight switching devices, only one DC source and one switched-capacitor. The inverter can produce five levels output voltage and the maximum amplitude can be twice the magnitude of DC voltage source. Moreover, it is also noticed that the charging as well as discharging of the switched-capacitor in the proposed multilevel inverter topology is symmetrical for both polarities of the output. Hence, the issue of capacitor voltage balancing is solved by using the switched capacitor of the suggested rating. The model of the recommended inverter-based grid-tied PV system is established in MATLAB/ Simulink environment and the performance of inverter under different modulation indexes is found satisfactory. The effectiveness of a grid-tied system was also investigated under different irradiance. Hence it can be resolved from the analysis that the proposed inverter is proficient for the application of a grid-tide PV system.

Abstract

Introduction

Methodology

PV efficienc

Data collectio

Experimental setup

Results and discussion

Effect of temperature on the power output of PV panels and TEGs

Conclusions

Nomenclature

References

Abstract

     Many factors affect the efficiency of photovoltaic panels (PV), which convert solar energy directly into electrical energy. Among these factors, temperature is one of the most important one. While some of the radiation from the sun is converted into electrical energy, part of it emerges as heat energy. This causes the photovoltaic cells to heat up and reduce their electrical efficiency. Different methods are used in the literature to reduce the temperature in PV panels. In this study, in order to reduce the adverse effects caused by the high temperature in the PV panels, 30 Thermoelectric Generators (TEG) were applied to the back surface of the PV panel to increase the PV panel output power and to produce additional electrical energy. Energy and exergy analysis made on the data obtained from both PV panels in the climatic conditions of the installation site showed that the temperature of the PV panel is reduced, and the energy and exergy efficiency is increased with the TEG application. At the end of July, August, and September, when the experiments were carried out, an average of 8.4% more electrical energy was obtained from a single PV panel with TEG, compared to the standard PV panel. Our results suggests that combination of TEG with PV panels could significantly increase the electrical energy, especially when a series of PV panels are used together.

Introduction

     Recently, investments in electricity generation from renewable energy sources, especially solar and wind energy, have been increasing. However, when the performance of photovoltaic cells in the natural field environment is compared with the version of the standard test conditions, the efficiency of the PV panels decreases with the increase in temperature due to radiation (Bel Hadj Brahim Kechiche, Hamza, and Sammouda 2016). Since the energy that cannot be converted into electricity increases the photovoltaic surface temperature, it causes damage to the PV panel module cells and leads to reduced service life of the PV panels (Enescu and Spertino 2017). When the studies in the literature about reducing the heat losses in photovoltaic panels (PV) are examined; A water-cooled nozzle spray system has been developed that significantly reduces the module cell temperature (Benato and Stoppato 2019). The factors affecting the performance of PV panels and the applications that can be made to increase the panel power are explained in detail (Fouad, Shihata, and Morgan 2017).To obtain higher efficiency by cooling the PV panel surface, the panel output power and the cell’s lifetime are increased with different cooling methods (Siecker, Kusakana, and Numbi 2017). To prevent the decrease in PV panel power output with temperature increase, new models are proposed on the bottom surface. In experiments carried out under natural conditions, it has been determined that the panel temperature can be reduced by 10°C with the evaporative cooling model and the power improvement is 5% (Haidar, Orfi, and Kaneesamkand 2021).

Conclusions

     In this study, the losses in energy production due to the increase in temperature in the PV panels, especially in the summer months, were reduced by TEG application. An increase in the PV Panel output power was achieved. According to the results obtained;

● More electrical energy was produced in the PV panel with a thermoelectric generator in July, August, and September when the experiments were carried out.

● With the application of a thermoelectric generator in the PV panel, an average of 8.4% more electrical energy was obtained per month. This indicates that when the number of PV panels combined with TEG is increased, the total energy could increase significantly

● The output power of TEGs also increases depending on the rise in air temperature and PV panel surface temperature

● Since the average temperature was higher in July, maximum energy was produced in the thermoelectric generator panel. Compared to the standard panel, the PV panel, in which a thermoelectric generator is applied, had 10.29% more electricity in July, 7.15% in August, and 7.09% more in September, respectively.

Abstract

Keywords

1. Introduction

2. Related work

3. Application research of Internet of Things in solar photovoltaic power station monitoring and management system

4. Development of integrated computer-aided design system for solar photovoltaic buildings

5. Conclusion

Declaration of Competing Interest

References

Abstract

At the same time of economic development, the increasing scarcity of energy has had a great impact on people’s development. People’s production and life demand for electricity is also increasing rapidly, and solar power technology has received more and more attention. As a new energy source, solar energy has the advantages of environmental protection and sustainability, and it has no regional restrictions, can be used on-site, and designed to scale. Solar power generation is an important way to use solar energy. As the main component of the grid-connected power generation system, solar grid-connected inverters complete the tracking problem of the maximum power point in the photovoltaic array and transmit electrical energy to the grid through a set of control algorithms. The electrical energy is transmitted to the grid through the inverter, consistent with solar energy. In order to solve the problems of low integration, low energy efficiency, low reliability, high power consumption and lack of effective monitoring measures for solar energy devices. This article starts with the design of the solar cell integrated system, and through detailed analysis of the solar production system and building integrated planning, establishes the shadow radiant energy model of the solar cell system building electrical and solar cell system based on the Internet of Things, and designs an object-based Networked comprehensive auxiliary platform.

1. Introduction

Today’s society is an information society centered on the Internet. Digitization, informationization and world economics are the hallmarks of the current era. With the continuous rapid development of information technology, the process of world economics has been continuously strengthened. The use of computer technology, communication data and the Internet to complete e-logistics and Internet commerce has been widely used in society. The continuous improvement of information technology and information storage is just the prelude to the transformation of the IT industry. The cost of information dissemination is getting less and less, and it is bound to usher in the era of the Internet of Things dominating. As a post-IP product, the Internet of Things is developing rapidly and will become popular in the future. This is a major plan to realize the intelligentization of the world.