Spintronic devices based on domain wall (DW) motion through ferromagnetic nanowire tracks have received great interest as components of neuromorphic information processing systems. Previous proposals ...for spintronic artificial neurons required external stimuli to perform the leaking functionality, one of the three fundamental functions of a leaky integrate-and-fire (LIF) neuron. The use of this external magnetic field or electrical current stimulus results in either a decrease in energy efficiency or an increase in fabrication complexity. In this article, we modify the shape of previously demonstrated three-terminal magnetic tunnel junction neurons to perform the leaking operation without any external stimuli. The trapezoidal structure causes a shape-based DW drift, thus intrinsically providing the leaking functionality with no hardware cost. This LIF neuron, therefore, promises to advance the development of spintronic neural network crossbar arrays.
Several issues of individual microgrids (MGs) such as voltage and frequency fluctuations mainly due to the intermittent nature of renewable energy sources’ (RESs) power production can be mitigated by ...interconnecting multiple MGs and forming a multi-microgrid (MMG) system. MMG systems improve the reliability and resiliency of power systems, increase RESs’ utilization, and provide cost-efficient power to the consumers. This paper provides a comprehensive review of the conducted studies in the MMG area summarizing different operational goals and constraints proposed in the literature for efficient operation of MMGs. Besides, different MMG architectures in which the MGs can be interconnected to form an MMG system and their characteristics are discussed. This paper also provides a state-of-the-art review on different control strategies and operation management methodologies for the operation and control of MMGs in centralized, decentralized, distributed, and hierarchical structures. A classification of different sources of uncertainties in an MMG system and proposed uncertainty handling strategies are also presented. Finally, the paper is complemented with a discussion of the main open issues and future research directions of MMG systems.
Space mission cost and feasibility depend mainly on the size and mass of the payload. This paper investigates the optimal photovoltaic (PV) array and battery size and mass for an islanded PV-battery ...powered space microgrid (MG) at the lunar south pole. The PV arrays are considered to be installed on top of towers to increase solar energy harvesting. Considering the dependency of the generated power from PV arrays on the tower height, different tower heights of 10, 50, and 100 m are investigated. The paper presents the methodology to estimate the available power from the PV system using the information of illumination time-series at the location of potential sites with different tower heights. Besides, considering the power demand of several power-consuming units at different operating states, the power demand profile of the lunar base is generated. The optimal sizing of the PV and battery system for a 1-year horizon, without considering battery degradation, results in a total mass of approximately <inline-formula> <tex-math notation="LaTeX">1.5 \times 10^{5}~\text{kg} </tex-math></inline-formula> to <inline-formula> <tex-math notation="LaTeX">3.5 \times 10^{5}~\text{kg} </tex-math></inline-formula> with a tower height of 10 m depending on the solar illumination profiles at different sites. For a 5-year optimization horizon of the same sites with 10 m tower height and considering the battery yearly capacity degradation, total system mass ranges approximately from <inline-formula> <tex-math notation="LaTeX">\mathrm {2 \times 10^{5}~kg} </tex-math></inline-formula> to <inline-formula> <tex-math notation="LaTeX">5.5 \times 10^{5}~\text{kg} </tex-math></inline-formula>. Although increasing the tower height may considerably reduce the total size and mass of the battery and PV system, the mass of the PV tower will increase. Thus, a satisfactory trade-off in selecting the site location and tower height is required. In this regard, 15 highly illuminated sites at different locations and with different PV tower heights are assessed in this paper. To improve the reliability and flexibility of the power system, the multi-microgrid (MMG) concept is deployed to distribute the power-consuming units of the base among different MGs having their local energy production and storage systems. Finally, based on the total power demand served at a candidate site and the corresponding total system mass, a criterion, mass-per-unit-load (MPUL), is used to identify the sites that serve the highest power demand with less total system mass.
Several space organizations have been planning to establish a permanent, manned base on the Moon in recent years. Such an installation demands a highly reliable electrical power system (EPS) to ...supply life support systems and scientific equipment and operate autonomously in a fully self-sufficient manner. This paper explores various technologies available for power generation, storage, and distribution for space microgrids on the Moon. Several factors affecting the cost and mass of the space missions are introduced and analysed to provide a comprehensive comparison among the available solutions. Besides, given the effect of base location on the design of a lunar electrical power system and the mission cost, various lunar sites are introduced and discussed. Finally, the control system requirements for the reliable and autonomous operation of space microgrids on the Moon are presented. The study is complemented by discussing promising future technological solutions that could be applied upon a lunar microgrid.
Energy management systems (EMS) and autonomous power control (APC) for space microgrids (MGs) on the Moon need properly designed operating points and references to ensure the mission's safety. The ...oxygen and water requirements of the lunar base are supplied by the In-Situ Resource Utilization (ISRU) from the lunar regolith. ISRU is one of the most power-demanding subsystems in the lunar base. This paper proposes an optimization methodology for sizing and optimal operation management of a photovoltaic (PV)-battery-based space microgrid (MG). By solving the optimization problem, the optimal size of the PV array and battery, as well as the PV power generation and battery charging/discharging profiles are determined. First, the ISRU power demand profile is presented considering the oxygen and water management systems of the lunar base. Then, the optimization algorithm is employed to minimize the PV and battery mass and the total unused PV power generation while maintaining the desired level of energy in the battery considering system constraints. It is observed that curtailing the excess PV power generation plays a crucial role in minimizing the battery size and mass, thereby reducing the cost of the space mission.
Autonomous power control (APC) and energy management system (EMS) for space microgrids (MGs) on the Moon require well-designed operating references to ensure their safe operation considering the ...long-term goals of the mission. Oxygen and water, as two vital elements for human survival on the Moon, can be produced from the lunar regolith using the In-Situ Resource Utilization (ISRU) and water treatment subsystems. Since ISRU is one of the highest power-demanding units in a lunar base, this paper proposes a methodology for modeling the power demand profile for ISRU, considering oxygen and water management systems, which was not addressed in the literature. The paper presents the power consumption model of the ISRU, considering the Sun's illumination profile at a candidate site near the Shackleton crater at the lunar south pole. Furthermore, a methodology is proposed to create oxygen and water consumption and wastewater generation profiles in the crew habitat. The paper proposes models and algorithms to maintain the oxygen level and pressure in the crew habitat, transfer oxygen from ISRU to the associated oxygen tank, filter wastewater in the wastewater subsystem, transfer water produced from ISRU and freshwater from the wastewater subsystem to the associated water tank, considering oxygen and water consumption, and wastewater generation profiles of the crew habitat. Finally, an optimization framework is proposed to determine the power demand profile of ISRU by maintaining the oxygen in ISRU, the crew habitat, and water tanks at desired levels. It is observed that the ISRU power demand profile depends on the desired levels of oxygen and water in their associated tanks and their consumption/production rates. In addition, the interaction of different oxygen and water generation and consumption subsystems and storage tanks is thoroughly analyzed.
•A novel technique to trace Sun location upon the lunar sky is proposed.•LOLA databases are used to recreate the lunar topography.•Harvesting solar energy from multi-sites on the Moon south pole is ...proposed.•The multi-site strategy removes the need of energy storage system.•Algorithm to reproduce time series illumination profiles of the Moon.
Recently, space organizations have considered the Moon to host lunar bases. Such bases require power and energy to function. However, the efficient and safe use of the energy resources on the Moon is a huge challenge. Space photovoltaic (PV) power systems are appealing technologies due to their maturity and high solar energy availability at some locations on the Moon. The effectiveness of these PV systems depends on their selenographic location, which might necessitate the deployment of energy storage technologies to cover the base’s energy demand. Some analysts have proposed the installation of PV modules on kilometers-tall towers near the lunar poles to harvest more solar energy and limit the need for energy storage systems (ESSs). Alternatively, this paper proposes to harvest the energy from multiple sites in the lunar South Pole region using a novel technique to compute the Sun illumination profile and the LOLA topographic databases to compute the terrain elevations. The proposed algorithm seeks the most optimal configuration of sites and tower heights to minimize the longest night period and total distance between the sites. This study assesses groups of 1 to 6 sites assuming the use of towers having heights of 10, 100, and 500 m. The time horizon for the analysis is one Axial Precession Cycle, which is approximately 18.6 years. According to the results, a system of two sites with a separation of 42.05 km and towers of 500 m height has a maximum darkness period of only 3 h while another solution proposes a system of three sites with towers of 10 m that removes the need of EES (solar eclipse periods by the Earth are not considered). The proposed technique is suitable for engineering applications, such as base planning and operation management.
Spintronic devices based on domain wall (DW) motion through ferromagnetic nanowire tracks have received great interest as components of neuromorphic information processing systems. Prior proposals ...for spintronic artificial neurons required external stimuli to perform the leaking functionality, one of the three fundamental functions of a leaky integrate-and-fire (LIF) neuron. The use of this external magnetic field or electrical current stimulus results in either a decrease in energy efficiency or an increase in fabrication complexity. Here, we modify the shape of previously demonstrated three-terminal magnetic tunnel junction neurons to perform the leaking operation without any external stimuli. The trapezoidal structure causes a shape-based DW drift, thus intrinsically providing the leaking functionality with no hardware cost. This LIF neuron, thus, promises to advance the development of spintronic neural network crossbar arrays.
Due to increase in availability of renewable energy sources, development of multilevel inverter topologies has become an interesting research area for researchers in recent years to further improve ...the effectiveness of inverter systems. Multilevel inverter (MLI) with switched capacitor as the basic unit is a notable development in MLI topologies which reduces the number of power supplies required in comparison to the conventional MLIs and are widely known as switched capacitor multilevel inverter (SCMLI). In SCMLI, multiple power supplies can be replaced by capacitors which are used in tandem to boost the output voltage. Further, they possess capacitor voltage balancing capability. In this paper, a novel switched capacitor based three phase MLI for renewable energy conversion systems is presented using phase disposition PWM (PDPWM) modulation technique. The proposed three phase MLI is modular in nature and number of source modules can be increased to get more number of outputvoltage levels. A comparison study between the proposed topology and the recently developed three phase MLI topologies has been discussed in different perspective such as required components, maximum output voltage generation, capacitor voltage balancing capability etc. Further, an extensive simulation study is done in MATLAB/SIMULINK to validate the effectiveness and feasibility of the proposed topology.
With the increase in the use of renewable sources, there has been a significant topological development of multilevel inverters (MLIs). A number of MLI topologies have been developed in recent years ...which opens significant possibilities for further improving the robustness and efficiency of the inverter systems. Switched Capacitor Multilevel Inverter (SC-MLI) is a novel MLI structure introduced recently which requires a reduced number of power supplies in comparison with the conventional multilevel inverters. In SC-MLI, capacitors are used as alternative dc sources. Further, SCMLI possesses the voltage boosting capability and self-capacitor voltage balancing ability. One of the major limitations of SCMLI is that the input current is discontinuous and has an extremely high peak which may damage the input source and the components associated with it. Hence, the controlling of input current is required. Further, the controlling of output current of inverter, an appropriate control strategy has to be employed. For achieving these, in this paper Model Predictive Control (MPC) strategy has been implemented for basic SC-MLI unit. Extensive simulation study of 5-level SCMLI in MATLAB/Simulink shows that by using MPC, the inverter can produce the voltage levels in such way that the desired load current is achieved. Further, the peak magnitude of input current and capacitor voltage ripple are significantly reduced as compared to open loop control strategy.
PDF
