The successful mission of CubeSat require reliable and fault-tolerant electrical power system (EPS) that powers all the other subsystems and payloads. Several studies have shown that EPS failure has ...been one of the main contributors for the CubeSat mission failure. The main objective of this paper is to enhance the lifetime of CubeSats EPS by proposing a distributed EPS architecture and power-down mode. The distributed architecture consists of independent converters for maximum power point tracking operation of photovoltaic (PV) panels. This is possible by using gallium nitride field-effect transistors to reduce the converter footprint and placing the converters on the back-side of the PV panels. Also, single-inductor based <inline-formula><tex-math notation="LaTeX">N</tex-math></inline-formula>-1 redundant converters for generation and load-side are proposed to provide uninterrupted operation during component failures. Thus, the proposed distributed architecture not only improves the reliability but also facilitates placement of redundant converters to achieve the fault-tolerant capability. To further reduce the electrical and thermal stresses on the semiconductor devices and thus, improve the EPS life span, a novel power-down mode is proposed for the power converters. In this mode, semiconductor devices are switched- off whenever the power processed is below the threshold level and/or no-load operation. Reliability block diagrams are illustrated to demonstrate the reliability improvement and calculations shows that the proposed distributed architecture has higher reliability than the conventional EPS architecture. All the proposed concepts are validated using a prototype developed based on the specifications of MYSAT-1, which is an 1U CubeSat launched by Khalifa University.
Proper modeling of inverter-based microgrids is crucial for accurate assessment of stability boundaries. It has been recently realized that the stability conditions for such microgrids are ...significantly different from those known for large-scale power systems. In particular, the network dynamics, despite its fast nature, appears to have major influence on stability of slower modes. While detailed models are available, they are both computationally expensive and not transparent enough to provide an insight into the instability mechanisms and factors. In this paper, a computationally efficient and accurate reduced-order model is proposed for modeling inverter-based microgrids. The developed model has a structure similar to quasi-stationary model and at the same time properly accounts for the effects of network dynamics. The main factors affecting microgrid stability are analyzed using the developed reduced-order model and shown to be unique for microgrids, having no direct analogy in large-scale power systems. Particularly, it has been discovered that the stability limits for the conventional droop-based system are determined by the ratio of inverter rating to network capacity, leading to a smaller stability region for microgrids with shorter lines. Finally, the results are verified with different models based on both frequency and time domain analyses.
Grid interconnected multi-microgrids provides potential benefits to the consumers, where the microgrids (MGs) equipped with distributed generators (DGs), energy storage systems (ESSs), and diesel ...generators. However, intermittency of DGs, high cost of ESSs, and depleting fossil fuels are the major challenges for the economic operation of interconnected multi-microgrids. One potential way to address these challenges is to develop an energy management strategy (EMS) for the grid interconnected multi-microgrids. This paper proposes an EMS to reduce consumer energy consumption cost (ECC) using fuzzy-based peer-to-peer (P2P) energy exchange algorithm with dynamic pricing. In this context, the MGs consumers load power demand (LPD) and DGs output behaviors are modeled using random vector functional link network approach to predict future time slot values. Then, a fuzzy-based P2P energy exchange algorithm is developed to enable the surplus energy transfer to grid and/or MGs with dynamic pricing. Furthermore, an ESS charging/discharging energy control and diesel generator turn on strategies are developed based on the MGs deficit power. Then, the MGs consumer LPD reduction strategy is implemented based on the consumer ECC margin and energy consumption index. Finally, an EMS is proposed that includes on demand-supply strategy and consumer energy consumption cost reduction strategy based on the future time slot values. The novelty of the proposed work lies within the energy management of grid interconnected multi-microgrids and the reduction of consumers ECC through surplus energy transfer to grid and/or MGs using fuzzy-based P2P energy exchange algorithm with dynamic pricing. Historical data are used to demonstrate the effectiveness of the proposed EMS for grid interconnected multi-microgrids.
In this paper, a modified backward/forward sweep (BFS) load flow algorithm is proposed to solve power flow for islanded droop-controlled ac microgrids. The proposed method has been formulated such ...that the system frequency is one of the system's unknown variables which is typical for an islanded network justifying further the absence of a slack bus. As a result, new equations have been systematically developed and incorporated with the conventional BFS method. The modified BFS method has been applied to the 33-bus test system and the results obtained are compared with simulation results from the direct BFS method as well as PSCAD/EMTDC. In comparison to the conventional methods, the proposed method is accurate, simple, and easy to implement thus serving as a useful tool for microgrid analysis and planning.
Microgrids are becoming popular because of the rise of distributed energy resources (DERs). The quest for efficient utilization of DERs resulted in the development of hybrid dc/ac microgrids, which ...consist of independent dc and ac subgrids. Controlling the power exchange across hybrid microgrids is an important aspect in maximizing the benefits. There are numerous techniques proposed in the literature to control the power flow; however, most of these techniques use proportional-integral controllers which are difficult to tune and exhibit slow response. To eliminate the drawback of existing control solutions, this letter proposes a novel strategy to exchange active power among dc and ac microgrids. The proposed control strategy is based on the hill climbing algorithm that uses perturbations of power angle δ and observes the corresponding changes in the active power. An average model of the hybrid microgrid is first developed for the evaluation of the proposed algorithm. The proposed algorithm is then applied to verify its effectiveness for achieving sufficient power exchange and enhancing the dynamic response. The model is implemented and tested using MATLAB/Simulink. Moreover, the proposed control strategy is experimentally validated using a real-time simulator, OPAL-RT.
Generalized integrator-based orthogonal signal generator phase-locked loops (GI-OSG PLLs) are very popular in single-phase grid synchronization. Generally speaking, the OSG of this PLL is realized ...from a second-order integrator perspective. As a result, the OSG implementation impacts the PLL dynamics. Improving the PLL performance by employing a reduced-order OSG implementation is the main motivation for this paper. Therefore, a reduced order-OSG PLL is proposed. In the proposed PLL, a single state and two output equations are employed to obtain a pair of orthogonal signals. This results in the loss of orthogonality between the OSG outputs and the single-phase supply voltage. Also, harmonic filtering capability provided by SOGI-OSG becomes non-existent. These issues are resolved by incorporating steady-state phase angle-offset error compensation at the PLL output and a moving average filter (MAF) within the PLL loop. To counteract the influence of MAF on the PLL's stability and dynamics performance, a phase-lead compensator is designed. Through experimental studies, it is shown that the proposed reduced order-OSG PLL offers excellent dynamic performance. Also, the proposed PLL achieves minimal fluctuation of PV power when employed for grid synchronization of a PV system.
Both the electrical conductivity and the magnetic permeability of a measured sample have significant impact on the detected signal in eddy current nondestructive testing. Therefore, the problem of ...obtaining accurate measurement for the electrical conductivity or magnetic permeability has been of great interest to design and manufacturing engineers. In this paper, the conductivity invariance phenomenon (CIP) is investigated and utilized to detect the magnetic permeability of metals. First, the CIP is introduced and its sensitivity factors are investigated using a finite-element method. An experimental platform is set up based on which the CIP is verified. Finally, a magnetic permeability measurement device is proposed, which separates the coupling impact of the sample's electrical conductivity and magnetic permeability. The work reported in this paper provides an effective approach to accurately estimate the magnetic permeability of metals without the influence of its conductivity.
CubeSats have been widely used for space research due to lower cost and faster development. The electric power system (EPS) is one of the key subsystems of CubeSat which powers all the other ...subsystems. One of the important steps in the EPS design is the selection of EPS architecture which should be done considering overall efficiency, battery size, reliability, and simplicity of control. In the literature, a general comparison between different architectures is performed without considering the mission parameters, power generation profile, and load profile based on the operational modes. Thus, the best possible EPS architecture may not be selected in the design phase. Therefore, the main objective of this article is to develop a systematic methodology to compare various peak power tracking EPS architectures of CubeSat in terms of orbital efficiency for all possible modes of operation, component count, reliability, and battery size to meet the required number of cycles of charge/discharge for the given mission duration. The proposed methodology has been demonstrated using the real data and scenarios of MYSAT-1, which is a 1U CubeSat developed and launched by Khalifa University. The results demonstrate that EPS architecture with series-connected maximum power tracking converters for solar panels and unregulated dc-bus has the highest efficiency for all operating modes, lower component count, higher reliability, and minimum battery capacity or longer lifetime for the same battery specifications.
Recent studies on power flow analysis of islanded microgrids have become increasingly important and different solutions have been proposed. However, they are often limited to only ac or only dc ...microgrids and hence, the power flow must be solved separately. This paper proposes a straightforward and efficient method to solve power flows of hybrid ac/dc microgrids simultaneously, based on the well-established Newton-Raphson approach. It considers the lack of slack bus during islanded operation, the coupling of ac frequency and dc bus voltage, as well as the droop control of distributed generators. To achieve power sharing between the ac and dc subgrids, this method incorporates the interlinking converter droop constants in the equation. The algorithm was tested on modified hybrid microgrids involving multiple ac-dc subgrids. The results are compared against results from time-domain simulations to validate the algorithm's accuracy. The proposed technique can be easily implemented to aid the design and planning process of hybrid microgrids.
This work proposes a real-time deep learning-based model for predicting the small-signal stability of an electrical network. The trained models equip power system operators with an accurate and fast ...monitoring tool which can be used during online operation. To achieve this objective, three different model architectures are employed in this research; stacked long short-term memory (LSTM), convolutional neural network (CNN)-LSTM and Convectional LSTM (Conv-LSTM). These models are trained using datasets which contain the oscillatory parameters (frequency and damping ratio) of both local and inter-area modes of oscillations. In addition, the voltage phasors at different buses are taken as the model input where the output comprises the real-time oscillatory patterns of the modes. Furthermore, the overall performance of proposed models is shown for the New-England 10-machine, 39-bus, IEEE 16-machine, 68-bus, 5-area, and IEEE 50-machine, 145-bus benchmark test cases. The main findings show that training CNN-LSTM and Conv-LSTM models provide better performance compared with the stacked-LSTM model. The former models have less number of parameters and thus shorter training time. In addition, CNN_LSTM and Conv-LSTM models are less prone to overfitting problems in the network and have a better ability in capturing spatial and temporal features inherent in input data.
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