Electronics
Zahra Ahangari
Abstract
This paper presents a comprehensive investigation of the electrical properties of a heterojunction tunnel field effect transistor with enhanced electrical tunneling current. The proposed device structure incorporates an extended source region and two parallel channels positioned above and below the source ...
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This paper presents a comprehensive investigation of the electrical properties of a heterojunction tunnel field effect transistor with enhanced electrical tunneling current. The proposed device structure incorporates an extended source region and two parallel channels positioned above and below the source region. This configuration effectively amplifies the tunneling area, leading to a significant improvement in the on-state current. Moreover, the inclusion of an embedded oxide region between the source and drain regions confers the device with a high resistance to short-channel effects. The combination of materials in both the source and channel region results in a staggered band alignment at the tunneling junction. This specific configuration leads to a lower threshold voltage for the initiation of tunneling. The impact of critical design parameters on the device performance has been thoroughly examined. A 2D variation matrix has been developed to compute the threshold voltage and on-state current variation based on the source doping density and gate workfunction, which serve as essential design parameters to optimize the electrical performance of the device. Furthermore, the device has achieved a unity current-ratio frequency of 300 GHz indicating its suitability for high-frequency applications. Additionally, the proposed structure provides an on-state current of 2.24×10-4 (A/µm), an off-state current of 1.24×10-15 (A/µm), an on/off current ratio of 1.81×1011, and a subthreshold swing of 5 (mV/dec). These characteristics make the device viable for energy-efficient, high-speed digital circuits.
Electronics
Seyed Ali Sadatnoori
Abstract
The output of a Digital Delta-Sigma Modulator (DDSM) is always a periodic signal and the input is constant. A hybrid DDSM is a premiere to its conventional counterpart for having a potential speed, by the choice of its smaller bus. This paper offers an implementation for multi-stage noise shaping (MASH) ...
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The output of a Digital Delta-Sigma Modulator (DDSM) is always a periodic signal and the input is constant. A hybrid DDSM is a premiere to its conventional counterpart for having a potential speed, by the choice of its smaller bus. This paper offers an implementation for multi-stage noise shaping (MASH) DDSMs that includes four modulators named hybrid DDSM-1, DDSM-2, DDSM-3, and DDSM-4. Also, it introduces a new solution, where the desired ratio in fractional frequency synthesizers is formed by combining four different modulos. The first stage modulator is a programmable modulus EFM1 and has a modulus M1 that is not a power of 2. The second, third, and fourth stage modulators are modified MASH 1-1, multi-modulus MASH 1-1-1, and the efficiently dithered MASH 1-1-1-1 modulator that has conventional modulus M2, M3, and M4, respectively. The M1 modulus is optimally selected to synthesize the new structure of the desired frequencies. Design results confirm the suppositional predictions. In addition, the results of the circuit implementation proposed method offer a 17% reduction in hardware complexity.
Power
Ramin Arjmandzadeh; Mahdi Banejad; Ali Akbarzadeh Kalat
Abstract
In conventional power systems, most of the power is produced by synchronous generators in the electric grid that have heavy and rotating rotors. As a result, there is an inherent inertia in the rotor of these generators. The presence of inertia in the grid prevents sudden frequency changes during imbalance ...
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In conventional power systems, most of the power is produced by synchronous generators in the electric grid that have heavy and rotating rotors. As a result, there is an inherent inertia in the rotor of these generators. The presence of inertia in the grid prevents sudden frequency changes during imbalance situations, thus, the frequency stability of the grid is maintained. Today, with the increase of renewable energy sources that are usually connected to the network by power electronic equipment. Such resources do not have rotating materials, therefore, the overall inertia of the grid decreases and the stability of the system deteriorates. To solve the problem of lack of inertia in the power electronic-based grid, the notion of the virtual synchronous generator (VSG) technology has been introduced in recent years. This technology can imitate the behavior of traditional synchronous generators for inverters connected to the grid. In this way, the inverters connected to the grid act like a synchronous generator during imbalance. One of the problems associated with the converters-based microgrid is the existence of DC deviations and additional harmonics, which disrupt the work of the converters. Therefore, in this article, a third-order generalized integrator (TOGI) -based VSG for grid-connected inverters is employed so that the system stability is maintained in the conditions of additional harmonics and DC deviation. To show the effectiveness of the proposed method, time domain simulations have been performed in Simulink/MATLAB software. The results of the simulation verify the performance of the proposed method.
Power
Ali Morsagh Dezfuli; Mahyar Abasi; Mohammad Esmaeil Hasanzadeh; Mahmood Joorabian
Abstract
The utilization of distributed generation (DG) in today's power systems has led to the emergence of the concept of microgrids, in addition to changing the mode of generating and supplying the energy required for network electrical loads. When a microgrid operates in the island mode, energy generation ...
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The utilization of distributed generation (DG) in today's power systems has led to the emergence of the concept of microgrids, in addition to changing the mode of generating and supplying the energy required for network electrical loads. When a microgrid operates in the island mode, energy generation sources are responsible for controlling the microgrid’s voltage and frequency. As the microgrid frequency is proportional to the amount of power generated by the DG, the microgrid requires a precise power-sharing strategy. Considering that DGs do not usually have stable output power despite the importance of power stability, the present paper addresses the voltage and frequency control of an islanded microgrid by considering the power generation uncertainties caused by disturbances and the varying power output of DGs. Given that the disturbance on the first DG's input current is 0.2 A, which is approximately 2.2% of the steady-state value, a simulation was performed, and it was observed that the maximum voltage variation of each bus in the worst case was 0.59% for the first bus and 0.53% for the second bus, which means that the controller could control the voltage and frequency values within the permissible range. If the controller is not used, the change in the frequency of each bus will be 10 times, and the voltage change will be 5 times as great as that of the case the controller is used.
Power
Zahra Gholami; Rahim Ildarabadi; Hamed Heydari-doostabad
Abstract
This paper discusses the application of the principle of duality to conventional voltage-based DC-DC converters, such as buck, boost, fly-back, cuk, sepic, and zeta topologies, in order to obtain their current-based DC-DC converters. The duality approach involves finding the dual of a circuit, which ...
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This paper discusses the application of the principle of duality to conventional voltage-based DC-DC converters, such as buck, boost, fly-back, cuk, sepic, and zeta topologies, in order to obtain their current-based DC-DC converters. The duality approach involves finding the dual of a circuit, which is a circuit equivalent to the original circuit but with certain parameters swapped. Therefore, this paper presents a comprehensive study on achieving the most commonly used topologies of DC-DC current converters by applying the duality approach to their DC-DC voltage converters. This approach serves as a solution for applications where a current source is available and there is a need for output current control. An application of these current converters is to power current-based loads, such as light-emitting diodes (LEDs), and to provide conversion for current sources, such as photovoltaics (PV). As an advantage, these converters do not require additional inductors at their input or output terminals. Additionally, the paper provides a detailed explanation of the principle of operation and mathematical analysis of the conversion ratio for the discussed current converters. The proposed current converters and their application as an interface between a PV and a high-power LED were simulated using MATLAB to verify the mathematical equations. Overall, this paper provides a useful study guideline for understanding the principle of duality and the application of DC-DC current converters for current-based loads and sources.
Power
Sajed Derakhshani Pour; Reza Eslami
Abstract
In the last few years, there has been growing attention to isolated DC microgrids (MGs) with robust voltage control and efficient responding to demand in the face of fluctuating demands and supply amounts. This attention is due to significant voltage mismatches originated ...
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In the last few years, there has been growing attention to isolated DC microgrids (MGs) with robust voltage control and efficient responding to demand in the face of fluctuating demands and supply amounts. This attention is due to significant voltage mismatches originated from the sudden transitions of the load demand and the active power of the supplies such as photovoltaic (PV) systems. To address these goals, a novel nonlinear robust voltage control strategy with a cascaded design consisting of proportional-integral (PI) and sliding mode control (SMC) techniques is developed in this research for the battery energy storage system (BESS). Additionally, this research considers a fuel cell as another power supply in addition to a solar PV system. For maximum power point tracking (MPPT) of the PV system, a novel backstepping sliding mode control (BSMC) technique is developed as well. The effective functioning of the suggested cascaded control strategy is examined using MATLAB/Simulink. The outcomes of the simulation represent the effectiveness of the proposed approach in robustly regulating the voltage level of the DC link at 50 V with small deviations in tracking, and quick reaction to fluctuations in both demand and supply sides, as well as guaranteeing an evenly-distributed responding to demand fluctuations from the DC MG.
Power
Arash Moghadami; Davood Azizian; Amin Karimi
Abstract
The healthy operation of high-power transformers plays a crucial role in the reliability of power systems. Given the thermal model of transformers under heavy-load and high-temperature conditions, the hot spot temperature exceeding the maximum allowable value may result in oil dissolution and cascading. ...
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The healthy operation of high-power transformers plays a crucial role in the reliability of power systems. Given the thermal model of transformers under heavy-load and high-temperature conditions, the hot spot temperature exceeding the maximum allowable value may result in oil dissolution and cascading. This paper uses a thermal model of transformers to analyze the hot spot temperature load level under predicted ambient temperature, which may cross the healthy conditions. Then, an Incentive-Based Demand Response (IBDR) and a thermal model of transformers are used to determine optimal load curtailment. On the other hand, as the paper uses the demand response (DR) for security reasons, the risk of load participation in IBDR programs should be minimized. Hence, a Response Fatigue Index (RFI) is employed to maintain the comfort level of demands participated in DR. Also, the feasible solution area for multi-objective optimization is determined, given costs and RFI, using the sequential solution of a single-objective problem with cost reduction as the objective and RFI as the constraint with different levels of maximum acceptable RFI. The developed model was applied to a real substation in Iran as a test case. The results show that DR can enhance the reliability and life expectancy of the transformer while keeping the comfort level of loads as high as possible.