The interleave boost converter (IBC) has been used as the interface converter between the low-voltage electrical energy sources, such as lithium-ion battery banks, solar panels, and fuel cells, and ...the dc bus of dc microgrids. With increasing penetration of tightly regulated power electronic loads, which behave as constant power loads, the stability of microgrid dc-bus voltage that is fed by the IBC is threatened by the loads' negative incremental impedance feature. To ensure the stability of the bus voltage, this article proposes a nonlinear disturbance observer (NDO)-based sliding-mode control algorithm. The proposed algorithm has excellent robustness, low computational burden, and no extra hardware cost. A generalized average state-space model is proposed to facilitate the control design. In addition, an NDO is employed to estimate the output power of IBC rapidly and accurately. To verify the effectiveness of the proposed algorithm, simulation and experimental results are presented.
Internet of Vehicles (IoV) is an emerging concept that is believed to help realize the vision of intelligent transportation systems (ITSs). IoV has become an important research area of impactful ...applications in recent years due to the rapid advancements in vehicular technologies, high throughput satellite communication, the Internet of Things, and cyber-physical systems. IoV enables the integration of smart vehicles with the Internet and system components attributing to their environments, such as public infrastructures, sensors, computing nodes, pedestrians, and other vehicles. By allowing the development of a common information exchange platform between vehicles and heterogeneous vehicular networks, this integration aims to create a better environment and public space for the people as well as to enhance safety for all road users. Being a participatory data exchange and storage, the underlying information exchange platform of IoV needs to be secure, transparent, and immutable in order to achieve the intended objectives of ITS. In this connection, the adoption of blockchain as a system platform for supporting the information exchange needs of IoV has been explored. Due to their decentralized and immutable nature, IoV applications enabled by blockchain are believed to have a number of desirable properties, such as decentralization, security, transparency, immutability, and automation. In this article, we present a contemporary survey on the latest advancement in blockchain for IoV. Particularly, we highlight the different application scenarios of IoV after carefully reviewing the recent literature. We also investigate several key challenges where blockchain is applied in IoV. Furthermore, we present the future opportunities and explore further research directions of IoV as a key enabler of ITS.
CLLC-type dc transformer (CLLC-DCT) is very popular in the hybrid ac-dc microgrid thanks to its high-power density advantage and good bidirectional power transfer capacity. In the hybrid ac/dc ...microgrid, the open-loop control is always utilized by the CLLC-DCT to cooperate with the bidirectional interlinking converter to realize the power and voltage conversion between the ac and dc bus. This paper first studies the circuit parameters design of the open-loop controlled CLLC-DCT with consideration of such a realistic problem: The real inductors/capacitors values are actually different with their theoretically designed values due to the operation power and temperature variation. To solve this problem, a robust circuit parameters design scheme is proposed for the CLLC-DCT in this paper. With the proposed scheme, the designed CLLC-DCT exhibits good power transmission and voltage regulation ability in the hybrid ac/dc microgrid even when its actual inductors/capacitors values vary with the practical power and temperature. The robust design method is experimentally verified in a hybrid ac/dc microgrid prototype.
The concept of smart grid has been introduced as a new vision of the conventional power grid to figure out an efficient way of integrating green and renewable energy technologies. In this way, ...Internet-connected smart grid, also called energy Internet, is also emerging as an innovative approach to ensure the energy from anywhere at any time. The ultimate goal of these developments is to build a sustainable society. However, integrating and coordinating a large number of growing connections can be a challenging issue for the traditional centralized grid system. Consequently, the smart grid is undergoing a transformation to the decentralized topology from its centralized form. On the other hand, blockchain has some excellent features which make it a promising application for the smart grid paradigm. In this article, we aim to provide a comprehensive survey on the application of blockchain in smart grid. As such, we identify the significant security challenges of smart grid scenarios that can be addressed by blockchain. Then, we present a number of blockchain-based recent research works presented in different literature addressing security issues in the area of smart grid. We also summarize several related practical projects, trials, and products that have emerged recently. Finally, we discuss essential research challenges and future directions of applying blockchain to smart grid security issues.
In the microgrid, virtual synchronous generator technology can significantly enhance the anti‐interference characteristics of the system frequency and bus voltage, as well as solve the problems of ...insufficient damping and low inertia. However, the system frequency and active power oscillation caused by power fluctuations and grid faults threaten the stable operation of the grid seriously. Therefore, for an alternating current (AC) microgrid multi‐virtual synchronous generator (VSG) parallel system, an improved virtual synchronous generator control algorithm based on a fuzzy inference system is proposed, which adjusts the values of virtual inertia and damping coefficient dynamically through fuzzy logic rules to realize the coordinated control of the two. The enhanced VSG algorithm described in this research has a substantial influence on power‐frequency oscillation suppression, decreases active power and frequency overshoot, shortens the adjustment time, and improves system frequency stability active power, according to simulation and experimental findings.
The dc offset and scaling errors in the voltage and current measurements cause the injection of undesired dc and unbalanced currents into the three-phase input currents and subsequently lead to ...voltage ripple at the dc output voltage of the ac/dc converter. This paper proposes a compensation scheme for current measurement error where the dc offset and scaling errors in the current measurement are estimated from the voltage ripple characteristics of the dc output voltage ripple combining with simple band-pass and low-pass filters. Meanwhile, the dc offset and scaling errors in the voltage measurement can be rejected by using an advanced current controller developed with a proportional resonant plus a repetitive controller designed in the synchronous ( d-q ) reference frame. The proposed control algorithm is able to effectively reject the impact of both voltage and current measurement error so that the three-phase input currents are regulated to be balanced and sinusoidal with ultralow dc current component. Meanwhile, the dc output voltage is also well regulated to be pure dc with a negligibly small voltage ripple. The proposed compensation method is developed without the need of extra hardware circuit, sensor, or precise information of system parameters so that it can be considered as more cost effective and robust solution. The effectiveness of the proposed solution is verified by experimental results.
In this paper, a distributed hierarchical control is proposed for ac microgrid, which could apply to both grid-connected (GC) mode and islanded (IS) mode as well as mode transitions. The control ...includes three control levels: 1) the basic droop control is adopted as the primary control; 2) the secondary control is based on the distributed control with a leaderâĂ"follower consensus protocol; and 3) the tertiary level is a mode-supervisory control, which manages the different control targets of four operation modes. Under the proposed control framework, the following targets are achieved: 1) the frequency/voltage recovery and accurate power sharing in IS mode; 2) flexible power flow regulation between utility-grid and microgrid in GC mode; 3) universal control strategy from GC to IS modes without control switching; and 4) smooth active-synchronization from IS mode to GC mode. In this sense, the proposed method can adapt to all four operation modes of microgrid. Compared with central-standard hierarchical control, the proposed method only requires local neighbor-to-neighbor interaction with a sparse distributed communication network. Thus, the scalability, flexibility, reliability, and robustness are greatly improved in practical application. In addition, stability analysis is added to facilitate the control parameter designs, and substantial simulation cases are provided to validate the control feasibility, link-failure-resiliency, and plug-and-play capability.
To study the impact of personal carbon trading (PCT) mechanism on the economy and reliability of the power distribution system operation, this article proposes an orderly charging and discharging ...strategy for electric vehicles (EVs) that integrates a dynamic update mechanism of charging tariff and carbon revenue, taking into account the travel characteristics of EVs and users' willingness to respond. First, the probability density of the travel time parameters for EVs is calculated based on an improved kernel density estimation (IKDE) method. Second, the carbon emissions at each stage of the lifecycle of EVs are calculated using a life cycle assessment approach (LCA), and a model for EV carbon quota and carbon revenue is constructed. Then, based on the net load data of the power distribution system, a dynamic updating model for the pricing of ordered charging and discharging is established. Finally, with the objective of reducing the dispatching cost for EV users and stabilizing the load fluctuation of the power distribution network, an optimization model for EV charging and discharging load dispatching is constructed. Based on the dynamic charging and discharging tariff information and state of charge (SOC) at the time of access to the grid, an evaluation model of the economic benefits of EV participation in orderly regulation is constructed. The response willingness of EV users to the dispatching strategy is inferred using the fuzzy logic control algorithm. The simulation results validate the effectiveness of this dispatching strategy in reducing the dispatching cost for EV users and stabilizing the net load fluctuation of the power distribution system. Furthermore, it is observed that as carbon prices increase, the optimization dispatching effect becomes more pronounced.
For a high penetration microgrid, improving its low-voltage ride-through (LVRT) capability under some minor or temporary faults can contribute to reinforcing power support and reducing network ...instability. In this paper, the comparison of a superconducting fault current limiter (SFCL) and a dynamic voltage restorer (DVR) for LVRT capability enhancement of a 10-kV microgrid is conducted. Concerning the microgrid which includes distributed photovoltaic generation, energy storage and loads, the effects of the SFCL and the DVR are compared in detail, and related theoretical analysis, simulation study, and economical evaluation are carried out. From the demonstrated results, the suggested two devices can both assist the microgrid to achieve the LVRT operation, but the economics of the DVR are weaker than the SFCL. Moreover, compared to the DVR, the SFCL enables the energy storage unit to offer better control effects in power stabilization. From technical and economic perspectives, the SFCL is a more preferable choice than the DVR.
Maintaining the stability of low-inertia microgrid becomes a key challenge in the presence of high penetration of renewable energy sources. However, in such systems, the virtual inertia values are ...often fixed constants, and the choice of their values will significantly affect the frequency and voltage stability of the microgrid. Higher frequency and voltage oscillations may occur due to improper selection of fixed virtual inertia values. Therefore, virtual inertia-based control has attracted a lot of attention. In this paper, an adaptive virtual inertia control system using a fuzzy system is proposed by setting fuzzy logic rules and affiliation functions to provide adaptive inertia control for the system to ensure the frequency and voltage stability. In the proposed adaptive control strategy, the virtual inertia values are automatically adjusted according to the signal deviation and rate of change of the actual system, avoiding the selection of inappropriate inertia values and providing fast inertial response. Simulation and experimental results show that the proposed adaptive control algorithm, by combining the advantages of large inertia and small inertia, enables effective improvement of the dynamic response of the system voltage and frequency in both rectifier and inverter modes. The effectiveness of the proposed control strategy is verified.
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