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With the rapid development of AC/DC hybrid microgrids and the widespread use of distributed power resources, planning strategies for microgrids with high-density distributed power generation have become an urgent problem. Because current research on microgrid planning has not considered line factors, this paper analyses the planning of an AC/DC hyb...
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Context 1
... AC/DC hybrid microgrid consists of AC sub-microgrids and DC sub-microgrids. The power capacity of an AC sub-microgrid and a DC sub-microgrid is relatively balanced with each respective load; as a result, the power transmission between the AC and DC sub-microgrids is reduced, thereby facilitating the control of the hybrid microgrid. Moreover, the AC or DC sub-microgrids can be networked or operated independently, which increases the flexibility of the operation mode. In the planning of an AC/DC hybrid microgrid, the principles of energy conservation, partition matching, distributed energy complementarity, and guaranteed power quality should be followed; therefore, these design principles must be considered in the expansion planning model and when devising the constraints [4][5][6]. Figure 2 shows a typical grid structure of an AC/DC hybrid microgrid. The hybrid microgrid system connects the AC and DC bus via a bi-directional AC/DC converter, forming AC and DC sub-microgrids. Photovoltaics, wind turbines, energy storage and other power generation units as well as AC and DC loads are connected to AC and DC buses through power electronic converters. As shown in Figure 2, distribution network is connected to the AC Bus, so the power energy transmits between distribution network and AC/DC hybrid microgrid. The point of common coupling (PCC) of the AC/DC hybrid microgrid system and the distribution network is set on the side of the AC sub-microgrid, and through the control of the PCC, the operation model of the AC/DC hybrid microgrid can be changed between grid-connected mode and islanding mode. The AC/DC hybrid microgrid has a simple structure and meets the access requirements of high-density distributed power supply, making the structure suitable for most AC/DC hybrid microgrid ...
Context 2
... AC/DC hybrid microgrid consists of AC sub-microgrids and DC sub-microgrids. The power capacity of an AC sub-microgrid and a DC sub-microgrid is relatively balanced with each respective load; as a result, the power transmission between the AC and DC sub-microgrids is reduced, thereby facilitating the control of the hybrid microgrid. Moreover, the AC or DC sub-microgrids can be networked or operated independently, which increases the flexibility of the operation mode. In the planning of an AC/DC hybrid microgrid, the principles of energy conservation, partition matching, distributed energy complementarity, and guaranteed power quality should be followed; therefore, these design principles must be considered in the expansion planning model and when devising the constraints [4][5][6]. Figure 2 shows a typical grid structure of an AC/DC hybrid microgrid. The hybrid microgrid system connects the AC and DC bus via a bi-directional AC/DC converter, forming AC and DC sub-microgrids. Photovoltaics, wind turbines, energy storage and other power generation units as well as AC and DC loads are connected to AC and DC buses through power electronic converters. As shown in Figure 2, distribution network is connected to the AC Bus, so the power energy transmits between distribution network and AC/DC hybrid microgrid. The point of common coupling (PCC) of the AC/DC hybrid microgrid system and the distribution network is set on the side of the AC sub-microgrid, and through the control of the PCC, the operation model of the AC/DC hybrid microgrid can be changed between grid-connected mode and islanding mode. The AC/DC hybrid microgrid has a simple structure and meets the access requirements of high-density distributed power supply, making the structure suitable for most AC/DC hybrid microgrid ...
Citations
... Typical AC/DC (Hybrid) microgrid structure[76]. ...
Most of the research in distributed generation focuses on power flow optimization and control algorithm development and related fields. However, microgrids are evolving on multiple levels with respect to the chemical processes used to manufacture the underlying technologies, deployment strategies, physical architecture (which is important to the economic factor) as well as environmental impact mitigation of microgrids. Special use cases and paradigms of deploying Distributed Generation (DG) in harmony with agricultural or decorative purposes for existing spaces are emerging, propelled by research in frontiers that the DG engineer would benefit from being aware of. Also, offshore photovoltaic (PV) has emerged as an increasingly important research area. Many nascent technologies and concepts have not been techno-economically analyzed to determine and optimize their benefits. These provide ample research opportunities from a big-picture perspective regarding microgrid development. This also provides the avenue for research in distributed generation from a physical integration and space use perspective. This study reviews a selection of developments in microgrid technology with the themes of manufacturing technology, optimal deployment techniques in physical spaces, and impact mitigation approaches to the deployment of renewable energy from a qualitative perspective.
... As a system with various distributed generators, AC and DC loads, and self-adjusting and control capabilities [1,2], the microgrid applies power electronic transformers, which not only enables it to carry out the power transmission and electrical isolation of traditional transformers, but also realizes harmonic and reactive power compensation. The microgrid supports accurate and bidirectional power flow regulations [3][4][5] and has broad application prospects in this field. ...
The AC/DC hybrid microgrid, which takes into account the access requirements of AC and DC sources and loads, optimizes the structure of traditional distribution networks. The application of power electronic transformers as the core of its energy management, with electrical isolation and accurate control of the voltage, current and power flow by the control system, enables the microgrid to achieve a more flexible and stable transmission mode. Because the power electronic transformer combines the power electronic device and the high-frequency transformer, its frequent switching causes the electromagnetic transient simulation to take too long. Therefore, by simplifying control loops and converters, this paper proposes a simplified model for the microgrid system power flow and the dynamic response under exposure to a fault. The mathematical model equivalent simplification method is used in this paper. This method is concise and efficient and does not rely on the performance of a computer or change the program algorithm of the software. The simplified model was built based on PSCAD (Power System Computer Aided Design) simulation software and was carried out under short circuit fault conditions to verify its validity. The comparison of the simulation’s time consumption and accuracy shows that model simplification can significantly improve the simulation speed, with an acceptable error rate, and its dynamic response maintains good consistency with that of the detailed electromagnetic transient model. Therefore, it can be applied to the transient electromagnetic simulation fault analysis of the AC/DC hybrid microgrid.
... How to access the distribution network of a DC microgrid or AC/DC hybrid microgrid has been discussed in [17][18][19][20][21][22]. A method of forming a DC network by replacing some AC lines with a DC line is proposed. ...
... A hybrid planning model of distributed energy and power generation system is proposed, and the type of microgrid is selected according to economic factors [18]. In Reference [19], considering the impact of line investment cost and interaction power cap on the planning results, the capacity and location of distributed power resources are optimized. For the distributed grid technology [20], the topology structure of synchronous AC/DC hybrid microgrid and the basic working principle of microgrid under different operation modes are proposed. ...
With the wide application of distributed generation (DG) and the rapid development of alternating current/direct current (AC/DC) hybrid microgrids, the optimal planning of distributed generation connecting to AC/DC distribution networks/microgrids has become an urgent problem to resolve. This paper presents a collaborative planning method for distributed generation access to AC/DC distribution (micro) grids. Based on the grid structure of the AC/DC distribution network, the typical interconnection structure of the AC/DC hybrid microgrid and AC/DC distribution network is designed. The optimal allocation models of distributed power supply for the AC/DC distribution network and microgrid are established based on analytical target cascading. The power interaction between the distribution network and microgrid is used to establish a coupling relationship, and the augmented Lagrangian penalty function is used to solve the collaborative programming problem. The results of distributed power supply allocation are obtained, solving the problem so that distribution generation with different capacity levels is connected to the power grid system in a single form.
... This is why the hybrid energy storage system (HESS) is becoming an interesting solution, able to extend batteries' useful life. By combining fast-dynamics high-power storage devices as supercapacitors and ultracapacitors with bulk-energy electrochemical units, the performance of classic grid forming ESSs has been improved [16][17][18][19]. The initial investment in supercapacitors can be paid off by extending the useful life of the batteries. ...
... There are some technical papers in the bibliography where the use of PLS is applied to enable communications between converters in a MG. In some of these works, the PLS is applied to DC MGs [18,20,24] where different control strategies can be found. For instance, in [24], the droop profile varies depending on the PLS frequency. ...
... This means there is a continuous injection of a sinusoidal signal into the DC bus. On the other hand, in [18] the control strategy is based not only on a droop control, but on keeping the RES units operating at their MPP while the batteries' SoC is in a safe zone. The moment this SoC is high enough to trigger the PLS, the RESs change to a different operation mode. ...
Energy management control is essential to microgrids (MGs), especially to single-phase ones. To handle the variety of distributed generators (DGs) that can be found in a MG, e.g., renewable energy sources (RESs) and energy storage systems (ESSs), a coordinated power regulation is required. The latter are generally battery-based systems whose lifetime is directly related to charge/discharge processes, whereas the most common RESs in a MG are photovoltaic (PV) units. Hybrid energy storage systems (HESS) extend batteries life expectancy, thanks to the effect of supercapacitors, but they also require more complex control strategies. Conventional droop methodologies are usually applied to provide autonomous and coordinated power control. This paper proposes a method for coordination of a single-phase MG composed by a number of sources (HESS, RES, etc.) using power line signaling (PLS). In this distributed control strategy, a signal whose frequency is higher than the grid is broadcasted to communicate with all DGs when the state of charge (SoC) of the batteries reaches a maximum value. This technique prevents batteries from overcharging and maximizes the power contribution of the RESs to the MG. Moreover, different commands apart from the SoC can be broadcasted, just by changing to other frequency bands. The HESS master unit operates as a grid-forming unit, whereas RESs act as grid followers. Supercapacitors in the HESS compensate for energy peaks, while batteries respond smoothly to changes in the load, also expanding its lifetime due to less aggressive power references. In this paper, a control structure that allows the implementation of this strategy in single-phase MGs is presented, with the analysis of the optimal range of PLS frequencies and the required self-adaptive proportional-resonant controllers.
The smart grid plays a vital role in energy management systems. It helps to mitigate the demand side management of electricity by managing the microgrid. In the modern era, the concept of hybrid microgrids emerged which helps the smart grid management of electricity. Additionally, the Internet of Things (IoT) technology is used to integrate the hybrid microgrid. Thus, various policies and topologies are employed to perform the task meticulously. Pakistan being an energy deficient country has recently introduced some new policies such as Energy Wheeling Policy (EWP), Energy Import Policy (EIP), and Net Metering/Distributed Generation Policy (NMP) to manage the electricity demand effectively. In addition, the Energy Efficiency and Conservation Act (EECA) has also been introduced. In this paper, we present the overview and impact of these policies in the context of the local energy market and modern information and communication mechanisms proposed for smart grids. These new policies primarily focus on energy demand-supply for various types of consumers such as the demand for bulk energy for industrial ventures and the distributed production by consumers. The EWP deals with obtaining power from remote areas within the country to ease the energy situation in populated load centers and the EIP highlights energy import guidelines from foreign countries. The NMP deals with the integration of renewable energy resources and EECA is more focused on the measures and standardization for energy efficiency and conservation. The benefits and challenges related to EWP, NMP, and EIP have also been discussed concerning the present energy crisis in Pakistan. The generalized lessons learned and comparison of a few aspects of these policies with some other countries are also presented.
