University of South Wales Master of Sciences Thesis
Distributed AC-coupled Hybrid Power Systems
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- 2.7.5. DC-coupled Hybrid Power Systems
| 2.7.4. Distributed AC-coupled Hybrid Power Systems.
AC-coupled HPSs is said to be distributed or decentralized when the different ECSs constituting it are not connected to a main AC-bus; otherwise, some or all of them are individually connected to the load. The following figure, Figure 2-37, depicts the configuration. Standalone hybrid generation system for the remote area of Thar, Pakistan Fig.2.37: Decentralized AC-coupled HPSs [3, 28, 29]. In this topology, the power sources do not need to be connected to one common bus as in the previous cases. These sources may not also be installed close to each other i.e. the sources are distributed in different geographical locations and each source is connected to the load separately. The DC powers obtained from the PV-system and the battery need to be converted to AC before feeding the AC load, thus appropriate inverters are required. This type of topology is advantageous in a sense that the different sources are appropriately located and installed geographically in such a way that the PV- systems are installed in places where there is more solar irradiation and the wind turbines in locations where there is more wind. However, there is also disadvantage with this topology in that controlling of the system is difficult [27]. Comparing the centralized and decentralized ones, centralized HPSs have advantages over decentralized HPSs in that they are robust as they can be controlled more easily. 2.7.5. DC-coupled Hybrid Power Systems In a dc-coupled system, all renewable energy sources are connected to a dc bus either directly or through appropriate power electronic converters. A block diagram of the system is shown in Fig. 1.1. This system can be connected to the dc loads through appropriate dc-dc converter, ac loads through a dc-ac converter or utility grid through a bi-directional dc-ac converter. The system is flexible and can be connected to an ac load of 50/60 Hz system frequency. The dc-coupling scheme is very simple and is not required to be synchronous with the ac system. However, a dc-coupled system suffers from various weaknesses. For example, if the system converter connecting the utility grid with the bus is out of service, the whole system will not be able to supply ac power. To rectify this, several inverters can be connected in parallel. As such, synchronization of output ac voltage and proper power sharing are required to achieve a desired load distribution [31]. tải về 6.62 Mb. Chia sẻ với bạn bè của bạn:
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