University of South Wales Master of Sciences Thesis
Standalone hybrid generation system for the remote area of Thar, Pakistan
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- 2.6.1.1. Three Phase
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Standalone hybrid generation system for the remote area of Thar, Pakistan example for such topology can be found in PV applications, where the dedicated DC-DC units are often designed to extract the maximum power output of the PV array. AC-to-AC converters can be used convert the AC source voltage magnitude and frequency to a fixed amplitude and frequency, making it compatible with the utility grid. The AC-to-AC converters are not typically used in modern DE applications due to some inherent disadvantages. A summary of the different power converters that are used for DE applications are given in Table 1 (Shepherd et al. 2004; DeBlasio et al. 2006). Fig. 2.24 Power electronics systems for different power conversions 2.6.1. PV Array Power Electronics and control Topology The power electronics topologies for the PV systems can be categorized on the basis of the number of power processing stages, the location of power decoupling capacitors, utilization transformers, and the types of grid interfaces (Carrasco et al. 2006). The basic classifications based on the number of inverter output phases are • Single phase • Single- multiple phase • Three phase In the report I am going emphasis only on the three-phase interface as the system required three phase supply to the micro-grid. 2.6.1.1. Three Phase For larger systems over 10kW, three-phase inverters are most often used. All the configurations for single-phase utility connection can be used for the three phase. But, using a line-frequency transformer or a high-frequency transformer can do the isolation from the grid either. In the later case, an additional converter is required for converting DC from PV into high-frequency AC. Figure 8 shows a typical topology for a three-phase PV inverter utilizing a line-frequency three-phase transformer. The DC output of the PV array is connected across a filter capacitor. The output of the capacitor connects to the input of a voltage-source three-phase inverter. The output of each phase of the converters is connected to an inductor and capacitor to limit the high-frequency harmonics injected into the AC system. A synthesized AC output voltage is produced by appropriately controlling the switches. A three-phase transformer is then used to connect the power to the utility. |