TAILIEUCHUNG - Renewable Energy Part 9

Tham khảo tài liệu 'renewable energy part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 274 Renewable Energy Fig. 2. AC-DC converter a low frequency b high frequency A three-phase controlled high frequency converter based on IGBT is shown in b . This circuit can change the input AC voltage into DC voltage. By controlling the duty cycle of the switches based on different modulation technique the amount of output DC voltage can be controlled. Since the switches drive in high frequency the amount of harmonic content in current waveform is decreased. In addition this configuration can provide bidirectional power flow between load and source. DC-DC Converter DC-DC converters are a kind of high frequency converters which convert unregulated DC power to regulated DC power. Since the output voltage of renewable energy systems or rectifier converter is basically unregulated DC voltage as shown in Fig. 3 DC-DC converters are necessary to adjust the DC voltage for different applications. Three basic configurations of DC-DC converters are buck boost and buck-boost converters. Unregulated DC voltage Fig. 3. DC-DC converter In a buck converter the output voltage is normally less than input voltage. However a boost converter has the ability to increase the input voltage based on duty cycle of the switch. A buck-boost converter can either buck or boost the input voltage. A boost converter is usually applied in renewable energy systems as the output voltage of these systems is low and unregulated. Configuration of the boost converter is illustrated in Fig. 4. In this converter output voltage is a function of the duty cycle of switch S which can be defined by a proper modulation technique. When the switch is on the inductor can be charged by the current flowing through it. However in the next subinterval when the switch is turned off the capacitor will be charged by the inductor current. Second order LC filter in this configuration can regulate the output voltage and remove the high frequency harmonics. Multilevel Converters in Renewable Energy Systems 275 .

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