170 MODELING CONVERTERS IN MICROGRID POWER SYSTEMS PV Generating Station AC Bus DC Bus PV DC Bus E Load-1 T1 DC/DC Boost Converter DC/AC Inverter 36 Local Power T2 Grid Load-2 PV Generating Station 3.3 3.2 Figure 3.67 A One-Line Diagram of Problem 3.2. grounded/13.2 kV A, 500 kVA with the reactance of 8%. Compute per unit impedance diagram of the microgrid system. Assume the volt base of 13.2 kV on the local power grid side and kVA base of 500. voltage of 240 V and transformer T1 is rated 5% impedan Consider the microgrid of Figure 3.67. Assume the inverter AC b 240 V A/120 V Y-grounded and 150 kVA. The transformer T2 is rated 10% impedance, 240 V A/3.2 kV Y-grounded and 500 kVA. The loc loads are rated at 100 kVA and a power factor of 0.9 lagging. Th inverter modulation index is 0.9. Compute the following: i) The DC bus voltage and inverter rating ii) The boost converter PV bus input voltage and input current rating for the required DC bus voltage of the inverter iii) The size of the microgrid PV generating station iv) The per unit model of the microgrid For Problem 3.2 depicted in Figure 3.67, assume the DC bus voltage inverter is equal to 800 V DC. The transformer T1 is rated 9% imp ance, 400 V A/220 V Y grounded and 250 kVA. The transformer rated at 10% impedance, 400 V Y grounded/13.2 kV A and 500 V The Load 1 is rated at 150 gging Comp i) T ii) 3.5 Cons grou feed line mil the for of bu 3.6 C tor. So, a tradeoff is reached between the ripple of the output voltage and the inductor current and the size and cost of the converter while designing it. PROBLEMS 3.1 Consider the microgrid of Figure 3.66. A three-phase transformer, T1, is rated 500 kVA, 220 Y grounded/440 V A, transformer with the reactance of 3.5%. The microgrid is supplied from an AC bus of a PV generating station with its DC bus rated at 540 V. The distribution line is 10 miles long and has a series impedance of 0.1 + j 1.0 2 per mile and local load of 100 kVA at 440 V. The microgrid is connected to the local power grid using a three-phase transformer T2, rated at 440 VY PV Generating Station DC Bus AC Bus Local Loads DC/AC Inverter 38 Zline T1 BE Local Power Grid T2 Figure 3.66 A One-Line Diagram for Problem 3.1.